Signal reproduction device, signal reproduction method, and signal reproduction program

Abstract

This signal reproduction device comprises: first and second addition units, which add together a right channel signal whose level has been adjusted and a left channel signal whose level has been adjusted; a head detection unit that detects the position of a listener's head; and a switching unit that, according to the detected position of the listener's head, switches an input condition of a first speaker and a second speaker to one among a first input condition in which the right channel signal is input into the first speaker and the left channel signal is input into the second speaker, a second input condition in which an output signal from the addition units is input into the second speaker and neither the right channel signal nor the output signal is input into the first speaker, and a third input condition in which neither the left channel signal nor the output signal is input into the second speaker and the output signal is input into the first speaker.

Description

[Technical Field]

[0001] The present disclosure relates to techniques for reproducing stereo signals in the vicinity of a listener. [Background technology]

[0002] In recent years, seats with built-in speakers that can play music inside the seats have come into practical use. In particular, when speakers are installed in the headrests of seats, the speakers are located close to the heads of listeners sitting in the seats. Therefore, the playback sound can be heard even if the playback sound level from the speakers is not very high, which helps to reduce sound leakage around the seats.

[0003] For example, in Patent Document 1, not only is a speaker installed near the head of the seat, but a mesh-like covering material with excellent sound permeability is used on the front side of the speaker, and a sound-insulating material with excellent sound insulation is used on the back side of the speaker, resulting in a configuration that allows for efficient audio output without sound leaking to the surrounding area.

[0004] As described above, Patent Document 1 describes the speaker installation method and the seat covering material on which the speakers are installed, but does not describe anything about the input signals to the speakers. In other words, when stereo signals are reproduced from speakers in Patent Document 1, the left channel signal is reproduced from the left speaker and the right channel signal is reproduced from the right speaker. This is normal stereo reproduction.

[0005] In this way, the left channel signal and the right channel signal are reproduced at the same level from the left and right speakers, respectively, on the premise that they will be listened to at the center of the left and right speakers.

[0006] However, the listener's head is not necessarily positioned in the center of the left and right speakers. If the listener's head is fixed in the same position for a long period of time, it may cause discomfort such as neck or shoulder pain. For this reason, even if the listener faces forward for a while, they will usually twist their neck or tilt their head when their neck or shoulders start to get tired. In other words, it is necessary to consider that the listener's head is constantly moving.

[0007] In particular, when listening to stereo sound with one's head tilted to the left or right of the seat, this deviates from the prerequisite for stereo sound reproduction, which is that the head must be positioned in the center of the left and right speakers, and there is a risk that the stereo sound will not be properly heard. For example, if the listener's head is tilted to the left speaker, the sound reproduced from the left speaker will sound louder to the listener because the left speaker is very close to the listener, and conversely, the sound reproduced from the right speaker may become so quiet that it cannot be heard because the listener is farther away from the right speaker.

[0008] In this way, if your head is too close to either the left or right speaker, not only will you not get a normal stereo sound, but you will also not be able to hear the sound being played from the farther speaker, meaning that information from that speaker will be lost. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] Japanese Patent Application Laid-Open No. 2006-271847 Summary of the Invention

[0010] The present disclosure has been made to solve the above problems, and aims to provide a technology that enables a listener to hear all of the information in the right channel signal and the left channel signal reproduced from the sound source, even if the listener's head is biased toward one of the left or right speakers, without missing any information from the other speaker.

[0011] A signal reproduction device according to the present disclosure includes a reproduction unit that reproduces a right channel signal and a left channel signal from a sound source, a first level adjustment unit that adjusts the level of the right channel signal reproduced by the reproduction unit, a second level adjustment unit that adjusts the level of the left channel signal reproduced by the reproduction unit, an addition unit that adds together the right channel signal adjusted by the first level adjustment unit and the left channel signal adjusted by the second level adjustment unit, a detection unit that detects the position of a head of a listener, and a head adjustment unit that is installed near the right ear of the listener according to the position of the head of the listener detected by the detection unit. an input switching unit that switches the input states of a first speaker installed near the left ear of the listener to one of a first input state in which the right channel signal is input to the first speaker and the left channel signal is input to the second speaker, a second input state in which the output signal from the adding unit is input to the second speaker and neither the right channel signal nor the output signal is input to the first speaker, and a third input state in which neither the left channel signal nor the output signal is input to the second speaker and the output signal is input to the first speaker.

[0012] According to the present disclosure, even if the listener's head is biased toward one of the left or right speakers, the listener can hear all of the information from the right channel signal and the left channel signal reproduced from the sound source without missing any information from the other speaker. [Brief explanation of the drawings]

[0013] [Figure 1] FIG. 2 is a diagram showing an example of the configuration of a signal reproduction system when the head of a listener is in a first head state in the first embodiment of the present disclosure. [Figure 2] FIG. 2 is a diagram showing an example of the configuration of the signal reproduction system immediately after the head of the listener changes from a first head state to a second head state in the first embodiment of the present disclosure. [Figure 3] 10 is a diagram for explaining measurement of a first transfer characteristic and a second transfer characteristic when the head of a listener changes from a first head state to a second head state. FIG. [Figure 4] FIG. 4 is a diagram showing an example of a first transfer characteristic and a first difference characteristic measured in a first head state and a second head state. [Figure 5] FIG. 10 is a diagram showing an example of a second transfer characteristic and a second difference characteristic measured in a first head state and a second head state. [Figure 6] FIG. 10 is a diagram for explaining a signal reproduction method in a second head state in which the listener's head is biased toward the second speaker. [Figure 7] FIG. 2 is a diagram illustrating an example of the configuration of a signal reproduction system when the listener's head is in a second head state in the first embodiment of the present disclosure. [Figure 8] FIG. 10 is a diagram for explaining measurement of the first transfer characteristic and the second transfer characteristic immediately after the head of the listener changes from the second head state to the first head state. [Figure 9] FIG. 10 is a diagram showing an example of a second transfer characteristic measured in a second head state, a second transfer characteristic measured immediately after changing from the second head state to the first head state, and a second difference characteristic. [Figure 10] FIG. 10 is a diagram showing an example of a first transfer characteristic measured in a second head state, a first transfer characteristic measured immediately after changing from the second head state to the first head state, and a first differential characteristic. [Figure 11] FIG. 2 is a diagram showing an example of the configuration of the signal reproduction system immediately after the head of the listener changes from a first head state to a third head state in the first embodiment of the present disclosure. [Figure 12] FIG. 4 is a diagram showing an example of a first transfer characteristic and a first difference characteristic measured in a first head state and a third head state. [Figure 13] FIG. 10 is a diagram showing an example of a second transfer characteristic and a second difference characteristic measured in a first head state and a third head state. [Figure 14] FIG. 2 is a diagram showing an example of the configuration of a signal reproduction system when the listener's head is in a third head state in the first embodiment of the present disclosure. [Figure 15] 5 is a flowchart illustrating the operation of the signal reproducing device according to the first embodiment of the present disclosure. [Figure 16] 10 is a first flowchart illustrating an operation of a head detection unit according to the first embodiment of the present disclosure. [Figure 17] 10 is a second flowchart illustrating an operation of the head detection unit according to the first embodiment of the present disclosure. [Figure 18] 10 is a third flowchart illustrating an operation of the head detection unit according to the first embodiment of the present disclosure. [Figure 19] FIG. 2 is a schematic diagram for explaining the relationship between a first head state, a second head state, and a third head state in the first embodiment. [Figure 20] 2 is a diagram showing an example of memory areas of a first memory and a second memory in the first embodiment. FIG. [Figure 21] FIG. 10 is a diagram illustrating an example of the configuration of a signal reproduction system when the listener's head is in a first head state in a second embodiment of the present disclosure. [Figure 22] FIG. 13 is a diagram illustrating an example of the configuration of a signal reproduction system when the listener's head is in a first head state in a third embodiment of the present disclosure. [Figure 23] FIG. 11 is a diagram showing an example of a first transfer characteristic and a first difference characteristic measured in a first head state before head movement and in a second head state after head movement in the third embodiment. [Figure 24] FIG. 11 is a diagram showing an example of a second transfer characteristic and a second difference characteristic measured in a first head state before head movement and in a second head state after head movement in the third embodiment. [Figure 25] 1 is a schematic diagram for explaining the state of the head of a listener sitting in a conventional speaker-equipped seat. [Figure 26] 10A and 10B are diagrams for explaining a signal reproduction method in a conventional speaker-embedded seat. DETAILED DESCRIPTION OF THE INVENTION

[0014] (Findings that formed the basis of this disclosure) As described above, conventional seats with built-in speakers have built-in speakers on the left and right sides of the headrest of the seat, and the left and right channel signals are reproduced from the left and right speakers, respectively. Patent Document 1 describes using a material with excellent sound permeability for the surface material on the front side of the speaker and, conversely, using a material with excellent sound insulation for the back side of the speaker, and also describes a method for installing speakers in a seat. However, Patent Document 1 does not describe what signals are input to the left and right speakers.

[0015] That is, Patent Document 1 does not disclose any technology for changing the signals input to each speaker depending on the state of the person sitting in the seat.

[0016] FIG. 25 is a schematic diagram illustrating the state of the head of a listener 10 sitting in a conventional speaker-equipped seat, and FIG. 26 is a diagram illustrating a signal reproduction method in a conventional speaker-equipped seat.

[0017] First, as shown in the first head position in Fig. 25, when the listener 10 sits normally in the seat 100, the listener's head is positioned centered between the right speaker 201 and the left speaker 202 mounted on the headrest. At this time, as shown in the first head position in Fig. 26, the levels of the right channel signal and the left channel signal reproduced by the reproduction unit 40, such as a CD player, are adjusted to the same initial value level by the level adjustment units 301 and 302 in the L / R balance circuit 300. Then, the output signals from the level adjustment units 301 and 302 are reproduced from the right speaker 201 and the left speaker 202. In other words, the right channel signal and the left channel signal from the stereo sound source are reproduced at the same level in the right speaker 201 and the left speaker 202. This allows the listener 10 to hear sounds with a normal stereo effect.

[0018] However, when the listener 10 is seated to the left side of the seat 100 as shown in the second head state in Fig. 25, the head of the listener 10 is positioned closer to the left speaker 202. In this case, the listener 10 hears the left channel signal reproduced from the left speaker 202 loudly, and conversely, the right channel signal reproduced from the right speaker 201 quietly. It is also possible that the right channel signal is not audible, and only the left channel signal is heard loudly.

[0019] When the left and right volume balance is thus disrupted, not only is it impossible to obtain a normal stereo sound, but there is also the risk of information being lost from one of the channel signals (the right channel signal in this example). Therefore, as shown in the second head position in Fig. 26, the level adjustment unit 301 in the L / R balance circuit 300 increases the level of the right channel signal, and the level adjustment unit 302 decreases the level of the left channel signal. This adjusts the volumes reproduced from the right speaker 201 and the left speaker 202, thereby restoring the left-right balance that the listener 10 feels to normal. This signal processing allows the listener 10 to once again hear sounds with a normal stereo sound.

[0020] However, with this method, for example, if the level adjustment unit 301 increases the volume beyond the input resistance of the right speaker 201, the sound reproduced from the right speaker 201 may become distorted, and normal reproduced sound may not be output. In particular, small speakers are often installed inside seats due to physical constraints. Small speakers generally have low input resistance, so the reproduced sound is easily distorted.

[0021] Furthermore, when the volume of the right speaker 201 is increased, the increased volume tends to cause sound to leak to the surroundings, which may cause inconvenience to people nearby.

[0022] In the technology of Patent Document 1, a mesh-like covering material with excellent sound permeability is used on the front side of the seat back, and a sound-insulating material is used on the rear side, making it easier for sound to pass in front of the speaker and harder for sound to pass behind the speaker. This allows listeners in front of the speaker to hear at a sufficient volume even when playing at a low volume, and also reduces sound leakage around the seat.

[0023] However, the technology of Patent Document 1 does not take into account a state in which the head of the listener 10 is biased toward the left speaker 202, as shown in the second head state in Fig. 25. Therefore, in such a state in which the balance between the left and right volumes is lost, the listener 10 cannot obtain a normal stereo sound, and furthermore, the problem of missing information on the right channel signal from the speaker 201 farther from the listener 10 cannot be solved.

[0024] Furthermore, if the level of the right channel signal input to the speaker 201 farther from the listener 10 is increased in order to solve this problem, as shown in the second head state in Figure 26, the volume may exceed the speaker's input capacity, resulting in a new problem of distorted reproduced sound.

[0025] Therefore, the inventors have conducted extensive research into technology that allows a listener to hear at the original volume without losing information contained in the channel signal of the speaker that is farthest from the listener's head, without exceeding the speaker's input resistance, and without leaking unnecessary sound to the surroundings, and have come up with the technology of each aspect of the present disclosure described below.

[0026] In order to solve the above problems, the following techniques are disclosed.

[0027] (1) A signal reproduction device according to one aspect of the present disclosure includes a reproduction unit that reproduces a right channel signal and a left channel signal from a sound source, a first level adjustment unit that adjusts the level of the right channel signal reproduced by the reproduction unit, a second level adjustment unit that adjusts the level of the left channel signal reproduced by the reproduction unit, an addition unit that adds together the right channel signal adjusted by the first level adjustment unit and the left channel signal adjusted by the second level adjustment unit, a detection unit that detects the position of a listener's head, and a signal reproduction unit that adjusts the level of a sound source near the right ear of the listener according to the position of the listener's head detected by the detection unit. and a second speaker installed near the left ear of the listener, and an input switching unit that switches the input states of the first speaker installed near the left ear of the listener to one of a first input state in which the right channel signal is input to the first speaker and the left channel signal is input to the second speaker, a second input state in which the output signal from the adder is input to the second speaker and neither the right channel signal nor the output signal is input to the first speaker, and a third input state in which neither the left channel signal nor the output signal is input to the second speaker and the output signal is input to the first speaker.

[0028] According to this configuration, depending on the position of the listener's head, the input states of the first speaker placed near the listener's right ear and the second speaker placed near the listener's left ear can be switched between one of a first input state in which the right channel signal is input to the first speaker and the left channel signal is input to the second speaker, a second input state in which an output signal obtained by adding together the level-adjusted right channel signal and the level-adjusted left channel signal is input to the second speaker and neither the right channel signal nor the output signal is input to the first speaker, and a third input state in which neither the left channel signal nor the output signal is input to the second speaker and the output signal is input to the first speaker.

[0029] For example, when the listener's head is on the first speaker side, an output signal obtained by adding together the level-adjusted right channel signal and the level-adjusted left channel signal is input to the first speaker, and neither the left channel signal nor the output signal is input to the second speaker.Furthermore, when the listener's head is on the second speaker side, neither the right channel signal nor the output signal is input to the first speaker, and the output signal is input to the second speaker.

[0030] Therefore, even if the listener's head is biased toward one of the left and right speakers, the listener can hear all the information from the right and left channel signals reproduced from the sound source without missing any information from the other speaker.

[0031] (2) In the signal reproduction device described in (1) above, the detection unit may detect whether the head of the listener is in a position between the first speaker and the second speaker, on the first speaker side, or on the second speaker side, and the input switching unit may switch to the first input state when the head of the listener is in a position between the first speaker and the second speaker, switch to the second input state when the head of the listener is in a position on the second speaker side, and switch to the third input state when the head of the listener is in a position on the first speaker side.

[0032] According to this configuration, when the listener's head is located between the first speaker and the second speaker, the right channel signal is output from the first speaker and the left channel signal is output from the second speaker. When the listener's head is located on the second speaker side, the first speaker does not output anything, and the second speaker outputs an output signal obtained by adding the level-adjusted right channel signal and the level-adjusted left channel signal. When the listener's head is located on the first speaker side, the first speaker outputs an output signal obtained by adding the level-adjusted right channel signal and the level-adjusted left channel signal, and the second speaker does not output anything.

[0033] Therefore, even if the listener's head is tilted toward the first speaker, an output signal obtained by adding the right channel signal and the left channel signal is output from the first speaker, so the listener can hear all of the information from the right channel signal and the left channel signal. In this case, the second speaker does not output anything, so it is possible to prevent unnecessary sounds from leaking to the surroundings and reduce power consumption. In addition, even if the listener's head is tilted toward the second speaker, an output signal obtained by adding the right channel signal and the left channel signal is output from the second speaker, so the listener can hear all of the information from the right channel signal and the left channel signal. In this case, the first speaker does not output anything, so it is possible to prevent unnecessary sounds from leaking to the surroundings and reduce power consumption.

[0034] (3) In the signal reproduction device described in (1) or (2) above, the first level adjustment section may reduce the level of the right channel signal, and the second level adjustment section may reduce the level of the left channel signal.

[0035] According to this configuration, an output signal obtained by adding a right channel signal with a reduced level and a left channel signal with a reduced level is input to the first speaker or the second speaker, so that the input resistance of the speaker can be prevented from being exceeded, and the output signal can be output from the speaker at the original level, thereby preventing unnecessary sound from leaking to the surrounding area.

[0036] (4) In the signal reproducing device described in any one of (1) to (3) above, the detection unit includes a first characteristic measurement unit that measures a first transfer characteristic from the first speaker to the first microphone using a first reproduced sound signal detected by a first microphone installed near the first speaker and the right channel signal reproduced by the reproduction unit, and a second characteristic measurement unit that measures a first transfer characteristic from the second speaker to the second microphone using a second reproduced sound signal detected by a second microphone installed near the second speaker and the left channel signal reproduced by the reproduction unit. a memory that stores in advance the first transfer characteristic and the second transfer characteristic when the head of the listener is located between the first speaker and the second speaker as a first initial transfer characteristic and a second initial transfer characteristic; a first difference calculation unit that calculates a difference between the first transfer characteristic currently measured by the first characteristic measurement unit and the first initial transfer characteristic stored in the memory as a first difference characteristic; and a difference between the second transfer characteristic currently measured by the second characteristic measurement unit and the second initial transfer characteristic stored in the memory. The and a determination unit that determines the position of the head of the listener based on the first difference characteristic calculated by the first difference calculation unit and the second difference characteristic calculated by the second difference calculation unit.

[0037] According to this configuration, a first transfer characteristic from the first speaker to the first microphone and a second transfer characteristic from the second speaker to the second microphone are measured. Then, a difference between the currently measured first transfer characteristic and a first initial transfer characteristic pre-stored in memory is calculated as a first differential characteristic. Then, a difference between the currently measured second transfer characteristic and the second initial transfer characteristic pre-stored in memory is calculated as a second differential characteristic. Then, the position of the listener's head is determined based on the calculated first differential characteristic and the calculated second differential characteristic.

[0038] Therefore, the position of the listener's head can be determined based on a first differential characteristic, which is the difference between the first transfer characteristic from the first speaker to the first microphone measured this time and the first initial transfer characteristic pre-stored in memory, and a second differential characteristic, which is the difference between the second transfer characteristic from the second speaker to the second microphone measured this time and the second initial transfer characteristic pre-stored in memory.

[0039] (5) In the signal reproducing device according to any one of (1) to (3), the detection unit includes a first characteristic measurement unit that measures a first transfer characteristic from the first speaker to the first microphone using a first reproduced sound signal detected by a first microphone installed near the first speaker and the right channel signal reproduced by the reproduction unit; a second characteristic measurement unit that measures a second transfer characteristic from the second speaker to the second microphone using a second reproduced sound signal detected by a second microphone installed near the second speaker and the left channel signal reproduced by the reproduction unit; a memory that stores the first transfer characteristic measured by the first characteristic measurement unit and the second transfer characteristic measured by the second characteristic measurement unit; a first difference calculation unit that calculates a difference between the first transfer characteristic currently measured by the first characteristic measurement unit and a first transfer characteristic measured in the past and stored in the memory as a first difference characteristic; and a second characteristic measurement unit that calculates a difference between the second transfer characteristic currently measured by the second characteristic measurement unit and a second transfer characteristic measured in the past and stored in the memory as a second difference characteristic. The and a determination unit that determines the position of the head of the listener based on the first difference characteristic calculated by the first difference calculation unit and the second difference characteristic calculated by the second difference calculation unit.

[0040] According to this configuration, a first transfer characteristic from the first speaker to the first microphone and a second transfer characteristic from the second speaker to the second microphone are measured. Then, a difference between the currently measured first transfer characteristic and a previously measured first transfer characteristic stored in memory is calculated as a first differential characteristic. Then, a difference between the currently measured second transfer characteristic and a previously measured second transfer characteristic stored in memory is calculated as a second differential characteristic. Then, the position of the listener's head is determined based on the calculated first differential characteristic and the calculated second differential characteristic.

[0041] Therefore, the position of the listener's head can be determined based on a first differential characteristic, which is the difference between the first transfer characteristic from the first speaker to the first microphone measured currently and the first transfer characteristic measured previously and stored in memory, and a second differential characteristic, which is the difference between the second transfer characteristic from the second speaker to the second microphone measured currently and the second transfer characteristic measured previously and stored in memory.

[0042] (6) In the signal reproducing device described in (5) above, when the head of the listener is located between the first speaker and the second speaker, the determining unit detects levels of the first differential characteristic and the second differential characteristic at a plurality of frequency points within a predetermined frequency band, and counts the number X of frequency points where the level is a positive value and the number Y of frequency points where the level is a negative value for each of the first differential characteristic and the second differential characteristic. When the number X of frequency points of the first differential characteristic is equal to or greater than a first threshold value, and the number Y of frequency points of the second differential characteristic is equal to or greater than a second threshold, it may be determined that the head of the listener has moved from a position between the first speaker and the second speaker to a position on the first speaker side; and if the number X of frequency points of the second differential characteristic is equal to or greater than the first threshold and the number Y of frequency points of the first differential characteristic is equal to or greater than the second threshold, it may be determined that the head of the listener has moved from a position between the first speaker and the second speaker to a position on the second speaker side.

[0043] With this configuration, it can be determined that the listener's head has moved from a position between the first and second speakers to a position closer to the first speaker when the first differential characteristic within the predetermined frequency band is greater than 0 and the second differential characteristic within the predetermined frequency band is less than 0. Furthermore, it can be determined that the listener's head has moved from a position between the first and second speakers to a position closer to the first speaker when the second differential characteristic within the predetermined frequency band is greater than 0 and the first differential characteristic within the predetermined frequency band is less than 0.

[0044] (7) In the signal reproducing device described in (6) above, the first threshold value is a value obtained by multiplying the number N of all frequency points in the predetermined frequency band by a constant α, and the second threshold value is a value obtained by multiplying the number N of all frequency points in the predetermined frequency band by a constant β, and the constant α is equal to or greater than 0.5 and equal to or less than 1. value and the constant β is 0.5 or more and 1 or less. value may be.

[0045] According to this configuration, by changing the values ​​of the constants α and β by which the number N of all frequency points within a predetermined frequency band is multiplied, it is possible to set the first threshold value and the second threshold value that enable accurate determination of the position of the listener's head.

[0046] (8) In the signal reproduction device described in (5) above, the determination unit may, when the head of the listener is located on the first speaker side, detect levels at a plurality of frequency points within a predetermined frequency band of the first differential characteristic, count a number Y of frequency points where the level is a negative value for the first differential characteristic, and, when the number Y of frequency points of the first differential characteristic is equal to or greater than a second threshold, determine that the head of the listener has moved from a position on the first speaker side to a position between the first speaker and the second speaker; when the head of the listener is located on the second speaker side, detect levels at a plurality of frequency points within the predetermined frequency band of the second differential characteristic, count a number Y of frequency points where the level is a negative value for the second differential characteristic, and, when the number Y of frequency points of the second differential characteristic is equal to or greater than the second threshold, determine that the head of the listener has moved from a position on the second speaker side to a position between the first speaker and the second speaker.

[0047] According to this configuration, when the listener's head is located on the first speaker side, if the first differential characteristic within a predetermined frequency band becomes smaller than 0, it can be determined that the listener's head has moved from the position on the first speaker side to a position between the first and second speakers. Furthermore, when the listener's head is located on the second speaker side, if the second differential characteristic within the predetermined frequency band becomes smaller than 0, it can be determined that the listener's head has moved from the position on the second speaker side to a position between the first and second speakers.

[0048] (9) In the signal reproducing device described in (8) above, when the head of the listener is located on the first speaker side, the second difference calculation unit calculates, as the second difference characteristic, a difference between the second transfer characteristic currently measured by the second characteristic measurement unit and the second transfer characteristic when the head of the listener is located between the first speaker and the second speaker; when the head of the listener is located on the first speaker side, the determination unit determines whether or not a level of all frequencies of the second difference characteristic is lower than a third threshold; and when the number Y of frequency points of the first difference characteristic is equal to or greater than the second threshold and the level of all frequencies of the second difference characteristic is lower than the third threshold, determines that the head of the listener has moved from a position on the first speaker side to a position between the first speaker and the second speaker. When the head of the listener is located on the second speaker side, the first difference calculation unit may calculate, as a first difference characteristic, a difference between the first transfer characteristic currently measured by the first characteristic measurement unit and the first transfer characteristic when the head of the listener is located between the first speaker and the second speaker. When the head of the listener is located on the second speaker side, the determination unit may further determine whether or not a level of all frequencies of the first difference characteristic is lower than the third threshold value, and may determine that the head of the listener has moved from a position on the second speaker side to a position between the first speaker and the second speaker when the number Y of frequency points of the second difference characteristic is equal to or greater than the second threshold value and the level of all frequencies of the first difference characteristic is lower than the third threshold value.

[0049] With this configuration, when the listener's head is located on the first speaker side, it is further determined whether the level of all frequencies of the second differential characteristic is lower than the third threshold value, thereby making it possible to more reliably determine whether the listener's head has moved from the first speaker side to a position between the first and second speakers. Also, when the listener's head is located on the second speaker side, it is further determined whether the level of all frequencies of the first differential characteristic is lower than the third threshold value, thereby making it possible to more reliably determine whether the listener's head has moved from the second speaker side to a position between the first and second speakers.

[0050] (10) In the signal reproduction device described in any one of (1) to (3) above, the detection unit may include an image acquisition unit that acquires an image of the head of the listener, and a determination unit that determines the position of the head of the listener by analyzing the image.

[0051] According to this configuration, the position of the listener's head can be determined based on an image of the listener's head.

[0052] Furthermore, the present disclosure can be realized not only as a signal reproduction device having the above-described characteristic configuration, but also as a signal reproduction method that executes characteristic processing corresponding to the characteristic configuration of the signal reproduction device. Furthermore, the present disclosure can also be realized as a computer program that causes a computer to execute the characteristic processing included in such a signal reproduction method. Therefore, the following other aspects can also achieve the same effects as the above-described signal reproduction device.

[0053] (11) A signal reproduction method according to another aspect of the present disclosure is a signal reproduction method in a computer, which reproduces a right channel signal and a left channel signal from a sound source, adjusts the level of the reproduced right channel signal, adjusts the level of the reproduced left channel signal, adds the level-adjusted right channel signal and the level-adjusted left channel signal, detects the position of a listener's head, and, depending on the detected position of the listener's head, switches the input states of a first speaker installed near the right ear of the listener and a second speaker installed near the left ear of the listener to one of: a first input state in which the right channel signal is input to the first speaker and the left channel signal is input to the second speaker; a second input state in which an output signal obtained by the addition is input to the second speaker and neither the right channel signal nor the output signal is input to the first speaker; or a third input state in which neither the left channel signal nor the output signal is input to the second speaker and the output signal is input to the first speaker.

[0054] (12) A signal reproduction program according to another aspect of the present disclosure includes a reproduction unit that reproduces a right channel signal and a left channel signal from a sound source, a first level adjustment unit that adjusts a level of the right channel signal reproduced by the reproduction unit, a second level adjustment unit that adjusts a level of the left channel signal reproduced by the reproduction unit, an addition unit that adds the right channel signal adjusted by the first level adjustment unit and the left channel signal adjusted by the second level adjustment unit, a detection unit that detects a position of a head of a listener, and a head position adjustment unit that adjusts a position of a head of the listener set near the right ear of the listener according to the position of the head of the listener detected by the detection unit. and a second speaker placed near the left ear of the listener. The computer functions as an input switching unit that switches the input states of a first speaker placed near the left ear of the listener to one of a first input state in which the right channel signal is input to the first speaker and the left channel signal is input to the second speaker, a second input state in which the output signal from the adder is input to the second speaker and neither the right channel signal nor the output signal is input to the first speaker, and a third input state in which neither the left channel signal nor the output signal is input to the second speaker and the output signal is input to the first speaker.

[0055] (13) A non-transitory computer-readable recording medium according to another aspect of the present disclosure records a signal reproduction program, the signal reproduction program including: a reproduction unit that reproduces a right channel signal and a left channel signal from a sound source; a first level adjustment unit that adjusts a level of the right channel signal reproduced by the reproduction unit; a second level adjustment unit that adjusts a level of the left channel signal reproduced by the reproduction unit; an addition unit that adds together the right channel signal adjusted by the first level adjustment unit and the left channel signal adjusted by the second level adjustment unit; a detection unit that detects a position of a head of a listener; and a head position adjustment unit that adjusts the position of the head of the listener detected by the detection unit. and a second speaker disposed near the left ear of the listener, the first speaker being placed near the right ear of the listener and the second speaker being placed near the left ear of the listener, are switched to one of a first input state in which the right channel signal is input to the first speaker and the left channel signal is input to the second speaker, a second input state in which the output signal from the adder is input to the second speaker and neither the right channel signal nor the output signal is input to the first speaker, and a third input state in which neither the left channel signal nor the output signal is input to the second speaker and the output signal is input to the first speaker, depending on the positions of the first and second speakers.

[0056] Hereinafter, embodiments of the present disclosure will be described with reference to the accompanying drawings. Note that each of the embodiments described below represents a specific example of the present disclosure. The numerical values, shapes, components, steps, and order of steps shown in the following embodiments are merely examples and are not intended to limit the present disclosure. Furthermore, among the components in the following embodiments, components that are not described in the independent claims that represent the highest concept are described as optional components. Furthermore, in all embodiments, the respective contents can be combined.

[0057] (Embodiment 1) The configuration of the signal reproduction system according to the first embodiment of the present disclosure will be described below.

[0058] 1 is a diagram showing an example of the configuration of a signal reproduction system when the head of a listener 10 is in a first head state in the first embodiment of the present disclosure. The first head state represents a state in which the head of the listener 10 is located between the first speaker 21 and the second speaker 22, and in particular, represents a state in which the head of the listener 10 is located at a midpoint between the first speaker 21 and the second speaker 22.

[0059] The signal reproduction system shown in FIG. 1 includes a signal reproduction device 1, a first speaker 21, a second speaker 22, a first microphone 31, and a second microphone 32.

[0060] The first speaker 21 and the second speaker 22 are installed in the headrest of the seat 100 on which the listener 10 sits. The first speaker 21 is installed near the right ear of the listener 10. The second speaker 22 is installed near the left ear of the listener 10. The first microphone 31 is installed near the first speaker 21. The second microphone 32 is installed near the second speaker 22.

[0061] The signal reproduction device 1 includes a first level adjustment unit 11, a second level adjustment unit 12, a third level adjustment unit 13, a fourth level adjustment unit 14, a first adder unit 15, a second adder unit 16, a reproduction unit 40, a first switch 51, a second switch 52, a head detection unit 7, and a switch switching unit 4.

[0062] The head detection unit 7 includes a first characteristic measurement unit 41, a second characteristic measurement unit 42, a first memory 61, a second memory 62, a first difference calculation unit 71, a second difference calculation unit 72, and a threshold determination unit 3.

[0063] The first level adjustment unit 11, the second level adjustment unit 12, the third level adjustment unit 13, the fourth level adjustment unit 14, the first adder 15, the second adder 16, the reproduction unit 40, the first switch 51, the second switch 52, the switch changeover unit 4, the first characteristic measurement unit 41, the second characteristic measurement unit 42, the first difference calculation unit 71, the second difference calculation unit 72, and the threshold determination unit 3 are realized by a processor. The processor is constituted by, for example, a central processing unit (CPU) or the like.

[0064] The first memory 61 and the second memory 62 are storage devices capable of storing various types of information, such as a random access memory (RAM), a hard disk drive (HDD), a solid state drive (SSD), or a flash memory.

[0065] The first level adjustment unit 11, the second level adjustment unit 12, the third level adjustment unit 13, the fourth level adjustment unit 14, the first adder 15, the second adder 16, the playback unit 40, the first switch 51, the second switch 52, the head detection unit 7, and the switch switching unit 4 may be configured as dedicated hardware circuits. Also, the first level adjustment unit 11, the second level adjustment unit 12, the third level adjustment unit 13, the fourth level adjustment unit 14, the first adder 15, the second adder 16, the playback unit 40, the first switch 51, the second switch 52, the head detection unit 7, and the switch switching unit 4 may be distributed and arranged in multiple devices.

[0066] The playback unit 40 plays back a right channel signal and a left channel signal from a sound source. The right channel signal is an audio signal that the listener 10 listens to with the right ear, and the left channel signal is an audio signal that the listener 10 listens to with the left ear. The sound source is, for example, an optical disc such as a CD (compact disc). The playback unit 40 plays back the right channel signal and the left channel signal stored on the optical disc.

[0067] The playback unit 40 may play back the right and left channel signals stored in memory, or may play back the right and left channel signals received from an external server, or may play back the right and left channel signals received from a terminal such as a smartphone.

[0068] The reproduction unit 40 outputs the right channel signal to the first level adjustment unit 11, the third level adjustment unit 13, and the first terminal 511 of the first switch 51. The reproduction unit 40 also outputs the left channel signal to the second level adjustment unit 12, the fourth level adjustment unit 14, and the first terminal 521 of the second switch 52.

[0069] The first level adjustment unit 11 adjusts the level of the right channel signal reproduced by the reproduction unit 40. The first level adjustment unit 11 reduces the level of the right channel signal. For example, the first level adjustment unit 11 reduces the level of the right channel signal by half.

[0070] The second level adjustment unit 12 adjusts the level of the left channel signal reproduced by the reproduction unit 40. The second level adjustment unit 12 reduces the level of the left channel signal. For example, the second level adjustment unit 12 reduces the level of the left channel signal by half.

[0071] The third level adjustment unit 13 adjusts the level of the right channel signal reproduced by the reproduction unit 40. The third level adjustment unit 13 reduces the level of the right channel signal. For example, the third level adjustment unit 13 reduces the level of the right channel signal by half.

[0072] The fourth level adjustment unit 14 adjusts the level of the left channel signal reproduced by the reproduction unit 40. The fourth level adjustment unit 14 reduces the level of the left channel signal. For example, the fourth level adjustment unit 14 reduces the level of the left channel signal by half.

[0073] The first adder 15 adds the right channel signal adjusted by the first level adjuster 11 and the left channel signal adjusted by the second level adjuster 12. The first adder 15 outputs an added signal obtained by adding the level-adjusted right channel signal and the level-adjusted left channel signal to the second terminal 512 of the first switch 51.

[0074] The second adder 16 adds the right channel signal adjusted by the third level adjustment unit 13 and the left channel signal adjusted by the fourth level adjustment unit 14. The second adder 16 outputs an added signal obtained by adding the level-adjusted right channel signal and the level-adjusted left channel signal to the second terminal 522 of the second switch 52.

[0075] Note that, although the signal reproducing device 1 in the first embodiment includes the first level adjustment unit 11, the second level adjustment unit 12, the third level adjustment unit 13, the fourth level adjustment unit 14, the first adder unit 15, and the second adder unit 16, the present disclosure is not particularly limited to this. The signal reproducing device 1 may include only the first level adjustment unit 11, the second level adjustment unit 12, and the first adder unit 15, without including the third level adjustment unit 13, the fourth level adjustment unit 14, and the second adder unit 16. In this case, the first adder unit 15 may output an added signal obtained by adding the level-adjusted right channel signal and the level-adjusted left channel signal to the second terminal 512 of the first switch 51 and the second terminal 522 of the second switch 52.

[0076] The head detection unit 7 detects the position of the head of the listener 10. The head detection unit 7 detects whether the head of the listener 10 is located between the first speaker 21 and the second speaker 22, on the first speaker 21 side, or on the second speaker 22 side.

[0077] The switch changeover unit 4 changes the input states of the first speaker 21 and the second speaker 22 according to the position of the head of the listener 10 detected by the head detection unit 7 between a first input state in which the right channel signal is input to the first speaker 21 and the left channel signal is input to the second speaker 22, a second input state in which the output signal from the second adder 16 is input to the second speaker 22 and neither the right channel signal nor the output signal from the first adder 15 is input to the first speaker 21, and a third input state in which neither the left channel signal nor the output signal is input to the second speaker 22 and the output signal from the first adder 15 is input to the first speaker 21. The switch changeover unit 4 controls the first switch 51 and the second switch 52 according to the position of the head of the listener 10 detected by the head detection unit 7.

[0078] The switch changeover unit 4 switches to the first input state when the head of the listener 10 is located between the first speaker 21 and the second speaker 22. Furthermore, the switch changeover unit 4 switches to the second input state when the head of the listener 10 is located on the second speaker 22 side. Furthermore, the switch changeover unit 4 switches to the third input state when the head of the listener 10 is located on the first speaker 21 side.

[0079] In the first input state, the first switch 51 inputs the right channel signal to the first speaker 21. In the second input state, the first switch 51 inputs neither the right channel signal nor the output signal from the first adder 15 to the first speaker 21. In the third input state, the first switch 51 inputs the output signal from the first adder 15 to the first speaker 21.

[0080] In the first input state, the second switch 52 inputs the left channel signal to the second speaker 22. In the second input state, the second switch 52 inputs the output signal from the second adder 16 to the second speaker 22. In the third input state, the second switch 52 inputs neither the left channel signal nor the output signal from the second adder 16 to the second speaker 22.

[0081] The first switch 51 includes a first terminal 511, a second terminal 512, a third terminal 513, and a fourth terminal 514. The first terminal 511 is connected to the reproduction unit 40. A right channel signal output from the reproduction unit 40 is input to the first terminal 511. The second terminal 512 is connected to the first adder 15. An output signal output from the first adder 15 is input to the second terminal 512. The third terminal 513 is not connected to either the reproduction unit 40 or the first adder 15. The fourth terminal 514 is connected to the first speaker 21 and the first characteristic measuring unit 41.

[0082] The fourth terminal 514 is connected to any one of the first terminal 511, the second terminal 512, and the third terminal 513. When the fourth terminal 514 and the first terminal 511 are connected, the right channel signal from the reproduction unit 40 is output to the first speaker 21 and the first characteristic measurement unit 41. When the fourth terminal 514 and the second terminal 512 are connected, the output signal output from the first adder 15 is output to the first speaker 21 and the first characteristic measurement unit 41. When the fourth terminal 514 and the third terminal 513 are connected, neither the right channel signal from the reproduction unit 40 nor the output signal from the first adder 15 is output to the first speaker 21 and the first characteristic measurement unit 41.

[0083] The second switch 52 includes a first terminal 521, a second terminal 522, a third terminal 523, and a fourth terminal 524. The first terminal 521 is connected to the reproduction unit 40. A left channel signal output from the reproduction unit 40 is input to the first terminal 521. The second terminal 522 is connected to the second adder 16. An output signal output from the second adder 16 is input to the second terminal 522. The third terminal 523 is not connected to either the reproduction unit 40 or the second adder 16. The fourth terminal 524 is connected to the second speaker 22 and the second characteristic measuring unit 42.

[0084] The fourth terminal 524 is connected to any one of the first terminal 521, the second terminal 522, and the third terminal 523. When the fourth terminal 524 and the first terminal 521 are connected, the left channel signal from the reproduction unit 40 is output to the second speaker 22 and the second characteristic measurement unit 42. When the fourth terminal 524 and the second terminal 522 are connected, the output signal output from the second adder 16 is output to the second speaker 22 and the second characteristic measurement unit 42. When the fourth terminal 524 and the third terminal 523 are connected, neither the left channel signal from the reproduction unit 40 nor the output signal from the second adder 16 is output to the second speaker 22 and the second characteristic measurement unit 42.

[0085] The first characteristic measuring unit 41 measures the first transfer characteristic from the first speaker 21 to the first microphone 31 using the first reproduced sound signal detected by the first microphone 31 installed near the first speaker 21 and the output signal from the fourth terminal 514 of the first switch 51 (corresponding to the right channel signal reproduced by the reproduction unit 40 in Figure 1).

[0086] The second characteristic measuring unit 42 measures the second transfer characteristic from the second speaker 22 to the second microphone 32 using the second reproduced sound signal detected by the second microphone 32 installed near the second speaker 22 and the output signal from the fourth terminal 524 of the second switch 52 (corresponding to the left channel signal reproduced by the reproduction unit 40 in Figure 1).

[0087] The first memory 61 stores in advance the first transfer characteristic when the head of the listener 10 is located between the first speaker 21 and the second speaker 22 as the first initial transfer characteristic.

[0088] The second memory 62 stores in advance the second transfer characteristic when the head of the listener 10 is located between the first speaker 21 and the second speaker 22 as the second initial transfer characteristic.

[0089] The first difference calculation section 71 calculates the difference between the first transfer characteristic currently measured by the first characteristic measurement section 41 and the first initial transfer characteristic stored in the first memory 61 as the first difference characteristic.

[0090] The second difference calculation section 72 calculates the difference between the second transfer characteristic currently measured by the second characteristic measurement section 42 and the second initial transfer characteristic stored in the second memory 62 as the second difference characteristic.

[0091] The first memory 61 may store the first transfer characteristic measured by the first characteristic measuring section 41. The second memory 62 may store the second transfer characteristic measured by the second characteristic measuring section 42. The first difference calculating section 71 may calculate, as the first differential characteristic, the difference between the first transfer characteristic currently measured by the first characteristic measuring section 41 and the first transfer characteristic measured in the past and stored in the first memory 61. The second difference calculating section 72 may calculate, as the second differential characteristic, the difference between the second transfer characteristic currently measured by the second characteristic measuring section 42 and the second transfer characteristic measured in the past and stored in the second memory 62.

[0092] The threshold value determining section 3 determines the position of the head of the listener 10 based on the first difference characteristic calculated by the first difference calculating section 71 and the second difference characteristic calculated by the second difference calculating section 72.

[0093] When the head of the listener 10 is located between the first speaker 21 and the second speaker 22, the threshold determination unit 3 detects the levels of the first differential characteristic and the second differential characteristic at multiple frequency points within a predetermined frequency band. The threshold determination unit 3 counts the number X of frequency points where the level is a positive value and the number Y of frequency points where the level is a negative value for each of the first differential characteristic and the second differential characteristic. When the number X of frequency points of the first differential characteristic is equal to or greater than a first threshold and the number Y of frequency points of the second differential characteristic is equal to or greater than a second threshold, the threshold determination unit 3 determines that the head of the listener 10 has moved from a position between the first speaker 21 and the second speaker 22 to a position on the first speaker 21 side. Furthermore, if the number X of frequency points of the second differential characteristic is equal to or greater than the first threshold value and the number Y of frequency points of the first differential characteristic is equal to or greater than the second threshold value, the threshold value determination unit 3 determines that the head of the listener 10 has moved from a position between the first speaker 21 and the second speaker 22 to a position on the second speaker 22 side.

[0094] The first threshold is a value obtained by multiplying the number N of all frequency points in a predetermined frequency band by a constant α. The second threshold is a value obtained by multiplying the number N of all frequency points in a predetermined frequency band by a constant β. The constant α is between 0.5 and 1. value The constant β is between 0.5 and 1. value is.

[0095] When the head of the listener 10 is located on the first speaker 21 side, the threshold determination unit 3 detects levels at multiple frequency points within a predetermined frequency band of the first differential characteristic. The threshold determination unit 3 counts the number Y of frequency points where the level is a negative value for the first differential characteristic. When the number Y of frequency points of the first differential characteristic is equal to or greater than the second threshold, the threshold determination unit 3 determines that the head of the listener 10 has moved from a position on the first speaker 21 side to a position between the first speaker 21 and the second speaker 22.

[0096] When the head of the listener 10 is located on the second speaker 22 side, the threshold determination unit 3 detects the levels of the second differential characteristic at multiple frequency points within a predetermined frequency band. The threshold determination unit 3 counts the number Y of frequency points at which the level is a negative value for the second differential characteristic. When the number Y of frequency points of the second differential characteristic is equal to or greater than the second threshold, the threshold determination unit 3 determines that the head of the listener 10 has moved from a position on the second speaker 22 side to a position between the first speaker 21 and the second speaker 22.

[0097] Furthermore, when the head of the listener 10 is located on the first speaker 21 side, the second difference calculation unit 72 may further calculate, as the second difference characteristic, the difference between the second transfer characteristic currently measured by the second characteristic measurement unit 42 and the second transfer characteristic when the head of the listener 10 is located between the first speaker 21 and the second speaker 22. When the head of the listener 10 is located on the first speaker 21 side, the threshold determination unit 3 may further determine whether the level of all frequencies of the second difference characteristic is lower than a third threshold. Then, when the number Y of frequency points of the first difference characteristic is equal to or greater than the second threshold and the level of all frequencies of the second difference characteristic is lower than the third threshold, the threshold determination unit 3 may determine that the head of the listener 10 has moved from a position on the first speaker 21 side to a position between the first speaker 21 and the second speaker 22.

[0098] Furthermore, when the head of the listener 10 is located on the second speaker 22 side, the first difference calculation unit 71 may further calculate, as the first difference characteristic, the difference between the first transfer characteristic currently measured by the first characteristic measurement unit 41 and the first transfer characteristic when the head of the listener 10 is located between the first speaker 21 and the second speaker 22. When the head of the listener 10 is located on the second speaker 22 side, the threshold determination unit 3 may further determine whether the level of all frequencies of the first difference characteristic is lower than a third threshold. Then, when the number Y of frequency points of the second difference characteristic is equal to or greater than the second threshold and the level of all frequencies of the first difference characteristic is lower than the third threshold, the threshold determination unit 3 may determine that the head of the listener 10 has moved from a position on the second speaker 22 side to a position between the first speaker 21 and the second speaker 22.

[0099] First, the first head state in which the head of the listener 10 is located between the first speaker 21 and the second speaker 22 will be described below.

[0100] 1 shows a first head state in which a listener 10 is normally seated in a seat 100, with the listener's head located between the first speaker 21 and the second speaker 22. At this time, a right channel signal from the playback unit 40 is input to the first speaker 21 via the first terminal 511 to the fourth terminal 514 of the first switch 51. The reproduced sound of this right channel signal is then detected by the first microphone 31 and input to the first characteristic measuring unit 41. The right channel signal from the playback unit 40 that has passed through the first switch 51 is also input to the first characteristic measuring unit 41. Therefore, the first characteristic measuring unit 41 measures a first transfer characteristic from the first speaker 21 to the first microphone 31 based on the first reproduced sound signal detected by the first microphone 31 and the right channel signal from the playback unit 40, and stores the measured first transfer characteristic in the first memory 61 as the first transfer characteristic in the first head state.

[0101] In parallel with the right channel signal, the left channel signal from the reproduction unit 40 is input to the second speaker 22 via the first terminal 521 to the fourth terminal 524 of the second switch 52. Then, the reproduced sound of this left channel signal is detected by the second microphone 32 and input to the second characteristic measuring unit 42. The left channel signal from the reproduction unit 40 that has passed through the second switch 52 is also input to the second characteristic measuring unit 42. Therefore, the second characteristic measuring unit 42 measures the second transfer characteristic from the second speaker 22 to the second microphone 32 based on the second reproduced sound signal detected by the second microphone 32 and the left channel signal from the reproduction unit 40, and stores the measured second transfer characteristic in the second memory 62 as the second transfer characteristic in the first head state.

[0102] Next, a case where the head of the listener 10 moves from a position between the first speaker 21 and the second speaker 22 to a position on the second speaker 22 side will be described.

[0103] 2 is a diagram showing an example of the configuration of the signal reproduction system immediately after the head of the listener 10 changes from the first head state to the second head state in the first embodiment of the present disclosure. The second head state indicates a state in which the head of the listener 10 is positioned on the side of the second speaker 22.

[0104] 2 shows a second head state in which the head of the listener 10 moves closer to the second speaker 22, as an example of head movement of the listener 10. At this time, similar to FIG. 1, the right channel signal from the playback unit 40 is input to the first speaker 21 via the first terminal 511 to the fourth terminal 514 of the first switch 51. The reproduced sound of this right channel signal is then detected by the first microphone 31 and input to the first characteristic measuring unit 41. The right channel signal from the playback unit 40 that has passed through the first switch 51 is also input to the first characteristic measuring unit 41. Therefore, the first characteristic measuring unit 41 measures a first transfer characteristic from the first speaker 21 to the first microphone 31 based on the first reproduced sound signal detected by the first microphone 31 and the right channel signal from the playback unit 40, and stores the measured first transfer characteristic in the first memory 61 as the first transfer characteristic in the second head state.

[0105] 1, the left channel signal from the reproduction unit 40 is input to the second speaker 22 via the first terminal 521 to the fourth terminal 524 of the second switch 52. Then, the reproduced sound of this left channel signal is detected by the second microphone 32 and input to the second characteristic measuring unit 42. The left channel signal from the reproduction unit 40 that has passed through the second switch 52 is also input to the second characteristic measuring unit 42. Therefore, the second characteristic measuring unit 42 measures the second transfer characteristic from the second speaker 22 to the second microphone 32 based on the second reproduced sound signal detected by the second microphone 32 and the left channel signal from the reproduction unit 40, and stores the measured second transfer characteristic in the second memory 62 as the second transfer characteristic in the second head state.

[0106] Here, the first transfer characteristic in the first head state and the second head state is stored in different areas in the first memory 61. That is, the first transfer characteristic is not overwritten. Also, the second transfer characteristic in the first head state and the second head state is stored in different areas in the second memory 62. That is, the second transfer characteristic is not overwritten.

[0107] FIG. 3 is a diagram for explaining the measurement of the first transfer characteristic and the second transfer characteristic when the head of the listener 10 changes from the first head state to the second head state.

[0108] The measurement of the first and second transfer characteristics in Fig. 2 can be simply expressed as shown in Fig. 3. In Fig. 3, first level adjustment unit 11, second level adjustment unit 12, third level adjustment unit 13, fourth level adjustment unit 14, first adder 15, and second adder 16, which are not directly related to the measurement of the first and second transfer characteristics, are omitted, and the first terminal 511 and fourth terminal 514 of first switch 51 are connected, and the first terminal 521 and fourth terminal 524 of second switch 52 are connected.

[0109] 3, the first transfer characteristic from the first speaker 21 to the first microphone 31 is measured using the right channel signal from the reproduction unit 40, and similarly, the second transfer characteristic from the second speaker 22 to the second microphone 32 is measured using the left channel signal from the reproduction unit 40. At this time, since the first microphone 31 is installed near the first speaker 21, the reproduced sound from the first speaker 21 detected by the first microphone 31 is louder. Similarly, since the second microphone 32 is installed near the second speaker 22, the reproduced sound from the second speaker 22 detected by the second microphone 32 is louder.

[0110] In other words, since the level of crosstalk sound from the first speaker 21 to the second microphone 32 and the level of crosstalk sound from the second speaker 22 to the first microphone 31 are negligibly small, the first characteristic measuring unit 41 can measure the first transfer characteristic using only the right channel signal, and the second characteristic measuring unit 42 can measure the second transfer characteristic using only the left channel signal.

[0111] If the first and second transfer characteristics are measured using a music signal, the frequency level of the music signal changes from moment to moment, so the measurement takes longer than for a measurement signal such as white noise. However, if a sufficient amount of time is allowed for averaging, the required characteristics can be obtained. As will be explained in more detail later, the first difference calculation unit 71 calculates the difference characteristic between the first transfer characteristic in the first head state and the first transfer characteristic in the second head state, and the threshold determination unit 3 determines whether the difference characteristic exceeds a threshold. The difference characteristic is also determined similarly for the second transfer characteristic. Therefore, the difference characteristic can be calculated relatively accurately even for a signal in which the level of each frequency changes, such as a music signal, rather than a signal with a flat frequency, such as white noise.

[0112] Therefore, when the playback unit 40 is a CD player, the first characteristic measurement unit 41 and the second characteristic measurement unit 42 can measure the first transfer characteristic between the first speaker 21 and the first microphone 31 and the second transfer characteristic between the second speaker 22 and the second microphone 32 at the same time that the listener 10 is listening to music.

[0113] Thereafter, the first transfer characteristic from the first speaker 21 to the first microphone 31 stored in the first memory 61 is input to the first difference calculation unit 71, and the second transfer characteristic from the second speaker 22 to the second microphone 32 stored in the second memory 62 is input to the second difference calculation unit 72, which calculates the first difference characteristic and the second difference characteristic. Then, the threshold determination unit 3 determines whether or not the first difference characteristic and the second difference characteristic satisfy a certain condition, and the first switch 51 and the second switch 52 are operated according to the determination result.

[0114] FIG. 4 is a diagram showing an example of a first transfer characteristic and a first differential characteristic measured in a first head state and a second head state, and FIG. 5 is a diagram showing an example of a second transfer characteristic and a second differential characteristic measured in a first head state and a second head state.

[0115] The upper diagram in Fig. 4 shows the first transfer characteristic from the first speaker 21 to the first microphone 31, with the dashed line showing the first transfer characteristic in the first head state and the solid line showing the first transfer characteristic in the second head state. The lower diagram in Fig. 4 shows the first differential characteristic obtained by subtracting the first transfer characteristic in the first head state before movement from the first transfer characteristic in the second head state after movement. In the first differential characteristic, the level of the frequency band surrounded by the dashed line (for example, 100 to 800 Hz) is uniformly 0 dB or less (approximately -4 to -1 dB).

[0116] On the other hand, the upper diagram in Fig. 5 shows the second transfer characteristic from the second speaker 22 to the second microphone 32, with the dashed line indicating the second transfer characteristic in the first head state and the solid line indicating the second transfer characteristic in the second head state. The lower diagram in Fig. 5 shows the second differential characteristic obtained by subtracting the second transfer characteristic in the first head state before movement from the second transfer characteristic in the second head state after movement. In the second differential characteristic, the level of the frequency band surrounded by the dashed line (for example, 100 to 800 Hz) is uniformly 0 dB or higher (approximately +1 to +2 dB).

[0117] In this way, when the head of the listener 10 changes from the first head state to the second head state, the level of the second differential characteristic of the second transfer characteristic from the second speaker 22 to the second microphone 32 increases in a frequency band of, for example, 100 to 800 Hz, and the level of the first differential characteristic of the first transfer characteristic from the first speaker 21 to the first microphone 31 decreases in a frequency band of, for example, 100 to 800 Hz. The first differential characteristic and the second differential characteristic are contradictory differential characteristics.

[0118] This is because, in the first head state, the head of the listener 10 is somewhat distant from the second speaker 22, the second microphone 32, the first speaker 21, and the first microphone 31, whereas in the second head state, the head of the listener 10 is closer to the second speaker 22 and the second microphone 32, causing the reproduced sound from the second speaker 22 and the reflected sound from the head of the listener 10 to become louder, resulting in in-phase superposition at low frequencies with long wavelengths and increasing the level, while, as the head of the listener 10 is farther away from the first speaker 21 and the first microphone 31, the reproduced sound from the first speaker 21 and the reflected sound from the head of the listener 10 become quieter, causing no in-phase superposition at low frequencies with long wavelengths compared to the first head state and decreasing the level.

[0119] 3 checks the range in which this characteristic change occurs. Specifically, for example, in the second differential characteristic, if the number of frequency points (X) where the level is a positive value out of the total number of frequency points (N) in a frequency band of, for example, 100 to 800 Hz is equal to or greater than a predetermined first threshold (for example, N / 2), and if the number of frequency points (Y) where the level is a negative value out of the total number of frequency points (N) in a frequency band of, for example, 100 to 800 Hz is equal to or greater than a predetermined second threshold (for example, N / 2), the threshold determination unit 3 determines that the head of the listener 10 has changed from the first head state to the second head state. Then, if it is determined that a change has occurred, the switch changeover unit 4 operates the first switch 51 and the second switch 52.

[0120] The first and second thresholds are not limited to N / 2. For example, the first and second thresholds may be N / 3, N, 0.8N, or 0.9N, as long as they are conditions that allow accurate determination of a state change. The first and second thresholds may be the same value or different values. For example, the first threshold may be 0.8N and the second threshold may be 0.9N.

[0121] Fig. 6 is a diagram for explaining a signal reproduction method in the second head state in which the head of the listener 10 is biased toward the second speaker 22. Fig. 6 shows a simplified configuration after the first switch 51 and the second switch 52 are operated.

[0122] 6, the level of the right channel signal from the reproduction unit 40 is reduced by the third level adjustment unit 13 and input to the second adder 16. Similarly, the level of the left channel signal from the reproduction unit 40 is reduced by the fourth level adjustment unit 14 and input to the second adder 16. The second adder 16 adds the right channel signal from the third level adjustment unit 13 and the left channel signal from the fourth level adjustment unit 14 and outputs the result to the second speaker 22. The second speaker 22 then reproduces an added signal obtained by adding the right channel signal and the left channel signal, while the first speaker 21 reproduces nothing. At this time, the level of the added signal reproduced from the second speaker 22 is adjusted by the third level adjustment unit 13 and the fourth level adjustment unit 14 so that it is the same as the levels of the right channel signal and the left channel signal reproduced from the first speaker 21 and the second speaker 22, respectively, in the first head position of FIG. 1.

[0123] As a result, in the second head state, the listener 10 can hear sounds at the same level as in the first head state of FIG. 1 , and therefore does not feel any discomfort due to volume changes. Furthermore, the listener 10 can hear the right channel signal and the left channel signal at the same level, and therefore does not feel any loss of information. Furthermore, the level of the sum signal obtained by adding the right channel signal and the left channel signal reproduced from the second speaker 22 is approximately the same as the levels of the right channel signal and the left channel signal reproduced from the first speaker 21 and the second speaker 22, respectively, in the first head state of FIG. 1 , so that an excessive input load is not imposed on the second speaker 22, and no distortion occurs. Furthermore, because no sound is reproduced from the first speaker 21, and the level of the sound reproduced from the second speaker 22 is not increased, sound leakage to the surroundings can be suppressed without using a special surface material with high sound insulation as in Patent Document 1, and people near the seat 100 will not be annoyed.

[0124] FIG. 7 is a diagram illustrating an example of the configuration of the signal reproduction system when the head of the listener 10 is in the second head state in the first embodiment of the present disclosure. FIG. 7 illustrates a configuration that details the state of FIG. 6. That is, in the configuration shown in FIG. 2, the first characteristic measurement unit 41 measures the first transfer characteristic from the first speaker 21 to the first microphone 31, the second characteristic measurement unit 42 measures the second transfer characteristic from the second speaker 22 to the second microphone 32, and the first difference calculation unit 71 and the second difference calculation unit 72 calculate the first difference characteristic and the second difference characteristic from the first transfer characteristic and the second transfer characteristic. Then, the threshold determination unit 3 determines that the listener 10 is in the second head state in which the head of the listener 10 is closer to the second speaker 22. As a result, the switch changeover unit 4 brings the third terminal 513 and the fourth terminal 514 of the first switch 51 into conduction, and brings the second terminal 522 and the fourth terminal 524 of the second switch 52 into conduction. As a result, the signal reproduction system has the configuration shown in FIG.

[0125] The sounds reproduced from the first speaker 21 and the second speaker 22 according to the states of the first switch 51 and the second switch 52 shown in Fig. 7 have been explained in Fig. 6, so they will not be explained here. The first speaker 21 does not reproduce anything, and the second speaker 22 reproduces an added signal obtained by adding the right channel signal and the left channel signal.

[0126] Next, when the head state of the listener 10 returns from the second head state shown in FIG. 7 in which the head of the listener 10 is positioned on the side of the second speaker 22 to the first head state in which the head of the listener 10 is positioned between the first speaker 21 and the second speaker 22, the configuration shown in FIG. 7 is shown as in FIG. 8.

[0127] FIG. 8 is a diagram for explaining the measurement of the first transfer characteristic and the second transfer characteristic immediately after the head of the listener 10 changes from the second head state to the first head state.

[0128] 8, the levels of the right channel signal and the left channel signal from the reproduction unit 40 are reduced by the third level adjustment unit 13 and the fourth level adjustment unit 14, respectively, and then added by the second adder 16. The added signal from the second adder 16 is reproduced from the second speaker 22 and detected by the second microphone 32. Then, the second characteristic measurement unit 42 calculates the second transfer characteristic from the second speaker 22 to the second microphone 32 using the added signal from the second adder 16 and the reproduced sound signal from the second microphone 32, and stores it in the second memory 62.

[0129] On the other hand, since no signal is input from the first switch 51 to the first speaker 21, the first speaker 21 does not reproduce anything. Furthermore, since no signal is input from the first switch 51 to the first characteristic measurement unit 41, the first characteristic measurement unit 41 cannot normally measure the first transfer characteristic from the first speaker 21 to the first microphone 31. In this case, the first characteristic measurement unit 41 measures a time characteristic of 0 (a frequency characteristic of -∞), or a characteristic at a very low level due to error noise. Then, this abnormal characteristic is stored in the first memory 61.

[0130] Here, the first difference calculation unit 71 compares the first transfer characteristic measured in the first head state of Figure 8 with the first transfer characteristic measured in the second head state of Figure 7, and the second difference calculation unit 72 compares the second transfer characteristic measured in the first head state of Figure 8 with the second transfer characteristic measured in the second head state of Figure 7.

[0131] Fig. 9 is a diagram showing an example of the second transfer characteristic measured in the second head state, the second transfer characteristic measured immediately after changing from the second head state to the first head state, and the second differential characteristic. Fig. 10 is a diagram showing an example of the first transfer characteristic measured in the second head state, the first transfer characteristic measured immediately after changing from the second head state to the first head state, and the first differential characteristic.

[0132] Specifically, first, the second difference calculation unit 72 reads out from the second memory 62 the second transfer characteristic from the second speaker 22 to the second microphone 32 in the second head state before the head movement of the listener 10. This second transfer characteristic is indicated by a dashed line in the upper diagram of FIG. 9. Next, the second difference calculation unit 72 reads out from the second memory 62 the second transfer characteristic from the second speaker 22 to the second microphone 32 in the first head state after the head movement. This second transfer characteristic is indicated by a solid line in the upper diagram of FIG. 9. Then, the second difference calculation unit 72 calculates the second difference characteristic indicated by a solid line in the lower diagram of FIG. 9 from these second transfer characteristics. The second difference calculation unit 72 calculates the second difference characteristic by subtracting the second transfer characteristic in the second head state before the movement from the second transfer characteristic in the first head state after the movement. In the second differential characteristic, the level in the frequency band indicated by the dashed line (for example, 100 to 800 Hz) is uniformly below 0 dB (about -2 to -1 dB). This characteristic enables threshold determination unit 3 to determine that the head state has changed from the second head state to the first head state.

[0133] That is, when the head of the listener 10 is located on the second speaker 22 side, the threshold determination unit 3 detects the levels of the second differential characteristic at multiple frequency points within a predetermined frequency band (for example, 100 to 800 Hz). The threshold determination unit 3 counts the number Y of frequency points at which the level is a negative value for the second differential characteristic. When the number Y of frequency points of the second differential characteristic is equal to or greater than the second threshold, the threshold determination unit 3 determines that the head of the listener 10 has moved from a position on the second speaker 22 side to a position between the first speaker 21 and the second speaker 22.

[0134] Furthermore, the threshold determination unit 3 may determine that the head state has changed from the second head state to the first head state by combining this with determining whether the level of all frequencies of the first differential characteristic calculated by the first differential calculation unit 71 is equal to or lower than a third threshold (e.g., −20 dB) shown by the dashed dotted line in the lower diagram of FIG. 10.

[0135] FIG. 10 will be explained in more detail. First, the first difference calculation unit 71 reads from the first memory 61 the first transfer characteristic from the first speaker 21 to the first microphone 31 in a first head state measured when the head of the listener 10 was positioned between the first speaker 21 and the second speaker 22. This first transfer characteristic is indicated by a dashed line in the upper diagram of FIG. 10. Next, the first difference calculation unit 71 reads from the first memory 61 the first transfer characteristic from the first speaker 21 to the first microphone 31 in a first head state after head movement. This first transfer characteristic is indicated by a solid line in the upper diagram of FIG. 10. Then, the first difference calculation unit 71 calculates the first difference characteristic indicated by a solid line in the lower diagram of FIG. 10 from these first transfer characteristics. The first difference calculation unit 71 calculates the first difference characteristic by subtracting the first transfer characteristic read from the first memory 61 from the first transfer characteristic in the first head state after movement. As shown in the lower graph of FIG. 10, it can be seen that the level of the first differential characteristic is a fairly small value over all frequencies.

[0136] From the above, the threshold determination unit 3 can determine that the listener 10 has changed from the second head state to the first head state by combining the second differential characteristic as shown in Figure 9 and the first differential characteristic as shown in Figure 10.

[0137] That is, when the head of the listener 10 is located on the second speaker 22 side, the first difference calculation unit 71 may further calculate, as the first difference characteristic, the difference between the first transfer characteristic currently measured by the first characteristic measurement unit 41 and the first transfer characteristic when the head of the listener 10 is located between the first speaker 21 and the second speaker 22. When the head of the listener 10 is located on the second speaker 22 side, the threshold determination unit 3 may further determine whether the level of all frequencies of the first difference characteristic is lower than a third threshold. Then, when the number Y of frequency points of the second difference characteristic is equal to or greater than the second threshold and the level of all frequencies of the first difference characteristic is lower than the third threshold, the threshold determination unit 3 may determine that the head of the listener 10 has moved from a position on the second speaker 22 side to a position between the first speaker 21 and the second speaker 22.

[0138] Although the second difference calculation unit 72 compares the second transfer characteristic measured in the first head state of FIG. 8 with the second transfer characteristic measured in the second head state of FIG. 7, the present disclosure is not limited to this. The second difference calculation unit 72 may compare the second transfer characteristic measured in the first head state of FIG. 8 with the second transfer characteristic measured in the first head state of FIG. 1, instead of the second transfer characteristic measured in the second head state of FIG. 7. In this case, since both are second transfer characteristics in the first head state, the second difference characteristic is approximately 0, and no characteristic change occurs in the frequency band indicated by the dashed line in the lower diagram of FIG. 9. Furthermore, the first difference calculation unit 71 may compare the first transfer characteristic measured in the second head state of FIG. 2 with the first transfer characteristic measured in the first head state of FIG. 8. In this case, the first transfer characteristic measured in the second head state of FIG. 2 becomes the first transfer characteristic in the second head state shown in FIG. 4, and the level of the first difference characteristic becomes significantly low, as in the lower diagram of FIG. 10.

[0139] Therefore, the second difference calculation section 72 may calculate, as the second difference characteristic, the difference between the second transfer characteristic currently measured by the second characteristic measurement section 42 and the second transfer characteristic when the head of the listener 10 is located between the first speaker 21 and the second speaker 22. Furthermore, the first difference calculation section 71 may calculate, as the first difference characteristic, the difference between the first transfer characteristic currently measured by the first characteristic measurement section 41 and the first transfer characteristic when the head of the listener 10 is located on the side of the second speaker 22. The threshold determination section 3 may determine that the listener 10 has changed from the second head state to the first head state when the second difference characteristic obtained as a result of comparing the two second transfer characteristics in the first head state is substantially zero and the level of all frequencies of the first difference characteristic obtained as a result of comparing the first transfer characteristic in the second head state with the first transfer characteristic in the first head state is lower than a third threshold.

[0140] Up to this point, an example has been described in which the head of the listener 10 moves from a position between the first speaker 21 and the second speaker 22 (first head state) to a position on the second speaker 22 side (second head state) and then moves again to a position between the first speaker 21 and the second speaker 22 (first head state), but it is also possible for the head of the listener 10 to move from a position between the first speaker 21 and the second speaker 22 (first head state) to a position on the first speaker 21 side (third head state). Therefore, an example in which the head of the listener 10 changes from the first head state to the third head state will be described below.

[0141] 11 is a diagram showing an example of the configuration of the signal reproduction system immediately after the head of the listener 10 changes from the first head state to the third head state in the first embodiment of the present disclosure. The third head state represents a state in which the head of the listener 10 is positioned on the side of the first speaker 21.

[0142] First, assume that the head of the listener 10 is in the first head state shown in Fig. 1 and then changes to the third head state shown in Fig. 11. In this case, the first characteristic measurement unit 41 measures the first transfer characteristic from the first speaker 21 to the first microphone 31 in the first head state and the third head state, and the second characteristic measurement unit 42 measures the second transfer characteristic from the second speaker 22 to the second microphone 32 in the first head state and the third head state. The first transfer characteristic measured in the first head state and the third head state is shown, for example, in Fig. 12, and the second transfer characteristic measured in the first head state and the third head state is shown, for example, in Fig. 13.

[0143] FIG. 12 is a diagram showing an example of a first transfer characteristic and a first differential characteristic measured in the first head state and the third head state, and FIG. 13 is a diagram showing an example of a second transfer characteristic and a second differential characteristic measured in the first head state and the third head state.

[0144] The upper diagram in Fig. 13 shows the second transfer characteristic from the second speaker 22 to the second microphone 32, with the dashed line showing the second transfer characteristic in a first head state before the head of the listener 10 moves, and the solid line showing the second transfer characteristic in a third head state after the head of the listener 10 moves. The lower diagram in Fig. 13 shows the second differential characteristic obtained by subtracting the second transfer characteristic in the first head state before the movement from the second transfer characteristic in the third head state after the movement. In the second differential characteristic, the level of the frequency band surrounded by the dashed line (for example, 100 to 800 Hz) is uniformly 0 dB or less (approximately -4 to -1 dB).

[0145] On the other hand, the upper diagram in Fig. 12 shows the first transfer characteristic from the first speaker 21 to the first microphone 31, with the dashed line showing the first transfer characteristic in a first head state before the head of the listener 10 moves, and the solid line showing the first transfer characteristic in a third head state after the head of the listener 10 moves. The lower diagram in Fig. 12 shows a first differential characteristic obtained by subtracting the first transfer characteristic in the first head state before the movement from the first transfer characteristic in the third head state after the movement. In the first differential characteristic, the level of the frequency band surrounded by the dashed line (for example, 100 to 800 Hz) is uniformly 0 dB or higher (approximately +1 to +4 dB).

[0146] In this way, when the head of the listener 10 changes from the first head state to the third head state, the level of the second differential characteristic of the second transfer characteristic from the second speaker 22 to the second microphone 32 decreases in a frequency band of, for example, 100 to 800 Hz, and the level of the first differential characteristic of the first transfer characteristic from the first speaker 21 to the first microphone 31 increases in a frequency band of, for example, 100 to 800 Hz. The first differential characteristic and the second differential characteristic are contradictory differential characteristics. Therefore, based on the same concept as described with reference to FIGS. 4 and 5, the threshold determination unit 3 can determine that the head of the listener 10 has changed from the first head state to the third head state by determining whether the levels of the first differential characteristic and the second differential characteristic within a predetermined frequency band are positive or negative.

[0147] Specifically, when the head of the listener 10 is located between the first speaker 21 and the second speaker 22, the threshold determination unit 3 detects the levels of the first differential characteristic and the second differential characteristic at multiple frequency points within a predetermined frequency band. The threshold determination unit 3 counts the number X of frequency points where the level is a positive value and the number Y of frequency points where the level is a negative value for each of the first differential characteristic and the second differential characteristic. When the number X of frequency points of the first differential characteristic is equal to or greater than a first threshold and the number Y of frequency points of the second differential characteristic is equal to or greater than a second threshold, the threshold determination unit 3 determines that the head of the listener 10 has moved from a position between the first speaker 21 and the second speaker 22 to a position on the first speaker 21 side.

[0148] FIG. 14 is a diagram showing an example of the configuration of the signal reproduction system when the head of the listener 10 is in the third head state according to the first embodiment of the present disclosure.

[0149] When the threshold determination unit 3 determines that the head of the listener 10 has changed from the first head state to the third head state, the switch changeover unit 4 operates the first switch 51 and the second switch 52 as shown in Fig. 14. The switch changeover unit 4 connects the second terminal 512 and the fourth terminal 514 of the first switch 51 and connects the third terminal 523 and the fourth terminal 524 of the second switch 52. The first level adjustment unit 11 reduces the level of the right channel signal from the reproduction unit 40, and the second level adjustment unit 12 reduces the level of the left channel signal from the reproduction unit 40. The first adder 15 then adds the level-reduced right channel signal and the level-reduced left channel signal and outputs the added signal to the second terminal 512 of the first switch 51. The added signal is reproduced from the first speaker 21 via the second terminal 512 to the fourth terminal 514 of the first switch 51. On the other hand, since the fourth terminal 524 of the second switch 52 is electrically connected to the third terminal 523 which is not connected to anything, the second speaker 22 does not reproduce anything.

[0150] Here, the sum signal obtained by adding the right channel signal and the left channel signal reproduced from the first speaker 21 is adjusted by the first level adjustment unit 11 and the second level adjustment unit 12 so that the level is the same as the level of the right channel signal and the left channel signal reproduced from the first speaker 21 and the second speaker 22, respectively, in the first head state of Figure 1.

[0151] As a result, in the third head state, the listener 10 can hear sounds at the same level as in the first head state of FIG. 1 , and therefore does not feel any discomfort from volume changes. Furthermore, the listener 10 can hear the right channel signal and the left channel signal at the same level, and therefore does not feel any loss of information. Furthermore, the level of the sum signal obtained by adding the right channel signal and the left channel signal reproduced from the first speaker 21 is approximately the same as the levels of the right channel signal and the left channel signal reproduced from the first speaker 21 and the second speaker 22, respectively, in the first head state of FIG. 1 , so that an excessive input load is not imposed on the first speaker 21, and no distortion occurs. Furthermore, because no sound is reproduced from the second speaker 22, and the level of the sound reproduced from the first speaker 21 is not increased, sound leakage to the surroundings can be suppressed without using a special, highly sound-insulating covering material as in Patent Document 1, and people near the seat 100 will not be annoyed.

[0152] FIG. 15 is a flowchart illustrating the operation of the signal reproducing device 1 according to the first embodiment of the present disclosure.

[0153] First, in step S1, the reproduction unit 40 reproduces the right channel signal and the left channel signal from the sound source.

[0154] Next, in step S2, the first level adjustment unit 11 and the third level adjustment unit 13 reduce the level of the right channel signal reproduced by the reproduction unit .

[0155] Next, in step S3, the second level adjustment unit 12 and the fourth level adjustment unit 14 reduce the level of the left channel signal reproduced by the reproduction unit 40.

[0156] Next, in step S4, the first adder 15 and the second adder 16 add the first level adjuster 11 and the third level adjustment unit 13 the right channel signal whose level has been reduced by the second level adjustment unit 12 and the fourth level adjustment unit 14 The left channel signal is added to the left channel signal whose level has been reduced by

[0157] Next, in step S5, the head detection unit 7 detects the position of the head of the listener 10. The head detection unit 7 detects whether the head of the listener 10 is located between the first speaker 21 and the second speaker 22, on the first speaker 21 side, or on the second speaker 22 side.

[0158] Next, in step S6, the switch changeover section 4 determines whether the head of the listener 10 is located between the first speaker 21 and the second speaker 22 or not.

[0159] If it is determined that the head of the listener 10 is located between the first speaker 21 and the second speaker 22 (YES in step S6), then in step S7 the switch changeover unit 4 changes the input states of the first speaker 21 and the second speaker 22 to a first input state in which the right channel signal is input to the first speaker 21 and the left channel signal is input to the second speaker 22. That is, the switch changeover unit 4 controls the first switch 51 to connect the first terminal 511 and the fourth terminal 514, and controls the second switch 52 to connect the first terminal 521 and the fourth terminal 524. As a result, the first speaker 21 outputs the right channel signal, and the second speaker 22 outputs the left channel signal.

[0160] On the other hand, if it is determined that the head of the listener 10 is not located between the first speaker 21 and the second speaker 22 (NO in step S6), in step S8, the switch control unit 4 determines whether the head of the listener 10 is located on the first speaker 21 side.

[0161] If it is determined that the head of the listener 10 is located on the side of the first speaker 21 (YES in step S8), in step S9 the switch changeover unit 4 changes the input states of the first speaker 21 and the second speaker 22 to a third input state in which the output signal from the first adder 15 is input to the first speaker 21, and neither the left channel signal nor the output signal from the second adder 16 is input to the second speaker 22. That is, the switch changeover unit 4 controls the first switch 51 to connect the second terminal 512 and the fourth terminal 514, and controls the second switch 52 to connect the third terminal 523 and the fourth terminal 524. As a result, the first speaker 21 outputs an added signal obtained by adding the level-reduced right channel signal and the level-reduced left channel signal, and the second speaker 22 outputs nothing.

[0162] On the other hand, if it is determined that the head of the listener 10 is not located on the side of the first speaker 21, that is, if it is determined that the head of the listener 10 is located on the side of the second speaker 22 (NO in step S8), in step S10, the switch changeover unit 4 changes the input states of the first speaker 21 and the second speaker 22 to a second input state in which neither the right channel signal nor the output signal is input to the first speaker 21, and the output signal from the second adder 16 is input to the second speaker 22. That is, the switch changeover unit 4 controls the first switch 51 to connect the third terminal 513 and the fourth terminal 514, and controls the second switch 52 to connect the second terminal 522 and the fourth terminal 524. As a result, the first speaker 21 does not output anything, and the second speaker 22 outputs an added signal obtained by adding the level-reduced right channel signal and the level-reduced left channel signal.

[0163] In this way, depending on the position of the head of the listener 10, the input states of the first speaker 21 placed near the right ear of the listener 10 and the second speaker 22 placed near the left ear of the listener 10 can be switched between one of a first input state in which the right channel signal is input to the first speaker 21 and the left channel signal is input to the second speaker 22, a second input state in which an output signal obtained by adding together the level-adjusted right channel signal and the level-adjusted left channel signal is input to the second speaker 22 and neither the right channel signal nor the output signal is input to the first speaker 21, and a third input state in which neither the left channel signal nor the output signal is input to the second speaker 22 and the output signal is input to the first speaker 21.

[0164] For example, when the head of the listener 10 is on the side of the first speaker 21, an output signal obtained by adding together the level-adjusted right channel signal and the level-adjusted left channel signal is input to the first speaker 21, and neither the left channel signal nor the output signal is input to the second speaker 22. Also, for example, when the head of the listener 10 is on the side of the second speaker 22, neither the right channel signal nor the output signal is input to the first speaker 21, and the output signal is input to the second speaker 22.

[0165] Therefore, even if the head of the listener 10 is tilted toward one of the left and right speakers, the listener 10 can hear all the information from the right and left channel signals reproduced from the sound source without missing any information from the other speaker.

[0166] Next, the operation of the head detection unit 7 that detects the position of the head of the listener 10 will be described.

[0167] Figure 16 is a first flowchart for explaining the operation of the head detection unit 7 in embodiment 1 of the present disclosure, Figure 17 is a second flowchart for explaining the operation of the head detection unit 7 in embodiment 1 of the present disclosure, and Figure 18 is a third flowchart for explaining the operation of the head detection unit 7 in embodiment 1 of the present disclosure.

[0168] 16 , in a first head state in which the head of the listener 10 is located between the first speaker 21 and the second speaker 22, the right channel signal output from the first speaker 21 is detected by the first microphone 31, and the measured first transfer characteristic is stored in the first memory 61 as the first initial transfer characteristic. The left channel signal output from the second speaker 22 is detected by the second microphone 32, and the measured second transfer characteristic is stored in the second memory 62 as the second initial transfer characteristic. Then, a difference between the first or second transfer characteristic measured in each of the first, second, and third head states and the first or second initial transfer characteristic is calculated. However, the present disclosure is not limited to this. For example, a difference between the first or second transfer characteristic measured previously in the first head state and the first or second transfer characteristic measured currently in the second head state may be calculated. That is, the threshold determination unit 3 can determine the head position more accurately by appropriately combining the first initial transfer characteristic, the second initial transfer characteristic, the first transfer characteristic for the first head state, the second transfer characteristic for the second head state, and the third transfer characteristic for the third head state each time depending on the state of head movement of the listener 10.

[0169] First, in step S101, as an initial condition, in a first head state in which the head of the listener 10 is located between the first speaker 21 and the second speaker 22, the first transfer characteristic and the second transfer characteristic when a right channel signal is output from the first speaker 21 and a left channel signal is output from the second speaker 22 are stored in advance in the first memory 61 and the second memory 62 as the first initial transfer characteristic and the second initial transfer characteristic.

[0170] The first and second initial transfer characteristics may be stored at the time of shipping the signal reproduction device 1. Alternatively, the first and second transfer characteristics may be measured when the listener 10 is first seated in the seat 100 in the first head position, and the measured first and second transfer characteristics may be stored as the first and second initial transfer characteristics.

[0171] Next, in step S111, the switch control unit 4 controls the first switch 51 and the second switch 52, and performs stereo output processing to output a right channel signal from the first speaker 21 and a left channel signal from the second speaker 22, assuming that the head of the listener 10 is located between the first speaker 21 and the second speaker 22.

[0172] Next, in step S112, the first characteristic measuring unit 41 measures the first transfer characteristic from the first speaker 21 to the first microphone 31, and the second characteristic measuring unit 42 measures the second transfer characteristic from the second speaker 22 to the second microphone 32.

[0173] Next, in step S113, the first characteristic measuring section 41 stores the measured first transfer characteristic in the first memory 61, and the second characteristic measuring section 42 stores the measured second transfer characteristic in the second memory 62.

[0174] Next, in step S114, the first difference calculation unit 71 calculates a first difference characteristic between the first transfer characteristic stored in the first memory 61 in step S113 and a first initial transfer characteristic previously stored in the first memory 61, and the second difference calculation unit 72 calculates a second difference characteristic between the second transfer characteristic stored in the second memory 62 in step S113 and a second initial transfer characteristic previously stored in the second memory 62.

[0175] Next, in steps S115 to S117, the threshold value determining section 3 determines the position of the head of the listener 10 based on the first differential characteristic and the second differential characteristic, and transitions to an appropriate state depending on the determination result.

[0176] That is, in step S115, the threshold decision unit 3 decides whether or not the levels of the first and second differential characteristics within the predetermined frequency bands are substantially 0. If the levels of the first and second differential characteristics within the predetermined frequency bands are substantially 0, the threshold decision unit 3 decides that the head of the listener 10 is located between the first speaker 21 and the second speaker 22. If it is decided that the head of the listener 10 is located between the first speaker 21 and the second speaker 22, the process returns to step S111. On the other hand, if the levels of the first and second differential characteristics within the predetermined frequency bands are not substantially 0, the process proceeds to step S116.

[0177] Next, in step S116, the threshold determination unit 3 determines whether the number Y of frequency points in the first differential characteristic is equal to or greater than the second threshold and whether the number X of frequency points in the second differential characteristic is equal to or greater than the first threshold. The number Y of frequency points in the first differential characteristic represents the number of frequency points in the first differential characteristic where the level is a negative value within a predetermined frequency band. The number X of frequency points in the second differential characteristic represents the number of frequency points in the second differential characteristic where the level is a positive value within a predetermined frequency band.

[0178] Here, if the number Y of frequency points in the first differential characteristic is equal to or greater than the second threshold and the number X of frequency points in the second differential characteristic is equal to or greater than the first threshold, the threshold decision unit 3 decides that the head of the listener 10 has moved toward the second speaker 22. If it is decided that the head of the listener 10 has moved toward the second speaker 22, the process proceeds to step S121 in Fig. 17. On the other hand, if the number Y of frequency points in the first differential characteristic is not equal to or greater than the second threshold or the number X of frequency points in the second differential characteristic is not equal to or greater than the first threshold, the process proceeds to step S117.

[0179] Next, in step S117, the threshold value determination unit 3 , thIt is determined whether the number of frequency points X of the first differential characteristic is equal to or greater than a first threshold value and the number of frequency points Y of the second differential characteristic is equal to or greater than a second threshold value. Note that the number of frequency points X of the first differential characteristic represents the number of frequency points in the first differential characteristic where the level is a positive value within a predetermined frequency band. The number of frequency points Y of the second differential characteristic represents the number of frequency points in the second differential characteristic where the level is a negative value within a predetermined frequency band.

[0180] Here, if the number X of frequency points of the first differential characteristic is equal to or greater than the first threshold and the number Y of frequency points of the second differential characteristic is equal to or greater than the second threshold, the threshold decision unit 3 decides that the head of the listener 10 has moved toward the first speaker 21. If it is decided that the head of the listener 10 has moved toward the first speaker 21, the process proceeds to step S131 in Fig. 18. On the other hand, if the number X of frequency points of the first differential characteristic is not equal to or greater than the first threshold or the number Y of frequency points of the second differential characteristic is not equal to or greater than the second threshold, the process returns to step S111.

[0181] In step S115, if the number of frequency points X of the first differential characteristic and the second differential characteristic is not equal to or greater than the first threshold and the number of frequency points Y of the first differential characteristic and the second differential characteristic is not equal to or greater than the second threshold, the threshold determination unit 3 may determine that the levels of the first differential characteristic and the second differential characteristic within a predetermined frequency band are substantially 0, and may determine that the head of the listener 10 is located between the first speaker 21 and the second speaker 22.

[0182] Next, an example in which the operation has shifted to step S121 in the second head state shown in FIG. 17 will be described.

[0183] In step S121, the switch control unit 4 controls the first switch 51 and the second switch 52 to perform mono output processing in which nothing is output from the first speaker 21 and an added signal of the right channel signal and the left channel signal is output from the second speaker 22.

[0184] Next, in step S122, the first characteristic measuring unit 41 measures the first transfer characteristic from the first speaker 21 to the first microphone 31, and the second characteristic measuring unit 42 measures the second transfer characteristic from the second speaker 22 to the second microphone 32.

[0185] Next, in step S123, the first characteristic measuring section 41 stores the measured first transfer characteristic in the first memory 61, and the second characteristic measuring section 42 stores the measured second transfer characteristic in the second memory 62.

[0186] Next, in step S124, the first difference calculation unit 71 calculates a first difference characteristic between the first transfer characteristic stored in the first memory 61 in step S123 and a first initial transfer characteristic previously stored in the first memory 61, and the second difference calculation unit 72 calculates a second difference characteristic between the second transfer characteristic stored in the second memory 62 in step S123 and a second initial transfer characteristic previously stored in the second memory 62.

[0187] Next, in steps S125 and S126, the threshold value determining section 3 determines the position of the head of the listener 10 based on the first differential characteristic and the second differential characteristic, and transitions to an appropriate state depending on the determination result.

[0188] That is, in step S125, the threshold determination unit 3 determines whether the levels of all frequencies in the first differential characteristic are lower than the third threshold and whether the number Y of frequency points in the second differential characteristic is equal to or greater than the second threshold. Note that the number Y of frequency points in the second differential characteristic represents the number of frequency points in the second differential characteristic whose levels are negative within a predetermined frequency band.

[0189] Here, if the level of all frequencies of the first differential characteristic is lower than the third threshold and the number Y of frequency points of the second differential characteristic is equal to or greater than the second threshold, the threshold determination unit 3 determines that the head of the listener 10 has moved between the first speaker 21 and the second speaker 22. If it is determined that the head of the listener 10 has moved between the first speaker 21 and the second speaker 22, the process proceeds to step S111 in Fig. 16. On the other hand, if the level of all frequencies of the first differential characteristic is not lower than the third threshold or the number Y of frequency points of the second differential characteristic is not equal to or greater than the second threshold, the process proceeds to step S126.

[0190] Next, in step S126, the threshold value determination unit 3 determines whether the level of all frequencies of the first differential characteristic is lower than the third threshold value and the level of the second differential characteristic within a predetermined frequency band is substantially 0 or not.

[0191] Here, if the levels of all frequencies of the first differential characteristic are lower than the third threshold value and the level of the second differential characteristic within the predetermined frequency band is substantially 0, the threshold value determination unit 3 determines that the head of the listener 10 is on the side of the second speaker 22. If it is determined that the head of the listener 10 is on the side of the second speaker 22, the process returns to step S121.

[0192] In step S126, if the number X of frequency points of the second differential characteristic is not equal to or greater than the first threshold and the number Y of frequency points of the second differential characteristic is not equal to or greater than the second threshold, the threshold determination unit 3 may determine that the level of the second differential characteristic within the predetermined frequency band is substantially 0.

[0193] Here, even if the head of the listener 10 approaches the first speaker 21 from the second speaker 22 side, the threshold value determination unit 3 may not be able to clearly determine whether the listener 10 is in the first head state, in which the head is in the center, or the third head state, in which the head is on the first speaker 21 side. In such a case, the listener 10 may transition to the first head state and then make a determination again to determine whether the head is in a position between the first speaker 21 and the second speaker 22, or on the first speaker 21 side.

[0194] Next, an example in which the operation has shifted to step S131 in the third head state of FIG. 18 will be described.

[0195] In step S131, the switch control unit 4 controls the first switch 51 and the second switch 52 to output a sum signal of the right channel signal and the left channel signal from the first speaker 21, and executes mono output processing in which nothing is output from the second speaker 22.

[0196] Next, in step S132, the first characteristic measuring unit 41 measures the first transfer characteristic from the first speaker 21 to the first microphone 31, and the second characteristic measuring unit 42 measures the second transfer characteristic from the second speaker 22 to the second microphone 32.

[0197] Next, in step S133, the first characteristic measuring section 41 stores the measured first transfer characteristic in the first memory 61, and the second characteristic measuring section 42 stores the measured second transfer characteristic in the second memory 62.

[0198] Next, in step S134, the first difference calculation unit 71 calculates a first difference characteristic between the first transfer characteristic stored in the first memory 61 in step S133 and a first initial transfer characteristic previously stored in the first memory 61, and the second difference calculation unit 72 calculates a second difference characteristic between the second transfer characteristic stored in the second memory 62 in step S133 and a second initial transfer characteristic previously stored in the second memory 62.

[0199] Next, in steps S135 and S136, the threshold value determining section 3 determines the position of the head of the listener 10 based on the first and second differential characteristics, and transitions to an appropriate state depending on the determination result.

[0200] That is, in step S135, the threshold determination unit 3 determines whether the number Y of frequency points in the first differential characteristic is equal to or greater than the second threshold and the levels of all frequencies in the second differential characteristic are lower than the third threshold. Note that the number Y of frequency points in the first differential characteristic represents the number of frequency points in the first differential characteristic whose levels are negative within a predetermined frequency band.

[0201] Here, if the number Y of frequency points of the first differential characteristic is equal to or greater than the second threshold and the level of all frequencies of the second differential characteristic is lower than the third threshold, the threshold determination unit 3 determines that the head of the listener 10 has moved between the first speaker 21 and the second speaker 22. If it is determined that the head of the listener 10 has moved between the first speaker 21 and the second speaker 22, the process proceeds to step S111 in Fig. 16. On the other hand, if the number Y of frequency points of the first differential characteristic is not equal to or greater than the second threshold or the level of all frequencies of the second differential characteristic is not lower than the third threshold, the process proceeds to step S136.

[0202] Next, in step S136, the threshold value determination unit 3 determines whether the level of the first differential characteristic within a predetermined frequency band is substantially 0 and whether the level of the second differential characteristic at all frequencies is lower than the third threshold value.

[0203] Here, if the level of the first differential characteristic within the predetermined frequency band is substantially 0 and the level of all frequencies of the second differential characteristic is lower than the third threshold, the threshold determination unit 3 determines that the head of the listener 10 is on the side of the first speaker 21. If it is determined that the head of the listener 10 is on the side of the first speaker 21, the process returns to step S131.

[0204] In step S136, if the number X of frequency points of the first differential characteristic is not equal to or greater than the first threshold and the number Y of frequency points of the first differential characteristic is not equal to or greater than the second threshold, the threshold determination unit 3 may determine that the level of the first differential characteristic within the predetermined frequency band is substantially 0.

[0205] In this way, by setting the first head state as the initial state and transitioning to the second head state or the third head state via the first head state, the head position can be determined stably.

[0206] Furthermore, the relationship between the first head state, the second head state, and the third head state will be further explained with reference to FIG.

[0207] FIG. 19 is a schematic diagram for explaining the relationship between the first head state, the second head state, and the third head state in the first embodiment.

[0208] FIG. 19 shows, as operations for measuring the first transfer characteristic and the second transfer characteristic when the head of the listener 10 is in the first head state, a first measurement operation (step S201) in which a right channel signal and a left channel signal are stereo-output from the first speaker 21 and the second speaker 22, a second measurement operation (step S202) in which an added signal is monaurally output from only the second speaker 22, and a third measurement operation (step S203) in which an added signal is monaurally output from only the first speaker 21.

[0209] Furthermore, as operations for measuring the first transfer characteristic and the second transfer characteristic when the head of the listener 10 is in the second head state, a fourth measurement operation (step S204) in which the right channel signal and the left channel signal are output in stereo from the first speaker 21 and the second speaker 22, and a fifth measurement operation (step S205) in which the sum signal is output in mono from only the second speaker 22 are shown.

[0210] Furthermore, as operations for measuring the first transfer characteristic and the second transfer characteristic when the head of the listener 10 is in the third head state, a sixth measurement operation (step S206) in which the right channel signal and the left channel signal are output in stereo from the first speaker 21 and the second speaker 22, and a seventh measurement operation (step S207) in which the sum signal is output in mono from only the first speaker 21 are shown.

[0211] 19, if the head of the listener 10 continues to be in the first head state, the first measurement operation of step S201 is repeated. Here, for example, if the head of the listener 10 changes from the first head state to the third head state, the sixth measurement operation of step S206 is performed. As a result, it is determined that the head of the listener 10 has changed from the first head state to the third head state, and the seventh measurement operation of step S207 is performed. Then, if the head of the listener 10 continues to be in the third head state, the seventh measurement operation of step S207 is repeated. Here, for example, if the head of the listener 10 changes from the third head state to the first head state, the third measurement operation of step S203 is performed. As a result, it is determined that the head of the listener 10 has changed from the third head state to the first head state, and the first measurement operation of step S201 is performed.

[0212] Similarly, for example, if the head of the listener 10 changes from the first head state to the second head state, the fourth measurement operation of step S204 is performed. As a result, it is determined that the head of the listener 10 has changed from the first head state to the second head state, and the fifth measurement operation of step S205 is performed. If the head of the listener 10 continues to be in the second head state, the fifth measurement operation of step S205 is repeated. Here, for example, if the head of the listener 10 changes from the second head state to the first head state, the second measurement operation of step S202 is performed. As a result, it is determined that the head of the listener 10 has changed from the second head state to the first head state, and the first measurement operation of step S201 is performed.

[0213] In this way, the first to seventh measurement operations shown in FIG. 19 are repeated depending on the state of the head of the listener 10, and each time, the first to seventh measurement operations measure the first and second transfer characteristics anew, and these are additionally stored in the first memory 61 and the second memory 62.

[0214] FIG. 20 is a diagram showing an example of memory areas of the first memory 61 and the second memory 62 in the first embodiment.

[0215] As shown in FIG. 20, the first memory 61 and the second memory 62 respectively reserve a memory area 601 for the first head state, a memory area 602 for the second head state, and a memory area 603 for the third head state.

[0216] The memory area 601 for the first head state stores in advance the first and second initial transfer characteristics measured in the initial measurement operation. The first and second initial transfer characteristics are stored in the first area of ​​the memory area 601.

[0217] Furthermore, the first head state memory area 601, the second head state memory area 602, and the third head state memory area 603 store the first transfer characteristic and the second transfer characteristic in different areas for each measurement operation. For example, the first transfer characteristic and the second transfer characteristic measured in the first measurement operation are stored in the second area of ​​the memory area 601, the first transfer characteristic and the second transfer characteristic measured in the second measurement operation are stored in the third area of ​​the memory area 601, and the first transfer characteristic and the second transfer characteristic measured in the third measurement operation are stored in the fourth area of ​​the memory area 601.

[0218] Furthermore, for example, the first and second transfer characteristics measured in the fourth measurement operation are stored in the first area of ​​the memory area 602, and the first and second transfer characteristics measured in the fifth measurement operation are stored in the second area of ​​the memory area 602. Furthermore, for example, the first and second transfer characteristics measured in the sixth measurement operation are stored in the first area of ​​the memory area 603, and the first and second transfer characteristics measured in the seventh measurement operation are stored in the second area of ​​the memory area 603.

[0219] For example, if the head of the listener 10 continues to be in the first head state, the first measurement operation in step S201 in Fig. 19 is repeated during that time. In this case, the first transfer characteristic and the second transfer characteristic corresponding to the number of times measured in the first measurement operation are stored in the memory area 601 for the first head state in Fig. 20. Also, if the head state shifts to the second head state once and then returns to the first head state again, the previous data is not overwritten but is additionally stored in the memory area 601.

[0220] Similarly to the memory area 601, the first transfer characteristic and the second transfer characteristic are also stored in the memory area 602 for the second head state and the memory area 603 for the third head state.

[0221] In this way, since a large amount of data is stored in the first memory 61 and the second memory 62, the first difference calculation unit 71, the second difference calculation unit 72, and the threshold determination unit 3 simply select the most appropriate data and its combination from the stored data.

[0222] (Embodiment 2) In the first embodiment, the position of the head of the listener 10 is detected using the first transfer characteristic from the first speaker 21 to the first microphone 31 and the second transfer characteristic from the second speaker 22 to the second microphone 32. In contrast, in the second embodiment, the position of the head of the listener 10 is detected based on an image of the head of the listener 10 captured by a camera.

[0223] FIG. 21 is a diagram showing an example of the configuration of the signal reproduction system when the head of the listener 10 is in the first head state according to the second embodiment of the present disclosure.

[0224] 21 includes a signal reproducing device 1A, a first speaker 21, a second speaker 22, and a camera 5. In the second embodiment, the same components as those in the first embodiment are denoted by the same reference numerals, and the description thereof will be omitted.

[0225] The signal reproduction device 1A includes a first level adjustment unit 11, a second level adjustment unit 12, a third level adjustment unit 13, a fourth level adjustment unit 14, a first adder unit 15, a second adder unit 16, a reproduction unit 40, a first switch 51, a second switch 52, a head detection unit 7A, and a switch switching unit 4.

[0226] The camera 5 is placed in front of the listener 10 and captures an image of the head of the listener 10. The camera 5 outputs the captured image to a head detection unit 7A of the signal reproduction device 1A.

[0227] The head detection unit 7A detects the position of the head of the listener 10. The head detection unit 7A includes an image acquisition unit 73 and a head position determination unit 74.

[0228] The image acquisition unit 73 acquires an image of the head of the listener 10. The image acquisition unit 73 acquires an image captured by the camera 5.

[0229] The head position determination unit 74 determines the position of the head of the listener 10 by analyzing the image acquired by the image acquisition unit 73. The head position determination unit 74 recognizes the head of the listener 10, the first speaker 21, and the second speaker 22 in the image, and determines whether the head of the listener 10 is located between the first speaker 21 and the second speaker 22, on the first speaker 21 side, or on the second speaker 22 side.

[0230] The switch changeover unit 4 changes the input states of the first speaker 21 and the second speaker 22 according to the position of the head of the listener 10 detected by the head detection unit 7A between a first input state in which the right channel signal is input to the first speaker 21 and the left channel signal is input to the second speaker 22, a second input state in which the output signal from the second adder 16 is input to the second speaker 22 and neither the right channel signal nor the output signal from the first adder 15 is input to the first speaker 21, and a third input state in which neither the left channel signal nor the output signal is input to the second speaker 22 and the output signal from the first adder 15 is input to the first speaker 21. The switch changeover unit 4 controls the first switch 51 and the second switch 52 according to the position of the head of the listener 10 detected by the head detection unit 7A.

[0231] The operation of the signal reproducing device 1A in the second embodiment other than the head detecting unit 7A is the same as the operation of the signal reproducing device 1 in the first embodiment other than the head detecting unit 7, and therefore a description thereof will be omitted.

[0232] In this way, the position of the head of the listener 10 can be detected from the image of the head of the listener 10.

[0233] (Embodiment 3) In the first embodiment, two microphones, a first microphone 31 and a second microphone 32, are used to detect the position of the head of the listener 10, but in the third embodiment, one microphone is used to detect the position of the head of the listener 10.

[0234] FIG. 22 is a diagram illustrating an example of the configuration of a signal reproduction system when the head of the listener 10 is in the first head state according to the third embodiment of the present disclosure.

[0235] The signal reproduction system shown in Fig. 22 includes a signal reproduction device 1B, a first speaker 21, a second speaker 22, and a microphone 33. 3 In this embodiment, the same components as those in the first embodiment are denoted by the same reference numerals, and the description thereof will be omitted.

[0236] The microphone 33 is disposed between the first speaker 21 and the second speaker 22, and in particular, at the midpoint between the first speaker 21 and the second speaker 22.

[0237] The signal reproducing device 1B includes a first level adjusting section 11, a second level adjusting section 12, a third level adjusting section 13, a fourth level adjusting section 14, a first adding section 15, a second adding section 16, a reproducing section 40, a first switch 51, a second switch 52, a head detecting section 7B, and a switch changing section 4. Note that in Fig. 22, the first level adjusting section 11, the second level adjusting section 12, the third level adjusting section 13, the fourth level adjusting section 14, the first adding section 15, the second adding section 16, the first switch 51, and the second switch 52 are omitted.

[0238] The head detection unit 7B includes a first characteristic measurement unit 41B, a second characteristic measurement unit 42B, a first memory 61, a second memory 62, a first difference calculation unit 71B, a second difference calculation unit 72B, a threshold determination unit 3B, a first measurement signal generation unit 81, a second measurement signal generation unit 82, a third addition unit 83, and a fourth addition unit 84.

[0239] The first measurement signal generator 81 generates a first measurement signal that does not overlap with the right channel signal. The first measurement signal is, for example, an ultrasonic signal of 20 kHz or higher, or a signal in the audio frequency band of 10 kHz to 20 kHz that is lower in level than the right channel signal.

[0240] The second measurement signal generator 82 generates a second measurement signal that does not overlap with the left channel signal and is different from the first measurement signal. The second measurement signal is, for example, an ultrasonic signal of 20 kHz or higher, or a signal in the audio frequency band of 10 kHz to 20 kHz that is lower in level than the right channel signal.

[0241] The third adder 83 adds the right channel signal reproduced by the reproduction unit 40 and the first measurement signal generated by the first measurement signal generation unit 81. The third adder 83 outputs an added signal obtained by adding the right channel signal and the first measurement signal to the first level adjustment unit 11, the third level adjustment unit 13, and the first terminal 511 of the first switch 51.

[0242] The fourth terminal 514 of the first switch 51 is connected to the first speaker 21 and the first characteristic measurement unit 41B. When the fourth terminal 514 and the first terminal 511 are connected, the output signal from the third adder 83 is output to the first speaker 21 and the first characteristic measurement unit 41B. When the fourth terminal 514 and the second terminal 512 are connected, the output signal output from the first adder 15 is output to the first speaker 21 and the first characteristic measurement unit 41B. When the fourth terminal 514 and the third terminal 513 are connected, neither the output signal from the third adder 83 nor the output signal from the first adder 15 is output to the first speaker 21 and the first characteristic measurement unit 41B.

[0243] Fourth adder 84 adds the left channel signal reproduced by reproduction unit 40 and the second measurement signal generated by second measurement signal generator 82. Fourth adder 84 outputs an added signal obtained by adding the left channel signal and the second measurement signal to second level adjuster 12, fourth level adjuster 14, and first terminal 521 of second switch 52.

[0244] The fourth terminal 524 of the second switch 52 is connected to the second speaker 22 and the second characteristic measurement unit 42B. When the fourth terminal 524 and the first terminal 521 are connected, the output signal from the fourth adder 84 is output to the second speaker 22 and the second characteristic measurement unit 42B. When the fourth terminal 524 and the second terminal 522 are connected, the output signal output from the second adder 16 is output to the second speaker 22 and the second characteristic measurement unit 42B. When the fourth terminal 524 and the third terminal 523 are connected, neither the output signal from the fourth adder 84 nor the output signal from the second adder 16 is output to the second speaker 22 and the second characteristic measurement unit 42B.

[0245] The first characteristic measuring unit 41B measures the first transfer characteristic from the first speaker 21 to the microphone 33 using a reproduced sound signal detected by a microphone 33 installed between the first speaker 21 and the second speaker 22 and an added signal obtained by adding the first measurement signal generated by the first measurement signal generating unit 81 to the right channel signal reproduced by the reproduction unit 40.

[0246] The second characteristic measuring unit 42B measures the second transfer characteristic from the second speaker 22 to the microphone 33 using a reproduced sound signal detected by a microphone 33 installed between the first speaker 21 and the second speaker 22 and an added signal obtained by adding the second measurement signal generated by the second measurement signal generating unit 82 to the left channel signal reproduced by the reproduction unit 40.

[0247] The first difference calculation unit 71B calculates the difference between the first transfer characteristic currently measured by the first characteristic measurement unit 41B and the first transfer characteristic previously measured and stored in the first memory 61 as the first difference characteristic.

[0248] The second difference calculation unit 72B calculates the difference between the second transfer characteristic currently measured by the second characteristic measurement unit 42B and the second transfer characteristic previously measured and stored in the second memory 62 as the second difference characteristic.

[0249] The first difference calculating section 71B may calculate, as the first difference characteristic, the difference between the first transfer characteristic currently measured by the first characteristic measuring section 41B and the first initial transfer characteristic stored in the first memory 61. The second difference calculating section 72B may calculate, as the second difference characteristic, the difference between the second transfer characteristic currently measured by the second characteristic measuring section 42B and the second initial transfer characteristic stored in the second memory 62.

[0250] The threshold value determining section 3B determines the position of the head of the listener 10 based on the first difference characteristic calculated by the first difference calculating section 71B and the second difference characteristic calculated by the second difference calculating section 72B.

[0251] FIG. 23 is a diagram showing an example of a first transfer characteristic and a first differential characteristic measured in a first head state before head movement and a second head state after head movement in this embodiment 3, and FIG. 24 is a diagram showing an example of a second transfer characteristic and a second differential characteristic measured in a first head state before head movement and a second head state after head movement in this embodiment 3.

[0252] The top diagram in FIG. 23 shows the first transfer characteristic from the first speaker 21 to the microphone 33 when the head of the listener 10 before head movement is located between the first speaker 21 and the second speaker 22 (first head state). The first transfer characteristic before head movement includes a first measurement signal 811 added to the right channel signal. The middle diagram in FIG. 23 shows the first transfer characteristic from the first speaker 21 to the microphone 33 when the head of the listener 10 after head movement is located on the side of the second speaker 22 (second head state). The first transfer characteristic after head movement includes a first measurement signal 812 added to the right channel signal. The level of the first measurement signal 812 is lower than the level of the first measurement signal 811. The bottom diagram in FIG. 23 shows the first differential characteristic obtained by subtracting the first transfer characteristic in the first head state before head movement from the first transfer characteristic in the second head state after head movement. In the first differential characteristic, the level of the first measurement signal 813 is a negative value.

[0253] The top diagram in FIG. 24 shows the second transfer characteristic from the second speaker 22 to the microphone 33 when the head of the listener 10 before head movement is located between the first speaker 21 and the second speaker 22 (first head state). The second transfer characteristic before head movement includes a second measurement signal 821 added to the left channel signal. The middle diagram in FIG. 24 shows the second transfer characteristic from the second speaker 22 to the microphone 33 when the head of the listener 10 after head movement is located on the second speaker 22 side (second head state). The second transfer characteristic after head movement includes a second measurement signal 822 added to the left channel signal. The level of the second measurement signal 822 is higher than the level of the second measurement signal 821. The bottom diagram in FIG. 24 shows the second difference characteristic obtained by subtracting the second transfer characteristic in the first head state before head movement from the second transfer characteristic in the second head state after head movement. In the second differential characteristic, the level of the second measurement signal 823 is a positive value.

[0254] In this way, when the head of the listener 10 changes from the first head state to the second head state, the level of the second measurement signal 823 included in the second differential characteristic of the second transfer characteristic from the second speaker 22 to the microphone 33 becomes greater than 0, and the level of the first measurement signal 813 included in the first differential characteristic of the first transfer characteristic from the first speaker 21 to the microphone 33 becomes less than 0.

[0255] Therefore, the threshold value determination unit 3B detects the level of the first measurement signal included in the first differential characteristic and the level of the second measurement signal included in the second differential characteristic when the head of the listener 10 is located between the first speaker 21 and the second speaker 22. When the level of the first measurement signal included in the first differential characteristic is less than 0 and the level of the second measurement signal included in the second differential characteristic is greater than 0, the threshold value determination unit 3B determines that the head of the listener 10 has moved from a position between the first speaker 21 and the second speaker 22 to a position on the second speaker 22 side.

[0256] Furthermore, if the level of the first measurement signal included in the first differential characteristic is greater than 0 and the level of the second measurement signal included in the second differential characteristic is less than 0, the threshold determination unit 3B determines that the head of the listener 10 has moved from a position between the first speaker 21 and the second speaker 22 to a position on the first speaker 21 side.

[0257] Furthermore, the threshold value determination unit 3B detects the level of the second measurement signal included in the second differential characteristic when the head of the listener 10 is located on the side of the second speaker 22. When the level of the second measurement signal included in the second differential characteristic is less than 0, the threshold value determination unit 3B determines that the head of the listener 10 has moved from a position on the side of the second speaker 22 to a position between the first speaker 21 and the second speaker 22.

[0258] Furthermore, the threshold value determination unit 3B detects the level of the first measurement signal included in the first differential characteristic when the head of the listener 10 is located on the side of the first speaker 21. When the level of the first measurement signal included in the first differential characteristic is less than 0, the threshold value determination unit 3B determines that the head of the listener 10 has moved from a position on the side of the first speaker 21 to a position between the first speaker 21 and the second speaker 22.

[0259] In this way, in the third embodiment, the position of the head of the listener 10 can be detected using one microphone, which makes it possible to further simplify the configuration of the signal reproduction system and further reduce the manufacturing costs of the signal reproduction system.

[0260] In each of the above embodiments, each component may be configured with dedicated hardware or may be realized by executing a software program suitable for that component. Each component may be realized by a program execution unit such as a CPU or processor reading and executing a software program recorded on a recording medium such as a hard disk or semiconductor memory. Furthermore, the program may be executed by another independent computer system by recording the program on a recording medium and transferring it, or by transferring the program via a network.

[0261] Some or all of the functions of the device according to the embodiments of the present disclosure are typically realized as an LSI (Large Scale Integration), which is an integrated circuit. These may be implemented individually on a single chip, or some or all of them may be integrated on a single chip. Furthermore, the integrated circuit is not limited to an LSI, and may be realized using a dedicated circuit or a general-purpose processor. It is also possible to use an FPGA (Field Programmable Gate Array), which can be programmed after LSI manufacturing, or a reconfigurable processor, which allows the connections and settings of circuit cells within the LSI to be reconfigured.

[0262] Furthermore, some or all of the functions of the device according to the embodiment of the present disclosure may be realized by a processor such as a CPU executing a program.

[0263] Furthermore, all the numbers used above are merely examples to specifically explain the present disclosure, and the present disclosure is not limited to the numbers used as examples.

[0264] The order in which the steps are executed shown in the above flowchart is merely an example for specifically explaining the present disclosure, and other orders may be used as long as similar effects are obtained. Also, some of the steps may be executed simultaneously (in parallel) with other steps. [Industrial Applicability]

[0265] The technology according to the present disclosure is useful as a technology for reproducing stereo signals in the vicinity of the listener, because even if the listener's head is biased toward one of the left or right speakers, the listener can hear all of the information from the right channel signal and the left channel signal reproduced from the sound source without missing any information from the other speaker.

Claims

1. a reproduction unit that reproduces a right channel signal and a left channel signal from a sound source; a first level adjustment unit that adjusts the level of the right channel signal reproduced by the reproduction unit; a second level adjustment unit that adjusts the level of the left channel signal reproduced by the reproduction unit; an adder that adds the right channel signal adjusted by the first level adjuster and the left channel signal adjusted by the second level adjuster; a detection unit for detecting the position of the head of a listener; an input switching unit that switches, depending on the position of the head of the listener detected by the detection unit, an input state of a first speaker installed near the right ear of the listener and a second speaker installed near the left ear of the listener, between one of a first input state in which the right channel signal is input to the first speaker and the left channel signal is input to the second speaker, a second input state in which the output signal from the addition unit is input to the second speaker and neither the right channel signal nor the output signal is input to the first speaker, and a third input state in which neither the left channel signal nor the output signal is input to the second speaker and the output signal is input to the first speaker; A signal reproducing device comprising:

2. the detection unit detects whether the head of the listener is in a position between the first speaker and the second speaker, a position on the first speaker side, or a position on the second speaker side; The input switching unit switching to the first input state when the head of the listener is located between the first speaker and the second speaker; switching to the second input state when the head of the listener is at a position on the second speaker side; switching to the third input state when the head of the listener is at a position on the first speaker side; 2. The signal reproducing device according to claim 1.

3. the first level adjustment unit reduces the level of the right channel signal; the second level adjustment unit reduces the level of the left channel signal; 3. A signal reproducing apparatus according to claim 1.

4. The detection unit a first characteristic measurement unit that measures a first transfer characteristic from the first speaker to the first microphone by using a first reproduced sound signal detected by a first microphone installed near the first speaker and the right channel signal reproduced by the reproduction unit; a second characteristic measurement unit that measures a second transfer characteristic from the second speaker to the second microphone using a second reproduced sound signal detected by a second microphone installed near the second speaker and the left channel signal reproduced by the reproduction unit; a memory that stores in advance the first transfer characteristic and the second transfer characteristic when the head of the listener is located between the first speaker and the second speaker as a first initial transfer characteristic and a second initial transfer characteristic; a first difference calculation unit that calculates a difference between the first transfer characteristic currently measured by the first characteristic measurement unit and the first initial transfer characteristic stored in the memory as a first difference characteristic; a second difference calculation unit that calculates a difference between the second transfer characteristic currently measured by the second characteristic measurement unit and the second initial transfer characteristic stored in the memory as a second difference characteristic; a determination unit that determines the position of the head of the listener based on the first difference characteristic calculated by the first difference calculation unit and the second difference characteristic calculated by the second difference calculation unit; Including, 3. A signal reproducing apparatus according to claim 1.

5. The detection unit a first characteristic measurement unit that measures a first transfer characteristic from the first speaker to the first microphone by using a first reproduced sound signal detected by a first microphone installed near the first speaker and the right channel signal reproduced by the reproduction unit; a second characteristic measurement unit that measures a second transfer characteristic from the second speaker to the second microphone using a second reproduced sound signal detected by a second microphone installed near the second speaker and the left channel signal reproduced by the reproduction unit; a memory that stores a first transfer characteristic measured by the first characteristic measuring unit and a second transfer characteristic measured by the second characteristic measuring unit; a first difference calculation unit that calculates a difference between a first transfer characteristic currently measured by the first characteristic measurement unit and a first transfer characteristic previously measured and stored in the memory, as a first difference characteristic; a second difference calculation unit that calculates a difference between the second transfer characteristic currently measured by the second characteristic measurement unit and a second transfer characteristic previously measured and stored in the memory, as a second difference characteristic; a determination unit that determines the position of the head of the listener based on the first difference characteristic calculated by the first difference calculation unit and the second difference characteristic calculated by the second difference calculation unit; Including, 3. A signal reproducing apparatus according to claim 1.

6. The determination unit detecting levels of the first difference characteristic and the second difference characteristic at a plurality of frequency points within a predetermined frequency band when the head of the listener is located between the first speaker and the second speaker; counting the number X of frequency points at which the level is a positive value and the number Y of frequency points at which the level is a negative value for each of the first differential characteristic and the second differential characteristic; if the number X of frequency points of the first differential characteristic is equal to or greater than a first threshold value and the number Y of frequency points of the second differential characteristic is equal to or greater than a second threshold value, it is determined that the head of the listener has moved from a position between the first speaker and the second speaker to a position on the first speaker side; if the number X of frequency points of the second differential characteristic is equal to or greater than the first threshold value and the number Y of frequency points of the first differential characteristic is equal to or greater than the second threshold value, it is determined that the head of the listener has moved from a position between the first speaker and the second speaker to a position on the second speaker side.

6. The signal reproducing device according to claim 5.

7. the first threshold is a value obtained by multiplying the number N of all frequency points in the predetermined frequency band by a constant α, the second threshold is a value obtained by multiplying the number N of all frequency points in the predetermined frequency band by a constant β, The constant α is a value of 0.5 or more and 1 or less, and the constant β is a value of 0.5 or more and 1 or less.

7. The signal reproducing device according to claim 6.

8. The determination unit when the head of the listener is located on the first speaker side, detects levels at a plurality of frequency points within a predetermined frequency band of the first differential characteristic, counts a number Y of frequency points at which the level is a negative value for the first differential characteristic, and determines that the head of the listener has moved from a position on the first speaker side to a position between the first speaker and the second speaker when the number Y of frequency points of the first differential characteristic is equal to or greater than a second threshold; when the head of the listener is at a position on the second speaker side, detects levels at a plurality of frequency points within a predetermined frequency band of the second differential characteristic, counts a number Y of frequency points at which the level is a negative value for the second differential characteristic, and determines that the head of the listener has moved from a position on the second speaker side to a position between the first speaker and the second speaker when the number Y of frequency points of the second differential characteristic is equal to or greater than the second threshold value; 6. The signal reproducing device according to claim 5.

9. the second difference calculation unit, when the head of the listener is located on the first speaker side, calculates, as the second difference characteristic, a difference between the second transfer characteristic currently measured by the second characteristic measurement unit and the second transfer characteristic when the head of the listener is located between the first speaker and the second speaker; the determination unit, when the head of the listener is located on the first speaker side, further determines whether or not a level of all frequencies of the second differential characteristic is lower than a third threshold, and, when the number Y of frequency points of the first differential characteristic is equal to or greater than the second threshold and the level of all frequencies of the second differential characteristic is lower than the third threshold, determines that the head of the listener has moved from a position on the first speaker side to a position between the first speaker and the second speaker; when the head of the listener is located on the second speaker side, the first difference calculation unit calculates, as a first difference characteristic, a difference between the first transfer characteristic currently measured by the first characteristic measurement unit and the first transfer characteristic when the head of the listener is located between the first speaker and the second speaker; When the head of the listener is located on the second speaker side, the determination unit further determines whether or not a level of all frequencies of the first differential characteristic is lower than the third threshold value, and when the number Y of frequency points of the second differential characteristic is equal to or greater than the second threshold value and the level of all frequencies of the first differential characteristic is lower than the third threshold value, determines that the head of the listener has moved from a position on the second speaker side to a position between the first speaker and the second speaker.

9. The signal reproducing device according to claim 8.

10. The detection unit an image acquisition unit that acquires an image of the head of the listener; a determination unit that determines the position of the head of the listener by analyzing the image; Including, 3. A signal reproducing apparatus according to claim 1.

11. A signal reproduction method in a computer, comprising: Reproducing the right channel signal and the left channel signal from the sound source; adjusting the level of the reproduced right channel signal; adjusting the level of the reproduced left channel signal; adding the level-adjusted right channel signal and the level-adjusted left channel signal; Detecting the position of the listener's head; and switching, according to the detected head position of the listener, an input state of a first speaker installed near the right ear of the listener and a second speaker installed near the left ear of the listener to one of: a first input state in which the right channel signal is input to the first speaker and the left channel signal is input to the second speaker; a second input state in which an output signal obtained by addition is input to the second speaker and neither the right channel signal nor the output signal is input to the first speaker; and a third input state in which neither the left channel signal nor the output signal is input to the second speaker and the output signal is input to the first speaker. Signal reproduction method.

12. a reproduction unit that reproduces a right channel signal and a left channel signal from a sound source; a first level adjustment unit that adjusts the level of the right channel signal reproduced by the reproduction unit; a second level adjustment unit that adjusts the level of the left channel signal reproduced by the reproduction unit; an adder that adds the right channel signal adjusted by the first level adjuster and the left channel signal adjusted by the second level adjuster; a detection unit for detecting the position of the head of a listener; and causing the computer to function as an input switching unit that switches, depending on the head position of the listener detected by the detection unit, an input state of a first speaker installed near the right ear of the listener and a second speaker installed near the left ear of the listener, between one of a first input state in which the right channel signal is input to the first speaker and the left channel signal is input to the second speaker, a second input state in which the output signal from the addition unit is input to the second speaker and neither the right channel signal nor the output signal is input to the first speaker, and a third input state in which neither the left channel signal nor the output signal is input to the second speaker and the output signal is input to the first speaker. Signal regeneration program.

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