Portable playback device

Abstract

Provided is a portable sound reproduction device that reduces the discomfort of sound quality changes accompanying changes in the orientation of a housing. A portable sound reproduction device (1) is provided with a plurality of speakers (21, 22) and an attitude sensor (3) that detects a change in the attitude of a housing. Furthermore, the sound processing unit (6) applies a transfer function (H-1 (psi, theta)), which maintains the sound characteristics of the sound wave signal reaching a fixed point in the actual space, to the sound signal having two or more channels on the basis of the attitude change (psi, theta) detected by the attitude sensor (3).

Description

Technical Field

[0001] This invention relates to a portable sound playback device that is free to carry and whose orientation can be changed. Background Technology

[0002] In the past, enjoying music required properly positioned large speakers and a specific listening location. However, in recent years, music can be listened to using mobile devices such as smartphones, eliminating the need for specific locations. On the other hand, mobile devices typically have small speakers, which limits the enjoyment of high-quality music, high volume, or group listening.

[0003] Therefore, a portable speaker device is known that differs from conventional fixed speakers in that it is small, lightweight, and easy to carry, and is equipped with a speaker larger than those found in smartphones and similar devices. This portable speaker device, with its built-in battery, can provide a listening environment both indoors and outdoors.

[0004] Portable music players are increasingly being used in daily life, for example, by being taken into the kitchen or placed in front of the listener in the living room, alongside other activities. This leads to situations where, for example, one might want to shift from being fully immersed in music in front of a portable music player to listening to music as background music while moving around, or vice versa. Furthermore, it leads to situations where one person is immersed in music, or multiple people gather around a portable music player to listen to music, or vice versa.

[0005] Here, a sound playback device is proposed, which consists of a zone player that can switch from stereo mode to mono mode, or vice versa, by changing its configuration orientation (see, for example, Patent Documents 1 and 2). By utilizing this idea in a portable sound playback device, it is possible, for example, to switch from a state of immersion in music to a state of stereo mode by oriented the speaker horizontally, and to switch from a state of immersion in music to a state of mono mode by oriented the speaker upwards, to listen to music as background music or to enjoy music with multiple people around.

[0006] Patent Document 1: Japanese Patent Application Publication No. 2005-136457

[0007] Patent Document 2: Japanese Patent Application Publication No. 2019-80342 Summary of the Invention

[0008] When playing audio in a 2-channel or higher mode, such as stereo, if the portable playback device is rotated, a change in volume may sometimes be heard due to frequency band changes during the rotation and before transitioning to mono mode. Figure 12 It is a graph showing the polar coordinates when playing sound in stereo mode, categorized by frequency band.

[0009] like Figure 12 As shown, for example, when the listener is positioned within 10 degrees to the left and right of the linear axis of symmetry of the left and right speakers, the volume at 1000Hz, 2000Hz, and 8000Hz is uniform. However, if the portable playback device is rotated more than 20 degrees, the volume at 2000Hz and 8000Hz shifts by approximately 5dB. This spectral change could potentially cause a listener rotating the portable playback device to experience a temporary, uncomfortable change in sound quality during the transition to mono mode.

[0010] The present invention is proposed to solve the problems of the prior art as described above, and its purpose is to provide a portable sound playback device that reduces the discomfort caused by changes in sound quality associated with changes in the orientation of the housing.

[0011] To achieve the above objectives, the portable audio playback device of the present invention includes: a plurality of loudspeakers; an attitude sensor that detects attitude changes of the frame; and an audio processing unit that, based on the attitude changes detected by the attitude sensor, applies a transfer function of the acoustic characteristics of an audio signal that maintains a fixed point in the actual space to an audio signal with two or more channels.

[0012] Alternatively, the transfer function may include an inverse filter of the head transfer function from the speaker after the posture change to the fixed point.

[0013] Alternatively, it may have a storage unit that stores the inverse filter for each degree of the attitude change.

[0014] Alternatively, the audio processing unit processes the audio signal in mono mode when at least one of the speakers is located on the upper surface; when the frame is rotated 90 degrees around the vertical axis from the mono mode facing the side of the speaker, it processes the audio signal in 2-channel or higher mode; and when the frame is rotated 90 degrees around the vertical axis from the 2-channel or higher mode facing the side of the speaker, it processes the audio signal in mono mode.

[0015] Alternatively, if the attitude change detected by the attitude sensor reaches a threshold, the audio processing unit generates a mono mode audio signal.

[0016] Alternatively, the threshold may be set for each frequency band, and the audio processing unit may switch to mono mode from the frequency band that reaches the threshold.

[0017] Alternatively, the audio processing unit may downmix the audio signals in the frequency band that reach the threshold into one channel.

[0018] Alternatively, the threshold may be set for each combination of volume and frequency band, and the audio processing unit may switch from a frequency band that reaches the threshold selected according to the volume to a mono mode.

[0019] Alternatively, the transfer function may also include a filter to eliminate crosstalk.

[0020] The effects of the invention

[0021] According to the present invention, it is possible to reduce the discomfort caused by changes in sound quality associated with changes in the orientation of a portable playback device. Attached Figure Description

[0022] Figure 1 This is a schematic diagram showing the appearance of a portable audio playback device.

[0023] Figure 2 This is a schematic diagram illustrating the setup of a portable audio playback device.

[0024] Figure 3 This is a block diagram showing the structure of the portable audio playback device according to the first embodiment.

[0025] Figure 4 This is a diagram illustrating the relationship between a portable audio player and a listener.

[0026] Figure 5 This is a flowchart illustrating an example of the operation of the portable audio playback device according to the first embodiment.

[0027] Figure 6 This is a schematic diagram representing the transfer function table.

[0028] Figure 7 This is a block diagram showing the structure of the portable audio playback device according to the second embodiment.

[0029] Figure 8 This is a flowchart illustrating an example of the operation of the portable audio playback device according to the second embodiment.

[0030] Figure 9 This is a flowchart illustrating an example of the operation of the portable audio playback device according to the second embodiment.

[0031] Figure 10 This is a block diagram showing the structure of the portable audio playback device according to the third embodiment.

[0032] Figure 11 This is a flowchart illustrating an example of the operation of the portable audio playback device according to the third embodiment.

[0033] Figure 12 This is a graph representing polar coordinates in stereo mode of a portable audio playback device. Detailed Implementation

[0034] Hereinafter, with reference to the accompanying drawings, the portable sound playback device according to each embodiment will be described in detail.

[0035] (First Embodiment)

[0036] Figure 1 This is a schematic diagram showing the appearance of the portable audio playback device 1. The portable audio playback device 1 is a device that processes audio signals received from an external source, converts them into sound wave signals, and then plays them back. This portable audio playback device 1 has a portable size that allows the listener to freely change the setting position and orientation. The setting orientation is 360 degrees on a horizontal plane with up and down as the axis, and 360 degrees on a vertical plane centered on axes such as left and right or front and back along the horizontal plane.

[0037] The portable audio playback device 1 has, for example, a cubic shape. Furthermore, it has speakers 21 and 22 arranged on two opposite sides of its six faces. Speakers 21 and 22 are, for example, moving-coil, conical, or dome-shaped, and have diaphragms that convert the acoustic signal, which is an electrical input, into a sound wave signal through physical vibration. Speakers 21 and 22 face each other directly and emit sound in opposite directions by 180 degrees.

[0038] Figure 2 This is a schematic diagram illustrating the configuration of the portable audio playback device 1. For example... Figure 2 (a) Thus, the portable sound playback device 1 is arranged such that speakers 21 and 22 are positioned on the left and right sides respectively when viewed from the listener's perspective. At this time, the portable sound playback device 1 operates in stereo mode. The speaker 21, which is positioned on the left side when viewed from the listener's perspective, mainly plays the left-side audio signal SL, and the speaker 22, which is positioned on the right side when viewed from the listener's perspective, mainly plays the right-side audio signal SR.

[0039] like Figure 2 (b) The portable sound playback device 1 is arranged such that one of the speakers 21 and 22 faces the upper surface when viewed from the listener's perspective. Or, as Figure 2 (c) The portable audio playback device 1 is set up with one of the speakers 21 and 22 facing the listener. In this case, the portable audio playback device 1 operates in mono mode. That is, it emits a composite signal (SL+SR) of the left-side audio signal SL and the right-side audio signal SR from the speakers 21 and 22. The audio signal output can be stopped for the speaker 21 or 22 that is blocked by the mounting surface, or for the speaker 21 or 22 that faces the opposite direction to the listener.

[0040] Figure 3 This is a block diagram showing the structure of the portable audio playback device 1. For example... Figure 3 As shown, the portable audio playback device 1 is equipped with an attitude sensor 3. By analyzing the detection signal from the attitude sensor 3, the portable audio playback device 1 senses the set orientation and drives in stereo mode or mono mode according to the set orientation. The attitude sensor 3 is, for example, an accelerometer that detects the direction of gravity and the acceleration of the XYZ axes, a gyroscope that detects the rotation of the XYZ axes, or a 6-axis sensor that detects both, sensing rotation along a horizontal plane with the vertical axis as the axis and rotation along a vertical plane centered on the axis along the horizontal plane.

[0041] Furthermore, such as Figure 3 As shown, the portable audio playback device 1, in addition to the speaker 21, speaker 22 and attitude sensor 3, also has an attitude analysis unit 4, a receiving unit 5, an audio processing unit 6, a transfer function table 7, a DAC 8 and an amplifier 9.

[0042] The attitude analysis unit 4 is a computer, microcomputer, or system-on-a-chip (SoC) equipped with a processor, ROM, and RAM. It obtains the orientation information 42 of the portable audio playback device 1 from the sensor signal of the attitude sensor 3 through calculation. Additionally, the attitude analysis unit 4 has mode switching threshold information 41. The mode switching threshold information 41 is orientation information that serves as the threshold for switching from stereo mode to mono mode or from mono mode to stereo mode. The attitude analysis unit 4 compares the orientation information 42 and the mode switching threshold information 41 to determine whether the orientation of the portable audio playback device 1 meets the requirements for mode switching.

[0043] The audio processing unit 6 is a computer, microcomputer, or SOC with a processor, ROM, and RAM, or a digital filter circuit. The audio processing unit 6 includes a decoder 61 and a mode-changing unit 62. The decoder 61 decodes the audio signal So output from the receiving unit 5 and restores it to a left audio signal SL and a right audio signal SR. When the audio signal So input from the receiving unit 5 is 5.1 channel surround sound data, the decoder 61 downmixes it to a left audio signal SL and a right audio signal SR.

[0044] The mode-changing unit 62 switches the mode of the portable audio playback device 1 based on the determination result 43 of the attitude analysis unit 4. If a mode switch is not initiated, the mode-changing unit 62 maintains the current mode. That is, in mono mode, the mode-changing unit 62 generates a composite signal (SL+SR) of the left audio signal SL and the right audio signal SR.

[0045] The mode-changing unit 62 is in stereo mode. When the current mode is maintained without switching modes, it performs audio processing to maintain the acoustic characteristics of the sound wave signal reaching a fixed point in the actual space, regardless of the orientation of the portable playback device 1. More specifically, the mode-changing unit 62 performs audio processing that simulates a symmetrical orientation of speakers 21 and 22 for the listener, i.e., stereo frontal orientation, even if the orientation of the portable playback device 1 is changed. In other words, the mode-changing unit 62 performs different audio processing according to the orientation of the portable playback device 1 to maintain the acoustic characteristics of the sound wave signal reaching a fixed point in the actual space. The fixed point in the actual space is a point on the stereo front when the portable playback device 1 is in stereo mode and the orientation of the portable playback device 1 has not changed.

[0046] Figure 4 This is a schematic diagram illustrating the relationship between the portable audio playback device 1 and the listener. For example... Figure 4 As shown, the portable playback device 1 is tilted horizontally at a yaw angle ψ and vertically at a pitch angle θ from the stereo front. At this time, the head transfer function from the left speaker 21 to the concha of the listener's left ear, as observed by the listener, is denoted as H. LL（ψ，θ） Let H be the head transfer function from speaker 21 to the concha of the listener's right ear. LR（ψ，θ） The head transfer function, from the right speaker 22 to the concha of the listener's right ear as observed by the listener, is denoted as H. RR（ψ，θ） Let the head transfer function from speaker 22 to the concha of the listener's left ear be H. RL（ψ，θ） .

[0047] When an unprocessed left-side acoustic signal SL is emitted from speaker 21 and an unprocessed right-side acoustic signal SR is emitted from speaker 22, the left-ear acoustic signal PL reaching the concha of the listener's left ear and the right-ear acoustic signal PR reaching the concha of the listener's right ear are represented by the following matrix (1). Furthermore, the path from speaker 21 and speaker 22 to the listener's ear is considered as a causally stable linear time-invariant system.

[0048]

Mathematical Formula 1

[0049] Replace the above matrix expression (1) with the following expression (2).

[0050]

Mathematical Formula 2

[0051] in,

[0052] In order to ensure that the left audio signal SL reaches the concha of the listener's left ear and the right audio signal SR reaches the concha of the listener's right ear without relying on the orientation of the portable playback device 1, the mode changing unit 62 only needs to change the inverse filter H in the following formula (3). －1 （ψ，θ） The signal is convolved with the left acoustic signal SL and the right acoustic signal SR. In the following equation (3), E is the identity matrix.

[0053]

Mathematical Expression 3

[0054] Inverse filter H －1 （ψ，θ） It is matrix H （ψ，θ） The inverse matrix is ​​therefore as shown in equation (4) below.

[0055]

Mathematical Expression 4

[0056] Inverse filter H －1 （ψ，θ） The information is stored in transfer function table 7. Transfer function table 7 is a memory that stores the inverse filter H for each orientation information, differentiated by the yaw angle ψ along the horizontal direction and the pitch angle θ along the vertical direction from the stereo front. －1 （ψ，θ） Each inverse filter H －1 （ψ，θ） The head transfer function H is obtained by measuring the impulse response from the speakers 21 and 22 of the portable sound playback device 1 to a simulated head microphone formed by placing a microphone at the ear of a human head model. LL（ψ，θ） Header transfer function H LR（ψ，θ） Header transfer function H RR（ψ，θ） and head transfer function H RL（ψ，θ） And generated.

[0057] If the mode switching is not achieved according to the determination result 43 of the attitude analysis unit 4, the mode switching unit 62 uses the orientation information of the attitude analysis unit 4 to call the inverse filter H from the transfer function table 7. －1 （ψ，θ） As shown in equation (5) below, a new left-side acoustic signal SL is generated by convolving the left-side acoustic signal SL and the right-side acoustic signal SR. N and the right-side audio signal SR N .

[0058]

Mathematical Expression 5

[0059] in,

[0060] The inverse filter H －1 （ψ，θ） It also eliminated the head transfer function H from speaker 21 to the concha of the listener's right ear. LR（ψ，θ） and the head transfer function H from speaker 22 to the concha of the listener's left ear. RL（ψ，θ） The mode change unit 62 also eliminates crosstalk.

[0061] The mode-changing unit 62 performs a Fourier transform on the left audio signal SL and the right audio signal SR, and then uses an inverse filter H. －1 （ψ，θ） The processing can be performed by performing an inverse Fourier transform. Alternatively, the mode-changing unit 62 can directly convolve the left acoustic signal SL and the right acoustic signal SR in the time domain using the inverse filter H, which is represented in the time domain. －1 （ψ，θ） .

[0062] DAC 8 processes the left-side audio signal SL after it has been processed in the audio processing unit 6. N and the right-side audio signal SR N A digital-to-analog converter transforms the signal into an analog signal. Amplifier 9 outputs the left-side audio signal SL as an analog signal. N and the right-side audio signal SR N The signal is amplified and output to speakers 21 and 22. Speaker 21 transmits the left-side audio signal SL. N The sound is converted into an audio signal and played back by the speaker 22, which transmits the right-side audio signal SR. N It is converted into an audio signal and then played back.

[0063] Furthermore, the left-side audio signal SL and the right-side audio signal SR can be stored in the memory of the portable playback device 1, or they can be received from the outside via the receiving unit 5. The receiving unit 5 has an antenna or an infrared light receiving unit, and receives audio signals in the form of radio waves via wireless communication standards such as Bluetooth (registered trademark), WiFi, ZigBee, wireless LAN, or infrared, demodulates them into audio signals in the form of digital data So, and outputs them to the audio processing unit 6.

[0064] Figure 5 This is a flowchart illustrating an example of the operation of the portable audio playback device 1. In this portable audio playback device 1, the attitude sensor 3 detects a change in the orientation of the portable audio playback device 1 (step S01). The attitude sensor 3 inputs the acceleration information corresponding to the change in the orientation of the portable audio playback device 1 as a detection signal to the attitude analysis unit 4. The attitude analysis unit 4 analyzes the acceleration represented by the detection signal through integration, etc., thereby generating orientation information 42 of the portable audio playback device 1 (step S02).

[0065] If the attitude resolution unit 4 generates orientation information 42, it compares the pre-stored mode switching threshold information 41 with the orientation information 42 (step S03). In the comparison, it determines whether the yaw angle ψ and pitch angle θ represented by the orientation information 42 reach the yaw angle ψ and pitch angle θ represented by the mode switching threshold information 41.

[0066] When the orientation information 42 reaches the mode switching threshold information 41 (step S03, Yes), the mode changing unit 62 of the audio processing unit 6 generates a composite signal (SL+SR) obtained by combining the left audio signal SL and the right audio signal SR generated by the decoder 61 (step S04). Then, the composite signal (SL+SR) is output to both the speaker 21 and the speaker 22 (step S05).

[0067] The synthesized signal (SL+SR) output from speaker 21, which is located on the left side when viewed from the listener's perspective, and the synthesized signal (SL+SR) output from speaker 22, which is located on the right side when viewed from the listener's perspective, are converted into analog signals by DAC 8, amplified by amplifier 9 to match the adjusted volume, and converted into sound wave signals by speakers 21 and 22 for playback.

[0068] Furthermore, the mode switching threshold information 41 only needs to be an angle at which the boundary of the stereo mode cannot be maintained, such as a value less than 90 degrees, like 70 degrees. Therefore, when one of the speakers 21 or 22 is located on the upper surface, the audio signal is already processed in mono mode. Additionally, when the portable playback device 1 rotates 90 degrees about the up-down axis from the mono mode state where the speakers 21 or 22 are facing to the side, the audio signal is already processed in stereo mode. When the portable playback device 1 rotates 90 degrees about the up-down axis from the stereo mode state where the speakers 21 and 22 are facing to the side, the audio signal is already processed in mono mode.

[0069] On the other hand, if the orientation information 42 does not reach the mode switching threshold information 41 (step S03, No), the mode changing unit 62 of the audio processing unit 6 maintains the stereo mode according to steps S06 to S10. That is, the mode changing unit 62 reads the inverse filter H corresponding to the orientation information 42 from the transfer function table 7. －1 (Step S06). The inverse filter H －1 The head transfer function, which varies with yaw angle ψ and pitch angle θ from the portable sound output device 1 to the listener, is canceled out, and crosstalk is also eliminated. Thus, the sound wave signal convolved with the head transfer function through propagation in actual space is transmitted to the listener as the left acoustic signal SL and the right acoustic signal SR.

[0070] Therefore, the mode change unit 62 reads the inverse filter H －1 Applied to the left audio signal SL, generating the left audio signal SL. N (Step S07) Additionally, the inverse filter H －1 Applied to the right-side audio signal SR, generating the right-side audio signal SR. N (Step S08). Inverse filter H －1 The application can perform convolution in the time domain, or perform Fourier transform and multiplication operations on the left acoustic signal SL and the right acoustic signal SR.

[0071] The generated left-side audio signal SL N The sound signal SR is output to the speaker 21, which is on the left side when viewed from the listener's perspective (step S09). N The output is directed towards the speaker 22, which is on the right side when viewed from the listener's perspective (step S10). Furthermore, the positional relationship between the speakers 21 and 22 can be determined by accumulating and integrating the detection signal from the attitude sensor 3. Depending on the orientation of the portable playback device 1, sometimes the speaker 22 is on the left side when viewed from the listener's perspective, and the speaker 21 is on the right side when viewed from the listener's perspective, thus the output target becomes reversed.

[0072] The left-side audio signal SL output to the speaker 21 located on the left side from the listener's perspective N And the right-side audio signal SR output from the speaker 22 located on the right side as observed by the listener. N The signal is converted into an analog signal by DAC 8, amplified by amplifier 9 to match the adjusted volume, and converted into an audio signal by speakers 21 and 22 for playback.

[0073] (Effects)

[0074] As described above, the portable audio playback device 1 includes multiple speakers 21 and 22 and an attitude sensor 3 that detects changes in the posture of the frame. Furthermore, the audio processing unit 6 can process the transfer function H of the audio characteristics of the sound wave signal that maintains a fixed point in the actual space based on the attitude changes (ψ, θ) detected by the attitude sensor 3. －1 （ψ，θ） It is used for audio signals with two or more channels.

[0075] Fixed point and generation transfer function H in actual space －1 （ψ，θ） The position of the simulated head microphone that collects impulse responses corresponds to the position of the microphone. The transfer function H represents the acoustic characteristics of the sound wave signal that maintains its arrival at a fixed point in actual space. －1 （ψ，θ） It is the inverse filter of the head transfer function from the speakers 21 and 22 after the posture change to the fixed point.

[0076] Therefore, since the head transfer function from the portable playback device 1 to the listener, which is caused by the change in orientation, is canceled in advance, the sound wave signal convolved with the head transfer function through propagation in actual space can be transmitted to the listener as the left acoustic signal SL and the right acoustic signal SR. Thus, during the change of orientation of the portable playback device 1, changes in timbre such as volume variations for each frequency will not be perceived by the listener, and discomfort to the listener can be suppressed.

[0077] Furthermore, the portable audio playback device 1 has been described using an example with two speakers 21 and 22, but it can also have a mode in which, for example, an intermediate speaker is arranged between the two speakers 21 and 22, and a 3-channel audio signal can be output.

[0078] Furthermore, an example was described in which the attitude change detected by the attitude sensor 3 was compared with the mode switching threshold information 41, which has a threshold as a threshold for attitude change. However, the method of changing between stereo mode and mono mode is not limited to this. Figure 6 This is a schematic diagram representing the transfer function in Table 7.

[0079] like Figure 6 As shown, in transfer function table 7, the inverse filter H is stored corresponding to orientation information 42. －1 （ψ，θ） Regarding the orientation information 42 for audio processing in mono mode, mono mode information is stored that indicates a change in the opposite mono mode.

[0080] When the mono mode information corresponds to the orientation information 42 received from the attitude resolution unit 4, the mode change unit 62 combines the left acoustic signal SL and the right acoustic signal SR to generate a mono signal. In this case, the transfer function table 7 also serves as the mode switching threshold information 41.

[0081] (Second Implementation)

[0082] Next, the portable sound playback device 1 of the second embodiment will be described in detail with reference to the accompanying drawings. Furthermore, for structures or functions identical to those of the first embodiment, the same reference numerals will be used, and detailed descriptions will be omitted.

[0083] Figure 7 This is a block diagram showing the structure of the portable audio playback device 1 according to the second embodiment. Figure 7As shown, the attitude analysis unit 4 stores thresholds for switching between stereo and mono modes for each frequency band. For example, the attitude analysis unit 4 stores low-frequency band mode switching threshold information 41L for the low-frequency band and high-frequency band mode switching threshold information 41H for the high-frequency band. Furthermore, the attitude analysis unit 4 compares the low-frequency band mode switching threshold information 41L and the high-frequency band mode switching threshold information 41H with the orientation information 42, respectively.

[0084] In the low-frequency band, the correction amount used to maintain the acoustic characteristics of the sound wave signal reaching a fixed point in the actual space sometimes becomes too large, exceeding the gain performance of amplifier 9 and the sound reproduction performance of speaker 21 and speaker 22. Therefore, if the low-frequency band reaches the orientation information 42 with the mode switching threshold information 41L, the mode changing unit 62, while maintaining stereo mode in other frequency bands, only mixes the low-frequency band into one channel and switches to mono mode.

[0085] Specifically, if the low-frequency band mode switching threshold information 41L reaches the orientation information 42, the mode changing unit 62 will change the low-frequency signal SL of the left audio signal SL. low And the low-frequency signal SR of the right-side audio signal SR low The low-frequency mono signal SM is synthesized and generated. For other frequency bands, if the orientation information 42 is not reached, the mode change unit 62 reads out the inverse filter H. －1 （ψ，θ） This signal is applied to the left audio signal SL and the right audio signal SR to generate the left high-frequency signal SL. NHi and the high-frequency signal SR on the right NHi .

[0086] Then, the mode change unit 62 will change the left high-frequency signal SL NHi The low-frequency mono signal SM is synthesized and output towards speaker 21, which is located on the left side from the listener's perspective, while the high-frequency signal SR on the right side is output. NHi and synthesized low-frequency signals (SL) low +SR low The synthesized signal is output to speaker 22, which is positioned on the right side when viewed from the listener's perspective.

[0087] Figure 8 and Figure 9 This is a flowchart illustrating an example of the operation of the portable audio playback device 1. If the attitude sensor 3 detects a change in the orientation of the portable audio playback device 1 (step S11), the attitude analysis unit 4 generates orientation information 42 (step S12), and then determines whether the orientation information 42 reaches the low-frequency band mode switching threshold information 41L (step S13). Additionally, the attitude analysis unit 4 determines whether the orientation information 42 reaches the high-frequency band mode switching threshold information 41H (step S14).

[0088] When both the low-frequency band mode switching threshold information 41L and the high-frequency band mode switching threshold information 41H are reached by the orientation information 42 (steps S13, Yes and S14, Yes), the mode changing unit 62 of the audio processing unit 6 generates a composite signal (SL+SR) obtained by combining the left audio signal SL and the right audio signal SR generated by the decoder 61 (step S15). Then, the composite signal (SL+SR) is output to both the speaker 21 and the speaker 22 (step S16).

[0089] If the orientation information 42 does not reach either the low-frequency band mode switching threshold information 41L or the high-frequency band mode switching threshold information 41H (steps S13, No and S14, No), the mode change unit 62 reads the inverse filter H corresponding to the orientation information 42 from the transfer function table 7. －1 (Step S17). Then, the mode change unit 62 reads the inverse filter H －1 Applied to the left audio signal SL, generating the left audio signal SL. N (Step S18) Additionally, the inverse filter H －1 Applied to the right-side audio signal SR, generating the right-side audio signal SR. N (Step S19). The generated left-side audio signal SL N The sound signal SR is output to the speaker 21, which is on the left side when viewed from the listener's perspective (step S20), and the right-side sound signal SR is output. N Output is directed toward speaker 22, which is located on the right side when viewed from the listener's perspective (step S21).

[0090] If the orientation information 42 reaches the low-frequency band mode switching threshold information 41L but does not reach the high-frequency band mode switching threshold information 41H (step S13, Yes and step S14, No), the mode change unit 62 of the audio processing unit 6 separates the left audio signal SL and the right audio signal SR into high-frequency band and low-frequency band signals respectively (step S22).

[0091] The mode change unit 62 will use the left low-frequency signal SL, which is a low-frequency signal, as the signal in the low-frequency band. low and the low-frequency signal SR on the right low Synthesizing, a low-frequency mono signal SM is generated (step S23). Additionally, the mode-changing unit 62 reads the inverse filter H corresponding to the orientation information 42 from the transfer function table 7. －1 (Step S24). Then, the mode change unit 62 reads the inverse filter H －1 The high-frequency signal SL applied as a high-frequency band signal on the left side Hi Generates the left high-frequency signal SL HiN (Step S25) Additionally, the inverse filter H－1 Applied to the right high-frequency signal SR Hi Generate the right-side high-frequency signal SR HiN (Step S26).

[0092] Next, the mode change unit 62 converts the low-frequency mono signal SM and the left high-frequency signal SL. HiN Synthesize and generate the left-side audio signal SL N (Step S27). The mode change unit 62 converts the low-frequency mono signal SM and the right-side high-frequency signal SR. HiN Synthesize and generate the right-side audio signal SR N (Step S28).

[0093] The generated left-side audio signal SL N The speaker 21, positioned on the left side from the listener's perspective, outputs (step S20), while the right-side audio signal SR... N Output is directed toward speaker 22, which is located on the right side when viewed from the listener's perspective (step S21).

[0094] (Effects)

[0095] As described above, in this portable playback device 1, the mode switching threshold information 41 is set for each frequency band. Furthermore, the audio processing unit 6 switches from the frequency band that reaches the mode switching threshold information 41 to mono mode. As a result, even if the correction amount used to maintain the acoustic characteristics of the sound wave signal reaching a fixed point in the actual space becomes too large, exceeding the gain performance of the amplifier 9 and the playback performance of the speakers 21 and 22, the listener's discomfort can be reduced.

[0096] (Third implementation)

[0097] Next, the portable sound playback device 1 of the third embodiment will be described in detail with reference to the accompanying drawings. Furthermore, for structures or functions identical to those of the first or second embodiments, the same reference numerals will be used, and detailed descriptions will be omitted.

[0098] Figure 10 This is a block diagram showing the structure of the portable audio playback device 1 according to the third embodiment. Figure 10 As shown, the attitude analysis unit 4 has a threshold information storage unit 4a that stores the threshold for switching between stereo and mono modes for each combination of volume and frequency band. For example, the attitude analysis unit 4 stores the mode switching threshold information 41L for the low-frequency band. V1 41 V2 , The attitude analysis unit 4 stores the frequency band mode switching threshold information 41H for each volume value Vo. Additionally, the attitude analysis unit 4 stores the frequency band mode switching threshold information 41H for the high-frequency band. Then, based on the currently set volume, the attitude analysis unit 4 retrieves the frequency band mode switching threshold information 41L from the low-frequency band. V1 41 V2 Select and compare with orientation information 42.

[0099] In the low-frequency band, the correction amount used to maintain the acoustic characteristics of the sound wave signal reaching a fixed point in the actual space sometimes becomes too large, exceeding the gain performance of amplifier 9 and the sound reproduction performance of speaker 21 and speaker 22, based on the set volume information Vo. Therefore, if the low-frequency band selected based on the volume information Vo is used with mode switching threshold information 41L... Vx Upon receiving the orientation information 42, the mode change unit 62, while maintaining stereo mode in other frequency bands, switches to mono mode by downmixing the low-frequency band into one channel.

[0100] Volume information Vo can also be obtained from any of the audio processing unit 6, DAC 8, or amplifier 9, which are related to volume adjustment. Figure 11 This indicates whether the attitude resolution unit 4 determines whether the orientation information 42 has reached the low-frequency band mode switching threshold information 41L. Vx The flowchart for the actions up to this point.

[0101] like Figure 11 As shown, the attitude sensor 3 detects the orientation change of the portable playback device 1 (step S31), and the attitude analysis unit 4 generates orientation information 42 (step S32). Additionally, the attitude analysis unit 4 acquires volume information Vo (step S33) and selects the low-frequency band mode switching threshold information 41L corresponding to the volume information Vo. Vx (Step S34). Then, it is determined whether the orientation information 42 reaches the low-frequency band mode switching threshold information 41L. Vx (Step S13). Then, execute. Figure 8 and Figure 9 The processing after step S13.

[0102] (Effects)

[0103] As described above, in this portable audio playback device 1, the mode switching threshold information 41 is set for each combination of volume information Vo and frequency band. Furthermore, the audio processing unit 6 switches from the frequency band reaching the low-frequency band selected based on the volume information Vo to mono mode. Therefore, even if the set volume information Vo sometimes exceeds the gain performance of the amplifier 9 and the playback performance of the speakers 21 and 22, the listener's discomfort can be reduced.

[0104] (Other implementation methods)

[0105] As described above, several embodiments of the present invention have been illustrated, but these embodiments are merely examples and are not intended to limit the scope of the invention. The new embodiments described above can be implemented in various other ways, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. The above embodiments or variations thereof are included in the scope or spirit of the invention and are included within the scope equivalent to the invention described in the claims.

[0106] Explanation of the label

[0107] 1 Portable audio playback device

[0108] 21, 22 speakers

[0109] 3 Attitude Sensor

[0110] 4 Attitude Analysis Department

[0111] 41 Mode switching threshold information

[0112] 41L Low-frequency mode switching threshold information

[0113] 41L v1 41L v2 Low-frequency mode switching threshold information

[0114] 41H High-frequency mode switching threshold information

[0115] 5 Receiving Unit

[0116] 6. Audio Processing Department

[0117] 61 Decoder

[0118] 62. Model Change Department

[0119] 7. Transfer Function Table

[0120] 8 DAC

[0121] 9 Amplifier

Claims

1. A portable sound playback device, comprising: Multiple speakers; An attitude sensor detects changes in the attitude of the frame; and The audio processing unit applies a transfer function of the acoustic characteristics of the sound wave signal that maintains a fixed point in the actual space to the audio signal with two or more channels, based on the attitude change detected by the attitude sensor.

2. The portable sound playback device according to claim 1, characterized in that, The transfer function includes an inverse filter of the head transfer function from the speaker after the posture change to the fixed point.

3. The portable sound playback device according to claim 2, characterized in that, It has a storage unit that stores the inverse filter for each degree of the attitude change.

4. The portable sound playback device according to claim 1, characterized in that, The audio processing unit processes the audio signal in mono mode when at least one of the loudspeakers is located on the upper surface. From the mono mode where the speaker faces to the side, when the frame rotates 90 degrees around the vertical axis, the audio signal is processed in a 2-channel or higher mode. When the frame is rotated 90 degrees around the vertical axis from the state where the speaker is facing to the side and has two or more channels, the audio signal is processed in mono mode.

5. The portable sound playback device according to any one of claims 1 to 3, characterized in that, If the attitude change detected by the attitude sensor reaches a threshold, the audio processing unit generates a mono mode audio signal.

6. The portable sound playback device according to claim 5, characterized in that, The threshold is set for each frequency band. The audio processing unit switches from the frequency band that reaches the threshold to a mono mode.

7. The portable sound playback device according to claim 6, characterized in that, The audio processing unit downmixes the audio signals in the frequency band that reach the threshold into one channel.

8. The portable sound playback device according to claim 6, characterized in that, The threshold is set for each combination of volume and frequency band. The audio processing unit switches from the frequency band that reaches the threshold selected according to the volume to mono mode.

9. The portable sound playback device according to claim 2, characterized in that, The transfer function also includes a filter to eliminate crosstalk.

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