Information processing device and information processing method

Abstract

The present invention provides an information processing device and an information processing method that correct the frequency characteristics of sound output from a speaker to make it easier to hear. [Solution] The information processing device includes a volume level information acquisition unit that acquires volume level information related to the volume level setting by the user, and a signal processing unit that corrects the frequency characteristics of the sound output from the speaker so that the amount of attenuation from the maximum volume of the sound output from the speaker at a predetermined frequency is within a lower volume limit relative to the maximum volume at the predetermined frequency, according to the volume level. The lower volume limit is determined based on the difference between the maximum volume of the speaker at a reference frequency and the minimum volume that can be set as the sound output from the speaker, according to a first sound pressure level difference between the maximum volume at a reference frequency and the minimum audible volume that a person can hear, and a second sound pressure level difference between the maximum volume and the minimum audible volume at a frequency other than the reference frequency.

Description

Technical Field

[0001] The present disclosure relates to an information processing apparatus and an information processing method.

Background Art

[0002] Human hearing has the characteristic that the perceived sound intensity varies depending on the frequency. Due to this characteristic, for example, when the sound is quiet, the low and high frequency sounds may be less audible compared to the mid-frequency sounds, resulting in sound quality degradation. Conventionally, techniques for reducing such sound quality degradation have been proposed. For example, Patent Document 1 discloses a technique for performing loudness correction using a correction equalizer curve obtained by approximating a correction curve obtained from the difference between a plurality of curves corresponding to the auditory levels of equal loudness curves as a polyline.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, depending on the known techniques, the sound quality may not be sufficiently improved. For example, a small speaker mounted on a mobile terminal such as a smartphone has a frequency characteristic in which the sound pressure in the mid-frequency range is higher than that in the low and high frequency ranges compared to a larger speaker. Therefore, even if the frequency characteristics are corrected using known techniques, there is a possibility that the sound pressure in the low and high frequency ranges may not be sufficiently ensured. In particular, when the volume level of the sound output from the speaker is low, the sound pressure in the low and high frequency ranges may not be high enough for the user to easily hear the low and high frequency sounds.

[0005] This disclosure has been made in view of the above-mentioned issues. The purpose of this disclosure is to provide an information processing device and an information processing method that correct the frequency characteristics of sound output from a speaker to make it easier to hear. [Means for solving the problem]

[0006] An information processing device in one embodiment of the present disclosure includes a volume level information acquisition unit that acquires volume level information relating to volume level settings by a user, and a signal processing unit that corrects the frequency characteristics of the sound output from the speaker so that the amount of attenuation from the maximum volume of the sound output from the speaker at a predetermined frequency is within a lower volume limit relative to the maximum volume at the predetermined frequency, according to the volume level indicated by the volume level information, wherein the lower volume limit is determined based on the difference between the maximum volume of the speaker at a reference frequency and the minimum volume that can be set as the sound output from the speaker, according to a first sound pressure level difference between the maximum volume at the reference frequency and the minimum audible volume that can be heard by a person, and a second sound pressure level difference between the maximum volume and the minimum audible volume at a frequency other than the reference frequency.

[0007] One form of information processing method in this disclosure is an information processing method executed by an information processing device, The system acquires volume level information related to the volume level setting by the user, and corrects the frequency characteristics of the sound output from the speaker so that the amount of attenuation from the maximum volume of the sound output from the speaker at a predetermined frequency is within a lower volume limit relative to the maximum volume at the predetermined frequency, based on the difference between the maximum volume of the speaker at a reference frequency and the minimum volume that can be set as the sound output from the speaker, according to a first sound pressure level difference between the maximum volume at the reference frequency and the minimum audible volume that a person can hear, and a second sound pressure level difference between the maximum volume and the minimum audible volume at a frequency other than the reference frequency. [Effects of the Invention]

[0008] According to this disclosure, it is possible to provide an information processing device and an information processing method that correct the frequency characteristics of sound output from a speaker to make it easier to hear. [Brief explanation of the drawing]

[0009] [Figure 1] A functional block diagram showing the schematic configuration of a sound output device according to one embodiment. [Figure 2] This diagram schematically illustrates the relationship between the human audible range and the sound pressure level of the sound output from a speaker. [Figure 3] This diagram schematically shows an example of the attenuation of the signal level of an audio signal at different volume levels. [Figure 4] This diagram schematically shows another example of the attenuation of the signal level of an audio signal at different volume levels. [Figure 5] This diagram schematically illustrates other examples of equalizer processing. [Figure 6] This diagram schematically illustrates an example of signal level attenuation during equalizer processing. [Figure 7] This diagram schematically illustrates another example of signal level attenuation during equalizer processing. [Figure 8] This diagram schematically illustrates another example of signal level attenuation during equalizer processing. [Figure 9] This diagram schematically illustrates another example of signal level attenuation during equalizer processing. [Modes for carrying out the invention]

[0010] Embodiments of this disclosure will be described below with reference to the drawings. In the drawings, identical or equivalent components are denoted by the same reference numerals, and descriptions of identical or equivalent components will be omitted where necessary.

[0011] Figure 1 is a functional block diagram showing the schematic configuration of a sound output device 1 according to one embodiment. As shown in Figure 1, the sound output device 1 comprises, as functional units, a control unit 11, a storage unit 12, an operation input unit 13, an audio signal input unit 14, a signal processing unit 15, an amplification unit 16, a speaker 17, and a volume level information acquisition unit 18. A portion of the functional units included in the sound output device 1 functions as an information processing device in this disclosure. In the example shown in Figure 1, the information processing device comprises at least a signal processing unit 15. In this embodiment, the sound output device 1 is implemented by a terminal device such as a smartphone. However, the sound output device 1 may be implemented by other devices.

[0012] The control unit 11 controls and manages the entire sound output device 1, including each functional unit of the sound output device 1. The control unit 11 performs various controls, for example, by running a program stored in the memory unit 12. For example, the control unit 11 can be composed of a control device such as a CPU (Central Processing Unit) or an MPU (Micro Processing Unit). The control unit 11 outputs sound from the speaker 17 based on user input, for example.

[0013] The storage unit 12 is a storage medium capable of storing programs and data. The storage unit 12 can be made up of, for example, semiconductor memory or magnetic memory. Specifically, the storage unit 12 can be made up of, for example, EEPROM (Electrically Erasable Programmable Read-Only Memory) or a hard disk drive. The storage unit 12 may store, for example, a program for operating the control unit 11. The storage unit 12 may also store, for example, sound data (for example, sound content) output from the speaker 17.

[0014] The operation input unit 13 receives operation inputs from the user. The operation input unit 13 can be constituted by, for example, operation buttons (operation keys) or a touch screen. The user can perform an operation input for starting or stopping the output of sound to the operation input unit 13. Alternatively, the user can perform an operation input for changing the volume level output from the speaker. When receiving an operation input by the user, the control unit 11 starts or stops the output of sound from the speaker 17 or changes the volume of the sound output from the speaker 17.

[0015] The sound signal input unit 14 receives the input of a sound signal. The sound signal is, for example, the sound signal of sound data stored in the storage unit 12. Alternatively, the sound signal may be the sound signal of content acquired from an external device through a communication connection. The sound signal input unit 14 provides the received sound signal to the signal processing unit 15.

[0016] The signal processing unit 15 executes signal processing on the sound signal acquired from the sound signal input unit 14. The signal processing unit 15 includes, for example, a DSP (Digital Signal Processor) and decodes the sound signal. The signal processing unit 15 performs signal processing such as delay processing and equalizer processing on the decoded sound signal. The signal processing unit 15 provides the processed sound signal to the amplifier unit 16.

[0017] In the present embodiment, the signal processing unit 15 corrects the frequency characteristics of the sound output from the speaker 17 as equalizer processing. Details of the correction processing of the frequency characteristics executed by the signal processing unit 15 will be described later.

[0018] The amplifier unit 16 amplifies the sound signal acquired from the signal processing unit 15 and provides it to the speaker 17.

[0019] The speaker 17 is driven based on the sound signal acquired from the amplifier unit 16 and outputs sound. Thereby, the sound is reproduced.

[0020] The volume level information acquisition unit 18 acquires volume level information related to the volume level setting by the user. Specifically, the volume level information acquisition unit 18 acquires volume level information indicating the set volume level based on the user's operation on the operation input unit 13 regarding the setting of the volume level. The volume level information acquisition unit 18 provides the acquired volume level information to the signal processing unit 15.

[0021] Next, the details of the frequency response correction process performed by the signal processing unit 15 will be explained. Figure 2 is a schematic diagram showing the relationship between the human audible range and the sound pressure level of the sound output from the speaker. In Figure 2, the horizontal axis represents frequency (Hz), and the vertical axis represents sound pressure level (dBs). Note that Figure 2 is a semi-logarithmic graph with a logarithmic scale on the horizontal axis.

[0022] In Figure 2, the frequency response SPH represents the maximum volume of sound output from speaker 17. Also in Figure 2, the frequency response AT represents the minimum audible volume that a person can hear, specifically the minimum audible volume on the equal-loudness level curves. Therefore, when speaker 17 outputs sound at maximum volume, a person can hear the sound within the frequency range where the maximum volume frequency response SPH is greater than or equal to the audible frequency response AT.

[0023] Suppose the user lowers the volume level output from the speaker by operating the operation input unit 13. If the signal processing unit 15 does not correct the frequency characteristics, as the volume level is lowered, the frequency characteristics of the sound output from speaker 17 will remain the same as the frequency characteristics SPH at maximum volume, while the sound pressure level decreases. For example, if no frequency characteristics correction is performed, the frequency characteristics of the sound output from speaker 17 will be as follows: when the volume level is lowered by one step from the maximum volume SPH, it will be as frequency characteristics SP1 in Figure 2; when lowered by two steps, it will be as frequency characteristics SP2 in Figure 2; when lowered by three steps, it will be as frequency characteristics SP3 in Figure 2; and when lowered by four steps, it will be as frequency characteristics SP4 in Figure 2. In this way, as the volume level is lowered, the frequency characteristics change from SPH to SP1, SP2, SP3, and SP4, and the range of frequencies in which the frequency characteristics of the sound output from speaker 17 are above the audible frequency characteristics AT becomes narrower. This tendency is particularly pronounced in the low and high frequency bands. Therefore, if frequency response correction is not performed, lowering the volume level narrows the range of sound frequencies that the user can hear. As a result, the user may not be able to hear sound with sufficient quality.

[0024] Therefore, in the sound output device 1 according to this embodiment, the signal processing unit 15 corrects the frequency characteristics of the sound output from the speaker 17. Specifically, the signal processing unit 15 corrects the frequency characteristics of the sound output from the speaker 17 so that, according to the volume level indicated by the volume level information, the amount of attenuation from the maximum volume SPH of the sound output from the speaker 17 at a predetermined frequency is within the lower limit of the volume relative to the maximum volume SPH at that predetermined frequency.

[0025] The lower volume limit is the frequency response at the lowest volume level at which sound is output from speaker 17, after frequency response correction. Therefore, the lower volume limit is the frequency response at the minimum volume, excluding the case where the sound output from speaker 17 is zero. The lower volume limit is set as an appropriate characteristic that is less than or equal to frequency response SPH and greater than or equal to frequency response AT within the frequency range where the frequency response SPH of the maximum volume is greater than or equal to frequency response AT. In Figure 2, the lower volume limit is shown by the frequency response SPL.

[0026] The frequency response SPL of the lower limit of sound volume is determined, for example, by the sound output device 1 or another external device. Here, an example of how to determine the lower limit of sound volume SPL is described. The lower limit of sound volume SPL can be determined by setting a specific frequency as a reference frequency and using the sound pressure level difference between the maximum sound volume SPH of speaker 17 and the minimum audible sound volume AT of a person at that reference frequency. The reference frequency can be determined as appropriate. The reference frequency can be, for example, a specific frequency in the midrange. The midrange frequency is, for example, in the range of 800Hz to 6kHz, more specifically in the range of 1kHz to 2kHz. Here, as shown in Figure 2, a frequency of 1kHz belonging to the midrange is used as the reference frequency fM.

[0027] In Figure 2, the sound pressure level difference between the maximum volume SPH of speaker 17 and the minimum audible volume AT of a human at a reference frequency fM is shown by dM. In this specification, the sound pressure level difference between the maximum volume SPH of speaker 17 and the minimum audible volume AT of a human at a reference frequency fM is also referred to as the "first sound pressure level difference" below.

[0028] When the difference in sound pressure levels between the maximum volume SPH and the minimum audible volume AT at a specific frequency different from the reference frequency fM is defined as the second sound pressure level difference, the lower limit of volume SPL is determined based on the difference between the maximum volume SPH of speaker 17 at the reference frequency fM and the minimum volume that can be set as the sound output from speaker 17, according to the first sound pressure level difference dM and the second sound pressure level difference. The difference between the maximum volume SPH of speaker 17 at the reference frequency fM and the minimum volume that can be set as the sound output from speaker 17 is shown as GM in Figure 2.

[0029] Here, we will explain an example where a particular frequency includes a low-frequency fL lower than the reference frequency fM and a high-frequency fH higher than the reference frequency fM. The low-frequency fL can be any appropriate frequency lower than the reference frequency fM, for example, in the range of 80Hz to 200Hz, or more specifically, in the range of 100Hz to 120Hz. The high-frequency fH can be any appropriate frequency higher than the reference frequency fM, for example, in the range of 8kHz to 16kHz, or more specifically, in the range of 10kHz to 12kHz.

[0030] When a specific frequency is a low frequency fL, the second sound pressure level difference dL is the sound pressure level difference between the maximum volume SPH and the minimum audible volume AT at the low frequency fL. Therefore, the lower limit of volume SPL at the low frequency fL is determined based on the difference GM at the reference frequency fM, according to the first sound pressure level difference dM and the second sound pressure level difference dL. As an example, the lower limit of volume SPL at the low frequency fL is determined by the following equation (1). SPL = SPH - (dL / dM)·GM (1)

[0031] Similarly, when a particular frequency is a high frequency fH, the second sound pressure level difference dH is the sound pressure level difference between the maximum volume SPH and the minimum audible volume AT at the high frequency fH. Therefore, the lower limit of volume SPL at the high frequency fH is determined based on the difference GM at the reference frequency fM, according to the first sound pressure level difference dM and the second sound pressure level difference dH. As an example, the lower limit of volume SPL at the high frequency fH is determined by the following equation (2). SPL = SPH - (dH / dM)·GM (2)

[0032] The lower limit of the sound volume (SPL) may be determined over a predetermined frequency range according to the difference between the first and second sound pressure levels (dM). For example, the lower limit of the sound volume (SPL) may be determined over the entire frequency range from 80Hz to 16kHz by calculation using equations (1) and (2) above. When determined in this way, the lower limit of the sound volume (SPL) exhibits frequency characteristics as shown in Figure 2, for example.

[0033] Alternatively, the lower limit of sound volume (SPL) may be determined for a reference frequency fM and a specific frequency according to the first sound pressure level difference dM and the second sound pressure level difference. In the example above, the lower limit of sound volume (SPL) may be determined for a reference frequency fM, a low frequency fL, and a high frequency fH according to the first sound pressure level difference dM and the second sound pressure level differences dL and dH. In this case, for frequencies other than the reference frequency fM and the specific frequency (i.e., in this example, frequencies other than the reference frequency fM, the low frequency fL, and the high frequency fH), the lower limit of sound volume (SPL) may be determined as the sum of the lower limit of sound volume determined for the reference frequency fM and the specific frequency. When determined in this way, the lower limit of sound volume (SPL) will show a frequency characteristic that is appropriately connected by a straight line or curve for the frequency band between the reference frequency fM and the specific frequency.

[0034] The above example described a case where a specific frequency includes both a low frequency fL and a high frequency fH. However, a specific frequency does not necessarily have to include both low frequency fL and high frequency fH. For example, a specific frequency may include at least one of either a low frequency fL or a high frequency fH. Furthermore, a specific frequency does not necessarily have to include one low frequency fL or one high frequency fH. A specific frequency may include multiple low frequencies fL or multiple high frequencies fH with different frequencies.

[0035] The signal processing unit 15 uses the volume limit value determined as described above to correct the frequency characteristics of the sound output from the speaker 17 so that the amount of attenuation from the maximum volume SPH of the sound output from the speaker 17 at a predetermined frequency is within the range of the volume limit value determined as described above, according to the volume level indicated by the volume level information. Since the volume level information is information related to the volume level setting by the user, the signal processing unit 15 can also correct the frequency characteristics of the sound output from the speaker 17 so that the amount of attenuation is within the range of the volume limit value, according to the volume level setting by the user. Note that in this specification, the amount of attenuation indicates the amount attenuated from the maximum volume SPH, so the numerical value indicating the amount of attenuation will be a positive value. That is, since the sound pressure level after attenuation is lower than the maximum volume SPH, the attenuation is a negative change when compared to the maximum volume SPH, but in this specification, the amount of this change is described as the amount of attenuation, so the amount itself is a positive value.

[0036] The signal processing unit 15 may pre-determine the corrected frequency characteristics of the sound output from the speaker 17 for each selectable volume level, based on the lower volume limit SPL. For example, let's assume that in addition to the maximum volume and volume 0, four volume levels can be set. In this case, as shown in Figure 2, the signal processing unit 15 can set the corrected frequency characteristics when the volume level is lowered by one level from the maximum volume SPH as SPE1, the corrected frequency characteristics when it is lowered by two levels as SPE2, the corrected frequency characteristics when it is lowered by three levels as SPE3, and the corrected frequency characteristics when it is lowered by four levels as the lower volume limit SPL. These frequency characteristics SPE1, SPE2, and SPE3 may be set so that the amount of attenuation from the maximum volume SPH at the reference frequency fM is equal to the amount of attenuation of the frequency characteristics before correction. Therefore, as shown in Figure 3, for example, the frequency characteristics SPE1, SPE2, and SPE3 coincide with the frequency characteristics SP1, SP2, and SP3, respectively, at the reference frequency fM (the graphs are tangent).

[0037] In this way, by setting the corrected frequency response between the maximum volume SPH and the lower volume limit SPL, the sound pressure level of the sound output from speaker 17 can be corrected according to the characteristics of speaker 17. As a result, even when the volume level of the output sound is reduced, the frequency range of sound that the user can hear does not narrow as much. For example, even when the volume level of the output sound is reduced, the user will be able to hear low and high frequencies more easily.

[0038] Here, we will explain in detail how the signal processing unit 15 determines the amount of attenuation from the maximum volume for each volume level of the speaker 17. Figure 3 is a schematic diagram showing an example of the signal level attenuation of an audio signal for each volume level, and is a diagram showing the equalization characteristics for a set volume level. In Figure 3, the horizontal axis represents frequency (Hz), and the vertical axis represents signal level (dB). Figure 3 is a semi-logarithmic graph with a logarithmic scale on the horizontal axis. In Figure 3, the state where the signal level is not attenuated is set to 0 dB, and the amount of signal level attenuation is shown by the magnitude of the negative displacement.

[0039] In Figure 3, graph SL0, where the signal level is 0 dB, represents the case where no signal level attenuation occurs, and in the frequency response shown in Figure 2, it corresponds to the case of maximum volume SPH. Also in Figure 3, graph SL6, where the signal level is lowest, represents the case where the signal level attenuation is maximum, and in the frequency response shown in Figure 2, it shows the signal level attenuation state that occurs at the lower volume limit SPL where the signal level attenuation is maximum. Note that Figure 2 shows an example where the volume level is reduced by 4 steps from the maximum volume SPH, while Figure 3 shows an example where the volume level is reduced by 6 steps from the maximum volume. Therefore, the signal level graph shown in Figure 3 does not perfectly correspond to the frequency response graph shown in Figure 2. However, it should be noted that the basic concept regarding frequency response correction is the same regardless of the number of steps. This point is also true for Figures 4 and onward.

[0040] The signal processing unit 15 can determine the amount of attenuation for each volume level in various ways. For example, the signal processing unit 15 can determine the amount of attenuation based on the ratio of the first sound pressure level difference to the second sound pressure level difference. In the example shown in Figure 3, the rate of attenuation at a predetermined frequency based on the volume level setting by the user is the same as the rate of attenuation at the reference frequency fM. In other words, the rate of attenuation is uniform at each frequency.

[0041] Specifically, as shown in Figure 3, GM is defined as the difference in signal levels between the maximum volume SPH of speaker 17 at the reference frequency fM and the minimum volume that can be set as the sound output from speaker 17, and GL is defined as the difference in signal levels between the maximum volume SPH of speaker 17 at the low frequency fL and the minimum volume that can be set as the sound output from speaker 17. GM and GL can be calculated based on the maximum volume SPH and the lower volume limit SPL at the reference frequency fM and low frequency fL, respectively. If the attenuation of the signal level at the reference frequency fM is gM, the attenuation of the signal level at the low frequency fL, gL, is determined by the following equation (3). gL = GL·(gM / GM) (3)

[0042] Here, the value of gM can be determined, for example, based on the frequency response before correction. For example, as described above, when the volume level is reduced from the maximum volume SPH, the amount of attenuation of the corrected frequency response at the reference frequency fM from the maximum volume SPH can be set to be equal to the amount of attenuation of the frequency response before correction. In this case, the value of gM can be the same as the amount of attenuation of the frequency response before correction.

[0043] In the example shown in Figure 3, gM and gL are shown based on the position of SL3 on the graph, which is three levels lower than the maximum volume. However, the volume level is not limited to the example shown in Figure 3; it is applicable to any reduction in volume level. This point also applies to the explanations that follow.

[0044] The signal level attenuation gH at high frequency fH can be determined in the same way. That is, if GH is the difference in signal levels between the maximum volume SPH of speaker 17 at high frequency fH and the minimum volume that can be set as the sound output from speaker 17, then the signal level attenuation gH at high frequency fH is determined by the following equation (4). gH = GH·(gM / GM) (4)

[0045] The rate of attenuation is not necessarily limited to that shown in Figure 3. For example, the rate of attenuation at a predetermined frequency based on the volume level set by the user may change depending on the predetermined volume level. An example of this case will be explained with reference to Figure 4.

[0046] Figure 4 schematically illustrates another example of the attenuation of the signal level of an audio signal at different volume levels. In Figure 4, the horizontal axis represents frequency (Hz), and the vertical axis represents signal level (dB). Figure 4 is a semi-logarithmic graph with a logarithmic scale on the horizontal axis. In Figure 4, the state where the signal level is not attenuated is defined as 0 dB, and the amount of signal level attenuation is shown by the magnitude of the negative displacement.

[0047] The graph shown in FIG. 4 has a different attenuation amount of the signal level of the sound signal for each volume level as compared with the graph shown in FIG. 3. For example, in the graph shown in FIG. 4, at the reference frequency fM, the intervals between the graphs SL0 to SL6 corresponding to the maximum volume and the six volume levels are constant. That is, in the graph shown in FIG. 4, the rate of attenuation of the attenuation amount at the reference frequency fM with the change in the volume level is constant. On the other hand, at the low-frequency fL, the intervals between the graphs SL0 to SL6 corresponding to the maximum volume and the six volume levels are not constant. Specifically, the interval from graph SL0 to graph SL4 is narrower than the interval from graph SL4 to graph SL6. This is the same for the high-frequency fH. Thus, in the example shown in FIG. 4, the rate of attenuation of the attenuation amount based on the setting of the volume level changes at a predetermined volume level (the volume level corresponding to graph SL4 in the example of FIG. 4). In the example here, when it is above the predetermined volume level (that is, when the volume level is close to the maximum volume from the predetermined volume level), the attenuation amount is smaller than when it is below the predetermined volume level (that is, when the volume level is farther from the maximum volume than the predetermined volume level).

[0048] The details of the processing by the signal processing unit 15 when performing such processing will be described. Let gM, GM, and GL be defined in the same manner as in the case of FIG. 3. Let the attenuation amount at the reference frequency fM at the volume level where the rate of attenuation of the attenuation amount changes (the volume level corresponding to graph SL4 in the example of FIG. 4) be GMk, and the attenuation amount at the low-frequency fL be GLk. GMk and GLk can be appropriately determined within the ranges of 0 < GMk < GM and 0 < GLk < GL, respectively. When the attenuation amount of the signal level at the reference frequency fM is gM, the attenuation amount gL at the low-frequency fL is determined by the following formula (5). gL = GLk·(gM / GMk) (when gM ≤ GMk) gL = GLk + (GL - GLk)·{(gM - GMk) / (GM - GMk)} (when GMk < gM) (5)

[0049] The attenuation amount gH of the signal level at the high frequency fH can be similarly defined. That is, let GH be defined in the same way as in the case of FIG. 3. Let the attenuation amount at the high frequency fH at the volume level at which the attenuation rate of the attenuation amount changes (the volume level corresponding to the graph SL4 in the example of FIG. 4) be GHk. GHk can be appropriately determined within the range of 0 < GHk < GH. When the attenuation amount of the signal level at the reference frequency fM is gM, the attenuation amount gH of the signal level at the high frequency fH is determined by the following formula (6). gH = GHk · (gM / GMk) (when gM ≤ GMk) gH = GHk + (GH - GHk) · {(gM - GMk) / (GM - GMk)} (when GMk < gM) (6)

[0050] In this way, the signal processing unit 15 can change the attenuation rate of the attenuation amount for any k indicating the boundary volume level. In the example shown in FIG. 4, an example in which the attenuation rate of the attenuation amount is divided into two cases, that is, an example in which the attenuation rate is different above and below the graph SL4 in FIG. 4 as the boundary, has been described. However, the attenuation rate of the attenuation amount does not necessarily have to be divided into two, and may be divided into three or more. For the case where the attenuation rate is divided into three or more, the processing by the signal processing unit 15 can be executed using the same concept as the above formulas (5) and (6) described with reference to FIG. 4.

[0051] In the above embodiment, the case where the signal processing unit 15 executes the equalizer processing by attenuating the signal level according to the volume level has been described. However, the signal processing unit 15 does not necessarily have to execute the equalizer processing by attenuating the signal level. For example, as shown in FIG. 5, the signal processing unit 15 can execute the equalizer processing by attenuating the signal level regardless of the frequency according to the volume level and amplifying the signal level of a predetermined frequency according to the volume level. The frequency for amplifying the signal level and the amplification width can be appropriately determined using the same concept as the content described in the above embodiment.

[0052] Furthermore, the signal level attenuation may be determined for the entire predetermined frequency range using the method described with reference to Figures 2 and 3, similar to the lower volume limit SPL explained with reference to Figure 1. Alternatively, it may be determined only for the reference frequency fM and a specific frequency using the method described with reference to Figures 2 and 3, and for frequencies other than the reference frequency fM and the specific frequency (i.e., in this example, frequencies other than the reference frequency fM, the low frequency fL, and the high frequency fH), the attenuation determined for the reference frequency fM and the specific frequency may be set as the sum of the values ​​obtained by connecting these attenuations.

[0053] Furthermore, the reference frequency fM and the specific frequency in the above description are not necessarily a single frequency, but may be a frequency band with a predetermined width. For example, the reference frequency fM can be a frequency band with a predetermined width that includes the reference frequency fM. Below, with reference to Figures 6 to 9, several examples of frequency characteristic correction in equalizer processing will be described.

[0054] Figures 6 to 9 schematically illustrate an example of signal level attenuation during equalizer processing. In Figures 6 to 9, the horizontal axis represents frequency (Hz), and the vertical axis represents signal level (dB). Figures 6 to 9 are semi-logarithmic graphs with a logarithmic scale on the horizontal axis. In Figures 6 to 9, the state where the signal level is not attenuated is defined as 0 dB, and the amount of signal level attenuation is shown by the magnitude of the negative displacement. In the example shown in Figures 6 to 9, a mid-range frequency band with a predetermined width that includes the reference frequency fM is used as the reference frequency fM.

[0055] In the examples shown in Figures 6 to 9, the attenuation at the lower limit of the sound volume (SPL) and the attenuation of each signal level corresponding to the sound volume level are calculated and determined for the mid-range frequency band and specific frequencies, namely the low frequency fL and the high frequency fH, using the method described with reference to Figures 1 to 3. For frequency bands other than the mid-range frequency band and specific frequencies, the attenuation may be determined by an appropriate method.

[0056] For example, among the other frequency bands, the interval between the low frequency fL and the mid-frequency band, and between the mid-frequency band and the high frequency band fH, can be given a characteristic of continuous attenuation with a predetermined reduction amount corresponding to each volume level. In this case, the attenuation of the signal level may be determined by connecting the interval between the low frequency fL and the mid-frequency band, and between the mid-frequency band and the high frequency band fH with a curve as shown in Figure 3, or by connecting it with a straight line as shown in Figure 6.

[0057] Furthermore, the attenuation of the signal level does not necessarily have to change at low frequencies fL or high frequencies fH. For example, as shown in Figure 7, the attenuation of the signal level may be determined so that the signal level does not change within a certain range higher than the low frequency fL and within a certain range lower than the high frequency fH. This certain range may be the same regardless of the volume level, or it may differ depending on the volume level, as shown in Figure 7.

[0058] In the frequency bands below the low frequency fL and above the high frequency fH, the signal level can be the same as that of the low frequency fL and high frequency fH, respectively, as shown in Figures 3, 6, and 7. However, the signal level does not necessarily have to be constant in the frequency bands below the low frequency fL and above the high frequency fH. For example, in the frequency bands below the low frequency fL and above the high frequency fH, the signal level may be determined to approach 0 dB, as shown in Figure 8, or to deviate from 0 dB, as shown in Figure 9.

[0059] Thus, for frequencies other than the mid-range frequency band and specific frequencies (low frequency fL and high frequency fH) determined by calculation, the signal levels can be set as appropriate. The mid-range frequency band and specific frequencies can also be set as appropriate.

[0060] In the sound output device 1 according to this embodiment, equalization can be performed by setting appropriate values ​​according to the characteristics of the speaker 17, etc. For example, the mid-range frequency band can be set to a frequency range of 1kHz to 4kHz, the low-range frequency fL to 120Hz, and the high-range frequency fH to 12kHz. Also, when the signal level attenuation in the mid-range frequency band is 60dB, the signal level attenuation in the low-range frequency fL can be set to 25dB to 30dB, and the signal level attenuation in the high-range frequency fH can be set to 30dB to 35dB. However, it should be noted that the values ​​shown here are merely examples, and the above embodiment is not limited to using only the values ​​shown here.

[0061] As described above, in this embodiment, the signal processing unit 15 corrects the frequency characteristics of the sound output from the speaker 17 so that the attenuation from the maximum volume of the sound output from the speaker 17 is within the lower volume limit, according to the volume level indicated by the volume level information. The lower volume limit is determined based on the difference between the maximum volume of the speaker 17 at a reference frequency and the minimum volume that can be set as the sound output from the speaker 17, according to the first sound pressure level difference and the second sound pressure level difference. In this way, the frequency characteristics of the sound output from the speaker 17 are corrected according to the characteristics of the speaker 17. As a result, even if the volume level of the sound to be output is reduced, the frequency range of the sound that the user can hear does not narrow easily. Therefore, the sound output device 1 can make the sound output from the speaker 17 easier to hear.

[0062] The equalizer processing described in the above embodiment may be performed by hardware such as a circuit, or by software calculation. When performed by software calculation, infinite impulse response filters (IIR) and finite impulse response filters (FIR) can be used as calculation algorithms.

[0063] While this disclosure has been described based on the drawings and embodiments, it should be noted that those skilled in the art will find it easy to make various modifications and alterations based on this disclosure. Therefore, it should be noted that these modifications and alterations are within the scope of this disclosure. For example, the functions included in each functional part can be rearranged in a logically consistent manner, and multiple functional parts can be combined into one or separated. [Explanation of symbols]

[0064] 1. Sound output device 11 Control Unit 12 Storage section 13. Operation Input Section 14. Audio signal input section 15 Signal Processing Unit 16 Amplification section 17 speakers 18. Volume level information acquisition unit

Claims

1. A volume level information acquisition unit that acquires volume level information related to the volume level setting by the user, The system includes a signal processing unit that corrects the frequency characteristics of the sound output from the speaker so that, according to the volume level indicated by the volume level information, the amount of attenuation from the maximum volume of the sound output from the speaker at a predetermined frequency is within a range of the lower limit of the volume relative to the maximum volume at the predetermined frequency. The aforementioned lower volume limit is determined based on the difference between the maximum volume of the speaker at a reference frequency and the minimum volume that can be set as the sound output from the speaker, according to a first sound pressure level difference between the maximum volume at the reference frequency and the minimum audible volume that a person can hear, and a second sound pressure level difference between the maximum volume and the minimum audible volume at a frequency other than the reference frequency. Information processing device.

2. The information processing apparatus according to claim 1, wherein the lower limit of sound volume is determined for the reference frequency and the other frequencies according to the difference between the first sound pressure level and the difference between the second sound pressure level, and for frequencies other than the reference frequency and the other frequencies, it is determined as a value obtained by concatenating the lower limit of sound volume determined for the reference frequency and the other frequencies.

3. The information processing apparatus according to claim 1, wherein the other frequencies include low frequencies lower than the reference frequency and high frequencies higher than the reference frequency.

4. The information processing device according to claim 1, wherein the attenuation amount is determined based on the ratio of the first sound pressure level difference to the second sound pressure level difference.

5. The information processing apparatus according to claim 4, wherein the rate of attenuation of the attenuation amount at a predetermined frequency based on the volume level setting by the user is the same as the rate of attenuation of the attenuation amount at a reference frequency.

6. The information processing apparatus according to claim 4, wherein the rate of attenuation of the amount of attenuation at a predetermined frequency based on the volume level setting by the user changes with respect to the set predetermined volume level.

7. An information processing method performed by an information processing device, Retrieve volume level information regarding the volume level setting made by the user. In accordance with the volume level information indicated above, the frequency characteristics of the sound output from the speaker are corrected so that the amount of attenuation from the maximum volume of the sound output from the speaker at a predetermined frequency is within the lower limit of the volume relative to the maximum volume at the predetermined frequency. The aforementioned lower volume limit is determined based on the difference between the maximum volume of the speaker at a reference frequency and the minimum volume that can be set as the sound output from the speaker, according to a first sound pressure level difference between the maximum volume at the reference frequency and the minimum audible volume that a person can hear, and a second sound pressure level difference between the maximum volume and the minimum audible volume at a frequency other than the reference frequency. Information processing methods.

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