JP2019096947A - Audio device and level adjustment method for audio signal - Google Patents

Abstract

To suppress a sound pressure drop as the whole sound, while restraining generation of distortion due to a high level of an audio signal.SOLUTION: An audio device comprises a detector for detecting levels of audio signals of multiple channels, respectively, a determination part for determining whether or not a detected level exceeds a predetermined threshold for each channel, and an adjustment part for adjusting the levels of the audio signals for every channel. The adjustment part compresses the level of the audio signal below the predetermined threshold for the channel determined to exceed the predetermined threshold, and amplifies the level of the audio signal in a range not exceeding the predetermined threshold for the channel determined not exceeding the predetermined threshold.SELECTED DRAWING: Figure 3

Description

  The present invention relates to an audio apparatus and a method of adjusting the level of an audio signal.

  When the dynamic range of a sound source is wide in an audio device, distortion may occur beyond the allowable input of the power amplifier in areas where the audio signal level is high, and in areas where the audio signal level is low, the listener may Problems can arise that are difficult to hear. Therefore, it is known to use a compressor to compress the dynamic range of a sound source. By compressing the dynamic range of the sound source, the occurrence of distortion caused by the level of the audio signal exceeding the allowable input of the power amplifier and the problem of the listener becoming difficult to hear due to the low level of the audio signal are avoided. Be For example, Patent Document 1 describes a specific configuration of an audio device provided with this type of compressor.

  The audio apparatus described in Patent Document 1 is an apparatus for processing audio signals output from sound sources of a plurality of channels, and, for example, audio signals of each channel are added by an adder, and a level (volume value) is obtained from the added audio signal. Calculate). This audio apparatus amplifies the audio signal of each channel at an amplification factor (the amplification factor is smaller as the volume value is larger) according to the calculated volume value, and further, power is amplified by a power amplifier, and the speaker of each channel is Output as sound from.

JP 2001-238300 A

  In the configuration described in Patent Document 1, the audio signal of each channel is amplified at a smaller amplification factor as the larger volume value is calculated, so the level of the audio signal of each channel is suppressed. Therefore, in the channel where the level of the audio signal is high, distortion caused by exceeding the allowable input of the power amplifier is suppressed, while in the channel where the level of the audio signal is low, the audio signal is not sufficiently amplified and remains at a low level. There is. In this case, it is pointed out that it is difficult to secure sufficient sound pressure (sound pressure as the whole sound output from each channel).

  The present invention has been made in view of the above circumstances, and an object of the present invention is to suppress the decrease in sound pressure as a whole sound while suppressing the occurrence of distortion due to the high level of the audio signal. An audio device and a method of adjusting the level of an audio signal.

  An audio apparatus according to an embodiment of the present invention is an apparatus for processing audio signals of a plurality of channels, and a detection unit for detecting respective levels of audio signals for a plurality of channels, and a detected level exceeds a predetermined threshold. And a control unit configured to adjust the level of the audio signal for each channel. The adjustment unit compresses the level of the audio signal below a predetermined threshold for a channel determined to be at a level exceeding a predetermined threshold and the level of the audio signal for a channel determined to be at a predetermined threshold or less Is amplified within a range not exceeding a predetermined threshold.

  In the audio apparatus configured as described above, the levels of the audio signals of all the channels are compressed to a predetermined threshold or less, and the audio signals having a level lower than the predetermined threshold are amplified within a range not exceeding the predetermined threshold. Therefore, distortion does not substantially occur in the reproduced sound of each channel, and a decrease in sound pressure as a whole of the sound output from each channel is suppressed.

  In one embodiment of the present invention, the predetermined threshold value is, for example, a value corresponding to a limit level at which distortion does not occur in the audio signal.

  In one embodiment of the present invention, the adjustment unit calculates a level difference between audio signals before and after compression for a channel determined to have a level exceeding a predetermined threshold, and is determined to have a level below the predetermined threshold. The level of the audio signal may be amplified on the basis of the level difference for the channel.

  In an embodiment of the present invention, for a channel determined to have a level equal to or lower than a predetermined threshold value, the adjustment unit adds a predetermined threshold value to an addition value obtained by adding the level difference to the level of the audio signal before amplification. It is determined whether or not the channel exceeds the predetermined threshold, and the audio signal is amplified to the level of the above-mentioned additional value if the above-mentioned additional value does not exceed the predetermined threshold for a channel determined to have a level below the predetermined threshold. In the channel determined to have a level equal to or lower than the threshold, if the added value exceeds the predetermined threshold, the audio signal is not amplified to the level of the added value but is amplified to the predetermined threshold level. Good.

  The audio apparatus according to an embodiment of the present invention may be configured to include a holding unit that holds a magnification value in association with each level exceeding a predetermined threshold. In this case, for the channel determined to be at a level exceeding the predetermined threshold value, the adjustment unit reads from the holding unit the magnification value associated with the level detected by the detection unit, and uses the read magnification value as audio. By multiplying the signal, the level of the audio signal is compressed below a predetermined threshold.

  A method of adjusting the level of an audio signal according to an embodiment of the present invention is a method executed by an audio device processing audio signals of a plurality of channels, and detecting the levels of audio signals of a plurality of channels. The method further comprises the step of determining for each channel whether the received level exceeds a predetermined threshold and an adjusting step for adjusting the level of the audio signal for each channel. The adjustment step of the method compresses the level of the audio signal below a predetermined threshold for channels determined to be at levels above a predetermined threshold and audio for a channel determined to be at a level below the predetermined threshold. The level of the signal is amplified within a range not exceeding a predetermined threshold.

  According to an embodiment of the present invention, an audio apparatus and an audio signal level adjusting method capable of suppressing a decrease in sound pressure as a whole sound while suppressing the occurrence of distortion due to a high audio signal level are provided. Ru.

It is a figure showing typically the vehicle in which the audio system concerning one embodiment of the present invention was installed. It is a block diagram showing the composition of the audio device with which the audio system concerning one embodiment of the present invention is equipped. FIG. 6 is a flowchart showing the operation of the audio device according to the embodiment of the present invention. It is a figure which helps explanation of operation example 1 of the audio device concerning one embodiment of the present invention. It is a figure which helps the explanation of operation example 2 of the audio device concerning one embodiment of the present invention. FIG. 6 is a diagram illustrating the levels of audio signals of the front and back channels when the compressor operates in the conventional configuration.

  Hereinafter, an audio system according to an embodiment of the present invention will be described with reference to the drawings. An audio system according to an embodiment of the present invention is a system installed in a vehicle, and includes an audio device processing audio signals output from sound sources of a plurality of channels, and an audio signal of each channel output from the audio device. It has a plurality of speakers that output as sound. The sound source is, for example, a disk medium such as a compact disc (CD) or a super audio CD (SACD), or a storage medium such as a hard disk drive (HDD) or a universal serial bus (USB). The audio system according to the present invention is not limited to one installed in a vehicle, and may be installed in, for example, a room (living room etc.) of a building.

  FIG. 1 is a view schematically showing a vehicle A of a user in which an audio system 1 according to an embodiment of the present invention is installed. In FIG. 1, a part of the body of the vehicle A is shown as transparent so that the audio system 1 installed in the vehicle A can be visually recognized.

As shown in FIG. 1, the audio system 1 includes an audio device 10 and speakers SP _FR , SP _FL , SP _RR , and SP _RL connected to the audio device 10. The speakers SP _FR , SP _FL , SP _RR and SP _RL are respectively the door part D _FR on the driver's seat side, the door part D _FL on the passenger's seat side, the door part D _RR on the rear seat right side and the door part D on the rear seat left side _It is installed in _RL . In the present embodiment, for convenience, components to which the subscripts ( _FR , _FL , _RR , and _RL ) are attached will be described, for example, as “speakers SP _FR , SP _FL , SP _RR , SP _RL ,” in the case of being distinguished. If a subscript is attached like "and it does not distinguish and explain, it will not attach a subscript like" speaker SP ", for example.

The audio apparatus 10 is installed, for example, in a dashboard, processes audio signals input from sound sources of a plurality of channels, and outputs the processed signals to the speakers SP _FR , SP _FL , SP _RR , and SP _RL .

FIG. 2 is a block diagram showing the configuration of the audio apparatus 10 according to an embodiment of the present invention. As shown in FIG. 2, the audio device 10 includes a signal processing unit 100 _FR , 100 _FL , 100 _RR , 100 _RL, and a controller 200. The signal processing units 100 _FR , 100 _FL , 100 _RR and 100 _RL have the same configuration. For convenience showing simplicity of illustration, of the four signal processing unit 100, shown only components of the signal processing unit 100 _FR. Further, FIG. 2 illustrates main components necessary for the description of the present embodiment, and illustration of some components such as a casing which is a general component as an audio apparatus is appropriately omitted. doing.

  The controller 200 is an integrated circuit (IC) that controls the audio device 10, and includes a central processing unit (CPU), a read only memory (ROM) that stores a control program executed by the CPU, and various types of programs necessary for executing the control program. It has RAM (Random Access Memory) etc. which store data temporarily.

The signal processing units 100 _FR , 100 _FL , 100 _RR , 100 _RL respectively output audio signals S _FR , S _FL , which are output from sound sources of four channels (right front channel, left front channel, right rear channel, left rear channel). S _RR and S _RL are input. The signal processing units 100 _FR , 100 _FL , 100 _RR , and 100 _RL process the input audio signals S _FR , S _FL , S _RR , and S _RL , respectively, to produce the speakers SP _FR , SP _FL , SP _RR , and SP. Output to _RL .

  Generally, there are engine noise and road noise in the vehicle interior. The listener may turn up the volume to listen to music or the like under this kind of noise environment.

  Also, in general, in the vehicle interior, the listener does not feel discomfort when the user listens to music or the like mainly from the front, so the front channel (the present implementation) is more than the rear channel (in the present embodiment, the right rear channel and the left rear channel) In the embodiment, equalization is performed such that the sound pressure is increased in the right front channel and the left front channel. Therefore, when the volume is increased and the levels of the audio signals of all channels are increased, the audio signal of the front channel is distorted prior to the audio signal of the rear channel beyond the limit level (0 dB) where distortion does not occur.

  Therefore, in the conventional configuration, when the volume is raised and the level of the audio signal of the front channel reaches 0 dB, the compressor operates to suppress the occurrence of distortion. Here, for convenience of explanation, the audio signal is assumed to be a signal of constant sound (white noise or the like).

  In the conventional configuration, by operating the compressor, the level of the audio signal of the front channel is fixed at 0 dB, which is the limit level at which distortion does not occur. On the other hand, the level of the audio signal of the rear channel is fixed at the level when the compressor is activated even if the level is significantly below 0 dB. In the conventional configuration, distortion generated when the level of the audio signal exceeds the allowable input of the power amplifier is suppressed, while the sound pressure of the rear channel is low, so the sound pressure as the whole sound output from each channel is secured. It is difficult.

  The levels of the audio signals of the front and back channels when the compressor is activated in the conventional configuration are shown in the graph of FIG. The vertical axis of FIG. 6 indicates the level (unit: dB) of the audio signal, and the horizontal axis indicates time (unit: msec). As shown in FIG. 6, when the volume is gradually raised and the level of the audio signal of the front channel reaches a threshold (the level corresponding to 0 dB), the compressor operates to set the level of the audio signal of the front channel to 0 dB. In addition to being fixed, the level of the audio signal of the rear channel is fixed to the level at the time of operation of the compressor although the threshold has not been reached. As described above, in the conventional configuration, it is found that the sound pressure of the rear channel can not be sufficiently increased by operating the compressor, and it is difficult to secure the sound pressure as the whole sound output from each channel . In FIG. 6, the level of the audio signal of each channel when the compressor does not operate is indicated by a dotted line as auxiliary information.

  Therefore, in the audio apparatus 10 according to the present embodiment, as described later, the reproduction of music or the like is performed in a state in which the decrease in the sound pressure as the entire sound is suppressed while suppressing the occurrence of distortion due to the high level of the audio signal. As described, it processes audio signals output from sound sources of multiple channels.

  FIG. 3 is a flowchart showing the operation of the audio device 10 according to the present embodiment. The processing by this operation is referred to as "level adjustment processing".

  The audio device 10 is activated, for example, when the engine of the vehicle is started. When the audio device 10 is activated, execution of the level adjustment process shown in FIG. 3 is started. When the audio device 10 stops, the level adjustment process shown in FIG. 3 ends. By executing the level adjustment process shown in FIG. 3, the music and the like are reproduced in a state in which the decrease in the sound pressure as the entire sound is suppressed while the occurrence of distortion due to the high level of the audio signal is suppressed.

Audio signals S _FR , S _FL , S _RR , and S _RL output from the sound source are input to the signal processing units 100 _FR , 100 _FL , 100 _RR , and 100 _RL , respectively. As described above, the signal processing units 100 _FR , 100 _FL , 100 _RR and 100 _RL have the same configuration. In the present embodiment, the signal processing unit 100 _FR will be described in detail, for the sake of simplicity of the description, and the details of the signal processing units 100 _FL , 100 _RR and 100 _RL will be omitted as appropriate.

The signal processing unit 100 _FR includes a compressor unit 110. The compressor unit 110 includes an input-side level detection unit 112, a look-up table unit 114, and a multiplication unit 116. The audio signal _SFR is input to the input side level detection unit 112 and the multiplication unit 116.

The input-side level detection unit 112 sequentially detects the level (volume value) of the audio signal _SFR input from the sound source at minute time intervals, and outputs information of the detected level to the lookup table unit 114 and the controller 200 ( Step S11). Each time the input-side level detection unit 112 detects the level of the audio signal _SFR , the processes after step S12 are performed.

  If an audio signal S at a level exceeding 0 dB is output to the speaker SP even for a moment, a distorted sound is reproduced at least for that moment. In order to avoid the reproduction of distorted sound, the input-side level detection unit 112 detects not the average value but the level of the peak value. For example, envelope detection is used for level detection.

  The lookup table unit 114 holds a table in which each level of the audio signal S exceeding a predetermined threshold is associated with a predetermined magnification value α. The predetermined threshold is a value corresponding to a limit level (0 dB) at which distortion does not occur in the audio signal S. Below, an example of the table which the look-up table part 114 hold | maintains is shown.

[Example of table]
Level Lv of audio signal S: corresponding magnification value α
0 dB <Lv <+1 dB: α1
+1 dB ≦ Lv <+2 dB: α 2
+2 dB ≦ Lv <+3 dB: α3
+3 dB ≦ Lv <+4 dB: α4
...
(For each magnification value α associated with each level Lv of +4 dB or more, it is omitted for convenience)

  In the above example, the lookup table unit 114 associates and holds different magnification values α1, α2, α3,... In 1 dB steps. In another embodiment, the magnification value α may be associated with each finer or larger level. The higher the level of the audio signal S, the lower the magnification value α (in other words, the magnification value α at which the audio signal S is compressed at a higher rate as the level of the audio signal S is higher) is associated. More specifically, the magnification value α is a value to compress the audio signal S exceeding 0 dB to a value to be compressed to 0 dB, or to a level of 0 dB or less and close to 0 dB.

When the information on the level of the audio signal S _FR is input from the input-side level detection unit 112, the lookup table unit 114 determines whether the level exceeds 0 dB (step S12). If the level of the audio signal _{S FR} exceeds 0 dB (Step S12: YES), the look-up table unit 114 reads the magnification value α corresponding to the level from the table, and outputs to the multiplying unit 116 (step S13). If the level of the audio signal S _FR does not exceed 0 dB (is 0 dB or less) (step S12: NO), the lookup table unit 114 outputs 1 × information as the magnification value α to the multiplication unit 116 (step S18). ).

The signal processing unit 100 _FR includes an output side level detection unit 120 and an addition unit 130. The multiplying unit 116 multiplies the audio signal _SFR input from the sound source by the scaling factor value α input from the lookup table unit 114, and outputs the result to the output-side level detecting unit 120 and the adding unit 130 (steps S14 and S19). That is, when the audio signal S _FR input from the sound source has a level exceeding 0 dB, the multiplying unit 116 compresses and outputs the signal at the magnification value α according to the level (step S14) while the audio input from the sound source If the signal S _FR is 0 dB or less, the audio signal S _FR is output at the level as it is (step S19).

Thus, the multiplication unit 116, an audio signal _{S FR,} when the level at the input to the compressor portion 110 exceeds 0dB is a level (0dB or less not exceeding 0dB, e.g. 0dB or a level close to 0dB To the output side level detection unit 120 and the addition unit 130 (step S14).

The addition unit 130 outputs the audio signal _SFR input from the multiplication unit 116 through to a power amplifier (not shown) (step S15). Audio signal S _FR, after being power-amplified by a power amplifier, and outputted as sound from the speaker SP _FR. In step S14, the audio signal _SFR is compressed to a level not exceeding 0 dB. Therefore, distortion does not substantially occur in the sound reproduced by the speaker SP _FR .

The output-side level detection unit 120 sequentially detects the level of the audio signal _SFR input from the multiplication unit 116 at minute time intervals, and outputs information of the detected level to the controller 200 (step S16). For detection of the level, for example, envelope detection is used as in the level detection unit 112.

The controller 200 receives information on the level input from the input-side level detection unit 112 (that is, information on the level of the audio signal _SFR before compression by the multiplication unit 116) and information on the level input from the output-side level detection unit 120 ( That is, the difference value (difference in level of the audio signal S _FR before and after compression) is calculated by comparing the information of the level of the audio signal S _FR after compression by the multiplication section 116 (step S17).

As described above, when the level at the time of input to the compressor unit 110 is 0 dB or less, the multiplication unit 116 outputs the audio signal _SFR to the output-side level detection unit 120 and the addition unit 130 at the same level. (Step S19).

The level adjustment process shown in FIG. 3 is performed in parallel to the audio signals S _FR , S _FL , S _RR and S _{RL of} each channel input to the respective signal processing units 100 _FR , 100 _FL , 100 _RR and 100 _RL. Is being implemented. Therefore, for a channel in which the level of the audio signal at the time of input to the compressor unit 110 exceeds 0 dB, the controller 200 executes the step S17 to determine the level of the audio signal S input from the signal processing unit 100 corresponding to the channel. The difference value (the level difference between the audio signal S before and after compression) is calculated on the basis of the above information.

Among the audio signals S of other channels (here, audio signals S _FL , S _RR , S _RL other than the audio signal S _FR ), the controller 200 has a level exceeding 0 dB when input to the compressor unit 110 It is determined whether or not there is (step S20).

When it is determined that there is an audio signal S of another channel that has a level at the time of input to the compressor unit 110 exceeding 0 dB (step S20: YES), the controller 200 calculates the audio signal S exceeding 0 dB. The calculated difference value is added to the level of the audio signal _SFR input from the input-side level detection unit 112 (step S21). If there are a plurality of difference values calculated for the audio signal S exceeding 0 dB (three at the maximum in the present embodiment), for example, the largest difference value among them or the average value of those difference values is an audio signal _SFR is added to the level.

  The controller 200 determines whether the added value calculated in step S21 exceeds a predetermined threshold (0 dB) (step S22). When it is determined that the added value exceeds the predetermined threshold (step S22: YES), the controller 200 adds the values in step S21 so that the added value is at a level (0 dB or a level close to 0 dB) below the predetermined threshold. The difference value used to calculate the value (in other words, the difference value calculated for the audio signal S of the other channel) is changed to a value lower than the current value (step S23).

The controller 200 outputs the difference value changed in step S23 to the adding unit 130 (step S24). The addition unit 130 adds the amplification value corresponding to the difference value to the audio signal S _FR (with a level at the time of input to the compressor unit 110 being 0 dB or less) input from the multiplication unit 116 to obtain a power amplifier (not shown). (Step S25).

Audio signal S _FR, after being power-amplified by a power amplifier, and outputted as sound from the speaker SP _FR. In step S25, the audio signal _SFR is amplified (amplified to a level below 0 dB or 0 dB and close to 0 dB) in a range not exceeding 0 dB. Compression amount level of the audio signal S is in other channels of more than 0dB have been supplemented by amplifying the audio signal S _FR. By amplifying the audio signal S _FR without substantially causing distortion in the sound reproduced by the speaker SP _FR , the sound pressure as the whole sound output from each channel is secured (as the whole sound Decrease in sound pressure can be suppressed).

When it is determined that the added value calculated in step S21 is less than or equal to the predetermined threshold (step S22: NO), the controller 200 uses the difference value used when calculating this added value (in other words, audio signals of other channels) The difference value calculated for S is output to the adding unit 130 without changing it to a low value (step S26). The addition unit 130 adds the amplification value corresponding to the difference value to the audio signal S _FR (with a level at the time of input to the compressor unit 110 being 0 dB or less) input from the multiplication unit 116 to obtain a power amplifier (not shown). Output (step S27).

Audio signal S _FR, after being power-amplified by a power amplifier, and outputted as sound from the speaker SP _FR. In step S27, the audio signal _SFR is amplified by an amount that does not exceed 0 dB and is compressed by another channel (a channel in which the level of the audio signal S exceeds 0 dB). Compression component in the other channel are compensated by amplifying the audio signal S _FR. Therefore, also in this case, the sound reproduced from the speaker SP _FR is substantially distorted, and the audio signal S _FR is amplified, whereby the sound pressure as the whole sound output from each channel is secured. (The reduction in sound pressure as a whole sound can be suppressed).

In the case where it is determined that none of the audio signals S of the other channels at the time of input to the compressor unit 110 exceeds 0 dB (that is, the level of the audio signal S is 0 dB or less in all channels) (step S20) (NO), the controller 200 does not output the difference value to the adding unit 130. Therefore, the adding unit 130 outputs the audio signal _SFR input from the multiplying unit 116 through to the power amplifier (not shown) (step S28). Also in this case, distortion does not substantially occur in the sound reproduced by the speaker SP _FR , and since the compressor unit 110 does not operate, a decrease in sound pressure as a whole sound output from each channel does not occur.

  Next, three operation examples of the audio apparatus 10 will be described. In each of FIG. 4 and FIG. 5, the vertical axis and the horizontal axis respectively indicate the level (unit: dB) and the frequency (unit: Hz) of the audio signal S.

[Operation example 1]
FIG. 4A to FIG. 4D are diagrams to help explain the operation example 1 of the audio device 10. FIG. 4A shows the frequency characteristics of the audio signal S of each channel input from the sound source. For convenience of explanation, it is assumed that the audio signals S of the right front channel and the left front channel (that is, the front channel) have the same frequency characteristics, and the audio signals S of the right rear channel and the left rear channel (that is, the rear channel) have the same frequency characteristics. . As shown in FIG. 4A, in the operation example 1, the audio signal S whose level exceeds 0 dB is input from the sound source to the compressor unit 110 in the front channel, and the audio signal S whose level is less than 0 dB in the rear channel Are input to the compressor unit 110 from the sound source.

FIG. 4B shows the frequency characteristics of the audio signal S of the front channel compressed by the multiplication unit 116. As shown in FIG. 4B, in the operation example 1, the audio signal S of the front channel is compressed to 0 dB or less and is output to the speakers SP _FR and SP _FL (steps S13 to S15).

FIGS. 4C and 4D show the frequency characteristics of the audio signal S of the rear channel amplified by the adding unit 130. FIG. As shown in FIG. 4C and FIG. 4D, the audio signal S of the rear channel is amplified by an amplification value corresponding to the difference value (the level difference between before and after the compression of the audio signal S of the front channel) , And speakers SP _RR and SP _RL (steps S18 to S27). FIG. 4 (c) illustrates the case where the audio signal S of the rear channel is amplified to a level below 0 dB and close to 0 dB, and FIG. 4 (d) is the audio signal S of the rear channel is amplified to 0 dB The case is illustrated.

In the operation example 1, the levels of the audio signals S of all the channels are suppressed to 0 dB or less, and the audio signal S of the rear channel is amplified by an amount corresponding to the compression of the audio signal S of the front channel. . Therefore, distortion does not substantially occur in the sound reproduced by the speaker SP of each channel, and the sound pressure as the whole sound output from each channel is secured.

[Operation example 2]
FIGS. 5A to 5D are diagrams to help explain the operation example 2 of the audio apparatus 10. FIG. FIG. 5A shows the frequency characteristics of the audio signal S of each channel input from the sound source. Also in the operation example 2, the audio signals S of the right front channel and the left front channel (that is, the front channel) have the same frequency characteristics, and the audio signals S of the right rear channel and the left rear channel (that is, the rear channel) have the same frequency characteristics. I assume. As shown in FIG. 5A, in the second operation example, an audio signal S whose level exceeds 0 dB is input from the sound source to the compressor unit 110 in the rear channel, and an audio signal S whose level is less than 0 dB in the front channel. Are input to the compressor unit 110 from the sound source.

FIG. 5B shows the frequency characteristics of the audio signal S of the rear channel compressed by the multiplication unit 116. As shown in FIG. 5B, in the operation example 2, the audio signal S of the rear channel is compressed to 0 dB or less and is output to the speakers SP _RR and SP _RL (steps S13 to S15).

FIGS. 5C and 5D show the frequency characteristics of the audio signal S of the front channel amplified by the addition unit 130. FIG. As shown in FIGS. 5C and 5D, the audio signal S of the front channel is amplified by an amplification value corresponding to the difference value (the level difference between before and after the compression of the audio signal S of the rear channel) is output to the speaker _{SP FR} and _{SP FL} (step S18~S27). FIG. 5 (c) illustrates the case where the audio signal S of the front channel is amplified to a level below 0 dB and close to 0 dB, and FIG. 5 (d) is the audio signal S of the front channel is amplified to 0 dB The case is illustrated.

  Also in the operation example 2, the levels of the audio signals S of all channels are suppressed to 0 dB or less, and the audio signal S of the front channel is amplified by an amount corresponding to the compression of the audio signal S of the rear channel. There is. Therefore, distortion does not substantially occur in the sound reproduced by the speaker SP of each channel, and the sound pressure as the whole sound output from each channel is secured.

[Operation example 3]
In the operation example 3, the audio signal S whose level is less than 0 dB is input from the sound source to the compressor unit 110 in all the channels. In this case, the audio signals S of all the channels are output to the speaker SP without being compressed in the compressor unit 110 and not amplified in the adding unit 130 (step S28). Even in the operation example 3, substantially no distortion occurs in the sound reproduced by the speaker SP of each channel, and since the compressor unit 110 does not operate, the sound pressure as a whole of the sound output from each channel is also reduced. It does not occur.

  As a result of performing the level adjustment process shown in FIG. 3, if the balance between the volume of music such as music coming from the front and the volume of music coming back from the rear changes, some listeners may feel discomfort in this change. Therefore, the listener can change the sound field to such an uncomfortable feeling by correcting the frequency characteristics of the audio signal S of each channel by operating an equalizer (not shown) provided in the audio device 10 .

  This level difference is reduced when the level adjustment process shown in FIG. 3 is performed when the level difference between the audio signals S is large in the left and right channels. When the level difference processing is reduced by the execution of the level adjustment processing, there is a possibility that the sense of sound field and the sense of stereo perceived by the listener greatly change with respect to the case where the level adjustment processing is not performed. Therefore, the listener operates the equalizer to correct, for example, only the low frequency characteristic of the low directivity of the sound, thereby suppressing the change in the sound field feeling or the stereo feeling.

  The above is a description of an exemplary embodiment of the present invention. Embodiments of the present invention are not limited to those described above, and various modifications are possible within the scope of the technical idea of the present invention. For example, the contents of the embodiment of the present application also include the contents in which the embodiment etc. or the obvious embodiment etc. which are clearly illustrated in the specification are appropriately combined.

1 audio system 10 audio device 100 _FR , 100 _FL , 100 _RR , 100 _RL signal processing unit 110 compressor unit 112 input side level detection unit 114 look-up table unit 116 multiplication unit 120 output side level detection unit 130 addition unit 200 controller

Claims (10)

In an audio device for processing audio signals of multiple channels,
A detection unit that detects the level of each of the audio signals of the plurality of channels;
A determination unit that determines, for each channel, whether the detected level exceeds a predetermined threshold;
An adjustment unit that adjusts the level of the audio signal for each of the channels;
Equipped with
The adjustment unit is
The level of the audio signal is compressed below the predetermined threshold for a channel determined to be at a level exceeding the predetermined threshold, and the audio signal is compressed for a channel determined to be at a level lower than the predetermined threshold. Amplify the level without exceeding the predetermined threshold value,
Audio device. The predetermined threshold is
A value corresponding to a limit level at which no distortion occurs in the audio signal,
An audio device according to claim 1. The adjustment unit is
Calculating a level difference between audio signals before and after the compression for a channel determined to have a level exceeding the predetermined threshold value;
The level of the audio signal is amplified based on the level difference for a channel determined to be at a level below the predetermined threshold.
An audio device according to claim 1 or 2. The adjustment unit is
For a channel determined to be at a level below the predetermined threshold, it is determined whether an added value obtained by adding the level difference to the level of the audio signal before the amplification exceeds the predetermined threshold.
The audio signal is amplified to the level of the added value when the added value does not exceed the predetermined threshold for a channel determined to be at a level equal to or less than the predetermined threshold.
For a channel determined to have a level equal to or less than the predetermined threshold value, when the added value exceeds the predetermined threshold value, the audio signal is not amplified to the level of the added value and the level is increased to the predetermined threshold value. To amplify,
An audio device according to claim 3. A holding unit that holds a magnification value in association with each level exceeding the predetermined threshold value;
The adjustment unit is
For a channel determined to have a level exceeding the predetermined threshold value, a magnification value associated with the level detected by the detection unit is read from the holding unit,
Compressing the level of the audio signal below the predetermined threshold by multiplying the audio signal with the read out scaling value;
An audio device according to any one of the preceding claims. In an audio signal level adjustment method implemented by an audio device processing audio signals of multiple channels,
Detecting each of the levels of the audio signals of the plurality of channels;
A determining step of determining for each channel whether the detected level exceeds a predetermined threshold;
Adjusting the level of the audio signal for each of the channels;
Including
At the adjustment step
The level of the audio signal is compressed below the predetermined threshold for a channel determined to be at a level exceeding the predetermined threshold, and the audio signal is compressed for a channel determined to be at a level lower than the predetermined threshold. Amplify the level without exceeding the predetermined threshold value,
Level adjustment method. The predetermined threshold is
A value corresponding to a limit level at which no distortion occurs in the audio signal,
The level adjustment method according to claim 6. At the adjustment step
Calculating a level difference between audio signals before and after the compression for a channel determined to have a level exceeding the predetermined threshold value;
The level of the audio signal is amplified based on the level difference for a channel determined to be at a level below the predetermined threshold.
The level adjustment method according to claim 6 or 7. At the adjustment step
For a channel determined to be at a level below the predetermined threshold, it is determined whether an added value obtained by adding the level difference to the level of the audio signal before the amplification exceeds the predetermined threshold.
The audio signal is amplified to the level of the added value when the added value does not exceed the predetermined threshold for a channel determined to be at a level equal to or less than the predetermined threshold.
For a channel determined to have a level equal to or less than the predetermined threshold value, when the added value exceeds the predetermined threshold value, the audio signal is not amplified to the level of the added value and the level is increased to the predetermined threshold value. To amplify,
The level adjustment method according to claim 8. Including a holding step of associating and holding a magnification value with each level exceeding the predetermined threshold;
At the adjustment step
For a channel determined to have a level exceeding the predetermined threshold value, a magnification value associated with the level detected by the detection unit is read from the holding unit,
Compressing the level of the audio signal below the predetermined threshold by multiplying the audio signal with the read out scaling value;
The level adjustment method according to any one of claims 6 to 9.

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