JP4086019B2 - Volume control device - Google Patents

Description

  The present invention relates to a volume control apparatus suitable for volume control of a multi-channel audio signal.

When performing audio playback of movies, music, etc. at night, it is common to reduce the playback volume so as not to disturb the neighborhood. However, if the playback volume is reduced, it is difficult to hear the playback sound when the audio signal supplied from the audio source is at a low volume. In order to solve such a problem, a so-called dynamic range compression technique is used. In this technology, an audio signal supplied from an audio source is amplified and output by a variable gain amplifier, while a variable gain according to the volume of the audio signal so that the amplification gain at a low volume is larger than that at a high volume. Control the gain of the amplifier. By doing so, it is possible to avoid the difficulty in hearing the reproduced sound when the audio signal is turned down. This dynamic range compression technique is also applied to multi-channel audio signals. Conventionally, for this type of multi-channel audio signal, dynamic range compression has been performed by applying a uniform gain to all channels based on the overall volume of all channels. An apparatus for performing dynamic range compression is disclosed in Patent Document 1, for example.
Japanese Patent No. 3295440

  By the way, when the dynamic range compression of a multi-channel audio signal such as a movie is performed by the above-described conventional technique, for example, the volume of the center channel audio signal representing a dialogue is small, and the volume of the other channel audio signal is large. When there is a signal, the control of lowering the gain of the variable gain amplifier is performed according to the volume level of the loud audio signal. Therefore, comparing the audio signals of each channel after compression of the dynamic range, there is a problem that the volume of the dialogue of the center channel is buried in the volume of the other channels, and it becomes difficult to hear the dialogue from the reproduced sound. .

  The present invention has been made in view of the circumstances described above, and when performing dynamic range compression of a multi-channel audio signal, the volume of the audio signal of a specific channel after dynamic range compression is the same as that of the audio signal of another channel. An object of the present invention is to provide a volume control device that can correct a problem that is buried in the volume.

In order to solve the above problems, the present invention provides a plurality of variable gain amplifying means for amplifying a plurality of channels of audio signals, and the volume of at least one specific channel audio signal among the plurality of channels of audio signals for each channel. First volume detecting means for detecting; band dividing means for dividing an audio signal of at least one channel of the at least one specific channel into a plurality of frequency bands; and the specific channel of the audio signals of the plurality of channels. Second volume detecting means for detecting the volume of the audio signals of all channels except for, and the volume of the at least one specific channel based on the volume of the at least one specific channel detected by the first volume detecting means. The gain of the variable gain amplification means that amplifies the audio signal for each channel The gains of all variable gain amplifying means for amplifying audio signals of channels other than the specific channel are uniformly set based on the volume detected by the first gain control means and the second volume detecting means. Second gain control means for controlling, and for the audio signal of the channel band-divided by the band dividing means, the first gain control means divides the gain of the variable gain amplifying means into bands. Provided is a volume control device that controls each audio signal.
According to the present invention, for a specific channel, the audio signal is divided into a plurality of bands, and the amplification gain of the variable gain amplification means is controlled according to the volume of the audio signal for each band independently of the other channels. Therefore, when the audio signal of a specific channel is at a low volume, the audio signal is amplified with a gain corresponding to the volume and output at an appropriate volume. For this reason, the problem that the volume of the audio signal of a specific channel is buried in the volume of the audio signal of another channel can be corrected. In addition, since the amplification gain is controlled for each band, it is possible to perform volume control in accordance with human hearing.
In a preferred aspect, for the audio signal of the channel band-divided by the band dividing means, the first gain control means includes the volume of the audio signal input to the variable gain amplifying means and the gain at the time of amplification. So that the gains of the plurality of variable gain amplifiers may be controlled so that the relationship is different for each of the divided audio signals.
In another preferred aspect, the volume control device according to the present invention further comprises decay processing means for performing decay processing on the audio signal of at least one channel among the plurality of channels of audio signals, and the decay processing means includes: Decay processing may be performed so that the decay rate is linear with respect to time.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
<First Embodiment>
FIG. 1 is a block diagram showing a configuration of a volume control apparatus according to the first embodiment of the present invention. This volume control device includes L, R, LS (L surround), RS (R surround), SBL (surround back L), SBR (surround back R), LFE (low frequency effect), and C (center). This is a device for controlling the volume of an audio signal consisting of 8 channels. Here, the 8-channel audio signal is, for example, a movie audio signal, the C-channel audio signal represents a human voice (ie, speech), and the audio signals of other channels represent music, sound effects, and the like. Represents.

  The amplifiers 5L, 5R, 5LS, 5RS, 5SBL, 5SBR, 5LFE, and 5C are amplifiers that amplify the audio signals of the L, R, LS, RS, SBL, SBR, LFE, and C channels, respectively. These amplifiers are variable gain amplifiers capable of controlling a gain when an audio signal is amplified. Since the volume control apparatus in this embodiment handles digital audio signals, these amplifiers are configured by multipliers that multiply the digital audio signals by variable coefficients. When the volume control device handles analog audio signals, variable gain amplifiers configured by analog circuits may be used as these amplifiers.

  The volume control device according to the present embodiment has three processing systems 10, 20, and 30 as means for controlling the amplification gain of the audio signal in accordance with the level of the audio signal.

  The processing system 10 is a processing system for performing dynamic range compression of the audio signals of the L, R, LS, RS, SBL, and SBR channels. In the processing system 10, the volume detector 12 detects the overall volume level of the audio signals of the L, R, LS, RS, SBL, and SBR channels, and extracts the maximum volume level signal representing the detected volume level. To the unit 13. The maximum value extraction unit 13 obtains the maximum value of the volume level signal of the L, R, LS, RS, SBL, and SBR channels, and outputs the maximum value to the decay processing unit 14 as an overall volume level. Instead of the maximum value extraction unit 13, a square addition circuit that performs square addition of the audio signals of the L, R, LS, RS, SBL, and SBR channels and outputs the result as an overall volume level. It is good also as a structure using.

  The decay processing unit 14 is a circuit that performs a decay process on the input signal. FIG. 2 is a diagram illustrating a decay process according to this embodiment. When an input signal such as an impulse, which is indicated by an alternate long and short dash line in FIG. 2, is input, a decay that decreases the gain linearly without following the output with respect to the input signal that rapidly decreases after taking the maximum value. We were processing. However, according to the conventional processing, there is a case where a sense of incongruity is felt in the auditory sense. On the other hand, in the present embodiment, a nonlinear decay process such as a parabola is performed, for example, a gain that gradually decreases immediately after the input signal takes the maximum value, and a decrease rate increases with time. As a result, the change is suppressed immediately after receiving the impulse, and after a certain amount of time has passed, the change is made faster, so that the viewer can have a natural audibility.

  A description will be given with reference to FIG. 1 again. The gain controller 15 performs amplifiers 5L, 5R, 5LS, 5RS, 5SBL in order to perform dynamic range compression according to the overall volume level of the audio signals of the L, R, LS, RS, SBL, and SBR channels. This is a circuit for controlling the gains of 5SBR and 5LFE. 3 to 5 show examples of dynamic range compression performed under the control of the gain control unit 15. In each figure, the horizontal axis represents the volume level (hereinafter referred to as the volume level) of the audio signal input to the amplifier 5. , The input volume level), and the vertical axis represents the volume level of the audio signal output from the amplifier 5 (hereinafter, output volume level). 3 to 5, the broken line indicates the relationship between the input volume level and the output volume level when the gain of the amplifier 5 is fixed to a standard value. In the example shown in FIG. 3, the gain of the amplifier 5 is set to a standard value in a region where the output volume level is equal to or lower than the threshold th1, and decreases as the input volume level increases in a region where the output volume level is equal to or higher than the threshold th1. Therefore, in the latter region, the dynamic range of the audio signal is compressed, and the output volume level of the audio signal with a large volume is suppressed. In the example shown in FIG. 4, the gain of the amplifier 5 is a standard value in a region where the output volume level is equal to or higher than the threshold th2, and increases as the input volume level decreases in a region where the output volume level is equal to or lower than the threshold th2. Therefore, in the latter region, the dynamic range of the audio signal is compressed, and the output volume level of the low volume audio signal is raised. FIG. 5 shows an example in which the one shown in FIG. 3 and the one shown in FIG. 4 are used in combination. In this example, the gain of the amplifier 5 is a standard value in a region where the output volume level is between the thresholds th1 and th2, and the output volume level of a low volume audio signal is raised in a region below the threshold th2, and the threshold th1. In the above region, the output volume level of the loud audio signal can be suppressed. Furthermore, the audio signal in the region below the threshold th3 is regarded as noise, and the volume level is suppressed.

  The gain control unit 15 obtains a coefficient corresponding to the output volume level / input volume level (hereinafter referred to as gain coefficient) for various input volume levels in any of FIGS. A table in which levels are associated with respective coefficients (hereinafter referred to as gain table) is stored. The gain control unit 15 receives the volume level signal from the decay processing unit 14, reads out a gain coefficient corresponding to the volume level indicated by the volume level signal from the gain table, and via the delay circuit 16, the amplifiers 5L, 5R, 5LS. Give to 5RS, 5SBL, 5SBR, and 5LFE. In a preferred embodiment, the delay circuit 16 delays the signal by 1 ms in order to suppress a rapid change in gain. In order to synchronize the timing of the gain coefficient and the audio signal, a delay circuit 3L is provided. Then, the amplifiers 5L, 5R, 5LS, 5RS, 5SBL, 5SBR, and 5LFE multiply the audio signals of the respective channels by the common gain coefficients given in this way and output them. The output signals of these amplifiers are converted into analog audio signals by a D / A converter (not shown) and output from the speakers of the respective channels. By controlling the gains of the amplifiers 5L, 5R, 5LS, 5RS, 5SBL, 5SBR, and 5LFE by the gain controller 15 as described above, the dynamic range compression of the audio signal as illustrated in FIGS. Done.

  The processing system 20 is a processing system for performing dynamic range compression of the LFE channel. The processing system 20 includes a volume detection unit 22, a decay processing unit 24, a gain control unit 25, and a delay circuit 26. The configuration is the same as that of the processing system 10 except that the channels to be processed are different and the values of the gain coefficients in the gain table are different.

  The processing system 30 is a processing system for performing dynamic range compression of the C channel. The C-channel audio signal is band-divided into three bands, a low band, a mid band, and a high band, by a low pass filter (hereinafter referred to as LPF) 31L, a band pass filter (hereinafter referred to as BPF) 31B, and a high pass filter (hereinafter referred to as HPF) 31H And dynamic range compression is performed separately for each. In a preferred embodiment, the LPF 31L is a low-pass filter with a cutoff frequency of 100 Hz, the HPF 31H is a high-pass filter with a cutoff frequency of 1 kHz, and the BPF 31B is a bandpass with a low-frequency cutoff frequency of 100 Hz and a high-frequency cutoff frequency of 1 kHz. It is a filter.

  The volume detectors 32L, 32B, and 32H detect the volume levels of the low-frequency, middle-frequency, and high-frequency audio signals of the C channel, respectively, and the volume level signals that represent the detected volume levels are used as decay processing units 34L, 34B, and 34H. Output to. The decay processing units 34L, 34B, and 34H perform the same decay process as the decay processing unit 14 described above. The gain control units 35L, 35B, and 35H are gains of the amplifiers 5CL, 5CB, and 5CH in order to perform dynamic range compression in accordance with the volume levels of the low-frequency, mid-frequency, and high-frequency audio signals of the C channel. Is a circuit for controlling The gain control units 35L, 35B, and 35H store separate gain tables, respectively, read out the gain coefficient corresponding to the volume level indicated by the volume level signal from the gain table, and supplies the gain coefficient to the amplifiers 5CL, 5CB, and 5CH. The amplifiers 5CL, 5CB, and 5CH multiply the individual gain coefficients given in this way by the low-frequency, mid-frequency, and high-frequency audio signals of the C channel divided by the LPF 4L, BPF 4B, and HPF 4F, respectively. (For convenience of explanation, a portion composed of LPF 4L, BPF 4B, HPF 4F, amplifiers 5CL, 5CB, and 5CH is referred to as “processing system 5C ′”). The audio signals in each band are weighted by a weighting coefficient and added, and are output from the C channel speaker in the same manner as the audio signals of other channels.

  Next, the effect of this embodiment will be described with reference to FIGS. First, it is assumed that the input volume level of the audio signal of each channel is as shown in FIG. In this example, the C channel audio signal is a signal representing a human voice. The L channel audio signal is a signal representing music, and the input volume level is the highest among all channels. If such a dynamic range compression of the audio signal is performed using a conventional volume control device, the output volume level of the audio signal of each channel obtained as a result is shown by a broken line in FIG. In FIG. 7, the input volume level of the audio signal of each channel is indicated by a solid line. In the example shown in FIG. 7, since the input volume level of the L channel is the highest, the amplification gains of the audio signals of all channels are determined based on the input volume level of the L channel. Thus, if volume control is performed with a uniform gain for all channels, the relative volume balance of each channel is the same as before volume control, as shown in FIG. It is buried in the audio signal of the channel. For this reason, the voice of a C channel person is buried in background sounds such as music and cannot be heard.

  On the other hand, in this embodiment, the dynamic range compression of the C channel, the dynamic range compression of the front LR channel, and the dynamic range compression of other channels are performed independently. Therefore, the output volume level of the audio signal of each channel is, for example, shown by a broken line in FIG. That is, in this embodiment, even if the amplification gains of the L, R, LS, RS, SBL, and SBR channels are kept low because the input volume level of the L channel is high, the input volume level of the C channel is If it is low, the C channel audio signal is amplified with a high gain, and the output volume level of the C channel is raised. For this reason, the voice of a C channel person is clearly heard without being buried in the background sound.

  Furthermore, in this embodiment, the dynamic range compression of the C channel is divided into a low band, a middle band, and a high band with 100 Hz and 1 kHz as boundaries, and is performed for each band. Thereby, the following effects are obtained. For example, it is assumed that the C channel input audio signal has a frequency characteristic indicated by a one-dot chain line in FIG. When dynamic range compression is performed using a common gain coefficient regardless of the band, frequency characteristics indicated by a broken line in FIG. 9 are obtained. The way human voices are heard, such as movie dialogue, is often affected by bands above 1 kHz, so if dynamic range compression is performed uniformly without band division, there is no problem in sound quality, but it is easy to hear. Then there will be problems. Therefore, when the dynamic range compression is performed by dividing the band and using each individual gain coefficient as shown in the present embodiment, as shown by the solid line in FIG. The output volume level is raised, and the optimum volume is obtained for each band. For this reason, even when dynamic range compression is performed, it becomes easy to hear human speech.

  In the present embodiment described above, the dynamic range compression performed in the processing system 10, the processing system 20, and the processing system 30 may be the same or different. In the preferred mode, the processing systems 10, 20, and 30 perform dynamic range compression in the mode shown in FIG. In another preferred embodiment, the processing system 10 performs the dynamic range compression shown in FIG. 4, and the processing systems 20 and 30 perform the dynamic range compression shown in FIG. 3 with different gain coefficients. In this aspect, even if all the channels are turned down, the output volume level of only the C channel is raised, so that an effect of clearly listening to human speech can be obtained. Furthermore, the C-channel audio signal is divided into bands, and dynamic range compression is performed individually for each band, so that an effect that a human voice is heard more clearly is obtained. Also, in a movie, the volume is often changed abruptly for sharpening, but the volume control apparatus according to the present embodiment can appropriately control the volume even in such a case.

Second Embodiment
FIG. 10 is a block diagram showing the configuration of the volume control device according to the present embodiment. As in the first embodiment, this volume control device is a device that controls the volume of an audio signal composed of eight channels of L, R, LS, RS, SBL, SBR, LFE, and C. Here, the 8-channel audio signal is, for example, a music audio signal, the C-channel audio signal represents vocals, the L- and R-channel audio signals represent performance, and the other-channel audio signals represent audiences. It expresses cheers etc.

  The volume control apparatus according to the present embodiment has a movie mode for handling movie audio signals and a music mode for handling music audio signals. The user switches between these by operation. Although a detailed configuration is omitted in order to prevent the drawing from being complicated, the processing system 30 and the processing system 5C ′ have the same configuration (FIG. 1) as that described in the first embodiment. In the movie mode, the switch 71 switches to the processing system 30 side, and the switch 72 switches to the processing system 5C 'side (both in the direction a in FIG. 10), and operates in the same manner as in the first embodiment.

  In the music mode, the switch 71 is switched to the processing system 40 side, and the switch 72 is switched to the amplifier 5C side (both directions in FIG. 10). That is, in the music mode, the volume control apparatus according to the present embodiment uses four processing systems 20, 40, 50, and 60 as means for controlling the amplification gain of the audio signal according to the level of the audio signal. Have.

  The processing system 20 is a processing system for performing dynamic range compression of the LFE channel, and has the same configuration as that described in the first embodiment (FIG. 1). The processing system 40 is a processing system for performing dynamic range compression of the C channel, and has the same functions and configuration as the processing system 20 except that the target channel and the gain table stored in the gain control unit 45 are different. Have. The processing system 50 is a processing system for performing dynamic range compression of the LS, RS, SBL, and SBR channels, and the processing system 60 is a processing system for performing dynamic range compression of the L and R channels. . These processing systems have the same functions and configurations as the processing system 10 in the first embodiment except that the target channel and the gain table stored in the gain control units 55 and 65 are different.

  By the way, when the volume control target is an audio signal of music, if the audio signal after dynamic range compression is output as it is from a speaker, music lacking in sound pressure is reproduced. For this reason, in this embodiment, in order to compensate for the sense of decrease in sound pressure due to dynamic range compression, tone control filters 7L and 7R for loudness control are placed in front of amplifiers 5L and 5R that perform dynamic range compression of the L and R channels. Are provided. It is possible to switch between the on state in which a specific band of an audio signal is emphasized and output, or the off state in which it is output without being emphasized, and the degree is switched when emphasizing a specific band Is possible. In the movie mode, the tone control filters 7L and 7R are both in the off state, and in the music mode, both the tone control filters 7L and 7R are in the on state.

  Also in the music mode according to the present embodiment, the gain control of the amplifiers 5L, 5R, 5LS, 5RS, 5SBL, 5SBR, 5LFE, and 5C is performed by the gain control units 25, 45, 55, and 65 in the same manner as in the first embodiment. Thus, the dynamic range compression of the audio signal as exemplified in FIGS. 3 to 5 is appropriately performed.

  Switching between the movie mode and the music mode is controlled by the control unit 101. The control unit 101 sets one of these as an operation mode in accordance with the operation of the operation unit 102, and controls each unit in the apparatus so that the operation in the set operation mode is performed.

The operation of this embodiment will be described below.
When reproducing the audio signal of a movie using the volume control device according to the present embodiment at night, the user operates the operation unit 102 to instruct the setting of the movie mode. In accordance with this instruction, the control unit 101 sets the operation mode to the movie mode. FIG. 11 shows the contents of the music mode / movie mode switching control performed by the control unit 101. As shown in FIG. 11, in the movie mode, the control unit 101 turns on the tone control filters 7L and 7R, and switches the switch 71 and the switch 72 in the direction a in FIG. Therefore, in the movie mode, the audio signals of the L and R channels are subjected to dynamic range compression without being subjected to enhancement processing (loudness control) of a specific band by the tone control filters 7L and 7R, and are output from the speakers as they are. On the other hand, the C-channel audio signal is divided into bands as described in the first embodiment, and is output from the speaker as a human voice that is easy to hear by performing dynamic range compression for each band.

  When playing back an audio signal of music at night, the user operates the operation unit 102 to instruct the setting of the music mode. In accordance with this instruction, the control unit 101 sets the operation mode to the music mode (FIG. 11). As shown in FIG. 11, in the music mode, the control unit 101 turns off the tone control filters 7L and 7R, and switches the switch 71 and the switch 72 in the direction b in FIG. Thereby, the loudness control processing of the L and R channel audio signals is performed, and the force of the sound lost from the audio signals due to the dynamic range compression is recovered.

  According to the present embodiment, dynamic range compression is performed on the C channel, LFE channel, L channel, and R channel independently of the other channels according to the input volume level of the audio signal. Therefore, when the volume of these channels is low, it is possible to avoid the inconvenience that the sound of these channels is buried in the sound of other channels and is difficult to hear.

<Modification>
The present invention is not limited to the above-described embodiment, and various modifications can be made.
Band division of the C channel is not limited to three divisions, and may be two divisions or four divisions or more. For example, band division may be performed so that a band separated by the LPF and a band separated by the BPF partially overlap.
Also, for example, a plurality of dynamic range compression ratios such as MIN, MID, and MAX may be prepared, that is, a plurality of gain tables may be stored in the gain control unit, and the user may select them.
In the above-described embodiment, the band division is performed only for the C channel. However, the band may be divided for a plurality of channels, and dynamic range compression may be performed for each band.
Moreover, it is good also as a structure which makes the cutoff frequency of each filter variable according to operation of an operation element. At that time, it is possible to change the cut-off frequency of the low-pass filter and the low-pass cut-off frequency of the band-pass filter while maintaining the same relationship by operating the operation element. The low-pass cutoff frequency of the pass filter may be controlled independently. The same applies to the high-pass cutoff frequency of the bandpass filter and the cutoff frequency of the high-pass filter.

It is a block diagram which shows the structure of the volume control apparatus which concerns on 1st Embodiment of this invention. It is a figure which illustrates the decay process which concerns on the same embodiment. It is a figure which shows an example of the dynamic range compression in the same embodiment. It is a figure which shows an example of the dynamic range compression in the same embodiment. It is a figure which shows an example of the dynamic range compression in the same embodiment. It is a figure explaining the effect of the embodiment. It is a figure explaining the effect of the embodiment. It is a figure explaining the effect of the embodiment. It is a figure which illustrates the dynamic range compression by the band division | segmentation in the same embodiment. It is a block diagram which shows the structure of the volume control apparatus which concerns on 2nd Embodiment of this invention. It is a figure which shows the content of the switching control of music mode / movie mode.

Explanation of symbols

DESCRIPTION OF SYMBOLS 3 ... Delay circuit, 4 ... Filter, 5 ... Amplifier, 7 ... Tone control filter, 10 ... Processing system, 12 ... Volume detection part, 13 ... Maximum value extraction part, 14 ... Decay processing part, 15 ... Gain control part, 16 DESCRIPTION OF SYMBOLS ... Delay circuit, 20 ... Processing system, 22 ... Volume detection part, 24 ... Decay processing part, 25 ... Gain control part, 26 ... Delay circuit, 30 ... Processing system, 31 ... Filter, 32 ... Volume detection part, 34 ... Decay Processing unit, 35 ... gain control unit, 36 ... delay circuit, 40 ... processing system, 42 ... volume detection unit, 44 ... decay processing unit, 45 ... gain control unit, 46 ... delay circuit, 50 ... processing system, 52 ... volume Detection unit 53... Maximum value extraction unit 54. Decay processing unit 55. Gain control unit 56. Delay circuit 60. Processing system 62. Volume detection unit 63. , 65 ... Gain system Parts, 66 ... delay circuit, 71 ... switch, 72 ... switch, 101 ... controller, 102 ... operating unit

Claims (3)

A plurality of variable gain amplifying means for amplifying each of a plurality of channels of audio signals;
First volume detection means for detecting the volume of at least one specific channel audio signal among the plurality of channels of audio signals for each channel;
Band dividing means for dividing an audio signal of at least one of the at least one specific channel into a plurality of frequency bands;
Second volume detection means for detecting the volume of audio signals of all channels except the specific channel among the plurality of channels of audio signals;
A first control unit that controls a gain of a variable gain amplification unit that amplifies an audio signal of the at least one specific channel for each channel based on the volume of the at least one specific channel detected by the first volume detection unit. Gain control means,
Second gain control means for uniformly controlling the gains of all variable gain amplifying means for amplifying audio signals of channels other than the specific channel based on the volume detected by the second volume detection means. And
The first gain control means controls the gain of the variable gain amplifying means for each band-divided audio signal with respect to the audio signal of the channel divided by the band dividing means. Volume control device.   For the audio signal of the channel band-divided by the band dividing means, the first gain control means has a relationship between the volume of the audio signal input to the variable gain amplifying means and the gain at the time of amplification. 2. The volume control apparatus according to claim 1, wherein gains of the plurality of variable gain amplifiers are controlled so as to be different for each of the divided audio signals. Further comprising decay processing means for performing decay processing on at least one channel of the plurality of channels of audio signals;
2. The volume control apparatus according to claim 1, wherein the decay processing means performs a decay process so that an attenuation rate is linear with respect to time.

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