Sound volume controller

A sound volume controller includes a level adjustment section that adjusts a level of an input audio signal and outputs the adjusted input audio signal as an output audio signal, a level detection section that detects the level of the input audio signal, a volume value detection section that detects a volume value set by a user, a coefficient table storage section that stores a coefficient table which describes a relation between levels of the output audio signal and levels of the input audio signal, a coefficient table change section that changes the coefficient table stored in the coefficient table storage section in accordance with the volume value detected by the volume value detection section, and a setting section that sets an amount of level adjustment of the level adjustment section in accordance with the level of the input audio signal detected by the level detection section and the coefficient table.

BACKGROUND

The present invention relates to a sound volume controller that controls a volume of an audio signal.

When a movie, music, or the like, is played back in the night time, a sound volume (loudnes level of sound) of the audio apparatus is generally set to be low. However, turning down of volume naturally makes a playback of sound hard to hear. In particular, when a movie is played back, turning down of volume makes it difficult to hear a small sound especially, such as words (speech), because the range of volume (a dynamic range) for the movie is wide. In the meantime, when the volume is totally turned up in order to make it easy to catch the words, sound effects and the like, are played back at a high volume level.

In order to solve the problem, there is proposed a sound volume controller that compresses a dynamic range on a per-channel basis; that turns up the volume of words, and the like, to thus make it easy to hear and plays back sound effects, and the like, in a suppressed manner (see; for instance, Patent Document 1).[Patent Document 1] JP-A-2006-42027

However, according to the configuration of the controller described in Patent Document 1, a coefficient of dynamic range compression is constant at all times. Therefore, depending on a viewing environment there still exists a case where a sound is felt as being too loud or small. In this case, there still exists a necessity for the user to adjust a volume control each time. When dynamic range compression is once set to an active position, a dynamic range is always compressed even in a viewing environment that does not require dynamic range compression as in the daytime, unless the user manually deactivates dynamic range compression.

SUMMARY

Accordingly, the present invention aims at providing a sound volume controller that enables real-time dynamic range compression reflecting a user's viewing environment.

In order to achieve the above object, according to the present invention, there is provided a sound volume controller, comprising:

a level adjustment section that adjusts a level of an input audio signal and outputs the adjusted input audio signal as an output audio signal;

a level detection section that detects the level of the input audio signal;

a volume value detection section that detects a volume value set by a user;

a coefficient table storage section that stores a coefficient table which describes a relation between levels of the output audio signal and levels of the input audio signal;

a coefficient table change section that changes the coefficient table stored in the coefficient table storage section in accordance with the volume value detected by the volume value detection section; and

a setting section that sets an amount of level adjustment of the level adjustment section in accordance with the level of the input audio signal detected by the level detection section and the coefficient table.

In this configuration, the coefficient of dynamic range compression is changed in accordance with a volume value set by the user. For instance, when the sound volume value is set to be high by the user, performance of dynamic range compression is determined not to be required or such compression is determined to be low. Dynamic range compression is set such that a characteristic identical with or close to a linear characteristic is achieved. In the meantime, when the sound volume value is made small, an increase in dynamic range compression is determined to be required, and turning up of a small volume and turning down of a large volume are performed. Further, when the sound volume value is made much smaller, only a small volume may be turned up, but sound of a large volume may not be turn down.

Preferably, the sound volume controller further comprising:

a volume shift section that adjusts a level of the output audio signal output from the level adjustment section; and

a volume shift control section that sets volume shift level of the volume shift section in accordance with the volume value detected by the volume value detection section.

In the configuration, the audio signal undergone dynamic range compression is subjected to a volume shift. For instance, the audio signal is subjected to an adjustment of; for example, 10 dB or thereabouts (a volume is slightly turned up). When the volume value is turned down, the volume is slightly adjusted, to thus eliminate an uncomfortable auditory feeling.

Preferably, the input audio signal is formed from signals of a plurality of channels. The level adjustment section adjusts respective levels of the signals of the plurality of channels. The level detection section detects the respective levels of the signals of the plurality of channels. The setting section sets amounts of level adjustment of the channels respectively in accordance with the respective levels of the signals of the plurality of channels.

In this configuration, dynamic range compression is performed on a per-channel basis. For instance, a channel including sound, such as words, a channel including sound, such as sound effects, and a channel including only a quiet voice are subjected to dynamic range compression by means of different lines. As a result, sound, such as words, can be clear heard without being not lost in sound effects, and the like.

Preferably, the level detection section detects a level of an input audio signal of a channel having the maximum level among the signals except a signal of a specific channel. The setting section sets amounts of level adjustment for the channels except the specific channel in accordance with the level of the input audio signal having the maximum level.

In this configuration, audio signals except an audio signal of a specific channel (e.g., a channel including a voice, such as words) are collectively subjected to dynamic range compression while the level of an audio signal of a channel having the maximum level is taken as a reference. Lines except a specific channel are collectively subjected, as different lines, to dynamic range compression in accordance with the maximum level, and hence processing load is diminished, and sound of the specific channel is prevented from being lost.

Here, it is preferable that, the signals except the signal of the specific channel are an audio signal of an L channel, an audio signal of an R channel, an audio signal of an LS channel, and an audio signal of an RS channel.

According to the present invention, a coefficient of dynamic range compression is set in accordance with a volume level set by the user. Hence, dynamic range compression reflecting the users viewing environment can be set in real time.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

A sound volume controller of an embodiment of the present invention will be described. The sound volume controller of this embodiment relates to a so-called AV amplifier that receives, as an input, an audio signal output from a DVD player, or the like, and that produces an output after amplifying the signal.

FIG. 1is a block diagram showing an example configuration achieved when the sound volume controller of this embodiment is applied to a multichannel format for 5.1 channels. The present invention is not limited to the 5.1 channels, and the configuration of the sound volume controller shown inFIG. 1can be scaled up or down in accordance with the number of channels to be actually used.

The sound volume controller1has input lines for 5.1 channels, such as an L channel, an R channel, an LS (left surround) channel, an RS (Right surround) channel, a C (center) channel, and an LFE (Low-frequency effects) channel. When an input sound is an audio signal of a movie, the C channel primarily represents human voice, and the other channels represent music, sound effects, and the like. In this embodiment, all audio signals transmitted through the inside of the controller are assumed to be digital audio signals unless otherwise specified.

An audio signal of the L channel, an audio signal of the R channel, an audio signal of the LS channel, an audio signal of the RS channel, an audio signal of the C channel, and an audio signal of the LFE channel are input to delay circuits3L,3R,3LS,3RS,3C, and3LFE, respectively. The delay circuits3L,3R,3LS,3RS,3C, and3LFE delay the L channel audio signal, the R channel audio signal, the LS channel audio signal, the RS channel audio signal, the C channel audio signal, and the LFE channel audio signal, respectively. Delay operation is intended effect synchronization with processing of a dynamic range control section (seeFIGS. 2 and 3) to be described later, to thus diminish an uncomfortable auditory feeling.

The audio signals delayed by the delay circuits3L,3R,3LS,3RS,3C, and3LFE are input to amplifiers5L,5R,5LS,5RS,5C, and5LFE, respectively. The amplifiers5L,5R,5LS,5RS,5C, and5LFE adjust variably amplify levels of the respective audio signals. A dynamic range control section11C sets an amount of level adjustment of the amplifier5C; a dynamic range control section11LFE sets an amount of level adjustment of the amplifier5LFE; and a dynamic range control section13sets amounts of level adjustment of the respective amplifiers5L,5R,5LS, and5RS. Audio signals having undergone level adjustment in the amplifiers5L,5R,5LS,5RS,5C, and5LFE are further subjected to level adjustment (volume shift) in amplifiers7L,7R,7LS,7RS,7C, and7LFE. Amounts of volume shift are set by a volume shift control section15. Audio signals undergone a volume shift are output from L, R, LS, RS, C, and LFE output lines, respectively.

A C channel audio signal is input to the dynamic range control section11C, and an LFE channel audio signal is input to the dynamic range control section11LFE. Further, L, R, LS, and RS channel audio signals are input to the dynamic range control section13. A volume value set by the user is input to the dynamic range control section11C, the dynamic range control section11LFE, the dynamic range control section13, and the volume shift control section15, respectively.

FIG. 2Ais a block diagram showing the configuration of the dynamic range control section11C (a C channel processing line). The dynamic range control section11C has a level detection section21, a gain control section22, a delay circuit23, a coefficient table computing section24, and a coefficient table storage section25.

FIG. 2Bis a block diagram showing the configuration of the dynamic range control section11LFE (an LFE channel processing line). The dynamic range control section11LFE has the same configuration and function as those of the dynamic range control section11C shown inFIG. 2A. Therefore, respective constituent sections of the dynamic range control section11LFE are assigned the same reference numerals as those used for the dynamic range control section11C, and their explanations are omitted.

FIG. 3is a block diagram showing the configuration of the dynamic range control section13(L, R, LS, and RS channel processing lines). The dynamic range control section13has a maximum level detection section31, a gain control section32, a delay circuit33, a coefficient table computing section34, and a coefficient table storage section35.

InFIG. 2A, the level detection section21inputs a C channel audio signal and performs level detection. A detected level value is input to a gain control section22. The gain control section22determines an amount of level adjustment of the amplifier5C in accordance with the input level value. A dynamic range is compressed by setting the amount of level adjustment of the amplifier5C. The gain control section22reads a coefficient for dynamic range compression from a coefficient table storage section25; computes the level of an output in response to an input in accordance with the thus-read coefficient; and sets the amount of level adjustment of the amplifier5C.

The coefficient for dynamic range compression stored in the coefficient table storage section25is altered in real time by the coefficient table computing section24. The coefficient table computing section24inputs the volume value set by the user and computes a coefficient in accordance with the volume value.

FIG. 4is a view showing an overview of dynamic range compression. Horizontal axes of graphs shown inFIGS. 4A to 4Crepresent the level of an input (Input), and vertical axes of the graphs represent the level of an output (Output). Broken lines shown inFIGS. 4A to 4Cshow a case where dynamic range compression is not performed (a linear relationship exists between an input and an output). First,FIG. 4Ais a view showing an overview of dynamic range compression performed when an input volume level is high (in the vicinity of; for instance, 0 dB). In the descriptions, a linear relationship is achieved in a range where the level of an input is between h1and h2(an intermediate area between −96 dB and 0 dB). In a range where the level of the input is h2or more, the level of an output is reduced with an increase in the level of an input. In a range where the level of an input is less than h1, the level of an output is increased with a decrease in the level of an input. Therefore, the high volume level, such as sound effects, is reduced, and voice of a low volume value, such as whispers, is amplified.

A coefficient corresponding to the level of such an output responsive to the level of an input (the amount of level adjustment responsive to the level of an input) is stored as a coefficient table for each input level in a coefficient table storage section25. The gain control section22reads an amount of level adjustment corresponding to a level of a received input by reference to the coefficient table, and sets the thus-read table in an amplifier5C. Setting the amount of level adjustment of the gain control section22is delayed by the delay circuit23. Since the delay circuit23adjusts a level by imparting a predetermined delay (e.g., 1 ms), a change in volume becomes mild, so that an uncomfortable auditory feeling can be lessened.

FIG. 4Bis a view showing an overview of dynamic range compression achieved when an input volume level is in an approximate middle level (in the vicinity of; for example, −30 dB). In the embodiment, dynamic range compression shows a linear relationship in a range where the level of an input is between h3and h4(an intermediate range between −96 dB and 0 dB). A level of h3may also be identical with or differ from a level of h1. Likewise, a level of h4may also be identical with or differ from a level of h2.

In the range where the level of an input is h4or more, the level of an output is reduced with an increase in the level of the input. In the range where the level of an input is less than h2, the level of an output is increased with a decrease in the level of the input. In the case of an embodiment shown inFIG. 4B, a suppression of the high level range is greater (the level of the output is low) than that achieved in the embodiment shown inFIG. 4A. Further, an enhancement of the low level range is large (the level of the output is high). Consequently, when compared with the embodiment shown inFIG. 4A, sound of a high volume, such as sound effects, is reduced to a low level, and voice of a low volume, such as whispers, is amplified greatly. Therefore, dynamic range compression becomes higher than that performed in the embodiment shown inFIG. 4A.

FIG. 4Cis a view showing an overview of dynamic range compression performed when another input volume value is low (in the vicinity of; for example, −60 dB). In the embodiment, the level of the output is increased with a decrease in the level of the input in the range where the level of an input is less than h5. In a range between h5and h6(an intermediate range between −96 dB and 0 dB), an amount of change in input and an amount of change in output become proportional to each other, but a signal is output after slightly being amplified. In a range of h6or more, the level of the output is decreased with an increase in the level of the input. A level of h5may also be identical with or differ from the level of h1and the level of h3. Likewise, a level of h6may also be identical with or differ from the level of h2and the level of h4.

In the embodiment shown inFIG. 4C, even when the level of an input is maximum (0 dB), the input is not substantially suppressed (the output is close to 0 dB). Specifically, in the embodiment shown inFIG. 4C, the level of a low volume range is increased much greater than in the embodiment shown inFIG. 4B, thereby achieving a characteristic of involving an increase in overall volume and preventing substantial suppression of sound of high volume. Therefore, in the embodiment shown inFIG. 4C, dynamic range compression becomes higher when compared with that performed in the embodiment shown inFIG. 4B.

As mentioned above, a coefficient of dynamic range compression is altered by the volume value set by the user. Changing the coefficient by means of a volume value is performed by the coefficient table computing section24. For instance, when the volume value is less than −60 dB, a coefficient by means of which dynamic range compression, such as that shown inFIG. 4C, is performed is set in the coefficient table storage section25. When the volume value is −60 dB to −30 dB, a coefficient by means of which dynamic range compression shown inFIG. 48is performed is set. When the volume value is −30 dB or more, a coefficient by means of which dynamic range compression, such as that shown inFIG. 4A, is performed is set. When the volume value is increased to 0 dB or thereabouts, dynamic range compression may also not be performed (a linear characteristic is exhibited).

Coefficients of dynamic range compression shown inFIGS. 4A to 4Care examples. In reality, the essential requirement is to change the coefficient, as required, in accordance with a change in volume value.FIG. 5Ashows a view showing a relationship between a change in volume value and a dynamic range. A horizontal axis shown inFIG. 5Arepresents a volume value, and a vertical axis represents a dynamic range.

In the relationship shown inFIG. 4A, when the volume value is 0 dB, the dynamic range comes to 96 dB. Specifically, when the volume value is 0 dB, dynamic range compression is not performed (a relationship between an input and an output is made linear). When the volume value is −60 dB, the dynamic range comes to 60 dB and compressed. In a range from −60 dB to 0 dB, a change arises in such a way that the dynamic range decreases with a decrease in volume value and in proportion to a change in volume value. In a range where the volume value is less than −60 dB, no change arises in dynamic range in spite of an increase or decrease in volume value.

As mentioned above, the coefficient table computing section24changes the coefficient table stored in the coefficient table storage section25in such a way that the dynamic range changes in proportion to a change in volume value within a range where the volume value is from −60 dB to 0 dB.

Dynamic range compression, such as that shown inFIG. 7, may also be performed.FIG. 7is a view showing another example coefficient of dynamic range compression. The example of dynamic range compression shown inFIG. 7is an example application of dynamic range compression shown inFIG. 4C. In the graph shown inFIG. 7, the level of an output is reduced with an increase in the level of an input in the range where the level of the input is h9or more. In a range from h8to h9, an amount of change in input and an amount of change in output are proportional to each other, and an output is produced after being slightly amplified. In a range from h7to h8, the level of the output is increased with a decrease in the level of the input. In a range where the level of the input is less than h7, the level of the output is reduced with a decrease in the level of the input. As mentioned above, in a range where the level of the input is less than h7(in a range where a volume of the input is very low), unwanted sound components (noise) are larger in amount than required sound, such as words. If the level of the output is increased, the noise will grate on. For this reason, in the range of less than h7, the level of the output is reduced, to thus eliminate noise. In the embodiment shown inFIG. 7, the dynamic range is expanded when compared with that achieved in the embodiment shown inFIG. 4C. However, the increase in dynamic range is intended for eliminating noise, and a required sound, such as words, is increased as in the embodiment shown inFIG. 4C.

By means of such a configuration, when the user decreases the volume value, dynamic range compression becomes higher. When the user increases the volume value, dynamic range compression becomes lower. Therefore, even when the user decreases the volume value, a required sound does not become too small, so that sound control suitable for viewing a movie, or the like, can be practiced. Further, the user does not need to activate or deactivate dynamic range compression, and sound control reflecting the user's viewing environment can be performed in real time because the coefficient of dynamic range compression is changed in accordance with the volume value.

The embodiments shown inFIGS. 4A to 4Ccorrespond to illustrations intended for showing the concept of dynamic range compression, and do not show the level of an actually-output audio signal. In reality, an output audio signal (the level of a signal output to a speaker) is amplified, as an analogue audio signal, at an output in the final stage by a power amplifier in accordance with the volume value set by the user. Therefore, an actual output level totally differs from each other inFIGS. 4A to 4C, respectively.FIG. 6is a view showing an overview of an input/output gain characteristic achieved in the final stage when dynamic range compression of the present invention is practiced. As indicated by a graph shown in; for example,FIG. 6, the levels of audio signals output in the final stage are plotted at the same scale; the level achieved in the embodiment shown inFIG. 4Abecomes maximum; and the level achieved in the embodiment shown inFIG. 4Cbecomes minimum.

InFIG. 2A, a volume value set by the user is input to the volume shift control section15. In accordance with the volume value, the volume shift control section15sets a sound shift level of the amplifier7C. The volume shift is for eliminating an uncomfortable auditory feeling by slightly adjusting (increasing) the volume when the volume value becomes smaller.FIG. 5Bis a view showing a relationship between a volume value and an amount of volume shift. As shown in; for example,FIG. 5B, in a range where the volume value ranges from −30 dB to −60 dB, an amount of volume shift increases with a decrease in volume value and in proportion to the volume value. When the volume value is −60 dB, the amount of volume shift is set to +10 dB. In a range of less than −60 dB, the amount of volume shift is fixed to +10 dB even when the volume value is decreased. When the volume value is too small, noise components become great, and hence volume shift is not performed greater than necessary.

The sound volume controller of this embodiment performs dynamic range compression and volume shift control, such as those mentioned above, for each channel. InFIG. 2B, in the dynamic range control section11LFE, an audio signal of the LFE channel is input to level detection circuit21, and the gain control section22reads a coefficient of dynamic range compression in accordance with the level of an input of the LFE channel. The coefficient is updated in accordance with the volume value set by the user. The gain control section22sets the amount of level adjustment of the amplifier5LFE in accordance with the thus-read coefficient. Therefore, even in the LFE channel, dynamic range compression conforming to the volume value set by the user is performed. Further, even the amplifier7LFE performs volume shift in accordance with the volume value.

InFIG. 3, the maximum level detection section31of the dynamic range control section13inputs an audio signal of the L channel, an audio signal of the R channel, an audio signal of the LS channel, and an audio signal of the RS channel, and detects the highest level (maximum level) of these audio signals. A value of the thus-detected maximum level is input to the gain control section32. In accordance with the input level value, the gain control section32sets amounts of level adjustment of the amplifiers5L,5R,5LS, and5RS. Dynamic range compression is performed by setting the amounts of level adjustment of the amplifiers5L,5R,5LS, and5RS. The gain control section32reads the coefficient of dynamic range compression from the coefficient table storage section35and sets the amount of level adjustment.

The coefficient of dynamic range compression stored in the coefficient able storage section35is changed in real time by means of the coefficient table computing section34. The coefficient table computing section34computes a coefficient in accordance with the volume value set by the user. A coefficient computing technique employed by the coefficient table computing section34is the same as that employed in the embodiments shown inFIGS. 4 and 5. While taking, as a reference, the channel of the highest-level audio signal among the audio signal of L channel, the audio signal of R channel, the audio signal of LS channel, and the audio signal of RS channel, the dynamic range control section13performs dynamic range compression in accordance with the level of the input of the channel. In relation to the L, R, LS, and RS channels primarily including sound effects, and the like, dynamic range compression is carried out by means of taking the channel of the highest level as a reference. Hence, a sound, such as sound effects, tends to be entirely suppressed, and unwanted increase in sound is prevented. Therefore, sound of the C channel is not lost in sound effects. Further, coefficients for dynamic range compression are collectively read and processed in connection with signals of a plurality of channels, and therefore processing load can be lessened.

As mentioned above, dynamic range compression of the C channel, dynamic range compression of the LFE channel, and dynamic range compression of another channel are performed by means of different lines, so that a sound, such as whispers, can be clearly heard without being lost in sound effects, and the like.

The present application is based on Japan Patent Application No. 2007-150265 filed on Jun. 6, 2008, the contents of which are incorporated herein for reference.