JP4161983B2 - Sound quality adjustment device - Google Patents

Description

  The present invention relates to a sound quality adjusting device in various audio apparatuses and television receivers.

  Conventionally, as a sound quality adjusting device in various audio devices, for example, there are devices disclosed in Patent Literature 1 and Patent Literature 2. FIG. 10 is a block diagram showing the configuration of the sound quality adjusting device disclosed in Patent Document 1 and Patent Document 2. This sound quality adjusting device attenuates input audio signals of two channels L (left) and R (right) by attenuators 100a and 100b, respectively, and enhances the levels of specific frequency bands of these audio signals by tone filters 101a and 101b. Then, the level determination unit 102 determines the level of the audio signal after the enhancement process is completed, and the enhancement amount calculation unit 103 adjusts the enhancement amount by changing the filter coefficients of the tone filters 101a and 101b based on the result of the level determination. By doing so, sound quality adjustment is realized.

Japanese Patent No. 3206271 Japanese Patent No. 3329050

  However, since the sound quality adjusting apparatus shown in FIG. 10 detects the level of the sound signal after being processed by the tone filter and adjusts the enhancement amount of the tone filter by feedback control, There is a problem that a delay occurs in the adjustment of the enhancement amount with respect to various level fluctuations. For this reason, if the input audio signal suddenly increases, it takes time until the enhancement amount is suppressed by the feedback control. For example, a clip state due to overflow of digital signal processing occurs, and the clip sound is generated at the joint of the enhancement amount adjustment. Could occur.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to provide a sound quality adjusting device capable of high-speed response to level fluctuation of an audio signal.

The sound quality adjusting apparatus according to the present invention includes a filter circuit that extracts an audio signal of a desired frequency band from an input audio signal for at least one of multi-channel audio signals, and an audio signal extracted by the filter circuit. A boost circuit that performs dynamic range expansion / compression according to the input level; an adder that adds the input audio signal and the audio signal output from the boost circuit; and the filter circuit for the at least one audio signal A decay processing circuit for performing a decay process for gradually attenuating the output level in response to a decrease in the level of the audio signal extracted by the filter circuit, and the decay processing circuit is inputted between the boost circuit and the boost circuit. The audio signal is sampled at regular intervals, and the current time sample value and one sample before When the output value is compared with the output value, the higher level is selected and output as the output value at the current time, and the output value one sample before is selected, the value before the one sample due to the decay rate that increases with time Is attenuated to obtain an output value at the current time.
In addition, one configuration example of the sound quality adjusting device of the present invention further includes a subtracter that subtracts the audio signal extracted by the filter circuit from the input audio signal for the at least one audio signal, and the adder The input audio signal after the subtraction and the audio signal output from the boost circuit are added .

  According to the present invention, by adopting a feedforward configuration in which the dynamic range expansion / compression of the audio signal is adopted according to the level of the audio signal extracted by the filter circuit, the audio signal is compared with the conventional sound quality adjusting device. High-speed response to level fluctuations is possible. As a result, in the present invention, even if the input audio signal increases rapidly, no clip sound is generated.

  Further, in the present invention, by providing a subtractor that subtracts the audio signal extracted by the filter circuit from the input audio signal, no dip occurs in the frequency band for adjusting the sound quality, and the frequency characteristic of the audio is gently reduced. Can be connected.

  Further, in the present invention, by providing a decay processing circuit between the filter circuit and the boost circuit, it is possible to suppress excessive level fluctuation of the audio signal output from the sound quality adjusting device and to give the viewer a natural audibility. it can.

  Also, in the present invention, by providing a normalization processing circuit that expands / compresses the dynamic range of the audio signal of each channel with a common gain coefficient corresponding to the maximum level of the multi-channel audio signal, the sound is output at a high volume. While solving the problem of becoming too loud, it is possible to avoid making it difficult to hear the sound when the volume is low. Further, according to the present invention, it is possible to reduce a volume difference due to a difference in an audio source or the like, and to eliminate frequent user volume operations.

[First Embodiment]
Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram showing the configuration of a sound quality adjusting apparatus according to the first embodiment of the present invention. The sound quality adjustment apparatus of the present embodiment includes a low-pass filter (hereinafter referred to as LPF) 1, a high-pass filter (hereinafter referred to as HPF) 2, a bass boost circuit 3, a treble boost circuit 4, a multiplier 5, and a multiplier 5. 6 and 7 and an adder 8.

  Hereinafter, the operation of the sound quality adjusting apparatus according to the present embodiment will be described. LPF1, which is an IIR (Infinite Impulse Response) filter, extracts a second audio signal in a low frequency range of, for example, several hundred Hz or less from an input audio signal (hereinafter referred to as a first audio signal). The bass boost circuit 3 performs dynamic range expansion / compression on the second audio signal extracted by the LPF 1 in accordance with the input level.

  FIG. 2 is a block diagram showing one configuration example of the bass boost circuit 3. The bass boost circuit 3 includes an amplifier 30, a level detection unit 31, and a gain table 32. The level detector 31 detects the level of the second audio signal output from the LPF 1. In the gain table 32, the input level of the audio signal and the gain coefficient of the amplifier 30 are stored in association with each other in advance. The gain table 32 reads out a gain coefficient corresponding to the level detected by the level detection unit 31 and outputs it to the amplifier 30. The relationship between the input level and the gain coefficient stored in the gain table 32 incorporates linear-logarithmic conversion, ratio calculation, and logarithmic-linear conversion processing. Therefore, the value converted by the gain table 32 can be directly used as the gain of the input data. The amplifier 30 multiplies the second audio signal output from the LPF 1 by the gain coefficient output from the gain table 32, and outputs a second audio signal after multiplication. Thus, dynamic range expansion / compression according to the level of the audio signal can be performed.

  On the other hand, the HPF 2 that is an IIR filter extracts a third audio signal having a high frequency range of, for example, several kHz or more from the input first audio signal. The treble boost circuit 4 performs dynamic range expansion / compression on the third audio signal extracted by the HPF 2 according to the input level. The configuration of the treble boost circuit 4 is the same as that of the bass boost circuit 3.

  The multipliers 5, 6, and 7 multiply the first audio signal, the second audio signal output from the bass boost circuit 3, and the third audio signal output from the treble boost circuit 4 by a gain coefficient, respectively. Adjust to the desired level. The adder 8 adds the first audio signal, the second audio signal, and the third audio signal output from the multipliers 5, 6, and 7.

  FIG. 3 shows an example of input / output characteristics of the bass boost circuit 3. The horizontal axis in FIG. 3 is the input level of the second audio signal extracted by the LPF 1, and the vertical axis is the output level of the bass boost circuit 3. linear represents a linear characteristic with an input and output level of 1: 1. As shown in FIG. 3, the gain is increased (the slope of the input / output characteristics is large) when the volume is low, and the low frequency range component is emphasized, and the gain is decreased (input / output) when the volume is high. The inclination of the characteristic is small), and the emphasis of the low range is suppressed.

  Note that the output level of the bass boost circuit 3 is drastically reduced at an input level in the vicinity of 0 dB. The reason for reducing the output level in this way is to prevent output clipping. In other words, in the sound quality adjustment apparatus of the present embodiment, the low-frequency component existing in the first audio signal and the low-frequency component extracted from the first audio signal and emphasized by the bass boost circuit 3 are added. Therefore, the output may be clipped when the volume is high. Therefore, when the input level is very high, the output level of the bass boost circuit 3 is lowered to prevent the occurrence of clipping.

  In addition, as shown in FIG. 3, the bass boost circuit 3 has a plurality of input / output characteristics such as MIN (low-range emphasis effect), MID (medium emphasis effect), and MAX (high emphasis effect) in advance. Kinds may be prepared. In this case, the gain table 32 includes a plurality of tables corresponding to the respective input / output characteristics. Then, the user may select one of MIN, MID, and MAX. The input / output characteristics of the treble boost circuit 4 may be set in the same manner as in FIG.

  As described above, in the present embodiment, the bass component extracted from the first audio signal is emphasized by the bass boost circuit 3 and added to the first audio signal. Even in the case of a source with a low bass component, the sound can be put out. Similarly, since the treble component extracted from the first audio signal is emphasized by the treble boost circuit 4 and added to the first audio signal, the sound can be sharpened even in the case of a source having few high frequency components. .

  In this embodiment, the sound quality is adjusted by adopting a feed-forward configuration that performs dynamic range expansion / compression of the low-frequency component and the high-frequency component according to the level of the low-frequency component and the high-frequency component extracted by the LPF 1 and HPF 2. Since the subsequent feedback of the level of the audio signal is not used, a high-speed response to the fluctuation in the level of the audio signal is possible as compared with the sound quality adjustment apparatus shown in FIG. As a result, in this embodiment, even if the input audio signal suddenly increases, the enhancement of the low frequency range and the high frequency range can be quickly suppressed according to the increase in the level, so that a clip sound may be generated. Disappear.

[Second Embodiment]
Next, a second embodiment of the present invention will be described. FIG. 4 is a block diagram showing the configuration of a sound quality adjusting apparatus according to the second embodiment of the present invention. The same reference numerals are given to the same components as those in FIG. The sound quality adjusting device of this embodiment is obtained by adding subtractors 9 and 10 to the sound quality adjusting device of the first embodiment. The subtracter 9 subtracts the second audio signal in the low frequency range extracted by the LPF 1 from the first audio signal, and outputs the first audio signal after the subtraction. The subtractor 10 subtracts the third audio signal in the high sound range extracted by the HPF 2 from the output audio signal of the subtracter 9, and outputs the first audio signal after the subtraction. The operation of other components is the same as that of the first embodiment.

  Thus, in this embodiment, in addition to the same effects as those of the first embodiment, the following effects can be obtained. In the first embodiment, the low-frequency and high-frequency components existing in the first audio signal and the low-frequency and high-frequency components extracted from the first audio signal and emphasized by the boost circuits 3 and 4 Therefore, an unnatural dip (sound drop) may occur in the low and high sound ranges, and the sound frequency characteristics may not be smoothly connected. On the other hand, in the present embodiment, the subtracter 9 cuts out the low frequency range from the first audio signal, and the subtractor 10 extracts the high frequency range from the first audio signal. The first audio signal has only a mid-range component. Therefore, at the time of addition by the adder 8, the low frequency component of the first audio signal and the low frequency component of the second audio signal are added, or the high frequency component of the first audio signal and the third audio signal Since the high frequency range component is not added, dip does not occur in the low frequency range and the high frequency range, and the frequency characteristics of the sound can be smoothly connected.

  FIG. 5 shows an example of input / output characteristics of the bass boost circuit 3 of the present embodiment. Also in this embodiment, the input / output characteristics of the bass boost circuit 3 may be set in the same manner as in the first embodiment, but in the first embodiment, the output of the bass boost circuit 3 at an input level in the vicinity of 0 dB. While the level is drastically reduced, in the present embodiment, there is no possibility of a dip occurring in the low range or the high range as described above, so there is no need to reduce the output level at an input level in the vicinity of 0 dB. . The input / output characteristics of the treble boost circuit 4 may be set similarly to FIG.

[Third Embodiment]
Next, a third embodiment of the present invention will be described. FIG. 6 is a block diagram showing a configuration of a sound quality adjusting apparatus according to the third embodiment of the present invention. The same reference numerals are given to the same configurations as those in FIGS. The sound quality adjusting apparatus according to the present embodiment is the same as the sound quality adjusting apparatus according to the second embodiment, except that a decay processing circuit 11 is added between the LPF 1 and the bass boost circuit 3.

  The decay processing circuit 11 is a circuit that performs a decay process in which the output level is gradually attenuated in accordance with the level decrease of the second audio signal in the low range extracted by the LPF 1. FIG. 7 is a diagram illustrating an example of input / output time characteristics of the decay processing circuit 11. In FIG. 7, the horizontal axis represents time, and the vertical axis represents the level of the audio signal. IN indicates the second audio signal extracted by the LPF 1, and OUT indicates the output signal of the decay processing circuit 11.

  As shown in FIG. 7, the decay processing circuit 11 causes the level of the output signal OUT to follow the level of the audio signal IN that suddenly decreases after taking the maximum value when the impulse audio signal IN is input. Instead, a release time is provided so as to gradually attenuate. In the present embodiment, a decay process is performed in which the attenuation rate increases nonlinearly with the passage of time. As a result, immediately after an impulse-like change occurs in the low frequency range extracted by the LPF 1, the change in the output level is suppressed, and after a certain amount of time has passed, the attenuation of the output level is increased so that the viewer can naturally Can give you a good sense of hearing.

  In order to realize such a decay process, the audio signal input to the decay process circuit 11 is sampled at regular intervals, the sample value at the current time is compared with the output value one sample before, and the one with the higher level Is selected as the output value at the current time. Therefore, when the level of the input audio signal increases, the latest sample value is always selected, and the output level of the decay processing circuit 11 increases according to the input level. On the other hand, when the level of the input audio signal decreases, the output value one sample before is selected. In this case, the value before one sample is attenuated to obtain the output value at the current time. As described above, the attenuation rate at this time increases with time. This output value is used for level comparison as the output value of the previous sample in the next sampling.

  As described above, in the present embodiment, by providing the decay processing circuit 11, it is possible to suppress a level fluctuation that is too rapid in the low frequency range and to give the viewer a natural audibility. In the present embodiment, the decay processing circuit 11 is provided between the LPF 1 and the bass boost circuit 3, but a decay processing circuit may also be provided between the HPF 2 and the treble boost circuit 4. Further, a decay processing circuit may be applied to the first embodiment.

  In the first to third embodiments, only one-channel audio signal has been described, but it may be applied to a multi-channel audio signal. In this case, the sound quality adjusting device shown in FIG. 1, FIG. 4, or FIG. 6 is provided for each channel. The sound quality adjustment need not be performed for all channels, and may be performed for at least one channel. For example, in the case of a 5.1 channel surround system, the front left channel is L (Left) ch, the front right channel is R (Right) ch, the center channel is C (Center) ch, the rear left If the channel is SL (Surround Left) ch, the rear right channel is SR (Surround Right) ch, and the subwoofer is LFE (Low Frequency Effects) ch, the effect of sound quality adjustment is Lch, Rch, Cch. You can adjust the sound quality for each channel individually.

  The sound quality adjustment may be performed for each channel individually, but a common gain coefficient may be used. In order to use a common gain coefficient, for example, in the treble boost circuit 4 of each sound quality adjusting device for Lch, Rch, and Cch, among the high frequency components of the three audio signals Lch, Rch, and Cch extracted by the HPF 2 The maximum level is detected by the level detection unit, and the gain coefficient corresponding to the maximum level is read from the gain table. As a result, when adjusting the sound quality for the three channels of Lch, Rch, and Cch, a sound quality adjusting device is required for each channel, but the level detection unit and the gain table can be shared by the three treble boost circuits 4. The circuit scale can be reduced.

[Fourth Embodiment]
Next, a fourth embodiment of the present invention will be described. FIG. 8 is a block diagram showing a configuration of a sound quality adjusting apparatus according to the fourth embodiment of the present invention. The same reference numerals are given to the same configurations as those in FIGS. The present embodiment is a multi-channel sound quality adjusting device, which includes Lch, Rch, and Cch sound quality adjusting devices 12-L, 12-R, and 12-C, and further adjusts the volume of the audio signal of each channel. The normalization processing circuit 13 for performing the above is included. The configuration of the sound quality adjusting devices 12-L, 12-R, and 12-C may be any of those described in the first to third embodiments.

  The normalization processing circuit 13 includes amplifiers 14-L, 14-R, 14-C, 14-SL, 14-SR, 14-LFE, a level detection unit 15, and a gain table 16. The level detection unit 15 includes Lch, Rch, and Cch audio signals that have been adjusted by the sound quality adjusting devices 12-L, 12-R, and 12-C, and SLch, SRch, and LFEch audio signals that do not pass through the sound quality adjusting device. The maximum level is detected.

  In the gain table 16, the input level of the audio signal and the gain coefficients of the amplifiers 14-L, 14-R, 14-C, 14-SL, 14-SR, and 14-LFE are stored in association with each other in advance. . The gain table 16 reads the gain coefficient corresponding to the maximum level detected by the level detector 15 and outputs the gain coefficient to the amplifiers 14-L, 14-R, 14-C, 14-SL, 14-SR, and 14-LFE. . The amplifiers 14-L, 14-R, 14-C, 14-SL, 14-SR, and 14-LFE are gains output from the gain table 16 to the audio signals of Lch, Rch, Cch, SLch, SRch, and LFEch, respectively. Multiply the coefficients and output the Lch, Rch, Cch, SLch, SRch, and LFEch audio signals after multiplication.

  FIG. 9 shows an example of input / output characteristics of the normalization processing circuit 13. The horizontal axis in FIG. 9 is the input level detected by the level detector 15, and the vertical axis is the output level of the normalization processing circuit 13. Here, it is assumed that one channel of Lch, Rch, Cch, SLch, SRch, and LFEch shows the maximum level, and the input / output characteristics are shown for this channel. As shown in FIG. 9, when the volume is small, the gain is increased to increase the amplitude, and when the volume is large, the gain is decreased to suppress the amount of enhancement.

  As in the case of the bass boost circuit 3 and the treble boost circuit 4, a plurality of types of input / output characteristics such as MIN, MID, and MAX are prepared in advance so that the user can obtain desired input / output characteristics. May be selected. In this case, the gain table 16 has a plurality of tables corresponding to the respective input / output characteristics.

  Thus, in this embodiment, in addition to the same effects as those in the first to third embodiments, the following effects can be further obtained. That is, in this embodiment, the dynamic range expansion / compression of the audio signal of each channel is performed by a common gain coefficient corresponding to the maximum level of the multi-channel audio signal, so that the volume is low. The volume can be increased so that it is not hidden by noise, and the volume can be decreased so that it is not harsh when the volume is high.

  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 turned down, it will be difficult to hear the playback sound when the audio signal supplied from the audio device is low. If the playback volume of the audio device is increased, the sound will be too loud when the volume is high. This causes the harmful effect. According to the present embodiment, it is possible to avoid the difficulty of hearing the sound when the sound volume is reduced while solving the problem that the sound becomes too loud when the sound volume is high. In addition, the volume of programs and commercials in television broadcasts and the volume of audio sources may cause the user to frequently manipulate the volume. According to the present embodiment, it is possible to reduce a volume difference due to a difference in an audio source or the like, and to eliminate frequent user volume operations.

  In this embodiment, a common gain coefficient is used for each channel. However, a level detection unit is provided for each channel, and individual gain coefficients are assigned to the respective amplifiers 14-L, 14-R, 14-C, 14-SL, 14-SR, 14-LFE may be provided, or the channel is divided into several groups, a level detection unit is provided for each group, and a common gain coefficient for each group May be used. As a set of audio signals, there are, for example, a method of dividing such as a set of Lch and Rch and a set of other signals, a method of dividing such as a set of Lch and Rch, a set of only Cch, and a set of other signals.

  The present invention can be applied to audio devices and television receivers.

It is a block diagram which shows the structure of the sound quality adjustment apparatus used as the 1st Embodiment of this invention. It is a block diagram which shows one structural example of the bass boost circuit in the 1st Embodiment of this invention. It is a figure which shows one example of the input-output characteristic of the bass boost circuit in the 1st Embodiment of this invention. It is a block diagram which shows the structure of the sound quality adjustment apparatus used as the 2nd Embodiment of this invention. It is a figure which shows an example of the input-output characteristic of the bass boost circuit in the 2nd Embodiment of this invention. It is a block diagram which shows the structure of the sound quality adjustment apparatus used as the 3rd Embodiment of this invention. It is a figure which shows one example of the time characteristic of the input / output of the decay processing circuit in the 3rd Embodiment of this invention. It is a block diagram which shows the structure of the sound quality adjustment apparatus used as the 4th Embodiment of this invention. It is a figure which shows an example of the input-output characteristic of the normalization processing circuit in the 4th Embodiment of this invention. It is a block diagram which shows the structure of the conventional sound quality adjustment apparatus.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Low pass filter, 2 ... High pass filter, 3 ... Bass boost circuit, 4 ... Treble boost circuit, 5, 6, 7 ... Multiplier, 8 ... Adder, 9, 10 ... Subtractor, 11 ... Decay processing circuit, 12 -L, 12-R, 12-C ... sound quality adjustment device, 13 ... normalization processing circuit, 14-L, 14-R, 14-C, 14-SL, 14-SR, 14-LFE, 30 ... amplifier, 15 , 31 ... level detection unit, 16, 32 ... gain table.

Claims (2)

For at least one of the multi-channel audio signals,
A filter circuit for extracting an audio signal of a desired frequency band from the input audio signal;
A boost circuit that performs dynamic range expansion / compression according to the input level of the audio signal extracted by the filter circuit;
An adder for adding the input audio signal and the audio signal output from the boost circuit;
A decay processing circuit for performing a decay process for gradually attenuating an output level according to a decrease in the level of the audio signal extracted by the filter circuit between the filter circuit and the boost circuit for the at least one audio signal; Have
The decay processing circuit samples the input audio signal at regular intervals, compares the sample value at the current time with the output value one sample before, and selects the higher level as the output value at the current time. When the output value is selected and the output value one sample before is selected, the sound quality adjusting device is characterized in that the value one sample previous is attenuated by an attenuation rate that increases with time to obtain an output value at the current time. The sound quality adjusting device according to claim 1,
A subtractor for subtracting the audio signal extracted by the filter circuit from the input audio signal for the at least one audio signal;
The said adder adds the input audio | voice signal after the said subtraction, and the audio | voice signal output from the said boost circuit, The sound quality adjustment apparatus characterized by the above-mentioned .