JPH10224171A - Noise detector and automatic volume-adjusting device using the device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To detect noise characteristic in plural frequency bands with high accuracy and with few calculated quantities in a volume automatic adjusting device that automatically adjusts the volume and sound quality of a sound source signal, in accordance with a noise characteristic. SOLUTION: A noise detector 109 is provided with a noise analyzer 110, which partially analyzes characteristic of noise and a noise-characteristic calculating device 117, and the device 117 consists of a noise characteristic storage device 118 and an adder 119. They increase or decrease the level of a noise characteristic of the device 118, which has been preliminarily set in accordance with the noise level of one band that has been detected by the analyzer 110 and estimate a noise characteristic of whole frequency bands. Then, a noise characteristic is detected with high accuracy without detecting a noise characteristic of the whole frequency bands, and a volume automatic adjusting device can be realized with a little operation quantity.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to noise detection which detects ambient noise and automatically adjusts the volume and sound quality of a sound source signal in accordance with the amount and quality of the noise to provide an optimum listening environment. The present invention relates to a device and an automatic volume control device using the device.

[0002]

2. Description of the Related Art Conventionally, apparatuses for detecting noise and automatically adjusting the volume of a sound source signal are disclosed in Japanese Patent Application Laid-Open Nos. 5-218769 and 7-99417. 6 and 7 are schematic block diagrams illustrating a configuration example of a conventional automatic volume control device.

Next, a conventional automatic volume control device will be described.

In FIG. 6, reference numeral 601 denotes a sound source such as a CD;
Is an A / D converter, 603 is a volume controller such as a volume or an equalizer, 604 is a D / A converter, 605 is an amplifier, 606 is a speaker, 607 is a microphone that detects noise, 608 is an A / D converter, A noise detector 609 includes a level analyzer 610, a noise level calculator 611, and a level analyzer 612. 613 is a volume adjustment amount calculator.

Next, the operation will be described.

In FIG. 6, a signal output from a sound source 601 is converted from an analog signal to a digital signal by an A / D converter 602. The output signal of the A / D converter 602 is converted from a digital signal to an analog signal by the D / A converter 604 after the signal level is changed by the volume controller 603. The output signal of the D / A converter 604 is
It is amplified by the amplifier 605 and radiated to the space by the speaker 606.

On the other hand, the input signal to the microphone 607 is A / D
The converter 608 converts the analog signal into a digital signal. The output signal of the A / D converter 608 is analyzed by a level analyzer 610 for the amplitude level and energy level of the signal, and is input to a noise level calculator 611. The output signal of the volume controller 603 is input to the level analyzer 612,
The amplitude level and energy level of the sound source signal are analyzed, and they are used as the other input of the noise level calculator 611 and the other input of the volume adjustment calculator 613.

The microphone 607 has a speaker 6 in addition to the noise signal.
Because the sound source signal radiated into the space by 06 is also input,
The noise level calculator 611 detects only the noise signal by subtracting the sound source signal from the input signal to the microphone 607. The output signal of the noise level calculator 611 is input to the volume adjustment amount calculator 613, and calculates an optimum volume adjustment amount according to the noise signal level detected by the input from the level analyzer 612. Change the adjustment amount of 603.

Next, in FIG. 7, 701 is a sound source such as a CD, 702 is an A / D converter, 703 is a volume controller such as a volume and an equalizer, 704 is a D / A converter, 705 is an amplifier,
706 is a speaker, 707 is a microphone for detecting noise, and 708 is A
A / D converter 709 is a noise detector, which comprises a frequency analyzer 710, a noise characteristic calculator 711, and a frequency analyzer 712. 713 is a volume adjustment amount calculator.

FIG. 7 shows an example in which the conventional level analyzers 610 and 612 shown in FIG. 6 are replaced with frequency analyzers 710 and 712.

Next, the operation will be described.

In FIG. 7, a signal output from a sound source 701 is converted by an A / D converter 702 from an analog signal to a digital signal. The output signal of the A / D converter 702 is converted from a digital signal to an analog signal by the D / A converter 704 after the signal level of each of a plurality of frequency bands is changed by the volume controller 703. The output signal of the D / A converter 704 is amplified by the amplifier 705 and radiated to the space by the speaker 706.

On the other hand, the input signal to the microphone 707 is A / D
The converter 708 converts the analog signal into a digital signal. The output signal of the A / D converter 708 is analyzed by the frequency analyzer 710 for the amplitude level and energy level of the signal for each frequency band, and is input to the noise characteristic calculator 711. Further, the output signal of the volume controller 703 is input to the frequency analyzer 712, where the amplitude level and energy level of each band of the sound source signal are analyzed, and becomes the other input of the noise characteristic calculator 711.

The noise characteristic calculator 711 detects only the noise signal by subtracting the sound source signal from the input signal to the microphone 707. The output signal of the noise characteristic calculator 711 is input to the volume adjustment amount calculator 713, and the optimum volume adjustment amount of each frequency band according to the detected noise signal level of each frequency band is calculated. Change the adjustment amount of 703.

As described above, even in the above-mentioned conventional automatic volume control device, the volume control amount according to the detected noise characteristic is
The volume of the sound source signal could be automatically adjusted.

[0016]

However, in each of the conventional devices described above, in the example shown in FIG. 6, even though the overall noise level can be detected, the noise characteristics in a plurality of frequency bands cannot be detected. Was. Further, in the example shown in FIG. 7, since the noise signal and the sound source signal are analyzed by the number of frequency bands adjusted by the volume adjuster, there is a problem that the amount of calculation increases.

An object of the present invention is to solve the above-mentioned conventional problems and to provide an automatic volume control device with a small amount of calculation.

[0018]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems and to achieve the object, the present invention provides a noise detecting device including a noise analyzer and a noise characteristic calculator, and analyzing the whole noise characteristic from a part of the noise characteristic analysis results. Is calculated. Further, by using the noise detection device having the above function as the automatic volume control device, an automatic volume control device with a small amount of calculation can be obtained.

[0019]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The noise detecting apparatus according to the first aspect of the present invention is provided with a noise analyzer and a noise characteristic calculator, and calculates the whole noise characteristic from the analysis result of a part of the noise characteristic. This has the effect that the characteristics of the entire noise can be obtained with a small amount of calculation.

According to a second aspect of the present invention, there is provided an automatic volume control device including a noise detection device, a volume control amount calculator, and a volume control device. Is to adjust the volume of
This has the effect that the volume or sound quality can be automatically adjusted according to the noise with a small amount of calculation.

According to a third aspect of the present invention, the noise analyzer comprises a BPF, a level analyzer, a subtractor, and a logarithmic value calculator, and analyzes the noise characteristics with a smaller number of bands than the number of bands for volume control. The overall noise characteristics are calculated, and there is an effect that noise detection and automatic volume and sound quality adjustment of a sound source signal can be performed with a small amount of calculation.

According to a fourth aspect of the present invention, the noise characteristic calculator is composed of a noise characteristic storage and an adder, and the level of the stored noise characteristic is raised and lowered by using the one-band noise analysis result. The noise characteristics of all the bands are calculated, and there is an effect that noise detection and automatic volume and sound quality adjustment of a sound source signal can be performed with a small amount of calculation.

According to a fifth aspect of the present invention, a noise characteristic selector is provided in the noise characteristic calculator, and the stored noise characteristic used for calculating the noise characteristic is changed according to the result of the noise analysis. There is an effect that noise detection and automatic volume and sound quality adjustment of a sound source signal can be performed with a small amount of calculation. Furthermore, since the noise characteristics used for estimation are changed according to the noise level, there is an effect that noise can be calculated with high accuracy.

According to a sixth aspect of the present invention, an average value calculator is provided in the noise analyzer to calculate the noise characteristic from the average value of the noise analysis of a plurality of bands. This has an effect that detection and automatic adjustment of sound volume and sound quality of a sound source signal can be performed. Further, since the noise characteristics are determined using the noise data of a plurality of bands, there is an effect that the noise can be calculated with high accuracy.

According to a seventh aspect of the present invention, the noise characteristic calculator comprises an approximate expression constant calculator and an approximate expression calculator, and a noise characteristic approximate expression is obtained from a result of noise analysis of a plurality of bands to calculate a noise characteristic. This has the effect that noise detection and automatic volume control and sound quality control of a sound source signal can be performed with a small amount of calculation. Further, since the noise characteristic is calculated from the approximate expression, there is an effect that the noise can be accurately estimated.

According to another aspect of the present invention, the noise characteristic calculator is constituted by an interpolator, and the noise characteristic is calculated by interpolating the noise analysis results of a plurality of bands. This has the effect that noise detection and automatic volume and sound quality adjustment of the sound source signal can be performed by the amount. Furthermore, since noise data is interpolated, there is an effect that noise can be accurately calculated.

Hereinafter, embodiments of the present invention will be described with reference to FIGS. 1 to 5.

(Embodiment 1) FIG. 1 is a block diagram showing a configuration of an automatic volume control device according to Embodiment 1 of the present invention. In FIG. 1, 101 is a sound source such as a CD, and 102 is A
/ D converter, 103 is a volume controller such as a volume or an equalizer, 104 is a D / A converter, 105 is an amplifier, 106 is a speaker, 107 is a microphone for detecting noise, 108 is an A / D converter, and 109 is It is a noise detection device, and includes a noise analyzer 110 and a noise characteristic calculator 117. Reference numeral 120 denotes a volume adjustment amount calculator.

Here, the noise analyzer 110 is a BPF (Band P
ass Filter) 111, 116, level analyzers 112, 115, subtractor 113, and logarithmic value calculator 114. The noise characteristic calculator 117 includes a noise characteristic storage unit 118 and an adder 119.

Next, the operation of the first embodiment of the present invention configured as described above will be described. In FIG. 1, a sound source 101
The operation until the output signal is radiated into the space by the speaker 106 is the same as in the above-described conventional example. An input signal to the microphone 107 is converted from an analog signal to a digital signal by the A / D converter 108. The output signal of the A / D converter 108 is obtained by filtering the signal in the frequency band set by the BPF 111, analyzing the amplitude level and energy level of the signal by the level analyzer 112, and providing the input to the subtracter 113.

The output signal of the volume controller 103 is BP
The signal in the frequency band set by F116 is filtered, and the level analyzer 115 analyzes the amplitude level and energy level of the signal.

The subtractor 113 removes the sound source signal component from the signal input to the microphone 107 and calculates only the noise signal. The characteristics of the BPF 111 and the BPF 116 have the same characteristics in order to filter components in the same frequency band. In this example, the components of the frequency band set using the BPF are filtered. However, the characteristics of the BPF may be set to the all-bandpass characteristics, and the level of the entire frequency band may be calculated.

The noise signal calculated by the subtractor 113 is converted by the logarithmic value calculator 114 into an absolute sound pressure level. The output of the logarithmic value calculator 114 is input to the adder 119. The data stored in the noise characteristic storage 118 is the other input of the adder 119. Noise data having the same number of frequency bands as the volume adjuster 103 is stored in the noise characteristic storage 118 in advance. As data to be stored, for example, an average value of noise to be detected is used.
In particular, the traveling noise in the passenger compartment is the traveling road surface, traveling speed,
Even if the model changes, just the overall level changes,
The characteristic having a slope of about -6 dB per octave does not change, so the characteristic is stored.

The adder 119 changes the stored noise characteristic level based on the noise level calculated by the logarithmic value calculator 114, and calculates the noise characteristic of the entire band. The volume adjustment amount calculator 120 uses the output of the adder 119 to calculate an optimal volume adjustment amount in consideration of masking of the sound source signal due to noise, and changes the adjustment amount of the volume adjuster 103. Since the masking amount of the sound source signal due to the noise is defined by the noise level and the sound source level, the sound source signal may be used as the other input of the volume adjustment amount calculator 120.

As described above, according to the present embodiment, the level of the noise characteristics of all bands stored in advance is raised or lowered according to the noise detection result of one band, so that the noise characteristics of all bands are not analyzed. There is an effect that noise characteristics in all bands can be detected, and noise detection and automatic volume adjustment can be performed with a small amount of calculation.

(Embodiment 2) FIG. 2 is a block diagram showing a configuration of an automatic volume control device according to Embodiment 2 of the present invention. In the second embodiment, a noise characteristic calculator 117 is provided with a noise characteristic selector 121, and a logarithmic value calculator 114 and a noise characteristic storage 11 are provided.
8 is different from the first embodiment in FIG.
Other configurations are the same.

Next, the operation of the second embodiment of the present invention configured as described above will be described. In FIG. 2, a sound source 101
The operation until the output signal is emitted to the space by the speaker 106, the operation of the noise analyzer 110, and the operations of the adder 119 and the volume adjustment amount calculator 120 are the same as those in the first embodiment (FIG. 1). is there.

Next, the noise level calculated by the logarithmic value calculator 114 is input to the noise characteristic selector 121 and the adder 119. The noise characteristic selector 121 selects optimum data according to the noise level from a plurality of noise characteristics stored in the noise characteristic storage 118 in advance. The selected noise characteristics are
It is the other input of adder 119.

As described above, according to this embodiment, one set of the noise characteristics of all the bands stored in advance in accordance with the detected noise level is selected, and the level of the noise characteristic is set to one.
Since the noise level of the band is raised or lowered according to the result of the noise analysis, it is possible to cope with a case where the characteristics of the entire noise changes when the level of the noise changes. .

(Embodiment 3) FIG. 3 is a block diagram showing a configuration of an automatic volume control device according to Embodiment 3 of the present invention. The third embodiment has an average value calculator 128 for calculating an average value of noise signal levels in different frequency bands in the configuration of the noise analyzer 110. This average calculator 128
When the number of input signals is 2, the BPF (1) 111, the logarithmic value calculator 114, the level analyzer 115, and the signal route of the BPF (2) 116, the BPF (2) 122, the level analyzer 123, and the subtraction Unit 124, logarithmic value calculator 127 and level analyzer 125, BP
A signal route of F (1) 126 is provided.

Next, the operation of the third embodiment configured as described above will be described. 3, the operation until the output signal of the sound source 101 is radiated into the space by the speaker 106, the operation of the noise characteristic calculator 117, and the operation of the volume adjustment amount calculator 120 are the same as those in the second embodiment (FIG. 2). Is the same as

Next, the input signal to the microphone 107 is converted from an analog signal to a digital signal by the A / D converter 108. The output signal of the A / D converter 108 is a BPF (1) 111
And the BPF (2) 122 filters signals in different frequency bands, the level analyzer 112 and the level analyzer 123 analyze the amplitude level and energy level of each signal, and input the respective inputs of the subtractor 113 and the subtractor 124. Becomes

The output signal of the volume controller 103 is BP
The signals in different frequency bands are filtered by the F (2) 116 and the BPF (1) 126, and the amplitude level and energy level of the signals are analyzed by the level analyzer 115 and the level analyzer 125. The other input. Subtractor 113
The subtractor 124 subtracts the output signals of the level analyzer 115 and the level analyzer 125 from the output signals of the level analyzer 112 and the level analyzer 123.

The characteristics of the BPF (1) 111 and the BPF (2) 116 and the characteristics of the BPF (2) 122 and the BPF (1) 126 are the same. Output signals from the subtractor 113 and the subtractor 124 are converted into absolute sound pressure levels by the logarithmic value calculator 114 and the logarithmic value calculator 127, and are input to the average value calculator 128. The average value calculator 128 calculates the average value of the noise signal levels in different frequency bands, and becomes an input to the noise characteristic selector 121 and the adder 119. In this example, the number of input signals of the average value calculator 128 is 2
However, three or more pieces may be used.

As described above, according to the third embodiment of the present invention, the noise level is calculated by using the average value of the noise characteristics of a plurality of different frequency bands. In other words, it is possible to reduce the sudden rise and fall of the noise level in a single frequency band.

(Embodiment 4) FIG. 4 is a block diagram showing a configuration of an automatic volume controller according to Embodiment 4 of the present invention. The fourth embodiment is different from the third embodiment (FIG. 3).
In, except for the average value calculator 128 of the noise analyzer 110,
The noise level calculated by the logarithmic value calculators 114 and 127 is input to the noise characteristic calculator 117. The noise characteristic calculator 117 includes an approximate expression constant calculator 129 and an approximate expression calculator 130.

Next, the operation of the fourth embodiment of the present invention configured as described above will be described. Referring to FIG.
The operation until the output signal is emitted to the space by the speaker 106, the operation from the BPF (1) 111 and 122 of the noise analyzer 110 to the logarithmic calculators 114 and 127, and the operation of the volume adjustment amount calculator 120 are as follows. This is the same as Embodiment 3 (FIG. 3).

Next, the noise level calculated by the logarithmic value calculators 114 and 127 is input to the approximate expression constant calculator 129,
A constant of the approximate expression is calculated. The approximate expression calculator 130 uses the constants calculated by the approximate expression constant calculator 129 to calculate the noise characteristics in each frequency band using the approximate expressions, and inputs the calculated noise characteristics to the volume adjustment amount calculator 120.

The method of calculating the constants and noise characteristics in the approximate expression constant calculator 129 and the approximate expression calculator 130 will be described below.
The following case is described below. Noise characteristics are (Equation 1)
It is assumed that it can be expressed by a first-order approximate expression such as

[0050]

Y (x) = ax + b where x is a frequency expressing a logarithmic value, y (x) is a noise level expressing a logarithmic value at frequency x, and a and b are constants. The center frequency of BPF (1) 111 and BPF (2) 116 is x1, and the center frequency of BPF (2) 122 and BPF (1) 120 is x
Assuming that 2, constants a and b are x1 and x2, x1
And the noise levels y (x1) and y (x2) at x2
It can be calculated by substituting into (Equation 1).

It is also assumed that the noise characteristic can be expressed by a second-order approximation such as the following (Equation 2).

[0052]

Y (x) = a (x−b) ² + c where x is a frequency expressing a logarithmic value, y (x) is a noise level expressing a logarithmic value at frequency x, and a, b and c are Is a constant. It is also assumed that the noise characteristics are flat in a high frequency range. BPF (1) 111 and BPF
(2) The center frequency of 116 is x1, BPF (2) 122 and BPF (1) 1
The center frequency of 26 is x2, and x2 is set to a frequency at which the noise characteristic becomes flat. The constant c can be calculated by setting c = y (x2). The constants a and b are
noise level y at x1 and x2, x1 and x2
It can be calculated by substituting (x1) and y (x2) into (Equation 2).

The noise characteristic at each frequency can be calculated by substituting the frequency into a first-order or second-order approximate expression. In the present example, the case of the first-order or second-order approximation formula has been described, but the calculation can be similarly performed in the case of the third-order or higher approximation formula.

As described above, according to the fourth embodiment of the present invention, even when the noise characteristics are variously changed such that the noise characteristics cannot be set in the noise characteristic storage in advance, the noise can be accurately calculated with a small amount of calculation. There is an effect that detection and automatic volume adjustment can be performed.

(Embodiment 5) FIG. 5 is a block diagram showing a configuration of an automatic volume controller according to Embodiment 5 of the present invention. The fifth embodiment is different from the fourth embodiment (FIG. 4).
Is configured by an interpolator 131 to interpolate noise data in each frequency band.

Next, the operation of the fifth embodiment of the present invention configured as described above will be described. In FIG. 5, the sound source 101
Until the output signal of the speaker 106 is emitted to the space by the speaker 106, the operation of the noise analyzer 110, and the volume adjustment amount calculator 1
The operation of 20 is the same as that of the fourth embodiment (FIG. 4).

Next, the noise levels calculated by the logarithmic value calculators 114 and 127 are input to the interpolator 131. Interpolator 1
31 interpolates the noise data in each frequency band and inputs the data to the volume adjustment amount calculator 120.

The operation of the interpolator 131 will be described for a case where input data is 2, output data is 4, and linear interpolation is performed. BP
The center frequency of F (1) 111 and BPF (2) 116 is x1, BPF
(2) The center frequencies of 122 and BPF (1) 126 are x4, the noise levels at x1 and x4 are y (x1) and y (x2), respectively.
Then, the noise level at frequencies x2 and x3 between x1 and x4 can be calculated by (Equation 3) and (Equation 4).

[0059]

Y (x2) = y (x1) + (y (x4) -y (x1)) / 3

[0060]

Y (x3) = y (x1) +2 (y (x4) -y (x1)) / 3 where x1, x2, x3 and x4 are assumed to be at equal intervals. The same calculation can be performed even when the input data and the output data are not as described above. The interpolation method may be a function interpolation instead of a linear interpolation.

As described above, according to the fifth embodiment of the present invention, by interpolating data, even when noise that cannot store noise data beforehand changes, noise detection and detection can be performed with a small amount of calculation and with high accuracy. This has the effect that automatic volume adjustment can be performed.

[0062]

As described above, according to the present invention, an automatic volume control device using a noise detector provided with a noise analyzer and a noise characteristic calculator calculates the overall noise characteristic from the analysis result of a part of the noise characteristic. Can be calculated, so that it is possible to obtain the effect that the noise characteristics of the entire band can be estimated with high accuracy and with a small amount of calculation as compared with the related art.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a configuration of an automatic volume control device according to Embodiment 1 of the present invention.

FIG. 2 is a block diagram illustrating a configuration of an automatic volume control device according to Embodiment 2 of the present invention.

FIG. 3 is a block diagram showing a configuration of an automatic volume control device according to Embodiment 3 of the present invention.

FIG. 4 is a block diagram illustrating a configuration of an automatic volume control device according to Embodiment 4 of the present invention.

FIG. 5 is a block diagram showing a configuration of an automatic volume control device according to Embodiment 5 of the present invention.

FIG. 6 is a schematic block diagram showing a configuration of a conventional automatic volume control device.

FIG. 7 is a schematic block diagram showing another configuration example of a conventional automatic volume control device.

[Explanation of symbols]

101 ... sound source, 102, 108 ... A / D converter, 103 ... volume controller, 104 ... D / A converter, 105 ... amplifier, 106 ...
Speaker, 107… Microphone, 109… Noise detector, 11
0: Noise analyzer, 111, 116, 122, 126 ... BPF, 11
2, 115, 123, 125 ... Level analyzer, 113, 124 ... subtractor, 114, 127 ... logarithmic value calculator, 117 ... noise characteristic calculator, 118 ... noise characteristic storage, 119 ... adder, 120 ...
Volume adjustment calculator, 121: Noise characteristic selector, 128: Average calculator, 129: Approximate equation constant calculator, 130: Approximate equation calculator, 131: Interpolator.

Claims (8)

[Claims] 1. A noise analyzer for analyzing a part of noise characteristics, and a noise characteristic calculator for estimating an entire noise characteristic from an analysis result of a part of the noise characteristics from the noise analyzer. Noise detector. 2. A sound volume adjustment amount calculator that calculates a sound volume adjustment amount using a noise characteristic detected by the noise detection device;
An automatic volume control device, comprising: a volume control device for adjusting the volume of the sound source signal based on the volume control amount from the volume control amount calculator. 3. The noise analyzer according to claim 1, wherein the noise analyzer comprises a BPF, a level analyzer, a subtractor, and a logarithmic value calculator.
The overall noise characteristic is calculated by the logarithmic value calculator from the noise characteristic analyzed by the level analyzer with the number of bands smaller than the number of bands of the volume adjustment of the input signal filtered in the above. A noise detection device and an automatic volume control device according to claim 1. 4. The noise characteristic calculator includes a noise characteristic storage and an adder, and the level of the noise characteristic stored in the noise characteristic storage is calculated by the adder using a one-band noise analysis result. 3. The noise detection device and automatic volume control device according to claim 1, wherein the noise characteristics of all bands are calculated by moving the noise detection device up and down. 5. The noise characteristic calculator according to claim 1, further comprising a noise characteristic selector, wherein a stored noise characteristic used for calculating the noise characteristic is changed based on a result of the noise analysis. Or the noise detection device and the automatic volume control device according to 4. 6. The noise analyzer according to claim 1, wherein the noise analyzer has an average value calculator, and calculates a noise characteristic from an average value of noise analysis results of a plurality of bands. Noise detection device and automatic volume control device. 7. The noise characteristic calculator includes an approximate expression constant calculator and an approximate expression calculator, and obtains a noise characteristic approximate expression from a result of noise analysis of a plurality of bands to calculate a noise characteristic. The noise detection device and the automatic volume control device according to claim 1 or 2, wherein: 8. The noise characteristic calculator according to claim 1, wherein the noise characteristic calculator comprises an interpolator, and calculates a noise characteristic by interpolating a noise analysis result of a plurality of bands.
A noise detection device and an automatic volume control device according to the above description.