JPS63260210A - Automatic gain controller - Google Patents

Abstract

PURPOSE:To design the titled controller in such a manner that it hardly follows the noise at a no-sound period but follows a sound signal quickly in the sound period by dividing the amplitude of an input signal by a maximum value of the amplitude to obtain an amplitude ratio and controlling the time constant in a way that the leading time constant is longer as the amplitude ratio is larger and smaller as it gets smaller. CONSTITUTION:An input signal 21 inputted to an input terminal 11 is smoothed and rectified by an amplitude calculation section 12 and becomes an amplitude signal 22. The signal 22 is inputted to a division section 13 and a maximum value hold section 14. The division section 13 divides the signal 22 by a maximum value signal 24 from the hold section 24 to obtain an amplitude ratio signal 23, the result is outputted to the hold section 14. The trailing time constant of the hold section 14 is controlled longer by the signal 23 as the signal 23 is larger and to be short as the signal 23 gets smaller. Under the condition of time constant, the hold section 14 obtains a maximum signal 24 being a maximum value of the signal 22. A variable gain amplifier section 15 is controlled to have a gain 25 by using the signal 24 and an output signal 26 is outputted from an output terminal 16.

Description

[Detailed Description of the Invention] Industrial Field of Application The present invention relates to an automatic gain control device built into equipment for recording, amplifying, and transmitting audio signals, such as recording devices, loudspeaker devices, and telephones. .

Conventional technology In recent years, cassette tape recorders and video cameras.

The number of types of audio equipment used by general users, such as telephones, is increasing, and their functions are also becoming more sophisticated. In such devices, various adjustment functions are automated to the extent possible in order to reduce the burden on the user during use.

One of these automated adjustment functions is an automatic gain control function. Let's discuss the role and necessity of this automatic gain control function for recording.

The most popular thing to do when recording audio is adjusting the recording level. The sound level of the audio signal picked up by the microphone varies greatly depending on the speaker. This is because the distance between the speaker and the microphone is significantly different, rather than the speaker's voice power being different. Even if the pickup level varies greatly, it is necessary to constantly monitor the pickup level and adjust the recording level with a variable amplifier in order to prevent distortion due to excessive input or deterioration of S/N due to insufficient input. There is.

This level adjustment problem is a common problem in equipment that handles audio signals. For this purpose, automatic gain controllers or GGs have been developed and incorporated into equipment.

Hereinafter, the above-mentioned conventional automatic gain control device will be explained with reference to the drawings.

FIG. 3 shows a block diagram of a conventional automatic gain control device.

In FIG. 3, 31 is a signal input terminal, 32 is an amplitude calculation unit that rectifies and smoothes this signal to obtain an amplitude value, 33 is a maximum value hold unit that determines the thickest value of this amplitude value, and 34 is this maximum value hold unit. A variable gain amplification section whose gain is controlled by the output of the variable gain amplification section 35 is a signal output terminal.

The operation of the automatic gain control device configured as described above will be described below.

FIG. 4 shows signal waveforms at each part of FIG. 3, and the operation of FIG. 3 will be explained using this diagram.

In FIG. 4, 41 is the waveform of the input signal at point A in FIG.
Reference numeral 42 indicates the waveform of the amplitude value at the third point B, 43 indicates the waveform of the maximum value signal at the 0 point, 44 indicates how the gain of the variable gain amplifier 34 changes, and 45 indicates the waveform of the output signal at the D point.

First, the input signal 41 shown in FIG. 4 is input to the input terminal 31 shown in FIG. In this input signal 41, the time TO~TI
, T2-T3. The three sections T4 to T6 are silent sections in which only noise is collected, and no audio signals are included in these sections. Two sections from time T1 to T2 and from T3 to T4 are audio sections, and are sections in which the voices of speaker 1 and speaker B are collected, respectively. In this example of input signal 41,
Because the speaker's position is closer to the microphone than speaker B,
The amplitude of speaker B is larger than that of speaker B.

This input signal 41 is rectified and smoothed by the amplitude calculation section 32 shown in FIG. 3, and becomes an amplitude value 42 shown in FIG. Next, this amplitude value 42
is input to the maximum value holding section 33 to obtain a maximum value signal 43. This maximum value signal 43 traces the maximum value of the noise signal amplitude at time To-T1. When the speaker's voice is input at time T1, the value rises rapidly. After that, time T
2, the maximum value of the speaker's voice signal amplitude is traced. After the time T2 when the speaker's voice disappears, the value gradually decreases according to the falling time constant set by the maximum value holding section 33, and the maximum value of the noise signal amplitude is traced again. I come to do it. When the voice of speaker B is input at time T3, the local maximum value signal 43 rises rapidly again, and traces the maximum value of the amplitude of the voice signal of speaker B until time 4.

The gain 44 of the variable gain amplification section 34 is based on this maximum value signal 43.
controlled by The larger the maximum value signal 43, the higher the gain 4.
4, and the smaller the gain 44 is, the higher the gain 44 is controlled. As a result, the output signal 45 outputted to the outside from the output terminal 36 includes the voice signal of speaker A at time T1-T2 as well as the voice signal at time T3-T4.
The audio signal of speaker B is also adjusted to have approximately the same amplitude level.

Problems to be Solved by the Invention However, in the above configuration, as shown at times T2 to T3 of the output signal 45, when the speaker remains silent for a long time, the gain gradually increases, and the noise is reduced. This has the problem of amplification. -To prevent this,
The fall of the local maximum value holding section 33 lengthens the time constant of
There is a need to slow down the decreasing speed of the maximum value signal 43 in the silent section, that is, the increasing speed of the gain. However, if it is too long, the gain control speed for the audio signal will decrease.
Pass. Once a signal with a very large amplitude is input and the gain is once reduced, the gain does not return to the original level easily, resulting in a disadvantage that the output signal level remains insufficient for some time.

In the conventional configuration, it has been impossible to achieve both gain stability in a non-speech section and gain followability with respect to a voice signal in a speech section.

The present invention solves the above problems, and controls the falling time constant of the local maximum value hold section to different values for the voice section and the no-voice section, so that the voice signal in the voice section can be quickly followed, and the The present invention provides an automatic gain control device that is difficult to follow noise in sections.

Means for Solving the Problems In order to achieve this object, the automatic gain control device of the present invention includes an amplitude calculation unit that calculates the amplitude value of an input signal, and divides the amplitude value by the maximum value of the amplitude value. a dividing unit for determining the amplitude ratio; a maximum value holding unit for determining the maximum value of the amplitude value; a maximum value holding unit for determining the maximum value of the amplitude value; It is comprised of a variable gain amplification section which amplifies or attenuates the input signal and outputs it to the outside, which controls the gain to be low as the value is large and the gain to be high as the value is small.

Effect: With this configuration, it is possible to realize an automatic gain control device in which the gain accurately and quickly follows the audio signal in the audio section, but does not easily follow the noise signal in the non-speech section. In this way, gain control can be performed using only the audio signal in the input signal, so the gain does not increase excessively even if there is a relatively long silent period, and the noise is over-amplified and output to the outside. The phenomenon can be prevented.

EXAMPLE Hereinafter, an example of the present invention will be described with reference to the drawings.

FIG. 1 shows a block diagram of an automatic gain control device in one embodiment of the present invention.

In FIG. 1, 11 is a signal input terminal, 12 is an amplitude calculation unit that calculates the amplitude value of the input signal, 13 is a division unit that divides the amplitude value by the maximum value of this amplitude value to obtain an amplitude ratio, and 1
Reference numeral 4 denotes a maximum value hold unit for determining the maximum value of the amplitude value, which controls the falling time constant to be longer as the amplitude ratio is larger, and shortened as the amplitude ratio is smaller. A variable gain amplifying section 16 is a signal output terminal that amplifies or attenuates the input signal and outputs it to the outside, where the gain is controlled to be higher as the gain is lower.

The operation of the automatic gain control device configured as described above will be described below.

FIG. 2 shows signal waveforms at each part of FIG. 1, and the operation of FIG. 1 will be explained using this diagram.

In FIG. 2, 21 is the waveform of the input signal at point A in FIG. 1, 22 is the waveform of the amplitude value signal at the first point B, 23 is the waveform of the amplitude ratio signal at point 0, and 24 is the maximum at point D. Waveform of value signal, 2
5 shows how the gain of the variable gain amplifier 15 changes, and 26 shows the waveform of the output signal at point B.

First, the input signal 21 shown in FIG. 2 is input to the input terminal 11 shown in FIG. In this input signal 21, the time TO~TI
, T2-T3, and T4-T5 are silent sections in which only noise is collected, and no audio signals are included in these sections. Two sections from time T1 to T2 and from T3 to T4 are audio sections, and are sections in which the voices of speaker person and speaker B are collected, respectively. In this example of the input signal 21, since the position of the speaker M is closer to the microphone than the position of the speaker B, the amplitude of the speaker's sound is picked up to be thicker than that of the speaker B.

This input signal 21 is rectified and smoothed by the amplitude calculation section 12 shown in FIG. 1 to become an amplitude value signal 22 shown in FIG. This amplitude value signal 2
2 is input to the division section 13 and the maximum value holding section 14. The division section 13 divides the amplitude value signal 22 by the maximum value signal 24 sent from the maximum value hold section 14 to obtain an amplitude ratio signal 23, and outputs it to the maximum value hold section 14. The falling time constant of the local maximum value holding section 14 is controlled by this amplitude ratio signal 23. That is, the amplitude ratio signal 23
The larger the value, the longer the falling time constant, and the smaller the value, the shorter the time constant. Under such time constant conditions, the local maximum value holding unit 14 obtains the local maximum value signal 24 which is the local maximum value of the amplitude value signal 22.

Looking at the maximum value signal 24 obtained under such time constant control, we can see that the period during which the speaker is speaking from time T1 to T2, and from T3 to
In the speech section of speaker B speaking at T4, the amplitude ratio signal 2
3 is small, the time constant of the fall is controlled to be short,
As a result, it can be seen that the maximum value signal 24 quickly follows the maximum value of each speaker's voice and traces this maximum value. Conversely, from time TO to T1. T2-T3, T
In the silent period from 4 to T5, the amplitude ratio signal 23 has a very large value, and because the falling time constant is controlled to be extremely long, the maximum value signal 24 slowly decreases, and the amplitude ratio signal 23 has a very large value, and the maximum value signal 24 decreases slowly. It can be seen that the noise amplitude does not decrease to the value at the length of .

The variable gain amplifying section 15 is controlled to have a gain of 25 by this local maximum value signal 24. As a result, the output signal 26 outputted to the outside from the output terminal 16 is adjusted to approximately the same amplitude level for the voice signals of the speakers at times T1 to T20 and the voice signals of speaker B at times T3 to T4, and also has a noise level. is not overamplified.

As described above, according to this embodiment, a division section is introduced to obtain an amplitude ratio by dividing the amplitude value by the maximum value, and the larger the amplitude ratio is, the longer the time constant for the fall of the maximum value hold section is. , the smaller the time constant is controlled. Through this processing, the gain accurately and quickly follows the audio signal in the audio section,
An automatic gain control device that is difficult to follow noise signals in silent sections can be realized. In this way, gain control can be performed using only the audio signal in the input signal, so the gain does not increase excessively even if there is a relatively long silent period, and the noise is over-amplified and output to the outside. The phenomenon can be prevented.

Effects of the Invention The present invention includes an amplitude calculation unit that calculates an amplitude value of an input signal;
a dividing unit that calculates an amplitude ratio by dividing the amplitude value by the maximum value of the amplitude value; and a division unit that controls the falling time constant to be longer as the amplitude ratio is larger and to be shorter as the amplitude ratio is smaller;
a local maximum value holding unit that determines the local maximum value of the amplitude value; and a variable gain amplifier that amplifies or attenuates the input signal and outputs it to the outside, controlling the gain to be lower as the local maximum value is larger and higher as the local maximum value is smaller. By configuring an automatic gain control device with this section, the gain can accurately and quickly follow the audio signal in the voice section, but it is difficult to follow the noise signal in the non-speech section. can be realized. In this way, the gain control operation can be performed using only the audio signal in the input signal, so the gain does not increase excessively even if a relatively long silent period continues, and the noise can be over-amplified and output to the outside. It is possible to provide an automatic gain control device without

[Brief explanation of the drawing]

FIG. 1 is a block diagram of an automatic gain control device according to an embodiment of the present invention, FIG. 2 is a waveform diagram of signals in each part of FIG. 1, FIG. 3 is a block diagram of a conventional automatic gain control device, and FIG. The figure is a waveform diagram of signals at each part in FIG. 3. 12... Amplitude calculation unit, 13... Division unit, 14... Maximum value hold unit, 16...
・Variable gain amplification section. Name of agent: Patent attorney Toshio Nakao and 1 other person No. 1
figure

Claims (1)

[Claims] an amplitude calculation unit that calculates an amplitude value of an input signal; a division unit that divides the amplitude value by a maximum value of the amplitude value to obtain an amplitude ratio;
a local maximum value hold section for determining the maximum value of the amplitude value, which controls the time constant to be shorter as the time constant is smaller, and amplifying the input signal, which controls the gain to be lower as the maximum value is larger and higher as the maximum value is smaller. Alternatively, an automatic gain control device comprising a variable gain amplification section that attenuates and outputs to the outside.