JPH0773176B2 - Automatic gain control device - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an automatic gain control device incorporated in equipment for recording, amplifying, and transmitting voice signals such as a recording device, a loudspeaker, and a telephone. .

2. Description of the Related Art In recent years, the types of audio devices used by general users have increased, such as cassette tape recorders, video cameras, and telephones, and their functions have become more sophisticated. In such a device, various adjustment functions are automated as much as possible in order to reduce the burden on the user in use.

One of the automated adjustment functions is an automatic gain control function. Recording the role and necessity of this automatic gain control function.

The most important factor in recording voice is adjusting the recording level. The sound pickup level of the voice signal picked up by the microphone greatly differs depending on the speaker. This is because the voice power of the speaker is different, and the distance between the speaker and the microphone is significantly different. Even if the sound pickup levels are significantly different, it is necessary to constantly monitor the sound pickup level and adjust the recording level with a variable amplifier in order to prevent distortion due to excessive input and deterioration of S / N due to excessive input. There is.

This level adjustment problem is a common problem in devices that handle audio signals. To this end, an automatic gain controller or AGC has been developed and built into the instrument.

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

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

In FIG. 3, reference numeral 31 is a signal input terminal, 32 is an amplitude calculating section for rectifying and smoothing this signal to obtain an amplitude value, 33 is a maximum value holding section for obtaining a maximum value of this amplitude value, and 34 is this maximum value holding section. Variable gain amplifier whose gain is controlled by the output of 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 the signal waveforms at the respective parts of FIG. 3, and the operation of FIG. 3 will be explained using this figure.

In FIG. 4, 41 is the waveform of the input signal at point A in FIG.
Is the waveform of the amplitude value at the third point B, 43 is the waveform of the maximum value signal at point C, 44 is the change in the gain of the variable gain amplifying section 34, 45
Shows the waveform of the output signal at point D.

First, the input signal 41 of FIG. 4 is input to the input terminal 31 of FIG. In this input signal 41, time T0 to T1, T2 to T3, T4
The three sections from T5 to T5 are non-voice sections in which only noise is collected, and no voice signal is included in the sections. Time T1
~ T2, T3 ~ T4 are the voice sections, and are the sections in which the voices of speaker A and speaker B are picked up, respectively. In the example of the input signal 41, since the position of the speaker A is closer to the microphone than the speaker B, the amplitude of the speaker A is larger than that of the speaker B.

This input signal 41 is rectified and smoothed by the amplitude calculating section 32 of FIG. 3 and becomes the amplitude value 42 of FIG. Next, the amplitude value 42 is input to the maximum value holding unit 33 to obtain the maximum value signal 43. The maximum value signal 43 traces the maximum value of the noise signal amplitude from time T0 to T1. When the voice of speaker A is input at time T1,
Rises sharply. After that, the maximum value of the voice signal amplitude of the speaker A is traced until time T2. After the time T2 when the voice of the speaker A disappears, the value gradually decreases according to the falling time constant set by the maximum value holding unit 33, and the maximum value of the noise signal amplitude is traced again. become. When the voice of the speaker B is input at time T3, the maximum value signal 43 rises sharply again, and the maximum value of the voice signal amplitude of the speaker B is traced until time T4.

The gain 44 of the variable gain amplifying section 34 is controlled by this maximum value signal 43. The larger the maximum signal 43, the lower the gain 44,
The smaller the value, the higher the gain 44 is controlled. As a result, the output terminal
The output signal 45 output from 35 to the outside is adjusted so that the voice signal of the speaker A at the times T1 to T2 and the voice signal of the speaker B at the times T3 to T4 have substantially the same amplitude level.

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention However, in the above configuration, as shown in the time T2 to T3 of the output signal 45, the gain gradually increases when the speaker is silent for a long time, and the noise is increased. It had a problem of amplification.

In order to prevent this, it is necessary to lengthen the falling time constant of the maximum value holding unit 33 and slow down the decrease rate of the maximum value signal 43 in the non-voice section, that is, the increase rate of the gain. However, if it is set too long, the gain control speed for the voice signal becomes too low. When a very large amplitude signal is input and the gain is once reduced, the gain does not return to its original value, and the shortage of the output signal level continues for a while.

In the conventional configuration, it is impossible to achieve both the stability of gain in the non-voice section and the followability of gain to the voice signal in the voice section.

In view of the above problems, the present invention controls the falling time constant of the maximum value holding unit to a different value between the voice section and the non-voice section, and quickly follows the voice signal in the voice section, and the non-voice section. It is an object of the present invention to provide an automatic gain control device that does not easily follow the noise in.

Means for Solving the Problems To achieve this object, an automatic gain control device of the present invention is an amplitude calculation section for calculating an amplitude value of an input signal, and the amplitude value is divided by a maximum value of the amplitude value. And a maximum value holding unit for determining the maximum value of the amplitude value, in which the falling time constant is controlled to be longer as the amplitude ratio is larger, and the time constant is controlled to be shorter as the amplitude ratio is smaller, and the maximum value. The variable gain amplifier controls the gain to be low as the value is large and to be high as the value is small. The variable gain amplifying part amplifies or attenuates the input signal and outputs the amplified signal to the outside.

Operation With this configuration, it is possible to realize an automatic gain control device in which the gain accurately and quickly follows the voice signal in the voice section and hardly follows the noise signal in the non-voice section. In this way, since the gain control operation can be performed only by the voice signal in the input signal, the gain does not increase excessively even if a relatively long voiceless period continues, and noise is excessively amplified and output to the outside. The phenomenon can be prevented.

Embodiment An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram of an automatic gain control device according to an embodiment of the present invention.

In FIG. 1, 11 is a signal input terminal, 12 is an amplitude calculator for calculating the amplitude value of the input signal, 13 is a divider for dividing the amplitude value by the maximum value of the amplitude value to obtain an amplitude ratio, 14 The larger the amplitude ratio, the longer the fall time constant, and the shorter the time constant, the shorter the time constant is controlled.A maximum value holding unit for obtaining the maximum value of the amplitude value, and 15 has a lower gain as the maximum value increases. The variable gain amplifying section 16 amplifies or attenuates the input signal and outputs the amplified signal to the outside, the smaller the gain, the higher the gain is controlled, and 16 is a signal output terminal.

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

FIG. 2 shows the signal waveform in each part of FIG. 1, and the operation of FIG. 1 will be explained using this figure.

In FIG. 2, 21 is the waveform of the input signal at point A in FIG.
22 is the waveform of the first amplitude value signal at point B, 23 is the waveform of the amplitude ratio signal at point C, 24 is the waveform of the maximum value signal at point D, and 25 is the change in the gain of the variable gain amplifier 15. 26 shows the waveform of the output signal at point E.

First, the input signal 21 of FIG. 2 is input to the input terminal 11 of FIG. In this input signal 21, time T0 ~ T1, T2 ~ T3, T4
The three sections from T5 to T5 are non-voice sections in which only noise is collected, and no voice signal is included in the sections. Time T1
~ T2, T3 to T4 are voice sections, and are the sections in which the voices of speaker A and speaker B are picked up, respectively. In the example of the input signal 21, since the position of the speaker A is closer to the microphone than the position of the speaker B, the amplitude of the speaker A is larger than that of the speaker B.

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

Looking at the maximum value signal 24 obtained under such time constant control, the amplitude ratio signal can be seen in the period in which the speaker A is speaking at times T1 to T2 and the speech period in which the speaker B is speaking at T3 to T4. Since 23 is small, the falling time constant is controlled to be short, and as a result,
It can be seen that the maximum value signal 24 follows the maximum value of each speaker's voice or quickly and traces this maximum value. On the contrary, in the non-voice section of time T0 to T1, T2 to T3, T4 to T5, the amplitude ratio signal 23 has a very large value and the time constant of the fall is controlled to be extremely long. It can be seen that the noise amplitude value does not decrease in the length of the non-voice section that occurs in normal conversation.

The variable gain amplifying unit 15 receives the gain 25 by the maximum value signal 24.
Controlled by. As a result, the output signal 26 output from the output terminal 16 to the outside is adjusted to have substantially the same amplitude level for both the voice signal of the speaker A at times T1 to T2 and the voice signal of the speaker B at times T3 to T4. Noise is not amplified excessively.

As described above, according to the present embodiment, a division unit for dividing the amplitude value by the maximum value to obtain the amplitude ratio is introduced, and the larger the amplitude ratio is, the longer and smaller the time constant of the fall of the maximum value holding unit is. The more the time constant is controlled to be shorter. By this processing, the gain accurately and quickly follows the voice signal in the voice section,
It is possible to realize an automatic gain control device that does not easily follow a noise signal in a voiceless section. In this way, since the gain control operation can be performed only by the voice signal in the input signal, the gain does not increase excessively even if a relatively long voiceless period continues, and noise is excessively amplified and output to the outside. The phenomenon can be prevented.

Advantageous Effects of Invention The present invention has an amplitude calculation unit that calculates an amplitude value of an input signal,
A division unit that obtains an amplitude ratio by dividing the amplitude value by the maximum value of the amplitude value, and a longer time constant of the falling edge as the amplitude ratio is larger, and a shorter time constant as the smaller amplitude ratio is controlled.
A maximum value holding unit that obtains a maximum value of the amplitude value, and a variable gain amplifying unit that amplifies or attenuates the input signal and outputs it to the outside, in which the gain is controlled to be lower as the local maximum value is larger and to be higher as the local maximum value is smaller. By constructing an automatic gain control device with this part, an automatic gain control device with which the gain accurately and quickly follows the voice signal in the voice section and hardly follows the drive signal in the non-voice section is realized. it can. In this way, since the gain control operation can be performed only with the audio signal in the input signal, the gain does not increase excessively even if a relatively long unvoiced section continues, and noise is excessively amplified and output to the outside. It is possible to provide an automatic gain control device that does not have the above.

[Brief description of drawings]

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 in each part of FIG. 12 …… Amplitude calculation section, 13 …… Division section, 14 …… Maximum value hold section, 15 …… Variable gain amplification section.

Claims (1)

[Claims] 1. An amplitude calculation section for calculating an amplitude value of an input signal, a division section for dividing the amplitude value by a maximum value of the amplitude value to obtain an amplitude ratio, and a larger amplitude ratio for a fall time. A maximum value holding unit that obtains a maximum value of the amplitude value, where the time constant is controlled to be shorter as the constant becomes longer and smaller,
An automatic gain control device, comprising: a variable gain amplifying unit for amplifying or attenuating the input signal and outputting the amplified signal, which controls the gain to be lower as the maximum value is larger and to be higher as the local maximum value is smaller. .