JP3237350B2 - Automatic gain control device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

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

[0002]

2. Description of the Related Art An automatic gain control device is used for recording an audio signal,
This is a device that automatically adjusts while monitoring the recording level, the loudspeaker level, or the transmission signal level of a device for loudspeaking and transmission.

FIG. 4 shows a configuration example of a conventional automatic gain control device. In the figure, 41 is an input terminal of a signal, 42 is an input level detecting section for obtaining a signal level by smoothing and rectifying the signal, 43 is a variable gain amplifying section for adjusting a gain based on an output of the input level detecting section, 44 is a signal output terminal.

FIG. 5 shows signal waveforms at various points in FIG. 4. In FIG. 5, reference numeral 51 denotes a waveform of an input signal at point A in FIG. 4, and reference numeral 52 denotes a level value at point B in FIG. The waveform 53 indicates a change in the gain of the variable gain amplifier 43.
Numeral 54 indicates the waveform of the output signal at point C.

[0005] The operation of the automatic gain control device configured as described above will be described with reference to Figs.

First, an input signal 51 shown in FIG. 5 is input to an input terminal 42 shown in FIG. In this input signal 51, the section T
Three sections 0 to T1, T2 to T3, and T4 to T5 are non-speech sections in which only noise is collected, and the sections do not include a speech signal.

[0007] Two sections T1 to T2 and T3 to T4 are speech sections. Here, the sound of T1 and T2 is called sound A, and the sound of T3 and T4 is called sound B.

In the example of the input signal 51, the audio level A is higher than the audio level B. The input signal 51 is smoothed and rectified by the input level detection unit 42 in FIG. 4 to become the level value 52 in FIG.

At this time, in the input level detecting section 42, the rising time constant of the detection level is set smaller than the falling time constant, and the maximum value is traced.
Therefore, the level value 52 in FIG. 5 is a waveform tracing the maximum value, and the maximum value of the noise signal level is traced in the sections T0 to T1.

When voice A is input at time T1, the detection level rises sharply. Thereafter, the local maximum value of the audio signal of the audio B is traced until time T2. After the time T2 at which the sound is lost, the value gradually decreases in accordance with the falling time constant set by the input level detection unit 42, and the maximum value of the noise signal level is traced again.

When the sound B is inputted at time T3, the level value 52 detected by the input level detecting section 42 sharply rises again, and until the time T4, the maximum value of the sound signal level of the sound B is reached. Trace.

The control gain 53 of the variable gain amplifier 43 is controlled by the detection level 52.

When the detection level 52 does not exceed a preset threshold value, the control gain becomes the maximum gain that has been set. The control gain 53 is controlled to be smaller as the detection level 52 is lower, and the control gain 53 is controlled to be higher as the detection level 52 is lower.

As a result, the output signal 54 output from the output terminal 44 to the outside is adjusted so that both the sound A and the sound B have substantially the same signal level.

[0015]

However, in the above configuration, a constant time constant is always used as the rising time constant of the detection level.

For example, the techniques disclosed in JP-A-63-260209 and JP-A-63-260210 make the rising time constant of the detection level constant. For this reason, the following problems occurred when setting the rising time constant and the falling time constant of the input level detection unit 42.

First, when both the rising time constant and the falling time constant are set to small values, the input level detecting section 42 does not operate to trace the maximum value of the input signal.

That is, a waveform 5 obtained by smoothing and rectifying an audio signal
The gain does not change in accordance with the change of the level 2 but the change in the amplitude of the AC signal constituting the audio signal itself, that is, the input signal waveform 51 causes the gain to change in accordance with the cycle of the AC signal. However, there is a problem that the output waveform is distorted.

The falling time constant is set large enough to follow the level change when the audio signal is smoothed and rectified, and only the rising time constant is set small enough to completely follow the rising edge of the audio signal. in case of,
The control gain is smaller than the gain to be given to the actual audio signal level.

In addition, when a large level pulsed noise is input to the apparatus and then immediately after a small level speech signal is input, the gain is controlled to be small by the large level pulsed noise. Will be
Subsequent audio signals will not be given enough gain to be given.

If the rising time constant is not set small enough to completely follow the rising edge of the audio signal, the control gain 53 of the variable gain amplifier 43 cannot completely follow the rising edge of the audio signal. .

For this reason, in the rising portion of the audio signal, a large gain is added to the input signal during the time when the gain cannot be completely reduced to the value of the gain to be given to the signal yet. There has been a problem that an excessively high level signal is output and the rising portion of the audio signal is excessively emphasized.

As described above, in the prior art, even if the falling time constant of the gain is made small enough to completely or sufficiently follow the rising of the audio signal, the above problem still occurs. Was.

According to the present invention, in consideration of the above problems, the detection of the input signal level completely follows the steep rise of the input signal, and further, the gain is rapidly reduced accordingly, whereby the steepness of the input signal is reduced. An object of the present invention is to provide an automatic gain device that prevents an excessive level of output at a rising portion, and prevents a gain from becoming unnecessarily small even when a very large level of pulse noise is input simultaneously with voice.

Further, the present invention prevents the speech detector from judging that a noise input which is always generated, which is different from the speech signal, is a sound, and a stable operation can be performed even when noise is always inputted. It is intended to be obtained.

Further, the present invention is also applicable to a case where a very large pulse noise is suddenly input in a rising portion of a voice while the rising time constant is still small, and the gain is suppressed to an unnecessarily small level by the noise. This solves the problem of being done.

[0027]

In order to solve the above problems, an automatic gain control device according to the present invention comprises: an input terminal for an audio signal; an input level detection unit for detecting the level of the input signal;
An automatic gain control device including a variable gain amplifier that adjusts a gain according to a level detected by the input level detector and an output terminal of an amplified signal from the variable gain amplifier,
A time measuring unit for measuring a time when an input level detected by the input level detecting unit exceeds an input threshold at a rising edge of the input audio signal, and detecting the elapse of a predetermined reference time by the time measuring unit A reference time detection unit, and when the reference time detection unit detects the elapse of the reference time, the rising time constant of the input level detection unit is increased, and the level detected by the input level detection unit falls below the input threshold. And a time constant control unit for reducing the rising time constant of the input level detection unit.

Further, the automatic gain control device according to the present invention has an input terminal for an audio signal, an input level detecting section for detecting the level of the input signal, and a variable for adjusting the gain according to the level detected by the input level detecting section. An automatic gain control device having a gain amplifying unit and an output terminal for an amplified signal from the variable gain amplifying unit, wherein the noise level detecting unit detects an input noise level and the noise detected by the noise level detecting unit. An audio signal detection unit that detects that an audio signal of a level greater than the level has been input; a time measurement unit that measures time from when the audio signal detection unit detects the audio signal; A reference time detecting section for detecting the passage of a predetermined reference time, and when the reference time detecting section detects the passage of the reference time, the rising time constant of the input level detecting section is increased, and Detection unit when it detects an input of only silence or noise, characterized in that a constant control unit when the small rise time constant of the input level detector.

Further, the automatic gain control device according to the present invention
Faster than the detection of the elapse of the reference time by the reference time detector,
A limit value detection unit that detects that the input level detected by the input level detection unit exceeds a certain limit value, and a case where the limit value detection unit detects an input level exceeding a control value before a reference time has elapsed. And a time constant control section for increasing the rising time constant of the input level detection section.

[0030]

When no audio signal is input, or when the input audio signal is lower than the input threshold, the rising time constant control unit sets the rising time constant of the input level detection unit to the input audio signal. Set small enough to follow the rise.

The fall time constant is set to be large enough to always follow the fall of the envelope of the audio signal.

Next, in this state, when an audio signal is input and the level detected by the input level detecting section exceeds the input threshold, the time measuring section starts measuring time from that point. Further, when the time during which the detection level exceeds the threshold value elapses and the reference time detection unit detects the elapse of the reference time, the rise time constant control unit changes the rise time constant to a large value, and the detection level is input. The rising time constant is maintained until the value falls below the threshold, and when the detection level falls below the input threshold, the rising time constant control unit changes the rising time constant to a small value.

By this operation, since the control of the gain completely follows the steep rising of the voice, it is possible to prevent the output of an excessively high level signal.

If a large level of pulse noise is input while the audio signal is input at a level higher than the input threshold, the level of the pulse noise is
Since the input level detecting section rises with a large time constant, the gain applied to the audio signal does not decrease more than necessary, so that an appropriate gain is added.

Further, the rising time constant control section includes
Alternatively, when the input signal does not exceed the noise level detected by the noise level detecting section, the rising time constant of the input level detecting section is set small enough to follow the rising of the voice when the voice signal is input.

The fall time constant is set to a value large enough to always follow the fall of the envelope of the audio signal.

In this state, an audio signal is input,
When the sound detection unit detects that a sound signal larger than the noise level has been input, the time measurement unit starts measuring time after sound detection. Further, when it is detected that the reference time has elapsed after the time when the sound is detected to be detected, the rising time constant control unit sets the rising time constant to:
Change to a larger value.

The rising time constant is maintained while sound is detected, that is, until the next time silence is detected. However, when silence is detected, the rising time constant controller controls the rising time constant. To a smaller value.

By these operations, even if noise which is constantly generated and is different from the voice signal is input, the detection threshold of voice detection can be controlled to an appropriate value, and a loud noise exceeding the input threshold is generated. Even in the case of being input, the output of an excessively high level signal can be prevented by completely following the rising edge of the higher level audio signal. Furthermore, even when a large level of pulse noise is input while the audio signal is input at a level higher than the input threshold, the level of the pulse noise does not drop below the input level, and Appropriate gain is added.

In addition, while the rise time constant of the level detection unit is set to a small value until the detection of the elapse of the reference time, a signal of a large level exceeding a certain limit value is generated during that time. When input, the rise time constant is changed to a large value.

Accordingly, even when a large-level pulse noise that rises steeply is input, the gain is prevented from becoming unnecessarily small, and even if a small-level audio signal is input immediately after this noise. , The appropriate gain can be added to the signal.

[0042]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of an automatic gain control device according to the present invention will be described below with reference to the accompanying drawings.

FIG. 1 shows a block diagram of a first embodiment of the automatic gain control device according to the present invention. In FIG. 1, reference numeral 11 denotes an input terminal of an audio signal, 12 denotes an input level detecting unit for detecting the level of the input signal, 13 denotes a variable gain amplifying unit controlled by the input level detected by the input level detecting unit 12, and 14 denotes It is a time measuring unit that measures the time from when the input level exceeds the input threshold.

Further, reference numeral 15 denotes a reference time detecting section for detecting that the time measured by the time measuring section 14 has passed a predetermined reference time, and reference numeral 16 denotes a rising time for controlling a rising time constant of the input level detector 12. A constant control unit 17 is an audio signal output terminal.

When an audio signal is input from the input terminal 11, the input level detector 12 detects the level of the input signal. In this level detection, when the input level does not exceed a predetermined threshold, the rise time constant control section 16 sets the rise time constant to a value as small as possible.

During this time, since the input level does not exceed the threshold value, the variable gain amplifying section 13 adds the maximum gain to the input signal and outputs it from the output terminal 17.

In this state, when an audio signal having a level exceeding the threshold is input, the input level detecting section 12 can immediately detect the level with the small time constant.

According to the detection level, the variable gain amplifying unit 13 controls the gain to be small. At the same time, the time measuring unit 14 starts measuring time from this point. Further, when the state where the level of the input signal is larger than the threshold continues and the reference time detecting section 15 detects that the time measured by the time measuring section 14 has passed a predetermined reference time, the state is received. Rise time constant controller 16
Changes the rising time constant of level detection from a few milliseconds to a relatively large value of about several tens of milliseconds.

Thereafter, when the input level detected by the input level detection section 12 falls below the threshold, the rise time constant control section 16 returns the rise time constant to the original small value.

According to the above operation, in the portion where the gain must be controlled small at the rise of the audio signal,
Since the rising time constant of the level detection unit 12 is controlled to a small value, the gain control can completely follow the rising of the input signal, and the output of a signal having an excessive level can be prevented. After that, since the rising time constant is set to a large value, even if a very large level of pulsed noise or the like is input, the gain given to the voice is not immediately controlled to be small, so that the output signal is not controlled. Can be prevented from dropping sharply.

FIG. 2 shows a block configuration of a second embodiment of the automatic gain control device according to the present invention.

In the figure, reference numeral 21 denotes an input terminal of an audio signal;
Denotes an input level detector for detecting the level of an input signal;
Is a variable gain amplifier that is controlled by the input level detected by the input level detector, 24 is a noise level detector that detects the level of the input noise signal, and 25 is a noise level detector that detects the noise level detected by the noise level detector 24. Is a voice detection unit that determines that voice has been input when a large signal is input.

Further, reference numeral 26 denotes a time measuring unit for measuring the time from when the voice detecting unit 25 starts detecting the voice, and 27 denotes that the time measured by the time measuring unit 26 has passed a predetermined time. A reference time detecting section 28 is a rising time constant control section for controlling a rising time constant of the input level detecting section 22, and 29 is an audio signal output terminal.

When an audio signal is input from the input terminal 21, the input level detector 22 detects the level of the input signal. In this level detection, if the input level does not exceed a predetermined threshold, the variable gain amplifying section 23 adds the maximum gain to the input signal and outputs it from the output terminal 27.

Initially, when the input signal is silent, or when a substantially constant level of noise is continuously input, the noise level detecting section 24 detects a noise level other than the voice.

In the state in which the silence or only the noise is input, the rise time constant control section 28 sets the rise time constant of the input level detection section 22 to a value as small as possible.

In this state, if an audio signal exceeding the noise level is input, this audio is detected by the audio detection unit 25. However, since the rising time constant of the input level detection unit 22 is sufficiently small, the input level is low. The detection unit 22 can immediately detect the level.

In accordance with this detection level, the variable gain amplifying section 23 controls the gain to be small. At the same time, the time measuring section 26 starts measuring the time from this point.

Further, a signal of a level determined as a sound by the voice detecting section 25 is continuously input, and it is determined that the time measured by the time measuring section 26 has passed a predetermined reference time. Is detected, the rise time constant control unit 28 changes the rise time constant of the level detection from a relatively large value of several milliseconds to several tens of milliseconds.

Thereafter, when the input level detected by the input level detecting section 22 falls to the same level as the noise level detected by the noise level detecting section 24, the rising time constant control section 28 reduces the rising time constant to the original small value. Return to value.

By these operations, in a portion where the gain must be controlled to be small at the rising edge of the audio signal, the rising time constant of the level detector 22 is controlled to a small value. Can be completely followed.

Therefore, it is possible to prevent the output of an excessively high level signal, and since the rising time constant is set to a large value thereafter, an input of a very large level of pulse noise or the like may occur. Even if there is, the gain given to the voice is not immediately controlled to be small. As a result, it is possible to prevent the level of the output signal from dropping sharply.

In the second embodiment, even when noise having a level exceeding the threshold value is continuously input, the rise time constant is controlled by the presence or absence of an audio signal by detecting the noise level. be able to.

FIG. 3 shows a block diagram of a second embodiment of the automatic gain control device according to the present invention.

In the figure, reference numeral 31 denotes an audio signal input terminal;
2 is an input level detector for detecting the level of the input signal, 3
Reference numeral 3 denotes a variable gain amplifying unit controlled by the input level detected by the input level detecting unit, and reference numeral 34 denotes a time measuring unit for measuring a time from when the input level exceeds the input threshold.

Further, reference numeral 35 denotes a reference time detecting section for detecting that the time measured by the time measuring section has passed a predetermined reference time, and 36 denotes a rising time for controlling a rising time constant of the input level detector. A constant control unit, 37 is a limit value detection unit, and 38 is an audio signal output terminal.

When an audio signal is input from the input terminal 31, the input level detector 32 detects the level of the input signal. In this level detection, when the input level does not exceed a predetermined threshold, the rise time constant control unit 36 sets the rise time constant to a value as small as possible.

During this time, since the input level does not exceed the threshold, the variable gain amplifying section 33 adds the maximum gain to the input signal and outputs it from the output terminal 38.

In this state, when an audio signal having a level exceeding the threshold is input, the input level detection unit 32
Can detect its level immediately. The variable gain amplifying unit 33 controls the gain to be small according to the detection level, but at the same time, the time measuring unit 34 starts measuring the time from this point. Further, when the level of the input signal continues to exceed the threshold value and the reference time detection unit 35 detects that the time measured by the time measurement unit 34 has exceeded a predetermined reference time, the rising time constant control unit 36 Changes the rising time constant of level detection from a few milliseconds to a relatively large value of about several tens of milliseconds.

When the reference time has not elapsed,
When a large signal exceeding the threshold value and exceeding a predetermined control value is input, the time constant is changed to a large value.

When automatic gain control is performed by digital signal processing, the time constant is changed to a large value before the input level detected by the input level detection unit 32 becomes large due to a large-level signal exceeding the limit value. It is easily possible.

Thereafter, when the input level detected by the input level detection section 32 falls below the threshold, the rise time constant control section 36 returns the rise time constant to the original small value.

By these operations, in the part where the gain must be controlled small at the rise of the audio signal,
Since the rising time constant of the level detection unit 32 is controlled to a small value, the gain control can completely follow the rising of the input signal, so that the output of an excessively high level signal can be prevented.

After that, since the rising time constant is controlled to a large value, even if a very large level of pulse noise is input, the gain given to the voice is not immediately controlled to be small. Therefore, it is possible to prevent the level of the output signal from dropping sharply, and when a steeply rising signal such as a large level of pulse noise is input while the time constant is controlled to a small value. In addition, it is possible to suppress the gain from unnecessarily lowering.

[0075]

According to the automatic gain control device of the present invention, when a signal not exceeding the input threshold value is input, the time constant control section controls the rising time constant of the input level detection section to a small value, and the signal exceeding the input threshold value. At the time of input, the rising time constant of the input level detection unit is updated to a large value, so that an excessively high level signal is not output at the rising portion at the beginning of the input audio signal, and pulse noise is simultaneously output with the audio signal. Is input, it is possible to prevent the gain from being controlled unnecessarily small.

Further, even when a large level of noise is continuously input, it is possible to prevent an excessively high level signal from being output at the rising portion of the input voice signal louder than the noise, and to further reduce the rising time constant. Is controlled to a small value, even if a large level of pulse noise is input,
It is intended to suppress the gain from becoming smaller than necessary and to maintain an appropriate gain.

[Brief description of the drawings]

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

FIG. 2 is a block diagram of a second embodiment of the automatic gain control device according to the present invention;

FIG. 3 is a block diagram showing a third embodiment of the automatic gain control device according to the present invention;

FIG. 4 is a block diagram of a conventional automatic gain control device.

FIG. 5 is an explanatory diagram of a signal waveform of each part of the automatic gain control device of FIG. 4;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 11 Input terminal 12 Input level detection part 13 Variable gain amplification part 14 Time measurement part 15 Reference time detection part 16 Rise time constant control part 17 Output terminal

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H03G 3/20-3/34

Claims (3)

(57) [Claims] 1. An input terminal for an audio signal, an input level detector for detecting a level of an input signal, a variable gain amplifier for adjusting a gain according to the level detected by the input level detector, and a variable gain amplifier. an automatic gain control device and an output terminal of the amplified signal from the input audio signal
At the rise of, a time measuring unit that measures the time when the input level detected by the input level detecting unit exceeds the input threshold, a reference time detecting unit that detects the passage of a predetermined reference time in the time measurement, When the reference time detecting section detects the passage of the reference time, the rising time constant of the input level detecting section is made large, and when the level detected by the input level detecting section falls below the input threshold, the input level becomes low. An automatic gain control device comprising: a time constant control unit that reduces a rising time constant of a detection unit. 2. An input terminal for an audio signal, an input level detector for detecting a level of the input signal, a variable gain amplifier for adjusting a gain according to the level detected by the input level detector, and the variable gain amplifier. An automatic gain control device having an output terminal for an amplified signal from the apparatus, comprising: a noise level detection unit for detecting an input noise level; and an audio signal having a level higher than the noise level detected by the noise level detection unit. An audio signal detection unit that detects that an input has been made, a time measurement unit that measures time since the audio signal detection unit detected the audio signal, and detects the passage of a predetermined reference time in the time measurement When the reference time detection unit detects that the reference time has elapsed, the rising time constant of the input level detection unit is set to be large, and the audio signal detection unit receives an input of silence or only noise. Automatic gain control device when issued is characterized in that a constant control unit when the small rise time constant of the input level detector. 3. The automatic gain control device according to claim 1, wherein the input level detected by the input level detection unit is earlier than the detection of the passage of the reference time by the reference time detection unit. A limit value detecting section for detecting that a certain limit value has been exceeded, and a rising time constant of the input level detecting section when the limit value detecting section detects an input level exceeding a control value before a reference time has elapsed. An automatic gain control device, comprising: