JPH04131018U - Automatic gain control circuit for audio signals - Google Patents

Abstract

(57) [Summary] [Purpose] To automatically suppress the gain only when the level of the audio signal exceeds a preset level. [Structure] A level detection circuit 1 detects the level of an audio signal and inputs it to a differential amplifier circuit 3. A differential amplifier circuit compares a preset signal level with a reference voltage 2 corresponding to the preset signal level, outputs a control voltage when the signal level exceeds the set level, and controls the gain via a discrimination switching circuit 5 and an electronic volume 6. To automatically suppress the level of an audio signal within a dynamic range.

Description

[Detailed explanation of the idea]

0001

[Industrial application field]

This invention relates to gain control of audio signals, and the gain is suppressed for levels exceeding a set value. Concerning automatic gain control.

0002

[Conventional technology]

Techniques for limiting excessive signal levels that exceed the dynamic range of audio circuits include , a method of uniformly suppressing the entire signal level, and a method of suppressing excessive amplitude parts by placing a nonlinear amplifier. A limiting method or a method using a normal AGC circuit, etc., have been used. the whole While the uniform suppression method allows all signals to be amplified without distortion, it also suppresses medium and low levels. There is the problem that it is controlled and lacks impact. Non-linear amplifiers, e.g. diodes or logarithmic amplifiers Any amplitude limitation using a width filter or the like inevitably increases distortion. Normal AGC circuit In this method, the control response speed is slow due to the integral time constant of the gain control feedback loop. As a result, the gain control also affects the mid-level part and improves the naturalness of the sound as a whole. In addition, there are problems such as the need for a separate gain control element, which increases costs. Ta.

0003

[Problem that the idea aims to solve]

The present invention was developed in consideration of these points, and it improves the dynamic range of the audio circuit. Automatically via electronic volume control for volume control only for excessive signal levels The purpose of the present invention is to provide an automatic gain control circuit that suppresses the gain.

0004

[Means to solve the problem]

In order to solve the above-mentioned problems, the present invention is equipped with an electronic volume for adjusting the volume. In audio circuits, the level detection circuit that detects and outputs the audio signal level and the same level Compare the output of the level detection circuit with the reference voltage, and if it exceeds the reference voltage, the output will change depending on the level difference. A differential amplifier circuit that outputs a control voltage that is Discrimination switching circuit that selectively switches between the volume control voltage and output to the electronic volume. The differential amplifier circuit turns on the control voltage only when the audio signal level exceeds the set value. Audio signal that outputs pressure and automatically suppresses gain via electronic volume The present invention provides an automatic gain control circuit.

[0005]

[Effect]

With the above configuration, the automatic gain control circuit for audio signals according to the present invention can Output that detects the level of the voice signal and a reference voltage that corresponds to the preset signal level The gain is automatically suppressed only when the audio signal level exceeds the set level. control

[0006]

【Example】

Hereinafter, embodiments of the present invention will be described in detail based on the drawings. Figure 1 is based on this invention FIG. 2 is a block diagram of main parts of an automatic gain control circuit. In the figure, 1 is the level detection circuit. , detects and outputs the level of the audio input signal. 2 is the reference voltage and the preset audio This is a DC voltage that corresponds to the signal level. 3 is a differential amplifier circuit, which is connected to the level detection circuit. The output of the circuit is compared with a reference voltage, and if it exceeds the reference voltage, a control voltage is output. 4 is the volume Control voltage is a direct current voltage that is determined in response to volume adjustment operations. 5 is a discrimination switching circuit Then, the control voltage of the differential amplifier circuit and the volume control voltage are compared and determined, and one of them is selected. Outputs the control voltage of 6 is an electronic volume, which outputs audio from the discrimination switching circuit. Control signal level.

[0007] Next, the operation of the automatic gain control circuit for audio signals according to the present invention will be explained. Voice input The signal is detected and smoothed by the level detection circuit 1 using, for example, a diode and a capacitor. outputs a voltage approximately at the peak of the audio signal. During smooth integration to speed up control response Constants are set to the minimum required. Reference voltage 2 is the set level of the audio signal, that is, the gain Set the voltage to correspond to the threshold level of the audio signal at which suppression starts, and set the threshold. The threshold level provides a necessary margin for the upper limit of the dynamic range of the audio circuit. The differential amplifier circuit 3 operates only when the output voltage of the level detection circuit exceeds the reference voltage. A control voltage corresponding to the level difference is output. The value of its control voltage is the electronic volume is selected to obtain an attenuation amount corresponding to the level difference. Volume control voltage 4 is The volume adjustment method is a DC voltage that is determined in response to the volume adjustment up/down operation. It may be controlled by a microcomputer or by a potentiometer. The discrimination switching circuit 4 receives the control voltage and volume control voltage of the differential amplifier circuit. The discrimination switching circuit compares and discriminates the two types of control voltages and selects the one that provides a large amount of attenuation. Either one of the control voltages is output to the electronic volume 6. The electronic volume is powered by DC voltage. The attenuation amount changes depending on the pressure, for example, the attenuation amount is minimum at 4V, and the attenuation amount is minimum at 1V. works like maximum attenuation (minimum volume). In this case, the signal level is lower than the set level. Below, the output of the differential amplifier circuit is a constant value of 4V or more, and the volume control voltage is determined by the volume adjustment. is an arbitrary value between 4V and 1V, so the electronic volume can be controlled by the volume control voltage. be controlled. When the signal level exceeds the set level, the output of the differential amplifier circuit will be 4V or higher. The voltage corresponds to the required attenuation amount below, and when this value becomes less than the volume control voltage, the voltage The child volume is controlled by the control voltage of the differential amplifier circuit. In other words, the electronic volume The sound output level is controlled by the control voltage with the larger required attenuation, and the audio output level is dynamically controlled. Automatically suppressed within clean range.

[0008] FIG. 2 is a schematic diagram showing input/output characteristics of audio signals. The dotted lines at 11 and 12 are that The upper limit of the dynamic range of the amplifier circuit and the threshold level of gain suppression are show. 13 is the curve without automatic gain control, which exceeds the dynamic range. This indicates that the output for a given input level will be distorted and limited. 14 is the number Due to the characteristics of ordinary AGC circuits, there is a gain suppression effect even for medium level inputs. Show that. Curve 15 shows the input/output characteristics according to the present invention, and the threshold of dotted line 12 For inputs up to the current level, the original level will be output; This shows how the gain is suppressed.

[0009]

[Effect of the idea]

As explained above, the automatic gain control circuit for audio signals according to the present invention When the signal exceeds a preset level, the dynamic range of the audio circuit automatically It is dynamically suppressed and the occurrence of distortion is suppressed. On the other hand, signals below the set level are Since it is output at the same level, the naturalness of the sound as a whole is less affected. Ma In addition, the electronic volume control device can be used as a control element, making it inexpensive. can realize the purpose.

[Brief explanation of drawings]

FIG. 1 is a block diagram of essential parts of an embodiment of an automatic gain control circuit for audio signals according to the present invention.

FIG. 2 is a schematic diagram showing input/output characteristics of audio signals.

[Explanation of symbols]

1 Level detection circuit 2 Reference voltage 3 Differential amplifier circuit 4 Volume control voltage 5 Discrimination switching circuit 6 Electronic volume

Claims (1)

[Scope of utility model registration request] Claim 1: In an audio circuit including an electronic volume for volume adjustment, a level detection circuit detects and outputs an audio signal level, and the output of the same level detection circuit is compared with a reference voltage, and if the output exceeds the reference voltage, A differential amplifier circuit that outputs a control voltage corresponding to the level difference, and a discrimination switching circuit that selectively switches between the output of the differential amplifier circuit and a volume control voltage for volume adjustment and outputs it to an electronic volume. An automatic gain control circuit for audio signals, characterized in that the differential amplifier circuit outputs a control voltage only when the audio signal level exceeds a set value, and the gain is automatically suppressed via an electronic volume. .