JPH0715788A - Audio signal amplifier circuit - Google Patents

Abstract

PURPOSE:To form an audio signal amplifier circuit capable of improving sound quality by effectively eliminating howling. CONSTITUTION:While the howling occurs and a howling detection signal is being outputted from a howling detecting means 30, a howling elimination filter means (LPF) 28 is operated, and the howling can be eliminated. After that, when the howling detection signal ends, the operation of the howling elimination filter means 28 is stopped, and also, the loop coupling degree (gain) of the circuit can be decreased sequentially by a loop coupling degree adjusting means (automatic attenuator) 32. When no howling detection signal is outputted again at a certain coupling degree, the loop coupling degree is fixed at that level. Therefore, the howling can be automatically eliminated. and the loop coupling degree of the circuit can be adjusted where no howling occurs again.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an audio signal amplifier circuit, and more particularly to microphone howling.

[0002]

2. Description of the Related Art Generally, in a broadcasting studio, a recording studio, a music performance hall, etc., a microphone is used to increase the volume of a voice or to extract only a necessary voice. When using this microphone, an audio signal amplifier circuit as shown in FIG. 8 is required.

This conventional circuit includes a microphone 2, a head amplifier 4, a microphone amplifier 6, a power amplifier 8, a speaker 10, an LPF (low pass filter) 12, and a changeover switch 14. A microphone volume 16 is connected to the output of the head amplifier 4, and a master volume 18 is connected to the output of the microphone amplifier 6.

In this case, the entire circuit loop is in a positive feedback state due to the amplification of the circuit, the distance between the microphone 2 and the speaker 10, the reflected sound from the peripheral wall of the reproduced sound field, and the like.
There is a case where a kind of oscillation phenomenon (howling) occurs at a predetermined high frequency. In this case, the speaker 10 outputs an offensive high-pitched sound called "key". Once this howling occurs, it continues to output as it is without any measures.

One of the methods to prevent howling from being output,
Manually move the selector switch 14 to S ₁ to
There is a method of turning on 2 to remove only the high frequency component corresponding to the howling frequency from the audio signal. Once the LPF 12 is turned on, it is usually left as it is.

[0006]

However, the above-mentioned audio signal amplifier circuit has the following problems.

Microphone volume 16, master volume
When the howling is stopped by the method of lowering the volume of 18 or the like, there is a case where the LPF 12 is forgotten to be returned to the OFF state and is left in the ON state. In this case, the audio signal is always removed in the band of the LPF 12, and there is a problem that the high frequency characteristics of the microphone deteriorate.

An object of the present invention is to solve the above problems and improve sound quality while effectively removing howling.

[0009]

An audio signal amplifier circuit according to claim 1 is an audio signal amplifier circuit including an audio input means, an amplifier, a gain adjusting means, and an audio output means, wherein howling occurs in an audio signal. When detecting a howling detection means for outputting a howling detection signal that continues for a predetermined time,
It is provided in a predetermined portion of the circuit, operates while the howling detection signal is output, and stops the operation when the howling detection signal ends after a predetermined time elapses. A means for adjusting the coupling degree of the circuit loop, when the howling detection signal ends, the loop coupling degree is sequentially reduced, and when the howling detection signal is not output again when the operation of the howling removal filter means is stopped, A loop coupling degree adjusting means for fixing the loop coupling degree is provided.

[0010]

In the audio signal amplifying circuit according to the first aspect of the present invention, while howling occurs and the howling detection signal is output from the howling detection means, the howling removing filter means operates to remove the howling. After that, when the howling detection signal ends, the operation of the howling removal filter means is stopped, and the loop coupling degree adjusting means sequentially lowers the loop coupling degree of the circuit. Then, when the howling detection signal is not output again at a certain loop coupling degree, the loop coupling degree is fixed.

Therefore, it is possible to automatically remove howling and adjust the degree of circuit loop coupling so that howling does not occur again.

[0012]

1 shows the basic structure of an audio signal amplifier circuit 5 according to an embodiment of the present invention. This circuit 5 includes a voice input means 20 for inputting a voice signal and an amplifier for amplifying the voice signal.
22, a gain adjusting means 24 for adjusting the gain of the amplifier 22, and an audio output means 26 for outputting an audio signal. Further, a howling removal filter means 28 and a howling removal filter means are provided between the gain adjusting means 24 and the audio output means 26.
A howling detection means 30 and a loop coupling degree adjusting means 32 for adjusting the gain of the gain adjusting means to adjust the coupling degree (gain) of the circuit loop are also provided between the audio output means 26 and the audio output means 26.

When howling occurs in the audio signal, the howling detecting means 30 outputs a howling detection signal. While the howling detection signal is being output, the howling removing filter means 32 operates to remove howling. After that, when the howling detection signal ends, the operation of the howling removal filter means 28 is stopped, and the loop coupling degree adjusting means 32 sequentially lowers the loop coupling degree (gain) of the circuit 5. Then, when the howling detection signal is not output again at a certain gain, it is fixed to that gain.

FIG. 2 shows a block diagram of this circuit 5 in the case where each means of FIG. 1 is configured by concrete hardware. The circuit 5 includes a microphone 2 which is a voice input means, a head amplifier 4 which is an amplifier, a microphone amplifier 6 and a power amplifier 8, a speaker 10 which is a voice output means,
A microphone volume 16, a master volume 18, which is a gain adjusting means, an LPF (low-pass filter) 28 which is a howling removing filter means for removing high frequencies, a howling detecting circuit 30 which is a howling detecting means, and a loop coupling degree adjusting means. Automatic attenuator 32, changeover switch
Equipped with 70. Other microphones that process audio signals
A tone circuit 44, a microphone / echo circuit 46, and a mixer 48 for mixing a voice signal and a music signal are also provided. 3 and 4 are block diagrams of the howling detection circuit 30, and FIG. 5 is a time chart showing its operation. 2, in the normal howling does not occur, LPF 28 changeover switch 70 is connected to the terminal 70 ₁ is a OFF, the audio signal inputted to the microphone 2, a head amplifier 4, a microphone amplifier 6 Then, it is amplified and output from the speaker 10 via the microphone / tone circuit 44, the microphone / echo circuit 46, the mixer 48, and the power amplifier 8.

On the other hand, the audio signal is given to the howling detection circuit 30. In FIG. 3, the howling detection circuit 30 is
An amplifier 100, a rectification / integration circuit 102, comparators (voltage comparators) 104 and 108, and a differentiation circuit 106 are provided.

First, the audio signal is amplified by the amplifier 100, rectified and integrated by the rectifying / integrating circuit 102, and converted into a square wave by the comparator 104. Then, after being differentiated by the differentiating circuit 106, the comparator 10 having the threshold value Vth
Given to 8. When howling is not occurring, the audio signal does not exceed the threshold value Vth of the comparator 108, so that nothing is output from the comparator 104.

Here, it is assumed that the entire loop of the circuit 5 is in the positive feedback state and the howling P of the microphone 2 occurs (see FIGS. 5a and 6a). Once the howling P is generated, its amplitude is amplified one after another and continues to oscillate, so that the power amplifier 8 enters a saturation state and is a signal with a high frequency and a larger amplitude than a normal audio signal. Becomes

This howling P is a rectifying / integrating circuit 102.
Rectified and integrated by the comparator 104 and the comparator 104 in FIG.
It is output as a square wave as shown in. Then, it is differentiated by the differentiating circuit 106 and given to the comparator 108. As shown in FIG. 6B, if the threshold Vth of the comparator 108 is exceeded, a howling detection original signal HDG that rises with the occurrence of howling P and falls after a predetermined time (for example, about 1 second) is output ( Figure 5c). In this case, those exceeding the threshold value Vth are output regardless of the howling frequency. Then, in response to the howling detection original signal HD _G , the changeover switch 70 changes the terminal 7
0 connected ₂ to LPF28 is turned ON, the howling P is removed (Figure 6c).

In the audio signal amplifier circuit 5, while the howling is occurring and the howling detection original signal HD _G is being output, the corresponding LPF 28 is turned on and the howling is removed. About 1 second later, when the howling detection original signal HD _G ends, the LPF 28 is turned off, the howling detection signal HD is output to the automatic attenuator 32, the gain of the circuit 5 is adjusted, and the gain is sequentially decreased from the maximum. . Then, when howling does not occur again at a certain gain, it is fixed to that gain.

The howling detection signals HD _{1 to} HD _N are output from the howling detection circuit 30 of FIG. 4 based on the howling detection original signal HD _G. 2 automatic attenuator 32
Receives the howling detection signals HD _{1 to} HD _N and adjusts the loop coupling degree (gain) of the circuit 5. Automatic attenuator 32, an analog switch 72 (72 ₁ ~72 _N), and includes resistor (R ₂ ~R _N). Analog switch 72 _{1 to} 72 _N
Receives howling detection signals HD _{1 to} HD _N , only one of them is connected.

In this example, it is assumed that the howling does not stop by the gain adjustment in the first howling P1, but the howling stops by the gain adjustment in the second howling P2.

First, the first howling P1 occurs (FIG. 5a). Then, as described above, the LPF28
Receives the howling detection original signal HD _G (Fig. 5d),
It turns on (α in Fig. 5d) and removes howling P1,
After that, it is turned off (β in FIG. 5d). On the other hand, this signal HD _G is given to the reset FF 150 in the howling detection circuit 30 of FIG. The reset FF 150 outputs a signal γ in which “H” is maintained once howling occurs (FIG. 5e).

When howling is not occurring, the reset FF 150 is inverted by the inverter 154 and the howling detection signal HD ₁ is output (FIG. 5f). In other words, howling when not generated, it is connected to the analog switch 72 ₁ of the automatic attenuator 32 of Figure 2, and the gain of the circuit 5 to the maximum. Naturally, when howling is occurring, the analog switch 72 ₁
Is not connected.

Next, the howling detection original signal HD _G and the signal γ are given to the EXOR-1 152, and this output (FIG. 5g) is given to the reset FF 156. Therefore, the howling detection original signal HD _G ends (β in FIG. 5d), and the LPF 28 becomes OF.
At the time of F, the reset FF 156 outputs “H” (signal δ) (FIG. 5h).

Next, the howling detection original signal HD _G and the signal δ are given to the AND 158, and the output (FIG. 5i) is given to the reset FF 160.

The output ε (FIG. 5j) of the reset FF 160 and the signal γ are given to the EXOR-2 162. This output (Fig. 5k)
Is a howling detection signal HD ₂ to the automatic attenuator 32.
become. In response to this signal, the analog switches 72 ₂ O
The resistance R ₂ is connected to N and the gain of the circuit 5 is lowered by one rank (for example, 1 dB) to become GAIN1. At this time, as described above, the LPF 28 is in the OFF state,
If the howling P1 does not stop at this gain GAIN1, the second howling P2 occurs again.

That is, after the howling detection original signal HD _G by the howling P1 for the first time ends, when the LPF 28 is OFF, the gain is reduced to GAIN1 again and the gain becomes 2 again.
In the case where the howling P2 occurs for the second time, the reset FF 160 (reset FF 170 for the third time) outputs “H”, and the howling detection signal HD ₃ does not stop at the output of the howling detection signal HD _2. Will be output.

Next, as shown in FIG. 5m, the output of the AND 158 is inverted by the inverter 164 and reset FF166.
Given to. This output (Fig. 5n) is ANDed with the signal γ
168 and its output "L" (FIG. 5p) is provided to the reset FF 170. This output "L" ζ (Fig. 5q)
And the output ε of the reset FF 160 are given to the EXOR-3 172. The output becomes the howling detection signal HD ₃ to the automatic attenuator 32 (FIG. 5r). With this signal HD ₃ ,
Analog switch 70 ₃ is connected, the gain of the circuit 5 is lowered further one rank (for example, 2 dB) (GAIN
2). In this way, the circuit gain is reduced to GAIN2 upon receiving the howling detection signal HD ₃ , and the howling is stopped.

The output ζ of “L” is inverted by the inverter 174 and given to the reset FF 176. This output and the howling detection original signal HD _G are given to the AND 178, and its output “L” is given to the reset FF 180. Then, this output “L” and the output ζ of the reset FF 170 are given to the EXOR-4 182. Therefore, "L" is output from the EXOR-4 182 (Fig. 5s). Similarly, EXOR-5,
"L" is also output from 6, ... N.

In this way, the audio signal amplifier circuit 5 is provided so that howling does not occur again when the LPF 28 is OFF.
The gain of is fixed. As a result, the circuit gain is fixed to the maximum at which howling does not occur, and the LPF28
It is possible to prevent the deterioration of the frequency characteristic of the audio signal due to the passage of the.

In this embodiment, the automatic attenuator 32 using an analog switch and a resistor is used, but an automatic attenuator driven by a motor may be used. As shown in FIG. 7, the motor control signal in this case includes the howling detection signals HD _{1 to} HD _N as amplifiers 188 (G _{1 to} G _N ).
N) changes the voltage gain, that is, changes the output voltage of the amplifier 188 and uses the output from the mixer 190.

In this embodiment, howling is detected based on the output of the microphone amplifier 6, but any portion of the signal path, for example, any signal of the microphone 2, the head amplifier 4 or the power amplifier 8 is detected. Howling may be detected based on.

Further, in this embodiment, the howling elimination filter means 28 is provided between the gain adjusting means 24 and the audio output means 26, but any place in the signal path,
For example, it may be provided between the voice input means 20 and the amplifier 22.

[0034]

In the audio signal amplifier circuit according to the present invention, the howling removing filter means (LPF) operates to remove the howling while the howling occurs and the howling detection signal is output from the howling detecting means. . afterwards,
When the howling detection signal ends, the operation of the howling removal filter means is stopped and the loop coupling degree adjusting means (automatic attenuator) sequentially lowers the loop coupling degree (gain) of the circuit. Then, when the howling detection signal is not output again at a certain loop coupling degree, the loop coupling degree is fixed.

Therefore, howling can be automatically removed, and the degree of circuit loop coupling can be adjusted so that howling does not occur again. As a result, it is possible to provide an audio signal amplifier circuit that improves the sound quality while effectively removing howling.

[Brief description of drawings]

FIG. 1 is a diagram showing a basic configuration of an audio signal amplifier circuit according to an embodiment of the present invention.

FIG. 2 shows a block diagram of the audio signal amplifier circuit.

3 is a diagram showing a block diagram of a howling detection circuit 30. FIG.

FIG. 4 is a diagram showing a block diagram of a howling detection circuit 30.

5 is a time chart showing the operation of the howling detection circuit 30. FIG.

FIG. 6 is a diagram showing an example of howling.

FIG. 7 is a diagram showing a howling detection circuit according to another embodiment.

FIG. 8 is a diagram showing a conventional audio signal amplifier circuit.

[Explanation of Codes] 20 ... Voice Input Means (Microphone) 22 ... Amplifier 24 ... Gain Adjusting Means (Volume) 26 ... Voice Output Means (Speaker) 28 ... Howling Removal Filter Means (LPF) ) 30 ... Howling detection means 32 ... Loop coupling degree adjustment means (automatic attenuator)

Claims (1)

[Claims] 1. A voice input means, an amplifier, a gain adjusting means,
An audio signal amplifier circuit having an audio output means, which outputs a howling detection signal that continues for a predetermined time when a howling occurring in an audio signal is detected, and a howling detection means provided at a predetermined portion of the circuit. It operates while the signal is being output, and stops when the howling detection signal ends after a predetermined time has passed.Howling removal filter means and means for adjusting the gain of the gain adjusting means to adjust the coupling degree of the circuit loop. Then, when the howling detection signal ends, the loop coupling degree is sequentially decreased. When the howling detection signal is not output again when the operation of the howling removal filter means is stopped, the loop coupling degree adjusting means for fixing the loop coupling degree to the loop coupling degree is fixed. An audio signal amplification circuit comprising: