JPH077785A - Sound signal amplifier circuit - Google Patents

Abstract

PURPOSE:To improve sound quality while effectively removing howling. CONSTITUTION:A howling detection signal is received from a howling detection means 30, a howling removing filter means 28 is operated and the howling is removed. Thereafter, the gain of a test signal mixed in a sound by a mixing means 34 is lowered by a gain adjusting means 24 and when it becomes equal to or less than a threshold value, a howling stopping signal is outputted from a test signal reduction detection means 36. The howling stopping signal is received and the operation of the howling removing filter means 28 is stopped. Thus, the howling is automatically removed when the howling is generated in the sound signal, the operation of the howling removing filter means 28 is automatically prevented when the howling is stopped, the degradation of high band frequency characteristics is prevented and the sound quality can be improved.

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. 12 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. However, this method does not stop the howling itself, so once the LPF 12 is turned on, it is normally 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 voice signal is always removed in the band of the LPF 12, and there is a problem that the high frequency characteristics of the microphone 2 deteriorate.

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

[0009]

According to a first aspect of the present invention, there is provided an audio signal amplifier circuit comprising an audio input means, an amplifier, a gain adjusting means and an audio output means, the audio signal amplifying circuit being provided in the audio signal amplifier circuit. The howling removal filter means for removing the howling that occurs in the audio signal, which starts the operation upon receiving the howling detection signal, and the howling removal filter means for stopping the operation upon receiving the howling stop signal, the howling detection signal A test signal output means for receiving and outputting a test signal of a frequency outside the audible band and receiving a howling stop signal to stop the output of the test signal, provided in the audio signal amplifier circuit, and mixing the audio signal and the test signal Detection of howling in the mixing means and the audio signal amplifier circuit, and a howling elimination filter for the howling detection signal. If the value of the test signal after the howling detection means and the gain adjustment means output to the stage and the test signal output means changes below the threshold, the howling stop signal is output to the howling removal filter means and the test signal output means. It is characterized by including a decrease detecting means.

The audio signal amplifier circuit according to a second aspect of the present invention is the first aspect of the present invention.
In the audio signal amplifier circuit, the plurality of howling removal filter means are connected in series.

[0011]

In the audio signal amplifying circuit of the present invention, when howling occurs in the audio signal, the howling detection means outputs the howling detection signal. Upon receiving the howling detection signal, the howling removing filter means is operated to remove the howling, and the test signal output means outputs the test signal. After that, when the gain of the test signal mixed with the audio signal by the mixing unit is lowered by the gain adjusting unit and becomes less than or equal to the threshold value,
A howling stop signal is output from the test signal decrease detecting means. In response to the howling stop signal, the operation of the howling removal filter means is stopped and the output of the test signal from the test signal output means is stopped.

Therefore, when howling occurs in the audio signal, it is automatically removed, and when the howling is stopped, the howling removal filter means is not automatically operated to prevent the deterioration of the high frequency characteristic and to improve the sound quality. Can be improved.

In the audio signal amplifying circuit of claim 2,
Further, a plurality of howling removal filter means are connected in series. Therefore, even when a plurality of howlings occur at the same time, they can be removed by the howling removing filter means.

[0014]

1 shows the basic structure of an audio signal amplifier circuit 5 according to an embodiment of the present invention. The audio signal amplification circuit 5 is
The audio input means 20 for inputting the audio signal, the amplifier 22 for amplifying the audio signal, the gain adjusting means 24 for adjusting the gain of the amplifier 22 and the audio output means 26 for outputting the audio signal are provided. In the audio signal amplifier circuit 5, when howling occurs in the audio signal, the howling detection means 30 outputs a howling detection signal. Upon receiving the howling detection signal, the howling removing filter means 28 provided between the amplifier 22 and the gain adjusting means 24 is operated to remove the howling, and the test signal output means 32 outputs a test signal. . Thereafter, when the gain of the test signal mixed with the audio signal by the mixing means 34 provided between the audio input means 20 and the amplifier 22 is lowered by the gain adjusting means 24 and becomes less than the threshold value, the test signal decreases. A howling stop signal is output from the detection means 36. Upon receiving this howling stop signal, the operation of the howling removal filter means 28 is stopped and the output of the test signal from the test signal output means 32 is stopped.

FIG. 2 shows a block diagram of the audio signal amplifier circuit 5 more specifically showing each means of FIG. This audio signal amplification circuit 5 includes a microphone 2 which is an audio input means, a head amplifier 4 which is an amplifier, a microphone amplifier 6 and a power amplifier 8, a speaker 10 which is an audio output means, a microphone volume 16 which is a gain adjusting means, and a master volume. 18, BRF as howling removal filter means
(Band reject filter) 28 (28 _{1 in} this example)
To 28 _13), the howling detection circuit 30 (30 ₁ to 30 _13), OSC (oscillator) 32 is a test signal output circuit, a mixing means mixer 34, test signal reduction detection circuit 36, the changeover switch 70 (terminal s ₀ , S _{1 to} s ₁₃ ). Others, microphone tone, echo circuit 44, music signal output circuit
46, mixer 48, BPF (band pass filter) 5
2, LPF (low pass filter) 54 is also provided.

Since the terminal of the changeover switch 70 is normally connected to s ₀ , the audio signal input from the microphone 2 is amplified by the speaker 10 via the head amplifier 4, the microphone amplifier 6, and the power amplifier 8. Is output. In this example, the audio signal processed by the microphone / tone and echo circuit 44 and the music signal output by the music signal output circuit 46 are mixed by the mixer 48.

FIG. 3 shows a howling detection circuit 30. The howling detection circuit 30 includes each howling detection circuit (30 _{1 to} 3
0 ₁₃ ) for each BPF (band pass filter) 100
(100 _{1 to} 100 ₁₃ ), detection / integration circuit 102, amplifier 104, comparator (voltage comparator) 106, 110, 120, integration circuit 108,
The flip-flops 112, 124, 126, the differentiating circuit 114, the inverter 116, the mixer 118, the OR 128, 132, 134, and the AND 130 are provided. Further, FIG. 4 shows a time chart of the howling detection circuit 30. The operation of the howling detection circuit 30 will be described below with reference to FIGS.

In FIG. 3, the voice signal is first the BPF10.
It is given from 0 _{1 to} 100 ₁₃ . In FIG. 5A, BPF 100 _{1 to} 100 ₁₃
Shows a state with a pass band of 13 channels in the center frequency range of 364 Hz to 20.66 kHz. For example, when an audio signal is taken out from the BPF 100 ₈ center frequency 3.84 kHz, detected by the detection-integration circuit 102, after being integrated, given to the comparator 106 through the amplifier 104. When the howling does not occur, the audio signal does not exceed the threshold value Vth of the comparator 106, so that nothing is output from the comparator 106.

Here, the entire loop of the audio signal amplifier circuit 5 is in the positive feedback state, and the howling P of the microphone 2 is generated.
Is generated. Once the howling P is generated, its amplitude is amplified one after another and continues to oscillate. Therefore, the howling P is saturated in the power amplifier 8, has a high frequency, and has a larger amplitude than a normal audio signal. It becomes a signal of amplitude. An example of the generated howling P is shown in FIG. In this example, it is assumed that howling P ₈ having a center frequency of 3.84 kHz occurs (FIGS. 4a and 6a). This howling P8 is
The detection / integration circuit 102 outputs a waveform as shown in FIG. 4b. And, as shown in FIG. 6b, a comparator
If the threshold Vth of 106 is exceeded, the comparator 106 outputs the signal J which rises after a predetermined time (about 0.2 seconds in this example) from the occurrence of the howling P ₈ (FIG. 4).
c).

Next, this signal is further integrated by the integrating circuit 108 (FIG. 4d) and waveform-shaped by the comparator 110 to become the signal K which is further delayed (FIG. 4e). This signal K
Is applied to a toggle flip-flop (toggle FF) 112, and howling P ₈ is generated and a howling generation signal M which rises with a delay of a predetermined time (about 0.6 seconds in this example) is taken out (FIG. 4f). In this example, the howling generation signal M is also called a howling detection signal.

Next, the howling generation signal M is supplied to the differentiating circuit 11
Differentiate by 4. This differential output (FIG. 4g) and the signal obtained by inverting the differential output by the inverter 116 are mixer 118.
Is given to and mixed. This output (FIG. 4h) is given to the comparator 120. As a result, the howling detection original signal H becomes "H" 0.6 seconds after the occurrence of howling P ₈ and becomes "L" after a predetermined time (1.8 seconds in this example).
_D8G is output (Fig. 4i). That is, the howling detection original signal H _D8G is a signal that turns on the BRF 28 to remove the howling 0.6 seconds after the howling occurs, and turns off the BRF 28 after 1.8 seconds.

In this example, in consideration of the presence of sudden howling, the howling detection signal H _D8 is output only when the howling detection original signal H _D8G is continuously output twice as follows. I am trying.

The howling detection original signal H _D8G output from the comparator 120 is given to the toggle FF 124, and when its output (FIG. 4j) is further given to the toggle FF 126, its output (FIG. 4k) and howling detection original signal H. _D8G
Are given to the OR128, and this output becomes a howling detection signal H _{D8 in} which the howling detection original signal H _D8G is continuous twice (FIG. 4m). If howling does not stop even if the howling detection signal H _D8 is output,
BRF28 is turned on because it is judged not to be sudden feedback
The remaining howling is removed by leaving the state. It should be noted that a plurality of toggle FFs may be further connected to the toggle FF 126 and the howling detection original signal H _D8G may be continuously output many times. The howling detection original signal H _D8G may be used as it is as the howling detection signal H _D8 .

In FIG. 2, this howling detection signal H
_D8 is output to the changeover switch 70 of the BRF 28. By this output, s ₈ of the changeover switch 70 is connected and BRF 28 ₈
Turns on. FIG. 5B shows the rejection band frequencies of BRF 28 (28 _{1 to} 28 ₁₃ ). As shown in this Figure, BRF28 ₁ ~28
Each channel ₁₃ is set to the same channel as the BPF 100 ₁ to 100 ₁₃ in Figure 5A. Therefore, the BP shown in FIG. 5A
The howling P ₈ (201 in the figure) extracted from F100 ₈ is
It is removed by BRF28 ₈ (shown 202) shown in FIG. 5B (see FIG. 6c). Similarly, howling P picked from BPF 100 ₁ to 100 _13, the howling detection signal H _D1 to H _D13
By the outputs of BRF 28 _{1 to} 28 ₁₃ respectively.

On the other hand, when the BRF 28 is once turned on and the howling is removed, the voice signal is always removed in the band of the BRF 28, so that the band frequency characteristic is deteriorated. Here, for example, when the volume of the master volume 18 is lowered and the occurrence of howling itself is stopped, it is necessary to immediately turn off the BRF 28 to prevent the band from being removed to improve the sound quality.

Therefore, in the audio signal amplifying circuit 5, the audio signal is mixed with the test signal and output, and the stop of howling is detected by the test signal to detect BR.
I am trying to turn off F28.

In FIG. 2, when the OSC 32 receives the howling detection signal HD from the howling detection circuit 30, it oscillates an out-of-audible frequency (100 KHz in this example) as a test signal and outputs it to the mixer 34. The test signal may be any signal that can be distinguished from the audio signal, and may be 50 kHz, for example. The output value of the test signal is
The value of the howling saturation in the power amplifier 8 is made substantially the same.

The mixer 34 mixes the audio signal input from the microphone 2 with the test signal and outputs the mixed signal to the head amplifier 4. As a result, when howling occurs in the audio signal, the audio signal and the test signal are mixed and input to the audio signal amplifier circuit 5.

After that, when the volume of the master volume 18 is lowered, the generation of howling is stopped and the output of the test signal is also lowered. The decrease in the output value of the test signal is detected by the test signal decrease detection circuit 36. In this example, a BPF 52 (see FIG. 7) is provided between the microphone volume 16 and the microphone amplifier 6 to pass only signals in the audio signal band and the test signal band (100 KHz), and noise input is eliminated. ing.

FIG. 8 shows the test signal decrease detection circuit 36. The test signal decrease detection circuit 36 includes a 100 KHz BPF 62, a detection / integration circuit 64, and a comparator 66.

The voice signal and the test signal are 100 KHzB first.
Only the test signal of 100 KHz given to PF62 is taken out. Next, the test signal is given to the detection / integration circuit 64, detected and integrated, and the output value thereof is compared with the threshold value Vth of the comparator 66. And the master volume
When the volume of 18 is lowered and the output value of the test signal is lowered to be equal to or lower than the threshold value Vth, it is determined that howling has stopped and the howling stop signal H _S is output. In FIG. 2, when the howling stop signal H _S is output from the AND 130 to the BRF 28, the terminal of the changeover switch 70 is connected to s ₀ and the BRF 28 is turned off. As a result, the audio signal does not pass through the BRF 28, and its high frequency component is not removed. In addition, the howling stop signal H from OR134 via OR132
_{When S} is output to the OSC 32, the oscillation of the OSC 32 is stopped and the test signal is not output to the mixer 34.

Since the mixed test signal is applied to the LPF 54 which removes the high frequency component (100 KHz), only the audio signal is output from the speaker 10.

Here, when a plurality of howlings having different frequency bands occur at the same time, a plurality of BRFs 28 are connected by using a switch that connects a plurality of them at the same time, instead of the switch that is selectively selected like the changeover switch 70 of FIG. It is conceivable to simultaneously operate and remove howling.

For example, suppose that howling in the bands of the center frequency f ₇ and the center frequency f ₈ occurs at the same time. in this case,
As shown in FIG. 9a, BRF28 ₇ and BRF28 ₈ are simultaneously connected to the audio signal amplifier circuit by a plurality of changeover switches 72 connected at the same time. At this time, as shown in FIG. 9b, the BRF 28 ₇ operates to remove the band of the center frequency f ₇ (203), and as shown in FIG. 9c, the BRF 28 ₈ operates to remove the band of the center frequency f ₄ ( 204).

[0035] However, in practice, in BRF28 _7,
Howling in the band of the center frequency f ₇ is removed, but howling in the band of the center frequency f ₈ is passed, and BR
In F 28 _8, the bandwidth of the howling of the center frequency f ₈ is removed so that the feedback of the band of the center frequency f ₇ passes. After all, howling cut filter 50
Since the filter characteristic becomes flat, using only the switch 72 that connects a plurality of BRFs 28 at the same time does not eliminate howlings that are generated at the same time and have different frequency bands.

In such a case, the above problems can be solved by arranging the BRFs 28 in series and using an analog switch 74 for each BRF 28.

FIG. 10 shows an example of howling removal filter means 90 in an audio signal amplifier circuit according to an embodiment of the present invention. BRFs 28 _{1 to} 28 ₁₃ are arranged in series. In this case, the howling detection signal H _D, howling detection signal H _D1 to H in addition to the _D13, howling detection signal H _D1 to H _D13 howling detection signal is inverted by the inverter 180 ₁ ~180 ₁₃ HB _D1 ~HB _D13 Is used.

[0038] That is, when the howling occurs, howling detection signal H _D1 to H _D13 is output to the analog switch _{74 1 ~74 13, BRF28 1 ~28} 13 starts the band removal operation. On the other hand, when the howling does not occur, the howling detection signal HB _D1 ~HB _D13 is output to the analog switch _{74 1 ~74 13, BRF28 1 ~28} 13 stops the band removing operation.

[0039] In the above example, BRF28 ₇ receives the howling detection signal H _D7, starts band removal operation by the analog switch 74 _7, band by the analog switch 74 ₈ also receiving howling detection signal HD ₈ BRF28 ₈ Start the removal operation. The other BRF28, since howling in these bands does not occur, has stopped band elimination operation by receiving a howling detection signal HB _D. Figure 11
2 shows a state in which two howlings that occur simultaneously are removed. As shown in this figure, howling in the band of the center frequency f ₇ (205 in the figure) and howling in the band of the center frequency f ₈ (206 in the figure) are simultaneously removed.

Such howling removing filter means 90
Thus, even when a plurality of howlings having different frequency bands occur at the same time, the howling can be removed. Even in this case, the howling stop signal H
Upon receiving _S , the BRF 28 is turned off and the band elimination operation is stopped.

In this embodiment, howling is detected on the basis of the output of the master volume 18. However, any part of the signal path, for example, the microphone 2,
Howling may be detected based on the output of either the head amplifier 4 or the power amplifier 8.

Further, in this embodiment, the howling elimination filter means 28 is provided between the amplifier 22 and the gain adjusting means 24. However, at any place of the signal path, for example, the voice input means 20 and the amplifier 22. It may be provided between.

In this embodiment, the mixing means 34 is provided between the voice input means and the amplifier. However, the mixing means 34 is provided at any position before the gain adjusting means 24, for example, between the amplifier 22 and the gain adjusting means 24. May be provided.

[0044]

In the audio signal amplifier circuit according to the first aspect of the present invention, when howling occurs in the audio signal, the howling detection means outputs the howling detection signal. Upon receiving the howling detection signal, the howling removing filter means is operated to remove the howling, and the test signal output means outputs the test signal. Then, when the gain of the test signal mixed with the audio signal by the mixing unit is lowered by the gain adjusting unit and becomes equal to or less than the threshold value, the howling stop signal is output from the test signal decrease detecting unit. Upon receiving this howling stop signal, the operation of the howling removal filter means is stopped and the output of the test signal is stopped by the test signal output means.

Therefore, when howling occurs in the audio signal, it is automatically removed, and when the howling is stopped, the howling removal filter means is not automatically operated to prevent the deterioration of the high frequency characteristic and to improve the sound quality. Can be improved. As a result, it is possible to provide an audio signal amplifier circuit that improves the sound quality while effectively removing howling.

The audio signal amplifier circuit according to claim 2 further comprises:
A plurality of howling removal filter means are connected in series. Therefore, even when a plurality of howlings occur at the same time, they can be removed by the howling removing filter means. 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.

FIG. 3 is a diagram showing an example of howling.

FIG. 4 shows a block diagram of a howling detection circuit 30.

FIG. 5 is a diagram showing a pass band of the BPF 100 and a rejection band of the BRF 28.

6 is a diagram showing a time chart of a howling detection circuit 30. FIG.

FIG. 7 is a diagram showing a pass band of a BPF 52.

FIG. 8 is a diagram showing a test signal decrease detection circuit 36.

FIG. 9 is a diagram showing a state in which two howlings occur at the same time.

FIG. 10 shows an example of howling removal filter means 90 in an audio signal amplifier circuit according to an embodiment of the present invention.

FIG. 11 is a diagram showing a state in which two howlings that occur simultaneously are removed.

FIG. 12 is a diagram showing a conventional audio signal amplifier circuit.

[Explanation of symbols]

 20 ... Voice input means (microphone) 22 ... Amplifier 24 ... Gain adjustment means (volume) 26 ... Voice output means (speaker) 28 ... Howling removal filter means (BRF) 30 ... Howling detection means 32 ... Test signal output means (OSC) 34 ... Mixing means (mixer) 36 ... Test signal decrease detection means

Claims (2)

[Claims] 1. A voice input means, an amplifier, a gain adjusting means,
An audio signal amplification circuit equipped with an audio output means, which is a howling removal filter means provided in the audio signal amplification circuit for removing howling generated in an audio signal, and starts operation upon receiving a howling detection signal. Then, a howling elimination filter means for stopping the operation upon receipt of the howling stop signal, and a test signal for receiving the howling stop signal and outputting a test signal of an audible out-of-band frequency and stopping the output of the test signal upon receipt of the howling stop signal. Output means, mixing means provided in the audio signal amplification circuit for mixing the audio signal and the test signal, detecting occurrence of howling in the audio signal amplification circuit,
If the howling detection means for outputting the howling detection signal to the howling removal filter means and the test signal output means, and if the value of the test signal after the gain adjustment means changes below the threshold value, the howling stop signal is changed to the howling removal filter means and the test signal. An audio signal amplifier circuit, comprising: a test signal decrease detection means for outputting to an output means. 2. The audio signal amplifier circuit according to claim 1, wherein a plurality of howling removal filter means are connected in series.