JPH01175494A - Howling suppressing device - Google Patents

Abstract

PURPOSE:To suppress howling by providing plural gain controllers to control the gain of the variable gain amplifier of a corresponding band with a corresponding BPF output signal as an input signal. CONSTITUTION:When an input signal xi to generate the howling is supplied to a delta modulating circuit 6a of a gain controller 6i, the amplitude of a difference signal di between the input signal xi and a local decoding signal xi is enlarged. For the difference signal di, an absolute value ¦di¦ is operated by an absolute circuit 6b, compared with a reference signal with a comparing circuit 6c, at the time of ¦di¦<rho, it is judged to be the howling condition and a control signal gi to reduce the gain of a second variable gain amplifier 6i is outputted to a gain controller 4i. Thus, by controlling successively the gain of a second variable gain amplifier 4i with a control signal gi of the gain controller 6i, the howling can be suppressed.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a howling suppression device capable of suppressing howling in a public address system composed of a microphone, an amplifier, and a speaker.

BACKGROUND OF THE INVENTION FIG. 5 shows the configuration of a conventional howling suppression device.

In FIG. 5, before supplying an audio signal to the microbon (hereinafter referred to as microphone) 0 that constitutes the loudspeaker system, a switch 15 is opened to generate white noise from a white noise generator 14 into the loudspeaker system. via adder 1.5a. In order to increase the gain of the amplifier 11 without causing howling, four variable gain amplifiers 131 to 131 in each band are used so that the frequency characteristics of the loudspeaker system are flat.
Adjust the gain of 13n and open switch] 5;
.

After adjusting the gains of the variable gain amplifiers 131 to 13n in this way, the audio signal from the microphone 10 is amplified to the maximum gain by the amplifier 11 and passed through a bandpass filter (hereinafter referred to as BP).
It's called F. ) 121 to ] 2n. And B
The audio signals in each band with P
The signal is output from the speaker 16 with the crackling suppressed.

Problems to be Solved by the Invention However, in the conventional howling suppression device described above, the gain of each band must be set in advance using the white noise generator 14, and the microphone 10. Speaker 1
There was a problem in that the gain had to be reset each time depending on the setting position (setting state) of 6.

The present invention solves such conventional problems, and aims to provide an excellent hackling suppression device whose gain can be successively controlled.

Means for Solving the Problems In order to achieve the above object, the present invention provides a corresponding BPF.
A delta modulation circuit that uses the output signal as a human input signal, an absolute (comparison that compares the output signal of the direct circuit and absolute value circuit with a reference signal and outputs one control word) that calculates the absolute value of the output signal of the delta modulation circuit. The gain controller includes a plurality of gain controllers configured with a circuit, and a plurality of variable gain amplifiers that amplify the output signal of the corresponding BPF based on the control signal of the corresponding gain controller.

Therefore, according to the present invention (C), the gains of a plurality of corresponding variable gain amplifiers can be successively controlled by control signals output from a plurality of gain controllers.

Example FIG. 1 shows the configuration of an embodiment of the present invention.

In FIG. 1, 1 is a microphone, 2 is a first variable gain amplifier as an amplifier for amplifying the audio signal supplied from the microphone 1, and 31 to 3n are each frequency of the audio signal from the first variable gain amplifier 12. BPF passing through band branch, 41~4n
are gain controllers, and the output signals of BPF3+ to 3n are input signals and the control signals g+-gH
This outputs the following.

5, -7 41 to 411 are second variable gain amplifiers as variable gain amplifiers, and correspond to the output signals of the corresponding B P F 31 to 3n. The amplification is performed based on the control signals g1 to gn of the four controllers 61 to 6n.

51-- are adders that add the output signals of the variable gain amplifiers 41-4n, and 7 is a speaker.

FIG. 2 shows each interest rate controller 6 i (i=1.2 to 1).
), and FIG. 3 1'... shows a block diagram of the configuration of the delta modulation circuit.

The second factor, in FIG. 3, 6a is a delta modulation circuit, and the difference signal d obtained by subtracting the local decoded signal If the difference signal d1 is positive, the quantization circuit 14 adds a constant value △ to the previous decoded value, and if it is negative, subtracts the constant value △ from the previous decoded value.
2. Multiplier 143. Adder 144 and delay circuit] 45
acts.

6b is an absolute value circuit that calculates the absolute value 1 di l of the difference signal d1 output by the delta modulation circuit 6a, and 6C is a control signal gi that compares the absolute value 1 di l of the absolute value circuit 6b with the basic school signal ρ. This is a comparison circuit that outputs .

FIGS. 4(a) to (C) are timing charts of each signal of the controller. FIG. 4(a) shows the input signal X1 and the local decoded signal X1, and FIG. The absolute value of the difference signal d1 [No. 3 1dil and the reference signal ρ] is shown in FIG. 4(c), which shows the control signal g1.

-Audio signals in boat fishing are transient and do not show stationarity, but in the frequency band where howling occurs, such signals with large amplitude periodicity persist and show stationarity. Delta modulation circuit 1 as a means of detecting
4a was adopted.

Next, the operation of the above embodiment will be explained.

In FIG. 1, the input signal X1 in which howling occurs
is supplied to the delta modulation circuit 6a of the gain controller 61, the difference signal d1 between the input signal X1 and the locally decoded signal
The amplitude becomes large as shown in FIG. 4(a). The absolute value 1 dil of this difference signal d1 is calculated in the absolute circuit 6b, and compared with the reference signal ρ in the comparator circuit 6c7\-7, and when ldi 1>ρ, it is halved as a howling state (the fourth Figure (+)))
, outputs a control signal g8 for decreasing the gain of the second variable gain amplifier 61 to the gain controller 41 (see FIG. 4(C)
)).

In this manner, according to the embodiment described above, the gain of the second variable gain amplifier 41 is sequentially controlled by the control signal g1 of the gain controller 61. tjjl? 111, Mike 1,
This has the effect that the gain of the frequency band that causes feedback, which is determined from the set position of the speaker 7, can be controlled, and howling can be suppressed.

Effects of the Invention As is clear from the above embodiments, the present invention provides a gain controller that controls the gain of the variable gain amplifier in the corresponding band by using the output signal of the corresponding BPF as an input signal. Therefore, the gain of the loudspeaker system can be controlled sequentially to suppress hacking.

[Brief explanation of the drawing]

FIG. 1 shows howling suppression in one embodiment of the present invention.
Figure 2 is a configuration block diagram of the gain controller, Figure 3 is a configuration block diagram of the delta modulation circuit, Figure 4 is a timing chart of each signal for gain control 2, Fig. 5 is a block diagram of a conventional howling suppression device.■...Microphone, 2.First variable gain amplifier, 3.
1-311...Band pass filter, 61-6n...Gain controller, 41-4n...Second variable gain amplifier, 51
~ Adder, 7/Speaker. Name of agent: Patent attorney Toshio Nakao Haga18 No. 1
Figure 2 Figure 3

Claims (1)

[Claims] an amplifier that amplifies an audio signal, a plurality of bandpass filters corresponding to each band to which the output signal of the amplifier is supplied, a delta modulation circuit that uses the output signal of the corresponding bandpass filter as an input signal, and this delta modulation circuit. a plurality of gain controllers each comprising an absolute value circuit that calculates the absolute value of the output signal of the circuit and a comparison circuit that compares the output signal of the absolute value circuit with a reference signal and outputs a control signal; and the corresponding band. A howling suppression device comprising a plurality of variable gain amplifiers that amplify output signals of pass filters based on control signals of the corresponding gain controllers, and an adder that adds the output signals of the plurality of variable gain amplifiers.