JPS62154824A - Howling preventing device - Google Patents

Abstract

PURPOSE:To prevent the generation of howling prior to the convergence of an echo canceller and to reduce the frequency transient level of a frequency control device after the convergence of the echo canceller to reduce the change of sound by changing the frequency transient quantity in accordance with the echo attenuation value of the echo canceller. CONSTITUTION:Power detectors 11, 12 detect the power of respective signals Sin, Sout and an echo cancelling variable calculator 13 calculates an echo cancelling variable on the basis of the outputs L(Sin), L(Sout) of the detectors 11, 12. The echo attenuation variable signal is applied to a frequency control device 4 to control the frequency transient quantity. When the frequency transient quantity in the echo cancelling quantity calculator 13 is DELTAf, the frequency control quantity is controlled so that the shown formula e.g. is satisfied. Since the echo cancelling variable of the echo canceller 3 is small before the convergence of the echo canceller 3 and the variable is increased at the convergence, the frequency transient quantity in the frequency control device 4 becomes high before the convergence of the echo canceller, and after the convergence, the quantity is reduced by controlling the quantity as shown in the formula.

Description

[Detailed Description of the Invention] [Summary] In a howling prevention device that uses both an echo canceller and a frequency control device, the echo canceller To prevent howling before the echo canceller converges, and to reduce changes in the sound after the echo canceller converges.

[Industrial application field]

The present invention relates to a howling prevention device, and more particularly to a howling prevention device that includes an echo canceller and a frequency control device.

Howling is a problem in, for example, audio conferencing devices. FIG. 5 shows the schematic configuration of the audio conference device,
Speakers 1-1 and 1-2 in remote conference rooms A and B, respectively.
By installing microphones 2-1 + 2-2,
A voice call can be made between conference room A and conference room B in a conference format. In this case, based on the acoustic coupling between the speakers and microphones in each conference room,
Howling occurs and interferes with communication, so it is necessary to prevent howling.

Devices for preventing howling include echo cancellers and frequency control devices, but both have their own unique advantages and disadvantages, and there is a demand for a howling prevention device that combines the advantages of both.

[Conventional technology]

Conventionally, both an echo canceller and a frequency control device have been used independently as devices to prevent howling based on acoustic coupling in the echo bus from the speaker to the microphone. Adaptive type FI R (Fi
nite Impulse Re5p.

nce) having a filter and a subtracter, the FIR filter creates a compensation signal identical to the echo component from the speaker input signal, and the subtracter subtracts this from the microphone output signal, thereby producing an echo-cancelled output. This is to obtain a signal, thereby preventing the occurrence of howling.

In addition, the frequency control device reduces the amount of echo signal feedback by changing the frequency of the microphone output, thereby preventing howling. Therefore, if the amount of frequency transition is increased, the amount of echo cancellation can be increased. Howling can be effectively prevented.

[Problem that the invention seeks to solve]

In the case of an echo canceller, it takes a relatively long time for the FIR filter to adaptively converge to its characteristics, so when the characteristics of the echo bus change due to the microphone being used, the echo can be canceled during the transition period. This creates a state in which the amount of erasure is small, and it is unavoidable that howling occurs.

Further, in the case of a frequency control device, if the amount of frequency transition is increased, the amount of echo cancellation can be increased, but on the other hand, there is a problem in that the characteristics of the sound change, causing discomfort to the listener.

[Means for solving problems]

The present invention aims to provide a howling prevention device that solves the problems of the prior art, and has a basic structure as shown in FIG.

Reference numeral 101 denotes an echo canceller, which includes an adaptive FIR filter, changes its characteristics according to the state of the echo bus to create a compensation signal, subtracts this from the input signal, and outputs a signal with echo canceled. .

Reference numeral 102 denotes a frequency control device that reduces the amount of feedback of the echo signal by changing the frequency of the input signal, thereby preventing howling.

103 is a control means, which is an echo canceller (101)
The frequency transition amount in the frequency control device (102) is controlled according to the echo attenuation amount.

[For production]

The amount of echo cancellation by the echo canceller is small before the echo canceller converges, but increases when it converges. Therefore, by controlling the amount of frequency transition of the frequency control device according to the amount of echo cancellation, the amount of echo cancellation can be reduced before the echo canceller converges. The amount of frequency transition in the frequency control device is large, and after convergence, the amount of frequency transition becomes small, preventing howling before the echo canceller converges, and the amount of frequency transition becomes small after the echo canceller converges. There will be fewer changes in the voice.

〔Example〕

Figure 2 shows a configuration in which an echo canceller and a frequency control device are installed to prevent howling in an audio conference device, etc., where 3 indicates the echo canceller and 4 indicates the frequency control device. . In this case, the echo signal on the input side of the echo canceller is Rin,
The output echo signal from the echo canceller to the speaker is R
out, input echo signal from the microphone to the echo canceller, Sin.

The output echo signal of the echo canceller is defined as 5out, and the power (level) of each signal is L (Ri
n) + L (Rout), L (Sin)
, L (Sout).

FIG. 3 shows an embodiment of the present invention, and 11 and 12 are input echo signals Sin of the echo canceller 3, respectively.

A power detector for the output echo signal 5out, and 13 an echo cancellation amount calculator.

In FIG. 3, power detectors 11 and 12 detect the power of signals Sin and 5out, respectively. Therefore, the respective outputs are L (Sin) and L (Sout). The echo cancellation amount calculator 13 calculates the echo cancellation amount based on the following relationship. In FIG. 3, this is defined as the echo attenuation amount.

Lecho=101og L (S in) / L
(Sout) (dB) The echo attenuation amount signal in the echo cancellation amount calculator 13 is given to the frequency control device 4 to control the frequency transition amount. That is, when the frequency transition amount in the echo cancellation amount calculator 13 is Δf, for example, ΔfOcL (Sout) /L (Sin)
Control is performed to satisfy the relationship (1).

In FIG. 3, the amount of echo cancellation by echo canceller 3 is small before the echo canceller converges, but
Therefore, by controlling as in equation (1), the amount of frequency transition in the frequency control device 4 is large before the echo canceller converges, and after convergence, the amount of frequency transition becomes small, and the echo Howling can be prevented before the canceller converges, and the amount of frequency transition can be reduced after the echo canceller converges to reduce changes in the voice.

FIG. 4 shows another embodiment of the present invention, in which 21 and 22 are output devices for the input echo signal Rin and the output echo signal 5out of the echo canceller 3, respectively, and 23 is an echo cancellation amount and echo return loss calculator. .

In FIG. 4, power detectors 21 and 22 detect the power of signals Rin and 5out, respectively. Therefore, the respective outputs are L (Rin) and L (Sout). The echo cancellation amount and echo return loss calculator calculates the echo cancellation amount+echo return loss using the following relationship. In FIG. 4, this is defined as the echo attenuation amount.

Lecho=101og L (Rin) /L <5
out ) (dB) The signals of the echo cancellation amount and the echo attenuation amount in the echo return loss 1m08823 are given to the frequency control device 4 to control the frequency transition amount.

That is, when the amount of echo cancellation and the amount of frequency transition in the echo return loss calculator 23 is Δf, for example, Δf OcL (Sout) / L (Rin)
Control is performed to satisfy the relationship (2).

In the case of the embodiment shown in FIG. 4, the amount of frequency transition of the frequency control device 4 before convergence of the echo canceller can be increased, and the amount of frequency transition after convergence can be decreased, so howling can be suppressed before convergence of the echo canceller. In addition to preventing this, it is possible to reduce the amount of frequency transition after the echo canceller converges, thereby reducing changes in the voice.

In the embodiments shown in FIGS. 3 and 4, instead of making the frequency transition amount Δf proportional to the echo cancellation amount as in equations (1) and (2), an appropriate darkness value is set for the echo cancellation amount,
The value of the frequency transition amount may be changed when this dark value is exceeded.

Note that frequency transition control in the frequency control device can be realized by any of the following methods.

(1) The output signal frequency is changed by amplitude modulating the input signal and changing its center frequency.

That is, the output signal frequency f' in this case changes with respect to the input signal frequency f according to the following equation.

f'=f +Δ f This method uses the same frequency transition Δ throughout the frequency spectrum.
f, and when the amount of frequency transition is small, the scale of the passing device can be small.

(2) A pitch controller or the above-mentioned proposed method causes a frequency transition at a constant ratio to the input signal frequency.

1 = (1+Δ)f This method is applicable when the distortion is small and the amount of frequency transition is large, but the scale of the device becomes large.

〔Effect of the invention〕

As explained above, in the howling prevention device of the present invention,
Since the amount of frequency transition of the frequency control device is changed according to the amount of echo attenuation of the echo canceller, the amount of frequency transition is increased before the echo canceller converges, and the amount of frequency transition is decreased after convergence. Therefore, it is possible to prevent howling before the echo canceller converges, and to reduce the amount of frequency transition after the echo canceller converges, thereby reducing changes in the voice.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the basic configuration of the present invention, FIG. 2 is a diagram explaining the installation of an echo canceller and a frequency control device, and FIGS. 3 and 4 are diagrams each showing an embodiment of the present invention. , FIG. 5 is a diagram showing the configuration of the audio conference device. 3.-Echo canceller, 4-Frequency control device, 11, 12.21.22--Power detector, 13-.
・Echo cancellation amount calculator, edict...-Echo cancellation amount and echo return loss calculator

Claims (1)

[Claims] Echo canceller using adaptive FIR filter (101
) and a frequency control device (102) that changes the frequency, the echo canceller (
frequency control device (101) according to the amount of echo cancellation of
Control means (103) for controlling the amount of frequency transition in 2)
) Howling prevention device.