JPS6365722A - Howling canceller - Google Patents

Abstract

PURPOSE:To converge and cancel howling quickly by using an automatic gain controller so as to uniformize a signal level of a microphone and a signal level inputted from a speaker to an adaptive filter. CONSTITUTION:A signal of the microphone 1 is inputted to a talking terminal equipment 2, connected to the speaker of the talking terminal equipment at the opposite side via a channel, the signal of the microphone of the opposite side is inputted to the talking terminal equipment 2 via a channel, the terminal equipment 2 is connected to the speaker 3 to loudspeak two-way talking. Then the automatic gain controller 6 is provided to uniformize the signal level of the microphone and the signal level inputted from the speaker to the adaptive filte. The difference in the spectrum due to the impulse response of a feedback path is adjusted by the adaptive filter 4.

Description

[Detailed Description of the Invention] Overview A howling canceller using an adaptive filter,
The feature is that an automatic gain controller is used to equalize the microphone signal level and the signal level input from the speaker to the adaptive filter. With this configuration, howling can be rapidly converged and canceled.

INDUSTRIAL APPLICATION FIELD The present invention relates to a howling canceller for realizing amplified telephone calls by equipping a communication terminal device with a microphone and a speaker.

In order to have a microphone and a speaker coexist on the same terminal, and to reproduce speech and musical instrument sounds collected by the microphone on the speaker of the other party's terminal for a two-way loudspeaker call, it is necessary to use two-wire and four-wire communication in the sound field or communication line. Since the feedback path in the converter forms a closed circuit, depending on the circuit conditions, oscillation (howling) may occur and stable playback may not be possible, so effective measures to prevent howling are required. There is.

The characteristics of the feedback from the loudspeaker to the microphone are determined by the impulse response of the room environment containing the loudspeaker and microphone. This impulse response affects the spectrum of the feedback signal. In this way, the feedback path between the speaker and microphone causes a howling effect that interferes with the main signal.

2. Description of the Related Art A conventional howling canceller is constructed as shown in the block diagram of FIG. In the figure, microphone 1 picks up voice or musical instrument sound (No. 3), which is input to call terminal 2, connected to the speaker of the other party's call terminal via a communication path, and is picked up by microphone 1. The voice and other signals received by the other party are amplified by the speaker, and the voice and other signals collected by the microphone of the other party's call terminal are input to the call terminal 2 via the communication path, and the call terminal 2 is connected to the speaker 3. The sound is amplified by the speaker 3.

When microphone 1 and speaker 3 are installed in the same room or the like to form a closed circuit including a sound field, signals such as audio from speaker 3 may be input to microphone 1 again and interfere with the main signal of microphone 1. This interference is called howling. In order to prevent howling, an adaptive filter 4 is provided on the output side of the microphone 1 and the input side of the speaker 3, and this adaptive filter 4 predicts the feedback path between the speaker 3 and the microphone 1 and prevents howling. It acts to remove the signal from the main signal. That is, the subtracter 5 compares the signal of the microphone 1 with the output signal of the adaptive filter 4, and the adaptive filter 4 adjusts the signals so that they match, thereby canceling howling.

Problems to be Solved by the Invention However, the conventional howling canceller configured as described above has a drawback in that it takes time to converge and cancel howling. This is due to the difference between the microphone signal level and the speaker signal level. That is, the environment between the speaker and the microphone attenuates the signal, and in addition, the coefficient of energy conversion from an electrical signal to an acoustic signal or from an acoustic signal to an electrical signal is 1.
This is because it is not.

The present invention has been made in view of these points, and an object of the present invention is to provide a howling canceller that can rapidly converge and cancel howling.

Means for Solving the Problems A block diagram of the principle of the present invention is shown in FIG. 1st
In the figure, a signal from microphone 1 is input to call terminal 2 and connected to the speaker of the other party's telephone terminal via a communication path, and a signal from the other party's microphone is input to telephone terminal 2 via the communication path. , the call terminal 2 is connected to a speaker 3, and two-way calls are amplified. 4
is an adaptive filter that equalizes the signal level of the microphone 1 and the signal level of the speaker 3 to remove howling, and the signal level of the microphone 1 and the input signal level of the speaker 3 are compared and subtracted in the subtracter 5. .

Reference numeral 6 denotes an automatic gain controller (AGO), which is connected between the output side of the microphone 1 and the multiplier 7 and functions to equalize the signal level of the microphone 1 and the input signal level of the adaptive filter 4.

Function As described above, in the present invention, the automatic gain controller 6
Since the adaptive filter 4 is configured to equalize the microphone signal level and the signal level input to the adaptive filter from the speaker, the adaptive filter 4 only needs to adjust the difference in spectrum due to the impulse response of the feedback path. As a result, howling can be quickly stopped and canceled.

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described in detail below based on embodiments shown in the drawings.

Referring to FIG. 2, this figure shows a block diagram of one embodiment of the present invention, in which the signal of the microphone 1 is transmitted to the telephone terminal 2.
The signal from the other party's microphone is input to the telephone terminal 2 via the communication path, and the signal from the microphone of the other party is input to the telephone terminal 2 via the communication path, and the telephone terminal 2 is connected to the speaker 3. , the microphone signals are mutually amplified. 8 and 9 are effective value circuits, which generate an effective value RMS of the signal level of the microphone 1 and an effective value RMS of the input signal level of the speaker 3, respectively.

The effective value circuit 9 is connected to the multiplier 10 and multiplies the effective value RMS of the input signal of the speaker 3 by a gain factor K (n). In the subtracter 11, the effective value RMS of the signal level of the microphone 1 obtained by the effective value circuit 8 and the multiplier 1
The output signal is compared with 0, and the error signal is input to the code circuit 12.

The sign circuit 12 determines whether the sign obtained by the subtracter 11 is positive or negative, and if the error signal is less than a predetermined value ε, the sign is set to O by providing an insensitive body. That is, the code of the code circuit 12 is lazy (IaZ
V) When the absolute value of the error of the subtracter 11 is greater than or equal to ε, the result is a lazy code minus the error code −1, and when it is less than ε, the result is a lazy code −0. A predetermined value Δ,
For example, the output signal is multiplied by 0.01 and the subtracter 14
is input. In the 1lii calculator 14, the memory 1
The previous gain rate K(n-1) stored in step 5 is updated. The updated gain factor K(n> is sent to the multiplier 10, where it is multiplied by the effective value RMS of the input signal of the speaker 3, and also sent to the multiplier 7, where it is multiplied by the input signal of the speaker 3, and adaptively The level of the signal input to the filter 4 is adjusted.

The adaptive filter 4 is connected to a subtractor 5 to predict the impulse response in the feedback path between the loudspeaker 3 and the microphone 1 and to equalize the signal level of the microphone 1 and the input signal level of the loudspeaker 3. According to
Howling is removed from the main signal.

Since the automatic gain controller (AGC) of this embodiment is configured as described above, the input signal level of the adaptive filter 4 and the signal level of the microphone 1 are adjusted to be approximately the same, and then the adaptive filter 4, it is sufficient to finely adjust the signal level. Therefore, when the microphone 1 and the speaker 3 are placed in the same room and howling occurs, it is possible to rapidly converge and cancel the howling.

Effects of the Invention As described in detail above, the present invention is configured to provide an automatic gain controller so that the input signal level of the adaptive filter and the microphone signal level are approximately the same. It is only necessary to make a fine adjustment between the input signal level and the input signal level of the speaker, and the effect is that howling can be rapidly converged and canceled.

[Brief explanation of drawings]

Fig. 1 is a block diagram of the principle of the howling canceller of the present invention, Fig. 2 is a block diagram of an embodiment of the present invention, Fig. 3 is a graph of lazy codes and error codes, and Fig. 4 is a block diagram of a conventional howling canceller. It is a diagram. DESCRIPTION OF SYMBOLS 1... Microphone, 2... Call terminal, 3... Speaker, 4... Adaptive filter, 5.11.14... Subtractor, 6... Automatic gain controller (800), 7.10.
13... Multiplier, 8.9... Effective value circuit, 12... Code circuit, 15... Memory. Hon Biao Pharyogen Jri Block Sen 1 Figure 15 Moxibustion 1 ≧ Do ; Toin line number = Yoshiri and shame te 1 yo Kai no (1ku ε : Rei j par - Bamboo = 0 ik Block diagram of next column Figure 4

Claims (1)

[Scope of Claims] In a communication terminal device equipped with a microphone (1) and a speaker (3), when the sound etc. collected by the microphone (1) is reproduced and amplified by the speaker (3) of the other party's terminal. , said speaker (
3) and the microphone (1) and an adaptive filter (4) that predicts the feedback path between the input side of the speaker (3) and the microphone (1) and removes howling.
An automatic gain controller (6) is installed between the output sides of the adaptive filter (6) to equalize the signal level of the microphone (1) and the signal level input from the speaker (3) to the adaptive filter (4). 4) A howling canceller characterized in that it is provided on the input side.