JPH04287549A - Howling prevention device - Google Patents

Abstract

PURPOSE:To eliminate need for a training signal generating circuit and to attain optimum echo canceller control even when an echo path is changed. CONSTITUTION:A bell tone detection circuit 13 detects a bell tone with respect to an input signal from a telephone circuit and outputs a detection signal to an echo canceller circuit 12, which is driven. The echo canceller circuit 12 inputs an input signal and subject to adaptive control so that no howling takes place. That is, a voice output from a speaker 15 by the input signal is invaded in the echo path and collected by a microphone 16. The output of the microphone 16 and the output of the echo canceller circuit 12 are subtracted by an arithmetic section 18 and the result is fed back to the echo canceller circuit 12 and the echo canceller circuit 12 is subjected to adaptive control so that the feedback quantity is zero.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a howling prevention device used in telephones and the like.

0002

2. Description of the Related Art FIG. 5 is a block diagram showing the structure of a conventional howling prevention device. In FIG. 5, receiving terminal 1
The training signal generation circuit 2 that generates a training signal is connected to a changeover switch section 3, and the common terminal of the changeover switch section 3 is connected to the input terminal 1 and the training signal generation circuit 2 for switching between the input terminal 1 and the training signal generation circuit 2 for use with the echo canceller circuit 4 and the speaker. It is connected to amplifier 5. The speaker amplifier 5 is connected to a speaker 6 and outputs audio from the speaker 6. A microphone 7 from which the audio output from the speaker 6 goes around the echo path and collects the sound is connected to a microphone amplifier 8 , and output ends from the microphone amplifier 8 and the echo canceller circuit 4 are connected to an arithmetic unit 9 . , the output of the echo canceller circuit 4 is subtracted from the output of the microphone amplifier 8. The output terminal of the arithmetic unit 9 is connected to the echo canceller circuit 4 for feedback, and is also connected to the transmission side terminal 10.
connected to.

With the above configuration, when the telephone is installed, the built-in microcomputer (not shown) is connected before the telephone line is connected.
The changeover switch unit 3 is once switched to the training signal generation circuit 2 side, and the echo canceller circuit 4 is driven. A training signal from the training signal generating circuit 2 is used to output sound from the speaker 6 via the speaker amplifier 5. The audio output from the speaker 6 passes through an echo circuit and is collected by a microphone 7. microphone 7
The audio output from the microphone is amplified via a microphone amplifier 8 and then input to a computing unit 9. In the arithmetic unit 9, the outputs from the echo canceller circuit 4 and the microphone amplifier 8 are subtracted. The output from the calculator 9 is sent to the echo canceller circuit 4.
The echo canceller circuit 4 performs adaptive control so that the amount of feedback becomes zero.

[0004] Here, the reason why howling occurs between the speaker 6 and the microphone 7 is that the audio signal output from the speaker 6 is collected by the microphone 7 without being attenuated much, and is amplified by the microphone amplifier 8. This is because the phenomenon that the signal then goes around to the speaker 6 side through a hybrid circuit or the like and is further amplified is repeated. Therefore, as mentioned above,
Before making a call using the speakerphone, in order to prevent howling, the training signal generation circuit 2 sends out a training signal, and the echo canceller circuit 4 estimates the echo path so that howling is less likely to occur due to the environment in which the telephone is installed. There is.

After the adaptive control of the echo canceller circuit 4, the installation of the telephone is completed and the telephone line is connected.
The audio output from the speaker 6 based on the input signal from the telephone line passes through an echo circuit, is collected by a microphone 7, is amplified by a microphone amplifier 8, and is then input to a computing unit 9. The howling component is canceled and removed by the output of the canceller circuit 4, and is output from the transmitting terminal 10.

[0006]

[Problems to be Solved by the Invention] However, in the conventional configuration described above, the training signal generating circuit 2 is required for estimating the echo path when the telephone is installed, and the echo path changes due to changes in the environment after the telephone is installed. In some cases, there is a problem in that optimal echo canceller control cannot be performed from the beginning.

The present invention solves the above-mentioned conventional problems, and provides a howling prevention device that can eliminate the need for a training signal generation circuit and can perform optimal echo canceller control even when the echo path changes. The purpose is to provide the following.

[0008]

[Means for Solving the Problems] In order to solve the above problems, the howling prevention device of the present invention includes a bell sound detection means for detecting a bell sound in response to an input signal from a telephone circuit and outputting a detection signal; an echo canceller circuit that takes the input signal as an input and is driven by the detection signal from the bell sound detection means to perform adaptive control so as not to cause howling; a speaker that outputs audio based on the input signal; and an audio output from the speaker. This device includes a microphone whose sound is collected by going around an echo path, and arithmetic means for subtracting the output of the microphone and the output of the echo canceller circuit.

[0009]

[Operation] With the above configuration, the bell sound detecting means detects the bell sound from the input signal from the telephone circuit, outputs the detection signal to the echo canceller circuit, and drives the echo canceller circuit to prevent howling from occurring. adaptive control,
Since the output of this echo canceller circuit is subtracted from the microphone output by a calculation means to remove howling, the use of the bell ringer eliminates the need for the conventional training generation circuit and changes the echo path at the installation location. In each case, optimal echo canceller control can be performed in each case.

0010

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram of a howling prevention device according to an embodiment of the present invention. In FIG. 1, a receiving terminal 11 to which an input signal from a telephone line is input is connected to an echo canceller circuit 12, a bell sound detection circuit 13, and a speaker amplifier 14, so that howling does not occur in the echo canceller circuit 12. The bell sound is detected by the bell sound detection circuit 13, and the input signal is amplified by the speaker amplifier 14. Bell sound detection circuit 1
3 is connected to the echo canceller circuit 12 and outputs the detection signal of the bell sound detection circuit 13 to the echo canceller circuit 12. The speaker amplifier 14 is connected to a speaker 15, and audio is output from the speaker 15. On the other hand, microphone 16
is connected to a microphone amplifier 17, and the audio signal collected by the microphone 16 and coming around the echo path is amplified by the microphone amplifier 17. Output terminals from the microphone amplifier 17 and the echo canceller circuit 12 are connected to an arithmetic unit 18, and each output is subtracted. The output terminal from the calculation section 18 is connected to the echo canceller circuit 12, and the echo canceller circuit 12 adaptively controls the output from the calculation section 18 to zero. In addition, the output terminal from the calculation unit 18 is the transmission side terminal 1
9, and the subtracted output is output from the transmission side terminal 19.

The operation of the above configuration will be explained below. The reason why the howling prevention device is configured using the bell sound detection circuit 13 is as follows. That is, as shown in FIG. 2, the conventional method using training signals is based on the voice band of the telephone line (300 Hz to 3400 Hz).
White noise containing all W1 is used, but
The audio band W2 used for general conversation is 1KHz.
In addition, considering the training signal for the purpose of preventing howling in the first moment when the echo canceller circuit 12 starts adaptive operation, a narrow bandwidth matching the voice band W2 used for general conversation, Moreover, this is because the bell ringing signal W3, whose frequency is known, is used as a training signal.

FIG. 3 is a flowchart showing the howling prevention control procedure using the bell ringing signal in FIG. In FIG. 3, in step S1, a bell ringing signal is detected by the bell sound detection circuit 13. When the bell ringing signal is detected by the bell sound detection circuit 13, the echo canceller circuit 12 is operated in step S2, and the volume level of the bell sound output from the speaker 15 is adjusted, and this bell sound is transmitted through the echo path to the microphone. The volume level of the bell sound collected in step 16 is compared to find a level value at which howling does not occur. That is, the echo canceller circuit 12 performs adaptive control so that the output from the calculation unit 18 becomes zero, and in step S3, the level value at which no howling occurs, that is, the gain for the level frequency, is set in the coefficients in step S3. The maximum level value is derived and set as the initial value of each coefficient of the echo canceller circuit 12 shown in FIG. and,
As shown in FIG. 4, the input signal from the receiving terminal 11 is sequentially delayed by each delay element 12a in the same manner as the delay caused by an echo path, multiplied by its coefficient by each multiplier 12b, and then added by an adder 12c. and output to the subtracter 9. Then, in the calculation unit 18, the echo canceller circuit 1
Howling is removed from the output of the microphone amplifier 17 by the output of step S4, and preparation for a speakerphone call is completed in step S4.

[0013] Therefore, howling can be prevented from occurring by using the bell ringing signal W3 from the telephone line shown in Fig. 2, so that the training signal generating circuit conventionally used only when installing a telephone can be omitted.

[0014]

As described above, according to the present invention, it is possible to eliminate the need for a conventional training signal generation circuit, and even if the echo path in the environment changes after the telephone is installed, howling can be suppressed every time a bell is detected. This makes it possible to perform optimal echo canceller control that prevents echo from occurring.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the configuration of a howling prevention device according to an embodiment of the present invention.

FIG. 2 is a relationship diagram between frequency and signal level showing the voice band of a telephone line.

FIG. 3 is a flowchart showing a howling prevention control procedure using a bell ringing signal in FIG. 1;

4 is a block diagram showing the basic configuration of the echo canceller circuit 12 in FIG. 1. FIG.

FIG. 5 is a block diagram showing the configuration of a conventional howling prevention device.

[Explanation of symbols]

12 Echo canceller circuit 13 Bell sound detection circuit 15 Speaker 16 Microphone 18 Arithmetic unit

Claims (1)

[Claims] 1. A bell sound detecting means for detecting a bell sound in response to an input signal from a telephone circuit and outputting a detection signal; and a bell sound detecting means that receives the input signal as an input and is driven by a detection signal from the bell sound detecting means. an echo canceller circuit that performs adaptive control to prevent howling from occurring; a speaker that outputs audio based on the input signal; a microphone that collects the audio output from the speaker by going around an echo path; A howling prevention device comprising calculation means for subtracting a canceller circuit output.