JPH0537427A - Echo canceler - Google Patents

Abstract

PURPOSE:To sufficiently cancel echo even when excess signals are inputted from a voice adder circuit. CONSTITUTION:The output of a voice adder circuit 13 is always measured by a received signal level measuring circuit 9, and circuit 10 judges whether the measured signal level exceeds a threshold level decided in advance or not. When the ircuit 10 the possibility of excess load distortion in the case of generating the waveform distortion of a received signal at an echo path 5, the correction of an echo path model is stopped by controlling the output of an echo path characteristic measuring circuit at an echo canceler 12.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an echo canceller device for a voice adder used in a communication line, and more particularly to an echo canceller device having a control function.

[0002]

2. Description of the Related Art In recent years, as a result of adding voices of a large number of people by a voice addition service, it is difficult to secure a minimum echo attenuation amount because echoes generated by 2-line / 4-line conversion are also added. The loop gain of the line was positive and the communication line was in a reverberant state, which was a serious problem in call quality. To solve this problem, a voice adder with an echo canceller function has been developed.

In general, an echo canceller has an adaptive filter (echo path model) inside, and the echo path characteristic measuring circuit measures the characteristics from the reception output to the transmission input based on the speech signal, and the echo path model is measured. According to the echo path characteristics, a received signal is passed through this echo path model to create a pseudo echo that approximates the echo signal, and the subtracter subtracts the pseudo echo from the actual echo signal to cancel the echo.

[0004]

In the conventional echo canceller, when an excessive signal is input to the reception input of the echo canceller, a nonlinear distortion occurs in the echo path if there is a device with a small overload margin in the echo path. Since the echo canceller cancels the echo with a linear filter inside assuming that the echo path characteristic is a linear system, when the nonlinear distortion occurs, it operates as if noise was input to the echo path. For this reason, the operation of the echo path characteristic measuring circuit is disturbed, and it becomes impossible to measure a satisfactory echo path characteristic. As a result, the characteristics of the echo path model are disturbed, and it becomes impossible to cancel the echo sufficiently.

Therefore, when an excessive signal that causes a signal to be clipped is applied to the input of the echo canceller by the voice adder circuit, the clipped signal is input to the echo path and causes waveform distortion, which exceeds the overload level of the echo path and causes nonlinear distortion. To occur. As a result of this non-linear distortion, there is a problem that the error of the measurement result of the echo path characteristic measuring circuit becomes large, the disturbance occurs in the echo path model, and the canceling amount of the echo decreases.

[0006]

According to the present invention, a characteristic from a reception output to a transmission input is measured by an echo path characteristic measuring circuit based on a speech signal, and the reception signal is passed through an echo path model matching the measured echo path characteristic. In the echo canceller device for canceling the echo by the pseudo echo to be generated, the reception signal level measuring circuit for measuring the level of the reception signal, and the determination result by determining whether or not the measured reception signal is higher than a predetermined threshold level And a determination circuit for controlling the echo path characteristic measuring circuit based on the above.

[0007]

According to the present invention, when it is determined by the determination circuit that the received signal may cause overload distortion when waveform distortion occurs in the echo path, the output of the echo path characteristic measuring circuit is controlled to control the echo canceller. Stop modifying the echo path model.

[0008]

The present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing an embodiment of an echo canceller device according to the present invention, and FIG. 2 is a block diagram of the echo canceller. In FIG. 1, the reception input of the echo canceller 12 is connected to the output of the voice addition circuit 13 and the input of the reception signal level measuring circuit 9 constituting the control circuit 11, and the output of the reception signal level measuring circuit 9 is the output of the judgment circuit 10. It is connected to the input and the output of the decision circuit 10 is connected to the echo path characteristic measuring circuit 8 of the echo canceller 12 which will be described later. On the other hand, the echo path 5 is connected between the reception output and the transmission input of the echo canceller 12.

In FIG. 2, reference numeral 1 is an echo canceller 12.
Receiver signal input terminal, 2 is a receiver signal output terminal, 3 is a transmitter signal input terminal, 4 is a transmitter signal output terminal, and an echo path characteristic measuring circuit is provided between the receiver signal input terminal 1 and the transmitter signal output terminal. 8 is connected, and the output of the echo path characteristic measuring circuit 8 is connected to the input of the echo path model 6 connected to the reception signal input terminal 1. The output of this echo path model is input to the subtractor 7 together with the output of the echo path 5 connected between the reception signal output terminal 2 and the transmission signal input terminal 3, and the output 7 of the subtractor 7 is connected to the transmission signal output terminal. Has been done.

Next, the operation will be described. Echo canceller 1
Receiver signal level measuring circuit 9 connected to the receiver side input 2
Always measures the voice addition signal output from the voice addition circuit 13, and the output level of the measurement circuit 9 is a threshold level determined in advance by the judgment circuit 10 (overload distortion is generated in the echo path 5 above this threshold level). Value that may occur). This allows
When the received signal level is input to the echo path 5 and waveform distortion occurs, it is determined whether or not there is a possibility of exceeding the overload level of the echo path 5.

When the decision circuit 10 decides that the received signal may cause waveform distortion in the echo path 5,
The output of the judgment circuit 10 or the control circuit 11 controls the output of the echo path characteristic measuring circuit 8 of FIG. 2, and controls so as to stop the modification of the echo path model 6 of the echo canceller 12. As a result, the effect of disturbance after the occurrence of overload distortion is eliminated by setting the echo path model to the value of the echo path model before occurrence of overload distortion.

As described above, when the received signal level is input to the echo path 5 and the waveform distortion occurs, the echo canceller 12 stops the correction of the echo path model 6 when the overload level of the echo path 5 may be exceeded. Therefore, the disturbance of the echo path model can be prevented, and the echo can be sufficiently canceled even if an excessive signal is input.

Next, the operation of the echo canceller 12 will be described. The reception signal input from the reception signal input terminal 1 is sent to the reception signal output terminal 2 and at the same time the echo path model 6
Sent to. The signal sent to the echo path model 6 passes through the echo path 5 and is input as an echo to the transmission input terminal 3 of the echo canceller 12. On the other hand, the reception signal input to the echo path model 6 passes through the echo path model 6 having the same characteristics as the echo path 5 to generate the same pseudo echo as the echo input to the transmission signal input terminal 3.

At this time, the judgment circuit 10 or the control circuit 1
If there is a signal from 1, the correction of the echo path model 6 is stopped, and the value of the echo model 6 is fixed to the value before the occurrence of overload distortion. The generated pseudo echo is subtracted from the actual echo signal input from the transmission input terminal 3 by the attenuator 7. Therefore, the echo is canceled by the output of the attenuator 7, and the echo is output from the transmission signal output terminal 4.

[0015]

As described above, according to the present invention, the correction of the echo model is stopped when the overload level of the echo path may be exceeded. The echo canceller can be controlled so that it can be sufficiently canceled.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing an embodiment of an echo canceller device according to the present invention.

FIG. 2 is a block diagram of the echo canceller of FIG.

[Explanation of symbols]

 5 Echo Path 6 Echo Path Model 7 Attenuator 8 Echo Path Characteristic Measurement Circuit 9 Received Signal Level Measurement Circuit 10 Judgment Circuit 11 Control Circuit 12 Echo Canceller

Claims (1)

Claims: 1. A characteristic from a reception output to a transmission input is measured by an echo path characteristic measuring circuit based on a speech signal, and the reception signal is generated through an echo path model matching the measured echo path characteristic. In an echo canceller device for canceling an echo by a pseudo echo, a receiving signal level measuring circuit for measuring the level of the receiving signal, and whether the measured receiving signal is higher than a predetermined threshold level or not is determined based on the determination result. And a determination circuit for controlling the echo path characteristic measuring circuit.