JPH05110694A - Voice adder - Google Patents

Abstract

PURPOSE:To eliminate an echo by generating a pseudo echo closely resemble to the actual echo while applying an echo pass model adjusting the characteristic to the echo pass characteristic from the receiving addition output terminal to a transmitting input terminal to the actual receiving addition signal and subtracting the pseudo echo from the actual echo signal. CONSTITUTION:A receiving signal is inputted from a receiving signal input terminal 1. It is inputted to a receiving addition signal level controller 8 after the addition in a voice addition circuit 9, and outputted to a receiver addition signal output terminal 2. An echo pass model 6 is provided in the device, and the characteristic of an echo pass 5 from an output terminal 2 to a transmission signal input terminal 3 is measured by an echo pass measurement circuit 10. Then, a model 6 is adjusted to the measured echo pass characteristic, and a pseudo echo closely resemble to the echo signal of the input terminal 3 is generated by passing a receiver addition signal to the model 6, subtracting from the actual echo signal by a subtracter 7 Thus, an echo can be eliminated while keeping the linear characteristic of the echo pass at all times.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a voice adder having an echo canceller function used in a communication line.

[0002]

2. Description of the Related Art In recent years, when voices of a large number of people are added by a voice addition service, echoes generated by 2-line / 4-line conversion are also added and it becomes difficult to secure a minimum echo attenuation amount. , The loop gain of the line becomes positive and the communication line becomes reverberant, which is a serious problem in call quality.

In order to solve this problem, a voice adder with an echo canceller function has been developed.

The echo canceller has an adaptive filter (echo path model) inside, and the characteristics from the reception addition output to the transmission input are measured by the echo path characteristic measuring circuit based on the speech signal, and the echo path model is measured. According to the echo path characteristics, a received echo addition signal is passed through this echo path model to generate a pseudo echo that approximates the echo signal, and a subtractor subtracts the echo from the actual echo signal to cancel the echo.

[0005]

However, in the echo canceller, when an excessive signal is input to the reception input of the echo canceller, if there is a device with a small overload margin in the echo path, non-linear distortion occurs in the echo path, and The internal characteristics of the echo canceller are displaced, making it impossible to cancel the echo.

The present invention has been made to solve the above problems inherent in the prior art. Therefore, an object of the present invention is to provide an echo canceller function so that even if an excessive signal is input, the echo can be canceled sufficiently. Another object of the present invention is to provide a novel voice adder having a signal level controller at the reception addition input of the voice adder with a voice.

[0007]

In order to achieve the above object, a voice adder according to the present invention outputs a signal level detector for measuring a signal level after addition of received signals and an output from this signal level detector. It is composed of a judgment circuit for judging whether or not the signal level is higher than a predetermined threshold level, and a control circuit for controlling the reception addition signal level based on the output of this judgment circuit.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will now be described in detail with reference to the accompanying drawings with reference to the accompanying drawings.

FIG. 1 is a block diagram showing an embodiment of the present invention.

When an excessive signal that causes the received added signal input terminal to clip is applied, this clipped signal is input to the echo path to cause waveform distortion, which may exceed the overload level of the echo path and cause nonlinear distortion. ..

Referring to FIG. 1, received signals are input from a received signal input terminal 1 and added by a voice adder circuit 9.

In the present invention, the reception signal level controller 8 is provided at the reception side input after voice addition.

A concrete example of the configuration of the signal level controller 8 is shown in FIG.
Shown in.

Referring to FIG. 2, the signal level controller 8
Has a reception addition signal level measuring circuit 101 for measuring the reception addition signal level, and constantly measures the level of the reception addition signal. The output of the measurement circuit 101 is set to a threshold level 103 predetermined by the determination circuit 102 (the threshold level is set to a level at which there is no possibility of causing overload distortion even if waveform distortion occurs in the echo path). By comparing, when the reception addition signal level is input to the echo path and waveform distortion occurs in the echo path,
Determine if the echo path overload level is likely to be exceeded.

When the judgment circuit 102 judges that there is a possibility of causing overload distortion when the reception addition signal causes waveform distortion in the echo path, the signal level limiter 104 connected to the output of the judgment circuit. At, the received signal level is lowered to a level at which overload distortion does not occur even if waveform distortion occurs in the echo path.

The voice adder has an echo path model 6 inside, and the echo path characteristic measuring circuit 10 measures the characteristics of the echo path 5 from the reception addition output to the transmission input, and the echo path model 6 is measured. According to the echo path characteristics, a reception addition signal is passed through the echo path model 6 to generate a pseudo echo that is similar to the echo signal input from the transmission signal input terminal 3 and subtracted from the actual echo signal by the subtractor 7. To cancel the echo. The functions of the echo path model 6, the echo path characteristic measuring circuit 10, and the subtractor 7 are collectively referred to as an echo canceller.

[0017]

As described above, according to the present invention, the signal level limiter 10 of the reception signal level controller 8 prevents the overload distortion from occurring in the echo path even if the waveform distortion occurs in the echo path.
Since the reception addition signal is controlled at 4, even if waveform distortion is generated in the echo path, the echo path does not exceed the overload level, and the echo path always exhibits a linear characteristic. Therefore, the echo canceling amount does not decrease, and a sufficient echo canceling characteristic is always exhibited.

As described above, according to the present invention, it is easy to provide a voice adder having a signal level limiter at the reception input of the echo canceller so that the echo can be sufficiently canceled even if the overload reception addition signal is input. Can be provided to.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of a voice addition device according to the present invention.

FIG. 2 is a block configuration diagram showing a specific configuration example of a signal level controller.

[Explanation of symbols]

 1 ... Reception signal input terminal 2 ... Reception signal addition signal output terminal 3 ... Transmission signal input terminal 4 ... Transmission signal output terminal 5 ... Echo path 6 ... Echo path model 7 ... Subtractor 8 ... Reception addition signal level controller 10 ... Echo path Measuring circuit 101 ... Signal level measuring circuit 102 ... Comparator 103 ... Threshold level 104 ... Signal level limiter

Claims (1)

[Claims] 1. A signal level measuring device for measuring a reception added signal level, a judging circuit for judging whether or not a signal level output by the signal level measuring device is higher than a predetermined threshold level, and the judging circuit. A voice adder comprising: a control circuit for controlling a reception addition signal level based on an output of the circuit.