JPH05183472A - Voice addition device with echo canceler function - Google Patents

Abstract

PURPOSE:To provide the voice addition device with echo canceler function having a signal level controller at the receiving input of the echo canceler so as to fully cancel echo canceler even when overload reception and addition signals are inputted to the voice addition circuit. CONSTITUTION:A filter 8 with the representative echo path characteristic is connected to signals after adding the receiving signals by a voice addition circuit 9. When a signal passes through this filter 8, the waveform distortion generated at an echo path 5 is also generated at the filter 8. A signal level controller 11 controls the intensity of the signal having the possibility of exceeding the overload level of the inner echo path of the waveform distortion generated at the filter 8. The echo path 5 decreases the signal level so as not to exceed the overload level of the echo path even though the waveform distortion is generated at the echo path 5. Thus, by controlling the receiving addition signals, the linear characteristic of the echo path 5 is correctly kept, resulting in preventing the echo state of the communication line.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a voice adder used for a communication line.

[0002]

2. Description of the Related Art Impedance mismatch at a connection point which becomes a problem when connecting different types of communication lines such as balance / unbalance conversion of communication lines and mutual connection of 2-wire and 4-wire lines. May cause an echo.

In addition, by adding voice signals of a large number of people by using a voice addition service, it is possible to obtain a 4-line connection with a 2-wire line.
Since the echo generated at the connection point with the wire line is also added,
There is a phenomenon in which it becomes difficult to secure the minimum echo attenuation amount, the loop gain of the line becomes positive, and the communication line becomes a reverberant state, which deteriorates the communication quality.

As a method for removing this echo, there have been conventionally used an electronic hybrid method for directly adjusting the mismatch of the 2-wire to 4-wire converter and a processing by an echo suppressor or an echo canceller. The echo suppressor is a system that monitors the signal levels of the up and down lines in the 4-wire section and gives a large attenuation to the line with no signal so that the echo does not return substantially by making the line one direction. Is.

The echo canceller estimates the impulse response of the echo path, generates a pseudo echo to eliminate the echo component, and is inserted on the 4-wire line side. An example of an echo canceller is an internal adaptive filter (echo path model) that measures the characteristics from the reception addition output to the transmission input with an echo path characteristics measurement circuit based on the speech signal to measure the echo path model. Match the echo path characteristics. Then, a received echo addition signal is passed through this echo path model to create a pseudo echo that approximates the echo signal, and the attenuator subtracts this pseudo echo from the actual echo signal to cancel the echo.

[0006]

However, in the above echo canceller, when an excessive signal is input to the echo canceller as the reception input, if there is a device with a small overload margin in the echo path, nonlinear distortion occurs in the echo path, The characteristics inside the echo path and the echo canceller shift,
The echo cannot be canceled sufficiently.

SUMMARY OF THE INVENTION An object of the present invention is to provide a voice adder with an echo canceller function, which can sufficiently cancel an echo even if an excessive signal is input.

[0008]

SUMMARY OF THE INVENTION A solution of the present invention for solving the above-mentioned problems is a voice adder circuit for adding a plurality of input signals, and a pseudo echo signal which is similar to an echo generated in a built-in echo path. In the voice adding device with an echo canceller function, which comprises an echo canceller for canceling the echo generated in the echo path by the pseudo echo signal, a filter circuit for limiting the bandwidth of the reception addition signal which is the output signal of the voice adding circuit. And a signal level limiter for limiting the maximum value of the reception addition signal level from the output signal of the filter circuit are interposed between the voice addition circuit and the echo canceller.

[0009]

In the voice adder with an echo canceller function according to the present invention, when a filter circuit having a typical echo path characteristic is connected to the signal after addition of the received signals and the signal is passed through this filter circuit, the echo path of the echo canceller is obtained. The waveform distortion that occurs in this filter circuit also occurs. Therefore, the signal level limiter limits the level of the signal that may exceed the echo path overload level of the waveform distortion generated in this filter circuit, and even if the echo path waveform distortion occurs, the echo path overload level Do not exceed. As a result, the linear characteristic of the echo path is maintained, and even if an excessive signal is input, it is possible to favorably cancel the echo.

[0010]

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

When an excessive signal that causes the reception added signal input terminal 1 to clip is input, this clipped signal is input to the echo path 5 to cause waveform distortion, and nonlinear distortion occurs when the overload level of the echo path 5 is exceeded. May occur.

The reception signal input terminals 1a, 1b, 1c are connected to the voice addition circuit 9, the output terminal of the voice addition circuit 9 is connected to the input terminal of the filter 8, and the output terminal of the filter 8 is connected to the signal level limiter 11. It is connected to the input terminal.
The output terminal of the signal level limiter 11 is connected to the input terminals of the echo path model 6 and the echo path measurement circuit 10, respectively, and is also connected to the input terminal of the echo path 5 via the reception addition signal output terminal 2. .. The output terminal of the echo path 5 is connected to one input terminal of the subtractor 7 via the transmission signal input terminal 3. The output terminal of the echo path model 6 is also connected to the other input terminal of the subtractor 7. The output terminal of the subtractor 7 is connected to the other input terminal of the echo path measuring circuit 10 and also to the transmission signal output terminal 4.

In the configuration described above, the voice addition circuit 9 adds the reception signals input from the reception signal input terminals 1a, 1b, 1c, and outputs them to the filter 8. The filter 8 is a filter having a typical echo path characteristic, and when a signal is input to this filter 8, the waveform distortion generated in the echo path 5 is also generated in this filter 8. Therefore, the signal having waveform distortion generated by the filter 8 is input to the signal level limiter 11, and the signal that may exceed the overload level of the echo path 5 among the generated waveform distortion is limited by a preset threshold value. To do. As a result, even if waveform distortion occurs in the echo path 5, the overload level of the echo path is not exceeded, so that non-linear distortion does not occur in the echo path 5 and it is possible to prevent the communication circuit from entering a reverberant state.

The voice addition signal whose signal level is limited by the signal level limiter 11 is input to the echo path model 6 and the echo path measuring circuit 10 which are pseudo echo generators. Echo path 5 from the reception addition output of the signal level limiter 11 to the transmission output signal of the transmission signal output terminal 4
Is measured by the echo path measurement circuit 10 and the echo path model 6 is adjusted to the characteristics of the measured echo path to input the reception addition signal to obtain the echo signal input from the transmission signal input terminal 3. The approximate pseudo echo signal is created, and the subtracter 7 subtracts it from the actual echo signal to cancel the echo. The functions of the echo path model 6, the echo path measurement circuit 10, and the subtractor 7 are collectively referred to as an echo canceller.

[0015]

As described in the above embodiments, according to the present invention, by providing the internal filter and the signal level limiter, the reception addition of the voice addition circuit is performed so that the overload distortion is not generated in the echo path. Since the signal is limited, even if waveform distortion occurs in the echo path, the overload level of the echo path is not exceeded, and the echo path always exhibits a linear characteristic. Therefore, the echo canceling amount does not decrease, and a sufficient canceling characteristic is always exhibited, so that the communication circuit can be prevented from entering a reverberant state.

[Brief description of drawings]

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

[Explanation of symbols]

 1a, 1b, 1c reception signal input terminal 2 reception addition signal output terminal 3 transmission signal input terminal 4 transmission signal output terminal 5 echo path 6 echo path model 7 subtractor 8 filter 9 voice addition circuit 10 echo path measurement circuit 11 signal level limitation vessel

Claims (1)

[Claims] 1. An audio adder circuit for adding a plurality of input signals, and an echo canceller for generating a pseudo echo signal similar to an echo generated in a built-in echo path, and canceling the echo generated in the echo path by the pseudo echo signal. A voice addition device with an echo canceller function comprising: a filter circuit that limits the bandwidth of a reception addition signal that is an output signal of the voice addition circuit; and a maximum value of the reception addition signal level from the output signal of the filter circuit. And a signal level limiter for performing echo canceller function, which is connected between the voice adder circuit and the echo canceller.