JPH09275367A - Echo canceller - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize a confortable speech with a small scale circuit configuration in which natural and clear background noise is in existence without any echo even when the echo canceller circuit provides an output of a subtraction output signal including a residual echo and background noise having a high frequency component by allowing a residual echo suppression circuit receiving a speech direction detection signal in response to a speech state from a speech direction detection circuit to sufficiently suppress only the residual echo. SOLUTION: The echo canceller 100 connecting to a 2/4 wire converter 110 receiving a transmission signal including background noise is made up of an echo canceller circuit 100a of the similar configuration to that of a conventional device, a speech direction detection circuit 130 and a residual echo suppression circuit 120. The speech direction detection circuit 130 detects a speech direction from a subtraction output signal and a reception input signal and the residual echo suppression circuit 120 uses its built-in low pass filter to suppress the residual echo included in the subtraction output signal.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention mainly relates to an echo canceller device for removing an echo signal generated when a reception output signal wraps around a transmission input signal on the 4-wire side in a 2-wire to 4-wire converter.

[0002]

2. Description of the Related Art Conventionally, a two-wire to four-wire converter set to a predetermined impedance has been used for voice communication over a long-distance digital line via a communication satellite.
An echo signal is generated when the reception output signal output after the reception processing of the reception input signal at the reception side wraps around the transmission input signal at the transmission side due to impedance mismatch on the four-wire side, and in such a case, a voice call is generated. It becomes extremely difficult. Therefore, an echo canceller device is used to remove such an echo signal.

FIG. 3 shows a conventional echo canceller device 30.
1 is a circuit block diagram showing the basic configuration of a digital line including 0. FIG.

The echo canceller device 300 is connected to a 2-wire 4-wire converter 310 to which a transmission signal containing background noise is input, and is received and input for sending to the 2-wire 4-wire converter 301. It has a function of removing an echo signal generated by the reception output signal obtained by receiving and processing the input signal sneaking into the transmission input signal transmitted and input from the 4-wire side of the 2-wire to 4-wire converter 301.

That is, this echo canceller device 300
Is a transversal filter 301 that generates a pseudo echo signal for removing an echo signal by multiplying a received input signal by a filter coefficient, and a subtractor 302 that subtracts the pseudo echo signal from the transmission input signal from the 2-wire to 4-wire converter 310.
Echo canceller circuit 300a including
2, a residual echo suppressing circuit 320 that removes residual echo included in the subtraction output signal, and a noise storage circuit 3 that stores background noise on the transmitting side during a call from the subtraction output signal.
30 and an adder 340 that adds and adds the background noise output signal from the noise storage circuit 330 to the echo suppression output signal from the residual echo suppression circuit 320 and outputs it as a transmission output signal.
Consists of

Next, the operation of the echo canceller device 300 will be described. An echo signal is generated when the reception output signal wraps around the transmission input signal in the 2-wire 4-wire converter 310. This echo signal is transmitted through the 2-wire 4-wire converter 310 together with the transmission signal including the background noise on the 2-wire side. It is input to the subtractor 302 as a transmission input signal on the 4-line side via the. The transversal filter 301 also multiplies the received input signal by a filter coefficient to generate a pseudo echo signal which is expected to be generated in the 2-wire to 4-wire converter 310. The echo signal and the transmission input signal including the background noise are input to the subtractor 302, and the pseudo echo signal from the transversal filter 301 is also input. Therefore, the subtractor 302 subtracts the pseudo echo signal from the transmission input signal to cancel the echo signal. However, the echo signal is not completely erased, and the subtraction output signal output from the subtractor 302 contains residual echo and background noise.

The subtracted output signal in the mixed state is input to the residual echo suppressing circuit 320, and all signals including the residual echo component are suppressed, so that these signals are completely erased and the echo suppression output is obtained. Output as a signal. Further, the mixed subtraction output signal output from the subtractor 302 is also input to the noise storage circuit 330, and the background noise of the transmission input signal is stored. This background noise is sent to the adder 340 as a background noise output signal, and the adder 34
At 0, the echo suppression output signal and the background noise output signal are added and output as a transmission output signal. This allows
A call with no echo and natural and clear background noise is realized.

As a technique related to such echo removal, for example, an echo removal circuit disclosed in Japanese Patent Laid-Open No. 3-3428, an echo canceller device disclosed in Japanese Patent Laid-Open No. 3-171929, and the like are available. Can be mentioned.

[0009]

In the case of the echo canceller device described above, the background noise obtained from the noise storage circuit is added by the adder at the subsequent stage from the residual echo suppression circuit in the silent call state, and the background noise naturally disappears without echo. However, there is a problem that the high frequency component of the residual echo is not sufficiently suppressed.

There is also a problem that the cost is likely to increase because the circuit configuration other than the echo canceller circuit, which is the core function, is complicated and large-scaled.

The present invention has been made to solve such a problem, and its technical problem is to provide an echo canceller device capable of sufficiently suppressing the high frequency component of the residual echo with a small circuit configuration. To provide.

[0012]

According to the present invention, a receiver is connected to a 2-wire 4-wire converter to which a transmission signal containing background noise is input, and is received for sending to the 2-wire 4-wire converter. And a function of removing an echo signal generated by the reception output signal obtained by receiving and processing the input reception input signal circling around the transmission input signal sent out from the 4-wire side of the 2-wire to 4-wire converter. , An echo consisting of a transversal filter that generates a pseudo echo signal for removing the echo signal by multiplying the transmission input signal by a filter coefficient, and a subtractor that subtracts the pseudo echo signal from the transmission input signal to generate a subtraction output signal In an echo canceller device including a canceller circuit, a speech direction detection circuit for detecting the speech direction from a subtraction output signal and a reception input signal, and a residual signal included in the subtraction output signal Echo canceller system and a residual echo suppression circuit includes a low pass filter for suppressing co is obtained.

Further, according to the present invention, in the above echo canceller device, the call direction detecting circuit indicates a call direction detection result indicating a result of detecting single talk on the receiving side and at least one of single talk and double talk on the transmitting side. The signal is output, and the residual echo suppression circuit gradually increases the suppression of the high frequency when the single talk state on the receiving side is detected according to the speech direction detection signal, and the single talk or double talk on the transmitting side is suppressed. An echo canceller device is provided which performs high frequency control to gradually reduce suppression of high frequency when detected.

Further, according to the present invention, in the above echo canceller device, an echo canceller device can be obtained in which the residual echo suppressing circuit is provided with a low-pass filter having a predetermined frequency-gain characteristic for performing high frequency control.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION The echo canceller device of the present invention will be described below in detail with reference to the drawings.

FIG. 1 is a circuit block diagram showing a basic configuration of a digital line including an echo canceller device 100 according to an embodiment of the present invention.

This echo canceller device 100 is also a 2-wire to 4-wire converter 110 to which a transmission signal containing background noise is input.
And a reception output signal obtained by receiving processing of a reception input signal received and input to be sent to the 2-wire to 4-wire converter 110 is sent out from the 4-wire side of the 2-wire to 4-wire converter 110. A transversal filter 1 having a function of removing an echo signal generated by sneaking into a transmission input signal and further generating a pseudo echo signal for removing an echo signal by multiplying a reception input signal by a filter coefficient.
An echo canceller circuit 100a having a configuration similar to that of the conventional device, which includes a subtracter 102 that subtracts a pseudo echo signal from a transmission input signal from the 01 and 2-wire to 4-wire converter 110, is provided.

In addition to the echo canceller circuit 100a, the echo canceller device 100 further includes a call direction detection circuit 130 for detecting the call direction from the subtracted output signal and the received input signal, and a residual echo contained in the subtracted output signal. And a residual echo suppression circuit 120 having a low-pass filter for

Here, the call direction detection circuit 130 outputs a call direction detection signal representing a result of detecting single talk on the receiving side and at least one of single talk and double talk on the transmitting side. Further, the residual echo suppressing circuit 120 gradually increases the suppression of the high frequency when the single talk on the receiving side is detected according to the talking direction detection signal from the talking direction detecting circuit 130, and the single talk on the transmitting side or When double talk is detected, high frequency control is performed to gradually reduce suppression of high frequency. Therefore, in order to perform such high frequency control, the residual echo suppressing circuit 120 has a predetermined frequency f (k) as shown in FIG.
Hz) -gain G (dB) characteristic (described in detail later) is provided.

Next, the operation of the echo canceller device 100 will be described. Again, the 2-wire to 4-wire converter 110
An echo signal is generated when the reception output signal wraps around to the transmission input signal in the two-wire to four-wire converter 1 together with the transmission signal containing the background noise on the two-wire side.
Subtractor 102 as a transmission input signal on the 4-wire side via 10
Is input to In addition, the transversal filter 101 multiplies the received input signal by a filter coefficient to convert the 2-wire to 4-wire converter 1.
Generate a pseudo echo signal that is expected to occur at 10. The echo signal and the transmission input signal including the background noise are input to the subtractor 102, and the transversal filter 1
The pseudo echo signal from 01 is also input. Therefore, the subtractor 102 subtracts the pseudo echo signal from the transmission input signal to cancel the echo signal. However, the echo signal is not completely erased, and the subtraction output signal output from the subtractor 102 contains residual echo and background noise. Since the residual echo here includes a high frequency component, the residual echo can be eliminated by suppressing the high frequency.

The subtraction output signal in the mixed state is input to the residual echo suppressing circuit 120, and the residual echo suppressing circuit 120 is input.
Then, the residual echo is erased by the low-pass filter having the frequency-gain characteristic as shown in FIG. 2 and output as the transmission output signal. At this time, the call direction detection circuit 130 detects the single talk on the receiving side and sends the call direction detection signal to the residual echo suppression circuit 120, and the residual echo suppression circuit 120 replaces the filter coefficient and gradually suppresses the high frequency band. Is increased (in the order of the characteristic curves C1, C2, C3 ... In FIG. 2) to eliminate the residual echo.

On the other hand, when the talk direction detection circuit 130 detects single talk or double talk on the transmitting side and sends the talk direction detection signal to the residual echo suppressing circuit 120, the residual echo suppressing circuit 120 gradually replaces the filter coefficient. The residual echo is eliminated by changing the suppression of high frequency frequencies so as to decrease (in the order of characteristic curves C3, C2, C1 ... In FIG. 2).

As described above, the residual echo suppressing circuit 120 erases the residual echo by gradually changing the suppression amount of the high frequency in accordance with the transition of the call state.

That is, in the echo canceller device 100, when the subtraction output signal in which the residual echo and the background noise are mixed from the echo canceller circuit 100a is input to the residual echo suppressing circuit 120, only the residual echo is suppressed and erased. Since the background noise passes through the residual echo suppression circuit 120, the transmission output signal output from the residual echo suppression circuit 120 is sufficiently suppressed with respect to high frequency components, and the background noise is natural and clear without echo. The existing call is realized.

[0025]

As described above, according to the echo canceller device of the present invention, the subtraction output signal in which the residual echo including the high frequency component and the background noise are mixed is output from the echo canceller circuit having the same structure as the conventional device. Is output,
Since the residual echo suppressor circuit can sufficiently suppress only the residual echo in response to the call direction detection signal from the call direction detection circuit, it is necessary to use a noise storage circuit or adder as in the past. In addition, a small-scale circuit configuration enables a comfortable call with no echo and natural background noise.

[Brief description of drawings]

FIG. 1 is a circuit block diagram showing a basic configuration of a digital line including an echo canceller device according to an embodiment of the present invention.

FIG. 2 shows frequency-gain characteristics of a low-pass filter used in the residual echo suppressing circuit of the echo canceller device shown in FIG.

FIG. 3 is a circuit block diagram showing a basic configuration of a digital line including a conventional echo canceller device.

[Explanation of symbols]

 100,300 Echo canceller device 100a, 300a Echo canceller circuit 101,301 Transversal filter 102,302 Subtractor 110,310 2-wire 4-wire converter 120,320 Residual echo suppressor circuit 130 Call direction detection circuit 330 Noise storage circuit 340 Addition vessel

Claims (3)

[Claims] 1. A transmission signal including background noise is input 2
From the 4-wire side of the 2-wire 4-wire converter, the received output signal is connected to the wire 4-wire converter and is subjected to reception processing of the reception input signal received and input to be sent to the 2-wire 4-wire converter. A transformer that has a function of removing an echo signal generated by sneaking into a transmission input signal that is transmitted and input, and that further generates a pseudo echo signal for eliminating the echo signal by multiplying the transmission input signal by a filter coefficient. In an echo canceller device including an echo canceller circuit, which includes a Versal filter and a subtracter that subtracts the pseudo echo signal from the transmission input signal to generate a subtraction output signal, in the speech direction from the subtraction output signal and the reception input signal A residual direction detection circuit that performs detection, and a residual error signal that includes a low-pass filter that suppresses residual echo included in the subtracted output signal. Echo canceller system characterized in that it comprises a chromatography suppression circuit. 2. The echo canceller device according to claim 1, wherein the speech direction detection circuit indicates a speech direction detection signal indicating a result of detecting single talk on the reception side and at least one of single talk and double talk on the transmission side. The residual echo suppressing circuit gradually increases the suppression of high frequency when the single talk on the receiving side is detected according to the call direction detection signal, and the single talk or double on the transmitting side. An echo canceller device characterized by performing high frequency control for gradually reducing suppression of high frequency when a talk is detected. 3. The echo canceller device according to claim 2, wherein the residual echo suppressing circuit includes a low-pass filter having a predetermined frequency-gain characteristic for performing the high frequency control. .