JPH06101759B2 - Echo canceller - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a howling suppression circuit that suppresses echo and howling that occur in a hands-free telephone that communicates using a speaker and a microphone.

(Prior Art) Nowadays, a hands-free telephone is used for a car telephone, and it is necessary to remove echoes and howling in the car which are generated in the car. Therefore, an echo canceller system has been considered in the past. For example, "" Hands-free car phone terminal using echo canceller ", 1985, IEICE General Conference 2667, P.10
-380 ”. A conventional circuit will be described below with reference to the drawings.

FIG. 5 is a block diagram showing a hands-free telephone using a conventional echo canceller. In the figure, 51 is a far-end telephone, 52 is a 2-wire / 4-wire conversion circuit (hereinafter abbreviated as H), 53
Is a downlink transmission path, 54 and 55 are A / D converters, 56 is a received signal (hereinafter abbreviated as RIN), 57 and 58 are D / A converters, 59 is a speaker amplifier, 60 is a speaker, 61 is a microphone, 62 is a microphone amplifier,
63 is an acoustic echo signal (hereinafter abbreviated as SIN), 64 is an adaptive filter, 65 is an adaptive filter outgoing signal (hereinafter abbreviated as SINH), 66 is an adder, and 67 is an echo canceling output of the adder 66. A residual signal (hereinafter abbreviated as RES), 68 upstream is a transmission path.

Next, the operation of the hands-free telephone using the conventional echo canceller will be described with reference to FIG.

The far-end signal transmitted from the far-end telephone 51 passes through H52, the downlink transmission path 53 and the A / D converter 54 to become RIN56, and is input to the adaptive filter 64 in the automobile telephone. This RIN 56 is output from the speaker 60 through the D / A converter 57 and the speaker amplifier 59. The output signal is the speaker 60 and the microphone 61.
It wraps around to the microphone 61 by acoustic coupling between them. This route is called an echo path. Furthermore, the signal from the microphone 61 passes through the microphone amplifier 62 and the A / D converter 55, and
It becomes 63 and is input to the adder 66. And the adder 66
SIN63 and SINH65 which is the output signal of the adaptive filter 64 are phase-inverted and added, and RES67 is output. This RES67 is D / A
Far end telephone 51 through converter 58, upstream transmission line 68 and H52
Go back to. Therefore, the adaptive filter 64 is RIN56, SIN63
And an adaptive filter that estimates the transfer function H _{SM of the} echo path from the signal of RES67, and operates so that the value of RES67 becomes zero. That is, the echo canceller is the far end telephone 51.
The signal that wraps around from the speaker 60 to the microphone 61 so that the far-end signal input from the device does not return to the far-end telephone 51 again.
In other words, it is a device that cancels echoes.

(Problems to be Solved by the Invention) However, in the above-mentioned conventional apparatus, the characteristics of the echo path are estimated when there is a transmission signal (near-end signal) from the microphone and when the far-end signal from the far-end telephone is minute. The estimation operation of the adaptive filter is not performed correctly. Therefore, in this state, if the characteristics of the echo path change abruptly, the echo is not sufficiently erased, and there is a problem that howling occurs in a loop.

The present invention has been made to solve these problems, and an object of the present invention is to provide an echo canceller capable of high-quality telephone calls without causing howling.

(Means for Solving the Problem) In order to solve the above-mentioned problems, the present invention seeks by digital signal processing using an adaptive filter from acoustic echo generated by acoustic coupling between a speaker and a microphone of a hands-free telephone. In an echo canceller that eliminates acoustic echo by subtracting the pseudo echo, canceling means for canceling a sine wave generated in a closed loop formed by the acoustic system and electric system of the hands-free telephone, and howling occurring in the closed loop are detected, When howling is detected, it is characterized by including a detecting means for stopping the adaptive operation of the adaptive filter and operating the canceling means.

(Operation) According to the present invention having the above-described configuration, the pseudo echo obtained by the digital signal processing by the adaptive filter is subtracted from the acoustic echo that is usually generated by the acoustic coupling between the speaker and the microphone of the hands-free telephone. To eliminate the acoustic echo. Then, when the detecting means detects howling in the closed loop, the adaptive operation of the adaptive filter is stopped, and the canceling means is operated to cancel the sine wave generated in the closed loop, thereby suppressing the howling.

Therefore, the present invention can solve the above-mentioned problems, and can provide an echo canceller capable of performing a high quality call without causing howling.

(Example) Hereinafter, an example of the present invention will be described with reference to the drawings.

FIG. 1 is a schematic configuration diagram showing an embodiment of the present invention. FIG. 2 is a schematic configuration diagram showing the principle of the present invention. In FIG. 2, howling is a single sine wave with a large gain in the voice band when the loop loop gain is greater than 1 as shown in the figure, the signal entering this closed loop system is amplified while it circulates in the closed loop system. Is occurring. Therefore, howling is suppressed by using a sine wave canceller for canceling the sine wave instead of operating the adaptive filter during howling.

FIG. 3 is a diagram showing a state in which the amplitude and the phase of the sine wave of RIN and SIN in the present invention are different. As can be seen from the figure, the amplitude and phase of the sine wave at SIN are RIN during howling.
Therefore, it is considered that the amplitude and phase of the sine wave are different. Therefore, considering a sine wave canceller in such a case, the following calculation can be made.

First, the sine wave at RIN is x (kT) = R ₀ · sin (kω ₀ T) (1) The sine wave at SIN is y (kT) = R · sin (kω ₀ T + θ) (2) ) far. A circuit configuration for generating the equation (2) from the equation (1) is derived, and the sine wave is eliminated by using this circuit.

Next, Expanding equation (2), y (kT) = R · sin (kω 0 T + θ) = R {sin (kω 0 T) · cosθ + cos (kω 0 T) · sinθ} = (R · cosθ) · sin (kω ₀ T) + (R · sin θ) · cos (kω ₀ T) (3) Here, sin {(k-1) ω ₀ T} = sin (kω ₀ T) · cos (ω ₀ T) −cos (kω ₀ T) · sin (ω ₀ T) Substituting equation (4) into equation (3), here, I am trying.

Therefore, the configuration of the sine wave canceller is as shown in FIG. 4 from the equation (5). The adaptive control of a ₀ , a ₁ in FIG. 4 can be executed by using the usual steepest descent method.

Next, an embodiment of the present invention will be described with reference to FIG. In FIG. 1, 1 is a sine wave canceller, 2 is a double-talk / silence / howling detector that detects whether the closed-loop system state is double talk, silence, or howling from the signals of RIN and RES, and 3 is a transformer. This is an adaptive filter composed of a Versal filter. The echo canceller according to the present invention comprises a sine wave canceller 1, double talk / silence /
It is composed of a howling detector 2 and an adaptive filter 3. In operation, first, when the double-talk / silence / howling detector 2 detects any of double-talk, silence, and howling by RIN and RES, information for prohibiting update of the tap coefficient of the adaptive filter 3 is transmitted. When the double-talk / silence / howling detector 2 detects a howling state, the output of the sine wave cancel circuit 1 is turned on to suppress howling. Double talk /
When the silence / howling detector 2 does not detect a howling state, the output of the sine wave canceller 1 is turned off.

(Effects of the Invention) As described above, according to the present invention, the adaptive operation of the echo canceller when there is a transmission signal (near-end signal) from the microphone and when the far-end signal from the far-end telephone is minute. Even if the echo path characteristics change suddenly, the howling can be suppressed by operating the sine wave canceller by prohibiting the update of the tap coefficient of the adaptive filter when the howling state is detected. It is possible to provide an echo canceller capable of performing a high-quality call without suppressing howling by suppressing with a sine wave canceller.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram showing an embodiment of the present invention, FIG. 2 is a schematic configuration diagram showing the principle of the present invention, and FIG. 3 is different in amplitude and phase of sine waves of RIN and SIN in the present invention. FIG. 4 is a configuration diagram showing a sine wave canceller in the present embodiment, and FIG. 5 is a configuration diagram showing a hands-free telephone using a conventional echo canceller. 1 ... Sine wave canceller, 2 ... Double talk / silence / howling detector, 3 ... Adaptive filter.

Claims (1)

[Claims] 1. An echo canceller for eliminating the acoustic echo by subtracting a pseudo echo obtained by digital signal processing using an adaptive filter from an acoustic echo generated by acoustic coupling between a speaker and a microphone of a hands-free telephone. Canceling means for canceling a sine wave generated in a closed loop constituted by an acoustic system and an electric system of the handsfree telephone, and detecting howling occurring in the closed loop,
Stopping the adaptive operation of the adaptive filter when detecting a hammering, and comprising a detecting means for operating the canceling means, when the detecting means detects howling, stop the adaptive operation of the adaptive filter, An echo canceller, wherein howling is suppressed by operating the canceling means to cancel a sine wave generated in the closed loop.