JPS6319924A - Echo erasing device - Google Patents

Abstract

PURPOSE:To improve the converging speed and to obtain a long time of equalization by dividing with estimation an impulse answer of an echo path through an echo canceller of a small tap length and connecting the impulse answer to an echo canceller having a large tap length in response to increase of the cancelling value. CONSTITUTION:When the characterisitics of an echo path have a change and in a start mode, a control circuit 8 outputs the residual echoes of a 1st echo canceller EC1. Then the canceller EC1, the 2nd echo canceller EC2 and the 3rd echo canceller EC3 work independently of each other. When the residual echo output of the EC2 is smaller than that of the EC1, the circuit 8 selects the residual echo of the EC2 as an output and outputs the same correction coefficient to both cancellers EC1 and EC2. Thus the converging speed is improved and a long time of equalization is secured with an echo erasing device.

Description

Detailed Description of the Invention (Industrial Field of Application) The present invention is applicable to the removal of sidetone in a hub circuit that performs 2-wire to 4-wire conversion of a telephone, and the acoustic coupling between a speaker and a microphone in an electronic conference system. The present invention relates to an echo canceling device used for cutting etc.

(Prior Art) A conventional echo canceller will be explained with reference to FIG. Third
The figure is a schematic block diagram of a system including a conventional echo canceller used to break the acoustic coupling between a speaker and a microphone. In the figure, 31 is an input end for a far-end input signal, 32 is a D/A converter, 33 is a speaker, 34 is a microphone, 35 is an A/D converter, 36 is an output end for residual echo, and 37 is an echo canceller. It is. The far-end input signal input end 31 is connected to a D/A converter 32 and an echo canceller 37, and the D/A converter 32 is connected to a speaker 33 and an echo canceller 37, respectively. Microphone 3
4 is connected to an A/D converter 35, the A/D converter 35 is connected to an echo canceller 37, and the echo canceller 37 is connected to a residual echo output terminal 36. In addition, in the same figure.

(1') is the far-end input sample signal X1, (2') is the far-end input sample signal
') is a component z (t
The A/D converted sample signals 20 and (4') of ) represent the residual echo output e of the echo canceller, respectively.

Next, the operation will be explained. far end input sample signal X,
is radiated from the speaker 33 after being D/A converted, and a part of it z (t) goes around to the microphone 34 . Component z (t) that goes around from the speaker 33 to the microphone 34
is A/D converted and becomes sample signal 2. and is input to the echo canceller 37. On the other hand, the echo canceller 37 performs a far-end input sequence X1=(xlx, -1...
・・xJl. , ) 9 and the estimated impulse response of the echo path between the microphone 34 and the speaker 33 H,=(
A pseudo echo is generated by the convolution operation with h*-z)', and the sample signal 2. shown in (3') is generated. By subtracting the pseudo echo, a residual echo e is obtained, which is output from the residual echo output terminal 36. On the other hand, the estimated impulse response H1 is also successively corrected so as to minimize the output of the residual echo e.

In this way, as the estimated impulse response H4 approaches the impulse response of the echo pulse, the acoustic coupling between the speaker 33 and the microphone 34 can be weakened and the echo can be canceled.

(Problem to be Solved by the Invention) However, in the conventional configuration described above, when the impulse response length of the echo path is long and a long equalization time is required, the convergence speed of the echo canceller with a long tap length is slow. Therefore, there is a problem in that it takes time to eliminate the echo at startup or when the characteristics of the echo path change.

The present invention provides an echo canceling device that has a long tap length and has a fast convergence speed that can immediately follow changes in echo path characteristics.

(Means for Solving the Problems) In order to solve the above problems, the present invention generates a pseudo echo by convolving the estimated impulse response of the echo path with the far-end input string, and converts it from the transmission input. In a system in which multiple echo cancellers are connected, which has the function of outputting the residual echo by subtracting it and successively correcting the estimated impulse response so as to minimize the output of the residual echo by the far-end input string and the residual echo, and when the characteristics of the echo path change, each echo canceller with a short tap length is operated independently to estimate the impulse response of the echo path by dividing, and as the amount of cancellation increases, the echo canceller is gradually combined with the echo canceller with a longer tap length. It is.

(Function) With the above configuration, the present invention divides and estimates the impulse response of the echo path using the echo canceller with a short tap length at the time of startup and when the characteristic of the echo path changes, and as the amount of cancellation increases, these are combined to increase the tap length. Since the echo canceller is long, an echo canceling device with a long equalization time and a short convergence time can be realized.

(Example) An embodiment of the present invention will be described with reference to FIGS. 1 and 2.

FIG. 1 is a system block diagram showing the configuration of an embodiment of the present invention, and FIG. 2 is a system block diagram showing the configuration of an embodiment of the present invention.
.) is a functional block diagram of an echo canceller corresponding to the i-th one from the left, that is, EC.

In FIG. 1, C11 is the input end of the far-end input sample signal, 2 is the output end of the far-end input sample signal, and 3 is the input end of the transmission signal in which the near-end input is superimposed on the echo.

4 is the output end of the residual echo, 5 is the first echo canceller EC1 with a short tap length, 6 is the second echo canceller EC2 with the short tap length, 7 is the third echo canceller EC3 with the short tap length, and 8 is the input end. Output control and first echo canceller ECI, second echo canceller EC2, third echo canceller
This is a control circuit that calculates a correction coefficient for the echo canceller EC3.

The far end input sample signal input end 1 is the far end input sample signal output end 2. The input terminal 3 of the transmission signal in which the near-end input is superimposed on the echo is connected to the first echo canceller (ECI) 5 and the control circuit 8, respectively. The residual echo output terminal 4 is connected to a control circuit 8 through a first echo canceller (EC).
I) 5 is connected to the second echo canceller (EC2) 6 and the control circuit 8, and the second echo canceller (EC2) 6 is connected to the third
The third echo canceller (EC3) 7 is connected to the control circuit 8, and the third echo canceller (EC3) 7 is connected to the control circuit 8.

In FIG. 2, reference numeral 11 denotes an input end for a far-end input signal.

12 is the output end of the far-end input signal which has passed the delay corresponding to the tap length, 13 is the input end of the correction coefficient, 14 is the residual echo input end from the previous stage echo canceller (ECi-1), and 15 is the output end of the residual echo. , 16 is a subtracter, 17 is an estimated impulse response, 18 is a register for correcting the estimated impulse response 17, 19 is an adder, 20 is a product-sum calculator, and 21 is a shift register for far-end input.

The input end 11 of the far-end input signal is connected to the estimated impulse response correction register 18 and the shift register 21 for far-end input, and the output end 12 of the far-end input signal is connected to the shift register 2 for far-end input.
1, the correction coefficient input terminal 13 is connected to the estimated impulse response correction register 8, and the residual echo input terminal 14 is connected to the subtractor 16.
The subtracter 16 is connected to the residual echo output terminal 15 and the product-sum calculator 20, respectively.

The estimated impulse response 17 is an adder 19 and a product-sum calculator 2
0, the estimated impulse response correction register 8 is connected to the adder 19 and the far-end input shift register 21, and the product-sum calculator 20 is connected to the far-end input shift register 21.

In FIG. 2, the value of the estimated impulse response 17 is Hl, the contents of the estimated impulse response correction register 8 are ΔH+j, and the contents of the far-end input shift register are X.
, residual echo (1) is eyl+-11, residual echo (2
) are expressed as e and lil, respectively.

Next, the operation will be explained.

At startup and when the characteristics of the echo path change, the control circuit 8 in FIG. 1 outputs the residual echo eyll of the first echo canceller EC1,
The second echo canceller EC2 and the third echo canceller EC3 operate independently. Here, in FIG. 2, the product-sum calculator 20 generates a pseudo echo by convolving the value Hij of the estimated impulse response 17 with the value X of the far-end input shift register 21, and the subtracter 16 generates the residual echo. The pseudo echo is subtracted from the residual echo l+-11 from the (i-1)th echo canceller in the previous stage inputted from the input terminal 14, and a residual echo ejTil is outputted to the residual echo output terminal 15. On the other hand, in the figure, the estimated impulse response correction register 8 calculates the amount of correction for the value HIJ of the estimated impulse response 17 based on the external control input input from the correction coefficient input terminal 13, and the adder 19
The value Hl of the estimated impulse response 17 is corrected using H
Obtain i j *L. First echo canceller ECI
, the second echo canceller EC2 and the third echo canceller EC3 initially perform these operations independently;
The output of the residual echo e,'1 of the echo canceller EC2 is the residual echo e,il of the first echo canceller ECI.
When the output becomes clearly smaller than the output of +, the control circuit 8 in FIG. The same correction coefficient is output to the echo canceller EC2. After that, compare the outputs of the residual echo e, I2I of the second echo canceller EC2 and the residual echo e, 13' of the third echo canceller EC3, and if the residual echo ej peak of the latter is clearly smaller, , the control circuit 8 in FIG. 2 outputs the residual echo e,+31 of the third echo canceller EC3, and outputs the residual echo e,+31 of the third echo canceller EC3, and the third echo canceller EC1, the third echo canceller EC2,
The same correction coefficient is output to the third echo canceller EC3.

In this way, the impulse response of the echo path is divided and estimated by the echo canceller with a short tap length, and as the amount of cancellation increases, it is coupled to the echo canceller with a long tap length, so the convergence speed can be improved. It is possible to realize an echo canceling device that has a long tap length and has good ability to follow changes in echo path characteristics.

(Effects of the Invention) According to the present invention, a plurality of echo cancellers with short tap lengths are connected, and each connected echo canceller is operated independently at the time of startup and when the characteristics of the echo path change to adjust the impulse response of the echo path. By performing split estimation and gradually coupling to an echo canceller with a longer tap length as the amount of cancellation increases, it is possible to rapidly reduce the echo level and achieve a long equalization time.

[Brief explanation of the drawing]

FIG. 1 is a system block diagram showing the configuration of an embodiment of the present invention, FIG. 2 is a functional block diagram of the first echo canceller from the left among the echo cancellers connected in FIG. 1, and FIG. 3 is a conventional 1 is a schematic block diagram of a system including an echo canceller. 1.11... far end input signal input end, 2,12.
... Output end of far-end input signal, 3... Input end of transmission signal where near-end input is superimposed on echo, 4.15... Output end of residual echo, 5... First echo canceller EC
I, 6...Second echo canceller EC2, 7...
・Third echo canceller EC3, 8...control circuit,
13... Correction coefficient input terminal, 14... Residual echo input terminal, 16... Subtractor, 17... Estimated impulse response, 18... Estimated impulse response correction register, 19... Adder, 20... Product-sum calculator, 21... Shift register for far-end input. Patent applicant Matsushita Electric Industrial Co., Ltd. Figure 1 1 ° Kazanfule IS number input staff 2 ° “
Ren S enter p bunpu 11/(1'j rahaka 3... two-l (power furnace ° superimposed l coma to Chikahato 31 manpower brown 4...
1 Cora mountain p misfortune 5 ... Sai 1 echo \ in elephant 6 ... 2nd 1 cor h 7 Tsuji] 7 ... Ya 3 L cor \ man zeu Fig. 2 11 To the place p fortune Enter the name of Ohan I2, enter the wrong place, enter ρ, hurt Ramukajima 13... Sei wo shoichitsu λ Rikihana 14 1 (Re-kou Jinrikibato 15 1) (cut echo ヱOhanawa 16. 1←Shiri Ebisu 941B-3 Ryuto^
Nme A/person lA: ≦19 with supplementary rough edges IJt+$
3 20 First day 11th

Claims (1)

[Claims] A pseudo echo is generated by convolving the estimated impulse response of the echo path with the far-end input string, a residual echo is output by subtracting the pseudo echo from the transmission input, and a residual echo is generated using the far-end input string and the residual echo. In a system that connects multiple echo cancellers that have the function of sequentially correcting the estimated impulse response to minimize the output, at startup and when the characteristics of the echo path change,
An echo canceling device characterized in that each echo canceller operates independently and is gradually coupled to an echo canceller having a longer tap length as the amount of cancellation increases.