JPH07154306A - Acoustic echo canceller - Google Patents

Abstract

(57) [Summary] [Purpose] By relatively detecting the temporal change of near-end noise mixed as a disturbance in the dependent variable and sequentially changing the coefficient correction loop gain threshold value according to the state, An object of the present invention is to provide an acoustic echo canceller with improved stability and convergence to a true value. [Structure] A reference signal on which a pseudo white noise signal of a known low power level such as a maximum period sequence code is superimposed is input to the sound field, and the power of the transmission signal as the output from the sound field and the pseudo white noise signal Using the power difference as the first evaluation value, the error signal power as the second input, and making the interpolation threshold of the coefficient correction loop gain correspond to the line state to improve the operation stability and the convergence speed to the true value. You can

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is used in a communication line, a room sound field control device, and a high-quality voice communication conference device, and removes acoustic reverberation components in which a signal on a receiving path appears through a transmitting path. The present invention relates to an echo canceller.

[0002]

2. Description of the Related Art Generally, an acoustic echo canceller is used in communication hygiene and long-distance telephone lines using a submarine cable.
It can be roughly divided into one that removes reflection caused by impedance mismatch of the line-to-four-line converter and one that removes reverberation due to acoustic coupling of speaker's voice in a loudspeaker telephone such as a video conference system. It is composed of a variable coefficient filter that generates a pseudo echo and a subtraction circuit. The basic operation of the acoustic echo canceller will be described below.

FIG. 3 is a diagram showing the basic structure of an acoustic echo canceller. The reception signal input terminal 1 is connected to the reception signal output 2, and the reception signal of the reception signal input terminal 1 is branched and supplied to the variable coefficient filter 3 to generate a pseudo echo. The transmission signal from the transmission signal input terminal 4 and the pseudo echo that is the output of the variable coefficient filter 3 are input to the subtraction circuit 5, the echo component in the transmission signal is removed, and the output of the subtraction circuit 5 is the transmission signal. The signal is output to the signal output terminal 6. Transmission signal output terminal 6
Output and the signal of the reception signal input terminal 1 are the correction amount calculation circuit 7
And the filter coefficient of the variable coefficient filter 3 is corrected by the output of the correction amount calculation circuit 7. The reception signal is input to the reception signal input register 8 in the variable coefficient filter 3, and the sum of products of the reception signal of the reception signal input register 8 and the pseudo impulse response of the pseudo impulse response register 9 is obtained by the sum of products circuit 10. The output of the product-sum circuit 10 is output as a pseudo echo. The reception signal output terminal 2 and the transmission signal input terminal 4 are connected to a two-wire to four-wire converter in the case of a long-distance telephone line, and to a speaker and a microphone in the case of a public telephone system.

Assuming that the signal propagation characteristic of the echo path is linear and represented by a FIR type digital filter, if the impulse response h (t) and the input received signal x (t) are used, the sampling time interval is The echo y _{k at} time kT is represented by y _k = h'x _k (1). However, h = [h ₁ , h ₂ , ..., H _n ] '(2) x = [x _k-1 , ..., x _kn ]'': transposition of the vector.

On the other hand, the estimated value of h at time kT is h
If s _k , the estimated value ys _k of y _k is given by ys _k = hs _k ′ x _k (3). In the acoustic echo canceller, when there is a voice signal at the reception signal input terminal 1 and there is no voice signal at the transmission signal input terminal 4 but only an echo exists, the echo elimination operation is performed as an adaptive operation state. A learning identification method is generally adopted for this adaptive operation algorithm. Successive correction of hsk by the learning identification method is performed by _{hs k + 1 = hs k +} α (x k e k) / x k 'x k (4). However, a _{e k = y k -ys k,} 0 <α ≦ 1 (5), the e _k is referred to as residual echo. Such an arithmetic operation is processed in the correction amount arithmetic circuit 7. The contents of the pseudo impulse response register 9 include the variable coefficient hs _k
Is stored. α is a correction loop gain for determining the sensitivity of estimation, and a larger correction amount can be given as it approaches 1.0, but it must be changed depending on near-end noise and line conditions.

[0006]

When a near-end noise of a relatively large level is inputted to the transmission signal input terminal, it is made to correspond only to the level of the average power of the error signal in a certain section. In the modified loop gain setting, when there is a disturbance such as near-end noise, the noise level carries the modified loop gain switching threshold to a carry value, resulting in setting a larger modified loop gain than necessary. Annoying reverberant sound is generated. In addition, there is a problem in that the estimated system impulse response coefficient sequence is oscillated and acoustic echo removal cannot be performed with high accuracy because a large amount of correction is added, although it cannot be identified more than at present.

The present invention has been made in view of the above points, and eliminates the above problems, detects the influence of a disturbance such as near-end noise other than the explanatory variables, and detects the impulse response of the sound field to be controlled. It is an object of the present invention to provide an acoustic echo canceller with improved stability of estimation and speed of convergence to a true value.

[0008]

SUMMARY OF THE INVENTION The present invention is to solve these problems and comprises a reception signal input terminal, a reception signal output terminal, a transmission signal input terminal, and a transmission signal output terminal. A variable coefficient digital filter that receives the received signal input from the received signal input terminal, a pseudo impulse response register that stores the coefficient series of the variable coefficient digital filter, the contents of the pseudo impulse response register, and the received signal input. A product-sum operation circuit that performs a convolution integral operation with the content of the reception-signal input register that stores the reception signal from the terminal, a pseudo-acoustic echo generated by the product-sum operation circuit, and the input from the transmission-signal input terminal. The subtraction circuit for obtaining the residual echo by subtracting the acoustic echo from the acoustic echo and the variable coefficient digital filter are supplied with the estimated approximate value of the echo. In an acoustic echo canceller having a coefficient correction amount calculation circuit for automatically updating a coefficient sequence of a pseudo impulse response register, a pseudo echo having an average value "zero" regardless of a reception signal at the reception signal input terminal. White noise generating circuit that generates and generates a typical white noise, a first integrating circuit that calculates the constant section average power of the pseudo white noise, a reception signal at the reception signal input terminal, and the pseudo white signal. An adder circuit that is added to generate a reception signal at the reception signal output terminal, a second integrating circuit that calculates a constant section average power of the transmission signal at the transmission signal input terminal, and a voiced section of the transmission signal. And a voiced unvoiced determination circuit for detecting an unvoiced sound section, a level comparison circuit for comparing a constant section average power of the unvoiced sound section of the transmission signal and an average power of the pseudo white noise, and the error signal And a loop gain setting circuit that determines a loop gain based on a ratio of a level difference obtained by the level comparison circuit and a constant section average power of the error signal. Pseudo white noise is used as a reference level between the reception signal input terminal and the transmission signal output terminal, and a correction loop gain that determines the correction amount of the pseudo impulse response is arbitrarily changed as a reference level to obtain the acoustic echo signal. Provided is an acoustic echo canceller that improves convergence characteristics. Furthermore, the power level of the near-end noise input from the transmission signal input terminal is detected by the internal evaluation value of the loop gain setting circuit, and the detected power level is used as a detection threshold value for two-way communication detection. An acoustic echo canceller according to claim 1 is provided.

[0009]

According to the present invention, the above-mentioned means does not treat meaningless near-end noise as an explanatory variable as a dependent variable while remaining unknown, but adaptively adjusts the modified loop gain while sequentially observing the situation of near-end noise. Since it is changed and reverberation control is performed,
It is always stable and enables high-speed dereverberation. Also, in this method, the steady level standard of the communication line can be set by oneself, and reverberation control can be performed with this standard as the target. By using this standard, it is possible to easily perform high-precision bidirectional communication detection and provide a high-quality voice communication conference space.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described in detail below with reference to the drawings. FIG. 1 is a block diagram showing the configuration of the acoustic echo canceller of the present invention. As shown in the figure, the present invention uses the conventional reception signal input terminal 1, reception signal output terminal 2, variable coefficient digital filter 3, transmission signal input terminal 4, subtraction circuit 5, transmission signal output terminal 6, coefficient correction amount. Arithmetic circuit 7, reception signal input register 8, pseudo impulse response register 9,
A pseudo white noise generating circuit 11, an adding circuit 12, an integrating circuit 13, an integrating circuit 14, a voiced / unvoiced determination is provided in a device having the same configuration as the acoustic echo canceling device adopting a learning identification method as an adaptive algorithm including a product-sum operation circuit 10. Circuit 15, level comparison circuit 16, integration circuit 17, loop gain setting circuit 1
8, an exclusive logical addition circuit 19, and a delay circuit 20 are added.

The reception signal input terminal 1, the reception signal output terminal 2, the transmission signal input terminal 4, the transmission signal output terminal 6, and the reception signal input from the reception signal input terminal 1 The variable coefficient digital filter 3 to be input, the pseudo impulse response register 9 storing the coefficient series of the variable coefficient digital filter 3, the contents of the pseudo impulse response register 9 and the reception signal from the reception signal input terminal 1. The sum of products calculation circuit 10 for performing a convolution integral calculation with the contents of the reception signal input register 8 storing the above, the pseudo acoustic echo generated by the sum of products calculation circuit 10 and the transmission signal input terminal 4 are inputted. The subtraction circuit 5 which takes the difference value from the acoustic echo and the variable coefficient digital filter 3 supply the pseudo-in so that the approximate value of the echo is supplied. In the acoustic echo canceller configured with the coefficient correction amount calculation circuit 7 for controlling so that the coefficient series of the loose response register is automatically updated, the pseudo white noise generated by the pseudo white generation circuit 11 is The adding circuit 12 applies the received signal to the received signal and outputs the signal from the received signal output terminal to the outside of the communication line. This reception signal passes through the echo path and is input to the communication line as the transmission signal from the transmission signal input terminal 4. The constant section average power of the transmission signal is calculated by the integration circuit 14, and the voiced / unvoiced determination circuit 1
5, the unvoiced sound portion is detected. Next, the level comparing circuit 16 compares the power level of the unvoiced sound portion with the output power level of the integrating circuit 13 for obtaining the constant section average power of the pseudo white noise generated by the pseudo white noise generating circuit 11.

On the other hand, the subtraction circuit 5 subtracts the pseudo reverberation generated from the transmission signal from the transmission signal input terminal 4 and the reception signal input from the reception signal input terminal 1, and outputs the error signal. The integrating circuit 14 calculates the average power of the error signal for a certain period. This average power, the constant section average power of the pseudo white noise obtained by the level comparison circuit 16 and the power level difference of the unvoiced part are used as two inputs, and the loop gain setting circuit 18 makes a correction loop corresponding to the line state. Set the gain to operate the adaptive processing. That is, the output of the level comparison circuit 16 serves as a standard for evaluating the influence of the attenuation characteristic of the unknown system and the near-end noise, and the ratio in the loop gain setting circuit 18 serves as a standard for evaluating the level of the near-end noise. ing. Since this reference value is consistent during the control operation, the two-way communication in which the voice signal of the speaker is simultaneously present in the voice signal of the voice signal output terminal 2 and the voice signal input terminal 4 during communication is performed. At this time, the power ratio, which is an internal reference of the loop gain setting circuit 18, is used as a detection reference for bidirectional communication.

FIG. 2 shows an example of the configuration of the pseudo white noise generating circuit 11 described above. This is a 10-stage maximum period sequence code, and a circuit which can generate and generate pseudo white noise having a period of 1023 samples with a simple configuration including two elements of the exclusive logical adder circuit 19 and the delay circuit 20. Is.

[0014]

As described in detail above, according to the present invention, the following excellent effects are expected.

(1) Since the near-end noise can be relatively observed, the relationship between the explanatory variable and the dependent variable is clarified, and stable dereverberation control considering the influence of the near-end noise can be performed.

(2) Since the control reference can be set by oneself and the arrival dereverberation amount is known, it is not necessary to forcibly give a large correction amount, and oscillation does not occur.

(3) Since a consistent reference is obtained during the control operation regardless of whether the near-end noise is large or small, efficient correction loop gain setting can be performed, and the speed of convergence to the true value can be increased. I can.

(4) Since a constant level of pseudo white noise is superimposed like background noise, annoying irregular sounds such as residual error signals are erased, and a sound field as a good communication conference system is provided. Can be provided.

(5) Since the power level of the near-end noise is sequentially obtained as known information, the threshold value for nonlinear conversion processing can be always clarified, and reliable reverberation control can be performed.

(6) Since it has a stable and constant standard independently for the line status, it is possible to detect bi-directional communication at high speed and with high accuracy, and to those who use a high-quality work space. It can be provided to.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration example of an acoustic echo canceller of the present description.

FIG. 2 is a block diagram showing a configuration example of a pseudo white noise generation circuit used in the present invention.

FIG. 3 is a block diagram showing a basic configuration of an acoustic echo canceller using a conventional general learning identification method.

[Explanation of symbols]

 1 reception signal input terminal 2 reception signal output terminal 3 variable coefficient digital filter 4 transmission signal input terminal 5 subtraction circuit 6 transmission signal output terminal 7 coefficient correction amount calculation circuit 8 reception signal input register 9 pseudo impulse response register 10 sum of products calculation Circuit 11 Pseudo white generation circuit 12 Addition circuit 13 Integration circuit 14 Integration circuit 15 Voiced / unvoiced determination circuit 16 Level comparison circuit 17 Integration circuit 18 Loop gain setting circuit 19 Exclusive logic addition circuit 20 Delay circuit

Claims (2)

[Claims] 1. A variable coefficient digital filter which receives a reception signal input terminal, a reception signal output terminal, a transmission signal input terminal, a transmission signal output terminal, and a reception signal input from the reception signal input terminal. And a pseudo impulse response register that stores the coefficient sequence of the variable coefficient digital filter, and a convolution integral of the contents of the pseudo impulse response register and the contents of the reception signal input register that stores the reception signal from the reception signal input terminal. A sum-of-products calculation circuit for performing a calculation, a subtraction circuit for obtaining a residual echo by making a difference between the pseudo-acoustic echo generated by the sum-of-products calculation circuit and the acoustic echo input from the transmission signal input terminal, and the variable A control for automatically updating the coefficient sequence of the pseudo impulse response register to which the estimated approximation value of the echo is supplied to the coefficient digital filter is provided. In the acoustic echo canceller having a coefficient correction amount calculation circuit, a pseudo white noise generating circuit for generating and generating pseudo white noise having an average value "zero" regardless of the reception signal at the reception signal input terminal, A first integrating circuit for calculating the constant section average power of the pseudo white noise; and an adder circuit for adding the reception signal at the reception signal input terminal and the pseudo white signal to generate a reception signal at the reception signal output terminal. A second integrating circuit for calculating a constant section average power of the transmission signal at the transmission signal input terminal, a voiced unvoiced determination circuit for detecting a voiced sound section and an unvoiced sound section of the transmission signal, and the transmission signal Level comparing circuit for comparing the average power of the unvoiced sound in the constant section and the average power of the pseudo white noise, and the third level for calculating the average power of the constant section of the error signal.
And a loop gain setting circuit that determines a loop gain from the ratio of the level difference obtained by the level comparison circuit and the constant section average power of the error signal, and inputs the pseudo white noise to the reception signal input. As a reference level between the terminal and the transmission signal output terminal, it is possible to improve the convergence characteristic of the acoustic echo signal by arbitrarily changing the correction loop gain that determines the correction amount of the pseudo impulse response as the reference level. Characteristic acoustic echo canceller. 2. A power level of near-end noise input from the transmission signal input terminal is detected by an internal evaluation value of the loop gain setting circuit, and the detected power level is a detection threshold value for detecting bidirectional communication. The acoustic echo canceller according to claim 1, wherein the acoustic echo canceller is used as.