JPH0897752A - Acoustic echo elimination device - Google Patents

Abstract

PURPOSE: To make high speed performance compatible with high stability by updating a coefficient update gain for a coefficient correction quantity arithmetic circuit based on a fluctuation rate of accumulated arithmetic average power of each variable coefficient stored in a pseudo impulse response register. CONSTITUTION: A coefficient correction amount arithmetic circuit 7 updates sequentially a coefficient series so as to minimize a residual signal obtained a pseudo sound echo generated in a variable coefficient digital filter 3 from an acoustic echo component of a received signal given to a transmission signal input terminal 4 via an acoustic echo path from a reception signal output terminal 6. Then a coefficient update gain is revised to the coefficient correction quantity arithmetic circuit 7 by a fluctuation rate of accumulated arithmetic average power of each variable coefficient stored in the pseudo impulse response register 9. The high speed performance and high stability of deduction are secured by the means and mixture of an echo component on a communication channel is less and highly quality sound control is attained.

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 an acoustic echo component in which a signal on a receiving path appears in a transmitting path via an acoustic echo path. The present invention relates to an acoustic echo canceller that removes noise.

[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 classified 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 such as a video conference system. It is composed of a variable coefficient filter and a subtraction circuit that generate pseudo-acoustic echo. The basic operation of the acoustic echo canceller will be described below.

FIG. 5 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 terminal 2, and the reception signal of the reception signal input terminal 1 is branched and supplied to the variable coefficient filter 3 to generate pseudo acoustic echo. The transmission signal from the transmission signal input terminal 4 and the pseudo-acoustic echo that is the output of the variable coefficient filter 3 are input to the subtraction circuit 5, the acoustic echo component in the transmission signal is removed, and the output of the subtraction circuit 5 is It is output to the transmission signal output terminal 6. The output of the transmission signal output terminal 6 and the signal of the reception signal input terminal 1 are input to the correction amount calculation circuit 7, and the filter coefficient of the variable coefficient filter 3 is corrected by the output of the coefficient 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. Sum of products circuit 10
Is output as a pseudo acoustic 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 acoustic echo path is linear and represented by an FIR type digital filter, if the impulse response h (t) and the input received signal x (t) are used, the sampling time interval is was T, the acoustic echo yk is at time kT, 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 in the reception signal input terminal 1 and there is no voice signal in the transmission signal input terminal 4 and only acoustic echo exists, the echo elimination operation is performed as an adaptive operation state. This adaptive motion algorithm is generally a learning identification method (Atsuhiko Noda, Jinichi Nagumo: “System Learning Identification Method” Measurement and Control, 7, 9, pp.597-605 (1
968)) is adopted. Successive correction of hsk by the learning identification method is performed by the _{hs k + 1 = hs k +} α (x k e k) / x k 'x k (4). However, e _k = y _k −y s _k , 0 <α ≦ 1 (5), and e _k is called residual acoustic echo. Such a calculation operation is processed in the coefficient correction amount calculation circuit 7. The contents of the pseudo impulse response register 9 include the variable coefficient series h.
sk is stored. α is a coefficient update gain for determining the sensitivity of estimation, and the closer it is to 1.0, the larger the amount of correction can be given, and high-speed acoustic echo removal can be performed. However, in actual use, near-end noise can be reduced. It is necessary to change the setting depending on the line status. The fact that the coefficient update gain α is currently determined depends on an empirical rule. There are also ones that variably control the coefficient updating gain α depending on the magnitude of the residual acoustic echo and ones that are set according to the indoor characteristics (for example, Shoji Makino and Nobuo Koizumi: “The adaptive characteristics of echo cancellers in the room sound field. Regarding improvement ”, J. A., J71-A, 12, pp.2212-2214 (1988-12).

[0006]

The method of least squares (LMS)
In the parameter estimation by the learning identification method based on, the estimation performance greatly depends on the amount of the coefficient update gain α. According to the equation (5), if the range of α is between 0 and 1, some performance can be obtained, but the convergence speed and the saturation echo removal amount differ due to the difference in the value. This situation is shown in FIG. 4, where the value of the coefficient update gain α is 1.0 when a in the figure is 1.0 and b in the figure is 0.5. It can be seen that as the α value increases, the speed increases, but the amount of saturated echo removal decreases. There is a trade-off relationship between speeding up and operation stabilization, and thus it is difficult to achieve both high speed and operation stability.

The present invention has been made in view of the above points, eliminates the above problems, and is excellent in high speed and operational stability.
An object of the present invention is to provide an acoustic echo canceller having high adaptive performance and performing acoustic control while always maintaining a large acoustic echo canceling amount.

[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 having a pseudo impulse response register that receives the reception signal of the reception signal input terminal, and the sound of the reception signal input from the reception signal output terminal to the transmission signal input terminal through the acoustic echo path. In an acoustic echo canceling apparatus in which a coefficient sequence is sequentially updated by a coefficient correction amount calculation circuit so as to minimize a residual signal obtained by subtracting a pseudo acoustic echo generated by the variable coefficient digital filter from an echo component, A sound for updating the coefficient update gain for the coefficient correction amount calculation circuit according to the variation rate of the cumulative average power of each variable coefficient stored in the pseudo impulse response register. To provide an echo removal device.

[0009]

According to the present invention, since the high speed and high stability of the estimation operation are ensured by the above means, the reverberation component is hardly mixed into the communication line, the deterioration of the communication voice sound quality is prevented, and the call itself. It is possible to reduce the risk of howling that would otherwise be impossible, and high-quality acoustic control becomes possible.

[0010]

Embodiments of the present invention will now be described in detail 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 FIG. 1, according to the present invention, a conventional receiving signal input terminal 1, 3 receiving signal output terminal 2,
Variable coefficient digital filter 3, transmission signal input terminal 4,
The learning identification method was adopted as an adaptive algorithm composed of a subtraction circuit 5, a transmission signal output terminal 6, a coefficient correction amount calculation circuit 7, a reception signal input register 8, a pseudo impulse response register 9, and a product-sum calculation circuit 10. A device having the same configuration as the acoustic echo canceller is provided with a cumulative addition average power calculation circuit 1
1, a power fluctuation rate calculation circuit 12, and a coefficient update gain selection circuit 13 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 pseudo impulse which receives the reception signal of the reception signal input terminal 1 The variable coefficient digital filter 3 having the response register 9 and the variable coefficient digital filter 3 from the acoustic echo component of the reception signal input from the reception signal output terminal 2 to the transmission signal input terminal 4 through the acoustic echo path. In the acoustic echo canceling apparatus in which the coefficient series is sequentially updated by the coefficient correction amount calculation circuit 7 so as to minimize the residual signal obtained by subtracting the pseudo acoustic echo generated by The accumulated arithmetic mean power calculation circuit 11 for calculating the accumulated arithmetic mean power of each stored variable coefficient, and the power variation circuit calculating the fluctuation rate of the accumulated arithmetic mean power of each variable coefficient. A rate calculation circuit 12, stored in the coefficient update gain selection circuit 13 corresponding to the variation rate of the cumulative addition average power 0.
The coefficient update gain α in the range of 0 to 1.0 is selected, the selected value is sent to the coefficient correction amount calculation circuit 7, and the correction amount is calculated by the equation (4) based on this value. Acoustic echo canceller. The coefficient update gain selection circuit 13 compares the coefficient power fluctuation rate value with each of several kinds of threshold values interpolated in the circuit, and selects a coefficient update gain corresponding to a suitable threshold range. . FIG. 2 shows this conceptual diagram.
At this time, if it is detected that the coefficient power variation rate is below a certain level, the amount of calculation can be reduced by setting the coefficient correction amount calculation circuit 7 not to perform the correction amount calculation and update calculation. It is possible to reduce the load and reduce the load on the hardware. The method of calculating the volatility is as follows.

Dh _{k + 1} = | hs _{k + 1} ² −hs _k ² | / hs _k ² (6) The fluctuation rate shown in the equation (6) is an example, and is not a definitive calculation method. For example, the numerator may be the present value instead of the past value. The present invention also works effectively by using the difference value between dhk + 1 and dhk.

FIG. 3 shows the result a of the adaptive processing operation according to the present invention when white noise is used as a reference input. As a comparison target, the result b of the model in which the coefficient update gain is fixed to 0.5 is shown in the same figure. The vertical axis represents the amount of acoustic echo cancellation, and the horizontal axis represents time. The maximum setting value of the coefficient update gain of the model according to the present invention is 1.0 and the minimum setting value is 0.05. The response speed in the initial elimination transient region is 30 [d
It can be seen that the model according to the present invention is superior to the model according to the present invention about twice as much when compared in the case of B]. Since the coefficient update gain is gradually set to a small value, it is not affected by disturbance.

[0013]

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

(1) By using the present invention, high speed and high stability can be realized at the same time, so that high quality voice communication can be maintained and the risk of howling can be suppressed to a low level. (2) In the adaptive operation process, a variable coefficient that does not need to be updated is generated. This reduces the amount of calculation,
The burden on the hardware can be reduced.

(3) Since the variable coefficient is not updated more than necessary, a calculation error or malfunction is less likely to occur when the digital signal processor or the like is used.

[Brief description of drawings]

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

FIG. 2 is a block diagram showing the concept of a state determination control unit used in this description.

FIG. 3 is a diagram showing an example of acoustic echo cancellation characteristics when white noise according to the present invention used as a reference input is used in the present invention.

FIG. 4 is a diagram showing an example of acoustic echo canceling characteristics according to a conventional method when white noise according to the present invention used in the present description is used as a reference input.

FIG. 5 is a block diagram showing an example of 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 filter 4 transmission signal input terminal 5 subtraction circuit 6 transmission signal output terminal 7 correction amount calculation circuit 8 reception signal input register 9 pseudo impulse response register 10 sum of products calculation circuit 11 Cumulative average power calculation circuit 12 Power fluctuation rate calculation circuit 13 Coefficient update gain selection circuit

Claims (1)

[Claims] 1. A variable having a reception signal input terminal, a reception signal output terminal, a transmission signal input terminal, a transmission signal output terminal, and a pseudo impulse response register to which the reception signal of the reception signal input terminal is input. A coefficient digital filter, and subtracts the pseudo-acoustic echo generated by the variable coefficient digital filter from the acoustic echo component of the reception signal input to the transmission signal input terminal from the reception signal output terminal through the acoustic echo path. In the acoustic echo canceller in which the coefficient sequence is sequentially updated by the coefficient correction amount calculation circuit so as to minimize the obtained residual signal, the fluctuation rate of the cumulative addition average power of each variable coefficient stored in the pseudo impulse response register. The acoustic echo canceling device is characterized in that the coefficient updating gain for the coefficient correction amount calculation circuit is updated by.