JP3217614B2 - Acoustic echo canceller - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is used for a communication line, an indoor sound field control device, and a high-quality audio communication conference device, and a signal of a receiving path appears on a transmission path via an acoustic reflection path. The present invention relates to an acoustic reverberation removing device for removing noise.

[0002]

2. Description of the Related Art In general, acoustic echo cancellers are used for long-distance telephone lines using communication sanitation and submarine cables.
It can be broadly divided into one that removes reflection caused by impedance mismatch of the line-to-wire 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 for generating a pseudo acoustic reverberation and a subtraction circuit. The basic operation of the acoustic reverberation removing device will be described below.

FIG. 5 is a diagram showing a basic configuration of an acoustic reverberation removing apparatus. 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 a pseudo acoustic echo. The transmission signal from the transmission signal input terminal 4 and the pseudo acoustic reverberation output from the variable coefficient filter 3 are input to a subtraction circuit 5, where the acoustic reverberation 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. In the variable coefficient filter 3, the reception signal is input to the reception signal input register 8, and the product sum 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 product sum circuit 10. Product-sum 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 / four-wire converter for a long-distance telephone line, and to a speaker and a microphone for a loudspeaker system.

[0004] Assuming that the signal propagation characteristics of the acoustic reverberation path are linear and represented by an FIR type digital filter, and using the impulse response h (t) and the input received signal x (t), a sample time interval is obtained. was T, the acoustic echo yk is at time kT, represented by _{y k = h'x k (1)} . Here, h = [h ₁ , h ₂ ,..., H _n ] ′ ′ (2) x = [x _k−1 ,..., X _kn ] ′ ′: Vector transposition.

On the other hand, the estimated value of h at time kT is expressed as h
if s _k, estimated value ys _k of y _k is given by _{ys k = hs k 'x k} (3). In the acoustic reverberation removing device, when there is an audio signal at the receiving signal input terminal 1 and no acoustic signal exists at the transmitting signal input terminal 4 and only acoustic reverberation exists, the acoustic reverberation operation is performed as an adaptive operation state. This adaptive operation algorithm generally includes a learning identification method (Atsuhiko Noda, Jinichi Nagumo: “System Learning Identification Method”, Measurement and Control, 7, 9, pp. 597-605 (1
968)). 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, the _{e k = y k -ys k,} 0 < a α ≦ 1 (5) ek called the residual acoustic echo. Such a calculation operation is performed in the coefficient correction amount calculation circuit 7. The contents of the pseudo impulse response register 9 include a variable coefficient series h.
sk is stored. α is a coefficient updating gain for determining the sensitivity of estimation, and the closer the correction gain is to 1.0, the greater the amount of correction can be given, and high-speed acoustic reverberation can be removed. It is necessary to change and set according to the line condition. The actual situation is that the determination of the coefficient update gain α currently depends on empirical rules. The coefficient update gain α may be variably controlled according to the magnitude of the residual acoustic reverberation, or may be set in accordance with the room characteristics (for example, Shoji Makino, Nobuo Koizumi: “The adaptation characteristics of the echo canceller in the room sound field. Improvement, "IEICE (A), J71-A, 12, pp. 221-2214 (1988-12)).

[0006]

SUMMARY OF THE INVENTION Least squares method (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 equation (5), a certain performance can be obtained if the range of α is between 0 and 1, but the convergence speed and the amount of saturation reverberation differ depending on the difference between the values. FIG. 4 shows the situation when the value of the coefficient update gain α is 1.0 in the figure and 0.5 in the figure. It can be seen that the higher the value of α, the faster the speed, but the amount of saturation reverberation decreases. There is a trade-off between speeding up and operation stabilization, and there is a problem that it is difficult to achieve both high speed and operation stability.

[0007] The present invention has been made in view of the above points, and eliminates the above-mentioned problems, and is excellent in high-speed operation and operation stability.
An object of the present invention is to provide an acoustic reverberation removing apparatus which has high adaptive performance and performs acoustic control while always maintaining a large acoustic echo canceling amount.

[0008]

SUMMARY OF THE INVENTION The present invention has been made to solve these problems, and includes a reception signal input terminal, a reception signal output terminal, a transmission signal input terminal, a transmission signal output terminal, and a variable coefficient digital filter having a pseudo impulse response register which receives from the reception signal input terminal, via the front acoustic echo path from said reception signal output terminal
A coefficient correction amount calculating circuit is used to minimize the residual signal obtained by subtracting the pseudo acoustic reverberation generated by the variable coefficient digital filter from the acoustic reverberant component of the received signal input to the transmission signal input terminal. In the acoustic reverberation apparatus in which the coefficient sequence is sequentially updated, the value of the variation rate of the cumulative average power of each variable coefficient stored in the pseudo impulse response register is compared with several types of threshold values inserted in the circuit, Provided is an acoustic reverberation removal apparatus having a coefficient update gain selection circuit capable of selecting whether a block is an update operation processing target depending on whether the block becomes a predetermined value or less.

[0009]

According to the present invention, since the high speed and high stability of the estimating operation are ensured by the above-mentioned means, reverberation components are hardly mixed into the communication line, the deterioration of the sound quality of the communication voice is prevented, and the communication itself is prevented. This can reduce the risk of howling occurrence, which makes it impossible to perform sound control, and enables high-quality sound control.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 is a block diagram showing a configuration of an acoustic reverberation removing apparatus according to the present invention. As shown in FIG. 1, the present invention provides a conventional reception signal input terminal 1, a conventional reception signal output terminal 2,
Variable coefficient digital filter 3, transmission signal input terminal 4,
A learning identification method is adopted as an adaptive algorithm comprising a subtraction circuit 5, a transmission signal output terminal 6, a coefficient correction amount operation circuit 7, a reception signal input register 8, a pseudo impulse response register 9, and a product-sum operation circuit 10. An accumulative average power calculation circuit 1
1, a power fluctuation rate calculation circuit 12, and a coefficient update gain selection circuit 13 are added. The pseudo-impulse which receives 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 of the reception signal input terminal 1. The variable coefficient digital filter 3 having a response register 9 and the variable coefficient digital filter 3 based on the acoustic reverberation component of the received signal input from the received signal output terminal 2 to the transmission signal input terminal 4 via the acoustic reverberation path. In the acoustic reverberation removing apparatus in which the coefficient sequence is sequentially updated by the coefficient correction amount calculating circuit 7 so as to minimize the residual signal obtained by subtracting the pseudo acoustic reverberation generated in the above, the pseudo impulse response register 9 The accumulated average power calculation circuit 11 for calculating the accumulated average power of each of the stored variable coefficients alone, and the power conversion circuit 11 calculating the variation rate of the accumulated average power of each of the variable coefficients alone. 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.
A 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 based on this value by equation (4). Acoustic echo canceller. The coefficient update gain selection circuit 13 performs an operation of comparing the value of the variation rate of the coefficient power with each of several threshold values inserted in the circuit and selecting 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 variation rate of the coefficient power has become equal to or less than a certain value, if the correction amount calculation and the update calculation of the coefficient in the coefficient correction amount calculation circuit 7 are not performed, the calculation amount is reduced. It is possible to reduce the load and reduce the load on the hardware. The calculation method of the fluctuation rate is as follows.

[0011] _{dh k + 1 = | hs k} + 1 2 -hs k 2 | / hs k 2 (6) fluctuation rate shown in equation (6) is an example, not a definitive calculation method. For example, the numerator may be a present value instead of a past value. Also, the present invention functions effectively even if a difference value between dhk + 1 and dhk is used.

FIG. 3 shows a 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 FIG. The vertical axis is the amount of acoustic echo cancellation, and the horizontal axis is time. The maximum set value of the coefficient update gain of the model according to the present invention was 1.0, and the minimum set value was 0.05. The response speed in the initial erasure transient region is 30 [d
B], it can be seen that the model according to the present invention is approximately twice as good as the model according to the present invention. Since the coefficient update gain is gradually set to a small value, the coefficient update gain is not affected by disturbance.

[0013]

As described 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 danger of howling can be suppressed. (2) In the adaptive operation process, a variable coefficient that does not need to be updated is generated. This reduces the amount of computation,
Hardware burden can be reduced.

(3) Since the variable coefficients are not updated more than necessary, when a digital signal processor or the like is used, calculation errors and malfunctions are less likely to occur.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration example of an acoustic reverberation removing apparatus according to the present invention.

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

FIG. 3 is a diagram illustrating an example of an acoustic reverberation elimination characteristic when white noise according to the present invention used in the present invention is used as a reference input;

FIG. 4 is a diagram showing an example of acoustic echo cancellation characteristics according to a conventional method when the 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 a conventional acoustic reverberation removing apparatus using a general learning identification method.

[Explanation of symbols]

 REFERENCE SIGNS LIST 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 operation circuit 8 reception signal input register 9 pseudo impulse response register 10 product sum operation circuit 11 Cumulative average power calculation circuit 12 Power fluctuation rate calculation circuit 13 Coefficient update gain selection circuit

Claims (1)

(57) [Claims] 1. A variable coefficient digital filter 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 input from the reception signal input terminal. When the residual obtained by subtracting the pseudo acoustic echo that is arising from the acoustic echo components of the received signal input from the reception signal output terminal to the transmission signal input terminal via the acoustic echo path in said variable coefficient digital filter In an acoustic reverberation removing apparatus in which a coefficient sequence is sequentially updated by a coefficient correction amount calculating circuit so as to minimize a difference signal, the value of the variation rate of the cumulative addition average power of each variable coefficient stored in the pseudo impulse response register is calculated.
Comparison with each of several threshold values interpolated in the circuit, below a certain value
Depending on whether or not
A coefficient update gain selection circuit that can select
Acoustic echo canceller characterized by having