JPH05145447A - Acoustic echo canceller - Google Patents

Abstract

PURPOSE:To provide the acoustic echo canceller in which the processing quantity per sample is reduced and deterioration in the converging speed is reduced. CONSTITUTION:An H register 2 storing an impulse response estimate corresponding to an X register 1 storing reception signals from the present till the prescribed past consists of a 1st H block 21 and a 2nd H block 22. A control means 5 revises the estimate value of the impulse response for either the 1st H block 21 or the 2nd H block 22 according to the ratio of the revision. Thus, the data convolution calculation of the X register 1 and the H register 2 is implemented by a product sum means 3 to calculate an echo replica and a subtractor means 4 is used to subtract it from an input transmission signal thereby canceling an echo at a high speed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an acoustic echo canceller which suppresses howling and echo due to acoustic coupling between a speaker and a microphone of a loudspeaker telephone.

[0002]

2. Description of the Related Art In recent years, a loudspeaker telephone has been developed which comprises an acoustic echo canceller using an adaptive filter, suppresses acoustic coupling between a speaker and a microphone, and enables simultaneous telephone calls.

Since the adaptive filter is realized by digital signal processing, it is usually realized by a digital signal processor (hereinafter referred to as DSP). However, because the DSP has a limited computing power, the method of updating only some of the coefficients without updating all the adaptive filter coefficients within one sample has been adopted. March 2-6-1).

Hereinafter, the acoustic echo canceller portion in the above-mentioned document will be described as an example with reference to the drawings. FIG. 5 shows the configuration of a conventional acoustic echo canceller. In FIG. 5, 1 is the past 128 from the current received signal.
The X register as the first register for storing the received signals of the number of samples (echo cancellation time of 16 msec at 8 kHz sample), 2 corresponds to the X register 1, and the impulse response estimation value consisting of 128 data is stored. Two
The first half of the impulse response is the first H block 21, and the second half of the impulse response is the second H block 22.
Stored in. Since 3 synthesizes an echo replica,
128 of X register 1 and H register 2 for each sample
The sum-of-products means for performing the convolution operation of the individual data, the reference numeral 4 is a subtraction means for canceling the echo by subtracting the echo replica calculated by the sum-of-products means 3 from the transmission input, and the first or the first one to be updated for each sample. Toggle switch for alternately selecting 2 H blocks, 6 updates the impulse response of the block selected by the toggle switch 7 for 1 sample, and coefficient update for updating all impulse response values in the H register 2 with 2 samples It is a means.

The operation of the acoustic echo canceller configured as described above will be described below.

The echo replica yhj in the sum-of-products means 3
In order to synthesize the above, the signal sequence of the X register 1 and the impulse response sequence of the H register 2 are convoluted according to (Equation 1). j represents the time.

[0007]

[Equation 1]

Here, hij is the impulse response signal of the H register 2 and x _ji is the signal sequence of the X register 1.

In the subtracting means 4, the echo replica yhj shown in (Equation 1) is subtracted from the transmission input signal yj, and the residual echo ej is output. 1st H with toggle switch 7
When the block 21 is selected, the coefficient updating means 6 updates the estimated values (h0j, h1j, ..., H63j) of the first 64 impulse responses of the H register 2 according to (Equation 2).

[0010]

[Equation 2]

In the next sample, since the toggle switch 7 selects the second H block 22, the echo replica yhj + 1 is transmitted from the transmission input yj + 1 as in the previous sample.
Using the residual echo ej + 1 after subtracting, the coefficient updating means 6 according to (Equation 3) the estimated values (h64j + 1, h65j + 1, ...) Of the 64 impulse responses in the latter half of the H register.
..., h127j + 1) is updated.

[0012]

[Equation 3]

By thus updating all the data in the H register 2 with two samples, the H register 2 is updated per sample as compared with updating all the H registers 2 in one sample. Approximately 1/2 the calculation required for
Therefore, the number of taps of the acoustic echo canceller that can be realized by one DSP can be increased.

[0014]

However, the H register 2 is replaced by the first H block 21 and the second H block 22.
And the H register 2 is updated in the first half and the latter half alternately for each sample, the speed at which the coefficient of the H register 2 approaches the optimum value (hereinafter, convergence speed) is 1/2.
Become. In other words, divide the H register into M,
If all the data in the H register is updated with M samples, the convergence speed becomes 1 / M and the convergence becomes slow.

In consideration of the above problems, the present invention provides an acoustic echo canceller capable of dividing and updating the H register into a plurality of pieces to reduce the amount of processing per sample and to suppress deterioration of the convergence speed to a small extent. ..

[0016]

A first register for storing the past N samples (N is an integer of 2 or more) of received signals from the present received signal, and N corresponding to the first register,
Second register that stores an impulse response estimation value consisting of a number of pieces of data, and a product sum that performs convolution operation of N pieces of data of the first register and the second register for each sample in order to synthesize an echo replica Means, subtraction means for canceling the echo by subtracting the echo replica calculated by the product-sum means from the transmission input, and M estimated value sequences of impulse responses stored in the second register (M is 1).
<M <N integer) blocks (first H block, second H block, ..., Mth H block),
The updating priority of the M blocks is set by the control means and the control means in which the first H block has the highest priority and the priority decreases from the second, third, ... And a coefficient updating means for updating the impulse response of any one block for each sample according to the updated ratio.

[0017]

In the sum of products means, the sum of products of the received signals of the N samples of the telephones in the first register and the N impulse response estimated values of the second register are summed, and the transmission input to be separately transmitted from the telephone or the like. A replica of the echo contained in the signal is synthesized. The echo is canceled by subtracting the echo replica from the transmission input signal by the subtracting means. If the impulse response of the actual echo path and the impulse response estimate of the second register are approximately equal, the echo is sufficiently canceled, but between the impulse response of the actual echo path and the impulse response estimate of the second register. When the difference is large, the estimated value of the impulse response of the second register is updated as follows. The second register is M
.. (first H block, second H block, ..., Mth H block), and the estimation value of the impulse response of any one block is updated for each sample. Update according to the ratio. Since only the estimated value of the impulse response of one block is updated per sample, the amount of calculation per sample can be reduced and the number of taps of the acoustic echo canceller that can be realized by one DSP can be increased as in the conventional technique. The priority of update of each block is that the impulse response of the acoustic echo path has the lowest energy in the order of the direct sound, the single reflection sound, and the multiple reflection sound. Two
The control means controls so that the update rate becomes lower as the third, ..., Mth. The coefficient updating means updates the impulse response of any one of the blocks for each sample in accordance with the updating ratio determined by the control means. In this way, the frequency of the actual impulse response is high when the energy is high, and the frequency of the energy is low when the energy is low. You will be able to quickly get closer to, and you will be able to accelerate the convergence speed and cancel the echo quickly.

[0018]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An acoustic echo canceller according to a first embodiment of the present invention will be described below with reference to the drawings. FIG. 1 shows the configuration of an embodiment of the present invention. As a constituent element, 1 is an X register as a first register for storing the past 320 samples (echo cancellation time of 40 msec at 8 kHz sample) of the present received signal, and 2 corresponds to the X register 1, and 320 pieces The first half of the impulse response is stored in the first H block 21, and the second half of the impulse response is stored in the second H block 22. In order to synthesize the echo replica, 3 is a product-sum means for performing a convolution operation of 320 data of the X register 1 and the H register 2 for each sample, and 4 is an echo replica calculated by the product-sum means 3 from the transmission input. These are subtraction means for canceling the echo by subtracting them, and these have the same function as the conventional example. 5 designates the coefficient update priority of the first H block 21 as “2”, the second block 22 as “1”, and the first H block 21 is twice in three samples.
Is selected to control the second H register 22 once, and 6 is a coefficient updating means for updating the impulse response of the block set by the controlling means 5.

With respect to the acoustic echo canceller configured as described above, the mutual operation of the constituent elements will be described below. To synthesize the echo replica yhj,
In the sum of products means 3, the signal sequence of the X register 1 and the impulse response sequence of the H register 2 are convolved according to (Equation 4). j represents the time.

[0020]

[Equation 4]

Here, hij indicates the impulse response signal of the H register 2, and x _ji indicates the signal sequence of the X register 1.

The subtracting means 4 subtracts the echo replica yhj from the transmission input signal yj and outputs the residual echo ej.

The control means 5 normally exponentially attenuates the energy of the impulse response of the acoustic echo path per fixed period, so that the first H block 21 is updated twice in three samples and the second H-block is updated twice. The coefficient updating means 6 is controlled so that the H block 22 is updated once. Coefficient updating means 6
Updates the estimated value (h0j, h1j, ..., H159j) of the impulse response of the first H block 21 according to (Equation 5).

[0024]

[Equation 5]

Further, the estimated value of the impulse response of the second H block 22 (h160j, h161j, ..., H31)
9j) is updated according to (Equation 6).

[0026]

[Equation 6]

The control means 5 repeats the loop of updating the impulse response estimation value of the first H block 21 twice and updating the impulse response estimation value of the second H block 22 once. Control.

FIG. 2 shows changes in the echo cancellation amount (ERLE) of the acoustic echo canceller. The horizontal axis represents time, and the vertical axis represents the echo cancellation amount (ERLE) shown in (Equation 7).

[0029]

[Equation 7]

At time t = 0, the data in the H register 2 are all zero, and as the time elapses, the H register 2
The estimated value of the impulse response becomes close to the actual impulse response and the echo is canceled. The input signal is white noise, and the acoustic echo canceller has 320 taps in both the conventional example and the example. From this graph, it can be seen that the present embodiment estimates the impulse response of the echo path faster and converges faster than the conventional example.

As described above, according to this embodiment, as in the conventional example, all the H registers are updated in one sample by updating half of the estimated value of the impulse response of the H register in one sample. Compared with the above, the calculation required for updating the H register is approximately halved, and the number of taps of the acoustic echo canceller that can be realized by one DSP can be increased. Furthermore, by updating the first H block having the direct sound or the initial reflected sound at twice the frequency of updating the second H block, the estimated value of the impulse response of the H register becomes the actual impulse response. You'll be approaching quickly,
The convergence speed can be increased and the echo can be canceled out quickly.

In the embodiment, the H register 2 is set to the first H
The block 21 and the second H block 22 are divided into two, and the energy of the impulse response of the acoustic echo path per a certain period decays exponentially. The control means 5 controls the second H block 22 to be updated once.
In the case of an echo response such as a loudspeaker, in which the speaker and the microphone are mounted in the same housing and the direct wave energy is very large regardless of the installation environment, as shown in FIG. It is possible to further improve the convergence speed by measuring the typical impulse response and setting the update rate of each H block corresponding to the square root of the energy of the impulse response part corresponding to each divided H block. .. In the case where the impulse response of the echo path is as shown in FIG. 3, the H register is divided into two, the first H register is updated three times in four samples, and the second H block is updated once in four samples. As shown in FIG. 4, when the first H register is updated twice in three samples and the second H block is updated once in three samples, as shown in FIG. 4, the amount of echo cancellation is short. And the convergence speed can be improved.

[0033]

As is apparent from the above description, the acoustic echo canceller according to the present invention has the H function as the second register.
The register is divided into M blocks (first H block, second H block, ..., Mth H block), 1
The estimation value of the impulse response of any one block in the sample is updated according to the update ratio of each block. Since only the estimated value of the impulse response of one block is updated per sample, the amount of calculation per sample can be reduced and the number of taps of the acoustic echo canceller that can be realized by one DSP can be increased as in the conventional technique. The priority of update of each block is that the impulse response of the acoustic echo path has the lowest energy in the order of the direct sound, the single reflection sound, and the multiple reflection sound. It is controlled by the control means so that the update ratio becomes lower as the second, third, ... The coefficient updating means updates the impulse response of any one block for each sample in accordance with the updating ratio determined by the control means. As described above, the frequency of update of the actual impulse response is high when the amount of energy in the impulse response is high and the frequency of update is low in comparison with the amount of energy when the energy is low. As the distance approaches, the convergence speed becomes faster and the echo can be canceled more quickly.

Further, in the case of a loudspeaker telephone and the like, a speaker and a microphone are mounted in the same housing, and in the case of an impulse response of an echo path in which the energy of a direct wave is very large irrespective of the installation environment, a typical Impulse response is measured, and each H is corresponding to the square root of the energy of the impulse response part corresponding to each divided H block.
The convergence speed can be further improved by setting the block update ratio.

[Brief description of drawings]

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

FIG. 2 is a graph showing changes in the amount of echo cancellation of the acoustic echo canceller of the same example.

FIG. 3 is a waveform diagram showing an impulse response example of the acoustic echo path of the loudspeaker telephone by the acoustic echo canceller of the same embodiment.

FIG. 4 is a graph showing changes in the amount of echo cancellation of the acoustic echo canceller when the update ratio is determined from the impulse response measured in advance according to another embodiment of the present invention.

FIG. 5 is a block diagram showing the configuration of a conventional acoustic echo canceller.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 X register (first register) 2 H register (second register) 3 Sum of products means 4 Subtraction means 5 Control means 6 Coefficient updating means 21 First H block 22 Second H block

Claims (3)

[Claims] 1. A first register for storing past N samples (N is an integer of 2 or more) of received signals from the present received signal, and N impulse response estimation values corresponding to the first register. From a transmission input signal, and a product-sum means for convoluting N data of the first register and the second register for each sample to synthesize an echo replica. Subtracting means for canceling the echo by subtracting the echo replica calculated by the sum of products means and M impulse response estimation value sequences stored in the second register (M is 1 <M <
N integer) blocks (first H block, second H block)
Block, ..., Mth H block)
A control means for controlling the update frequency ratio of the individual blocks such that the first H block has the highest update ratio and the update frequency ratio decreases as the second, third, ... Acoustic echo canceller comprising coefficient updating means for updating the impulse response of any one block for each sample according to a controlled update ratio. 2. The control means sets the number of updates of the 1st, 2nd, ... Mth H blocks at a ratio of 2 ^M-1 : 2 ^M-2 : ...: 1. The acoustic echo canceller described. 3. A first register for storing the past N samples (N is an integer of 2 or more) of received signals from the present received signal, and N impulse response estimation values corresponding to the first register. From a transmission input signal, and a product-sum means for convoluting N data of the first register and the second register for each sample to synthesize an echo replica. Subtracting means for canceling the echo by subtracting the echo replica calculated by the sum of products means and M impulse response estimation value sequences stored in the second register (M is 1 <M <
N integer) blocks (first H block, second H block)
,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,, the (Mth H block) are divided into blocks, and a typical impulse response measured in advance is used, at a ratio according to the square root of the energy of the impulse response corresponding to each block. ... Control means for setting the ratio of the number of times of update of the Mth H block, and coefficient updating means for updating the impulse response of any one block for each sample according to the update ratio set by the control means Acoustic echo canceller with and.