JP2012165280A - Echo cancelling method, echo cancelling device and program - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an echo cancelling device exhibiting a high-level echo cancellation performance even if a clipping distortion occurs on the sound collection side.SOLUTION: A difference signal generation part subtracts a second pseudo echo signal from an input digital collection signal to generate a transmission signal to be output to a transmission terminal. If a sample value of a first pseudo echo signal exceeds a predetermined upper limit value, a clip part determines the predetermined upper limit to be a sample value of the second pseudo echo signal corresponding to the sample of the first pseudo echo signal, whereas it determines a predetermined lower limit value to be a sample value of the second pseudo echo signal corresponding to the sample of the first pseudo echo signal if a sample value of the first pseudo echo signal exceeds the predetermined lower limit value. Otherwise, the clip part determines the sample value of the first pseudo echo signal as the sample value of the second pseudo echo signal corresponding to the sample of the first pseudo echo signal, thereby generating the second pseudo echo signal.

Description

  The present invention relates to an echo canceling method and apparatus and program capable of effectively canceling an echo.

  FIG. 5 shows a functional configuration of a conventional echo canceling apparatus 900. The echo canceling device 900 collects the speaker 2 that converts the received signal sample x (n) sent from the far-end speaker input to the receiving end 1 into an acoustic signal, and the sound emitted by the near-end speaker. It is provided between the sounding microphone 3. When the sound emitted from the speaker 2 is input to the microphone 3 as an echo by reverberating on a wall or the like, the far-end speaker listens to the voice he / she is a little late and is uncomfortable. is there. The echo canceller 900 is used for the purpose of removing this echo.

  The echo cancellation apparatus 900 includes an AD converter 5, a difference signal generation unit 6, and an adaptive filter unit 7. The AD converter 5 converts the collected sound signal collected by the microphone 3 into a digital signal sample y (n). The difference signal generation unit 6 outputs a transmission signal sample e (n) obtained by subtracting the pseudo echo signal sample y (n) generated by the adaptive filter unit 7 from the collected sound signal sample y (n) to the transmission end 4. To do. The adaptive filter unit 7 receives the transmission signal sample e (n) and the reception signal sample x (n) as input, and sets the component of the reception signal sample x (n) superimposed on the transmission signal sample e (n) to 0. Such pseudo echo signal samples ^ y (n) are generated. The echo can be canceled by generating an accurate pseudo echo signal sample ^ y (n). In FIG. 5, an AD converter that converts the received signal sample x (n) into a digital signal is omitted. The operation of the adaptive filter unit 7 is disclosed in Non-Patent Document 1, for example.

  When performing a hands-free call or the like, the distance between the speaker and the microphone is often relatively short, and the sound output from the speaker may be input as a large signal to the microphone. In addition, only a specific frequency may increase due to resonance or the like.

  At this time, even if the sensitivity of the AD converter 5 is appropriately adjusted with respect to the voice of the receiving end speaker, the input signal from the speaker 2 becomes excessive, and noise is generated in the collected sound signal. Specifically, in many cases, clipping distortion occurs in the collected sound signal sample y (n) output from the AD converter 5. In order to prevent the occurrence of clipping distortion, it is conceivable to increase the allowable range of the signal of the AD converter 5 or decrease the sensitivity of the microphone. However, there are cases where these values cannot be freely changed. In addition, the quantization error is added to the voice signal of the near-end speaker by the amount corresponding to the reduction of the microphone sensitivity, and the sound quality is deteriorated.

  As an echo canceling apparatus considering clipping distortion, one disclosed in Non-Patent Document 2 is known. The echo canceller 950 disclosed in Non-Patent Document 2 shown in FIG. 6 takes into account distortion generated by a speaker, and is characterized in that the receiver-side clipping distortion learning unit 8 is provided for the echo canceller 900. ing. The receiving side clipping distortion learning unit 8 learns the clipping distortion generated in the speaker 2 and inputs the received signal including the distortion to the applied filter unit 7.

  Since the applied filter unit 7 generates a pseudo echo signal in consideration of clipping distortion generated in the speaker 2, it can generate a more accurate pseudo echo signal than the case where the distortion is not considered.

Simon Haykin, Adaptive Filter Theory, Prentice Hall International Inc, third edition, 1996, p.432-437. A. Stenger and W. Kellermann, “Nonlinear acoustic echo cancellation with fast converging memoryless preprocessor,” Int. Conf. On Acoustics, Speech and Signal Processing, volume 2, pp.805-808, 2000.

  However, none of the conventional echo cancellers deal with distortion occurring on the collected sound signal side, particularly clipping distortion occurring in the AD converter. As a method for suppressing the occurrence of clipping distortion occurring in a conventional AD converter, a method of expanding the allowable range of the signal of the AD converter as described above or a method of reducing the sensitivity of the microphone to prevent the occurrence of clipping distortion is mainstream. Met. In this conventional idea, there are problems such as the adaptive filter unit 7 not converging and an echo remaining forever, and problems such as sound quality degradation.

  The present invention has been made in view of such a problem, and an object thereof is to provide an echo suppression method, apparatus, and program for dealing with clipping distortion based on a completely different idea from the conventional one.

  The echo canceling apparatus of the present invention includes a difference signal generation unit, an adaptive filter unit, and a clip unit. The difference signal generation unit generates a transmission signal to be output to the transmission end by subtracting the second pseudo echo signal from the input digital sound pickup signal. The adaptive filter unit receives the received signal and the transmitted signal that are input to the receiving end and reproduced by the speaker, and generates a first pseudo echo signal. When the sample value of the first pseudo echo signal exceeds a predetermined upper limit value, the clip unit sets the predetermined upper limit value of the sample of the second pseudo echo signal corresponding to the sample of the first pseudo echo signal. When the sample value of the first pseudo echo signal exceeds a predetermined lower limit value, the value of the sample of the second pseudo echo signal corresponding to the sample of the first pseudo echo signal is set to the predetermined lower limit value. In other cases, the second pseudo echo signal is obtained by setting the sample value of the first pseudo echo signal as the sample value of the second pseudo echo signal corresponding to the sample of the first pseudo echo signal. Generate.

  Since the adaptive filter unit operates so as to cope with the clipping distortion generated in the AD converter or the like, it is possible to effectively cancel the echo with respect to the clipping distortion generated on the collected sound signal side.

  Even when the allowable range of the AD converter and the sensitivity of the microphone cannot be adjusted, the echo cancellation method of the present invention can effectively cancel the echo.

The figure which shows the function structural example of the echo cancellation apparatus 100 of this invention. The figure which shows the operation | movement flow of the echo cancellation apparatus 100. The figure which shows the function structural example of the echo cancellation apparatus 200 of this invention. The figure which shows an evaluation experiment result. The figure which shows the function structure of the conventional echo cancellation apparatus 900. The figure which shows the function structure of the echo cancellation apparatus 950 disclosed by the nonpatent literature 2. FIG.

  Embodiments of the present invention will be described below with reference to the drawings. The same reference numerals are given to the same components in a plurality of drawings, and the description will not be repeated.

  FIG. 1 shows a functional configuration example of the echo canceling apparatus 100 of the present invention. The operation flow is shown in FIG. The echo canceling apparatus 100 includes an AD converter 5, a difference signal generation unit 6, an adaptive filter unit 7, and a clip unit 9. The echo canceling apparatus 100 is different from the above-described conventional echo canceling apparatus 900 in that the clip unit 9 is provided. The echo canceling apparatus 100 is realized by reading a predetermined program into a computer composed of, for example, a ROM, a RAM, a CPU, and the like, and executing the program by the CPU.

[AD converter]
The AD converter 5 converts the analog signal y (t) (t represents time) collected by the microphone 3 into a discrete digital sound collection signal z _c at a predetermined sampling frequency. Here, notation each sample included in the digital sound collection signal z _c and digital voice collecting signal samples y (n) (n is the sample number).

  When the AD converter is an AD converter 5 having a resolution of 16 bits, for example, signal samples y (n) corresponding to a predetermined time of the analog signal y (t) collected by the microphone 3 are −32768 to 32767. (Hereinafter, referred to as the dynamic range of the collected sound signal) is converted into a digital sound pickup signal sample y (n) (Equation (1)).

When such an AD converter 5 has an input signal exceeding the dynamic range, the input signal is converted into the upper limit value (32768) or the lower limit value (-32768), and the converted waveform is the upper and lower limits. The peak of the waveform with the portion exceeding the value cut is crushed. This is called a clipping phenomenon, and the generated distortion is called clipping distortion. A digital sound pickup signal sample including clipping distortion is denoted by y _c (n). For example, when the sampling frequency is 8 kHz, the clipping phenomenon is about 1 to 3 samples for audio.

[Clip part]
The clip unit 9 adds the same distortion as the clipping distortion generated by the AD converter 5 to the first pseudo echo signal sample y (n) output from the adaptive filter unit 7 by the clip function f (^ y). Two pseudo echo signals are generated. The clip function f (^ y) that applies the same distortion as the clipping distortion generated in the AD converter 5 is expressed by Equation (2) when the resolution of the AD converter 5 is 16 bits.

The first pseudo echo signal after being clipped is set as ^ y _c = f (^ y).

[Applicable filter section]
Update of the adaptive filter in the applied filter unit 7 is performed as shown in Expression (3) when an NLMS (Normalized Least Means Square) algorithm is used.

Here, mu is a step size (0 ≦ μ ≦ 1), e (n) is first pseudo echo signal samples ^ y c _(n subjected the clipped voice collecting signal samples y _{c (n)} a clip function ) Is a transmission signal sample e (n) which is a difference (e (n) = y _c (n) − ^ y _c (n)).

  In general, when the transmission signal sample e (n) including distortion is fed back to the adaptive filter unit 7, the adaptive performance deteriorates. However, in the present invention, since the digital sound pickup signal sample y (n) and the second pseudo echo signal sample ^ y (n) input to the difference signal generation unit 6 include clipping distortion, the adaptive filter unit 7 Works without problems.

  The reason will be explained. Assuming that the transmission signal sample in the case where the AD converter 5 has no clipping phenomenon and the clip unit 9 does not perform the clipping function is e ′ (n) = y (n) − ^ y (n), the adaptive filter is updated. It can be expressed by equation (4).

  Equation (4) is the original adaptive filter update equation. There is a relationship shown in Expression (5) between the transmission signal sample e (n) when there is clipping distortion and the transmission signal sample e ′ (n) when there is no clipping distortion.

  Furthermore, the relationship shown in Expression (6) always holds.

Regarding the lower limit of the reason why the relationship of Expression (6) holds, the digital sound pickup signal samples y (n) and y _c (n) and the second pseudo echo signal samples ^ y (n) and ^ y _c (n) are clipped. This is self-evident because the denominator and the numerator have the same sign.

The upper limit is established by y _c (n) − ^ y _c (n) = 0 when y (n) ≠ y _c (n) and ^ y (n) ≠ y _c (n). Also, when y (n) = y _c (n) and ^ y (n) = ^ y _c (n), y _c (n) − ^ y _c (n) = y (n) − ^ y (n ).

When y (n) ≠ y _c (n) and ^ y (n) = ^ y _c (n),

This holds true regardless of the sign of y (n) and ^ y (n). The same holds true when y (n) = y _c (n) and ^ y (n) ≠ ^ _c (n).

  Therefore, Formula (3) can also be expressed by Formula (8) using α such that 0 ≦ α ≠ 1.

  Equation (8) is the same as equation (4), and can be regarded as only the step size is reduced. Therefore, the echo canceling apparatus 100 of the present invention operates without any problem even if clipping distortion exists in the digital sound pickup signal, and does not adversely affect the adaptive operation of the adaptive filter unit 7. The result of the evaluation experiment that verified the operation will be described later.

  The echo canceling apparatus according to the present invention may perform the pseudo echo generation process using the adaptive filter in the frequency domain. FIG. 3 shows a functional configuration example of the echo canceling apparatus 200 in which the adaptive filter unit 7 ′ operates in the frequency domain.

  The echo cancellation apparatus 200 includes an adaptive filter unit 7 ′ that operates in the frequency domain, a transmission side frequency domain conversion unit 10, a reception side frequency domain conversion unit 11, and a time domain conversion unit 12. Different from the echo canceling apparatus 100.

[Transmitter frequency domain converter]
The transmission-side frequency domain conversion unit 10 converts the transmission signal sample e (n) into a frequency-domain transmission frequency signal.

[Receiver side frequency domain converter]
The reception side frequency domain converting unit 11 converts the reception signal sample x (n) input to the reception end 1 and reproduced by the speaker 2 into a reception frequency signal in the frequency domain.

[Time domain conversion unit]
The time domain conversion unit 12 converts the frequency domain first pseudo echo signal output from the adaptive filter unit 7 ′ into a time domain first pseudo echo signal.

  As described above, the same effect as that of the echo canceller 100 can be obtained only by the point that only the adaptive filter unit 7 ′ operates in the frequency domain.

  Further, the present invention is not limited to the above-described embodiments, and for example, a configuration to which another configuration requirement such as an echo suppressor is added can be considered.

[Evaluation experiment]
An evaluation experiment was conducted for the purpose of evaluating the performance of the echo canceling apparatus 100 of the present invention. The result is shown in FIG. In FIG. 4, the horizontal axis represents time (seconds), and the vertical axis represents echo cancellation amount (dB). The experiment was performed by using a digital sound pickup signal sample y (n) obtained by an AD converter having a sampling frequency of 16 kHz and a resolution of 16 bits.

  The broken line in the figure is the echo cancellation characteristic when there is no clipping distortion by the conventional method. An alternate long and short dash line represents echo cancellation characteristics when clipping distortion exists in the conventional method. A solid line represents an echo cancellation characteristic when clipping distortion obtained by the echo cancellation apparatus 100 of the present invention exists.

  As can be seen from the fact that the solid line indicating the echo canceling characteristic of the present invention shows a characteristic close to the characteristic of the broken line, the echo canceling apparatus 100 of the present invention is effective even when clipping distortion is present in the digital sound pickup signal. Echo can be erased.

  Note that the processes described in the above method and apparatus are not only executed in time series according to the order of description, but may also be executed in parallel or individually as required by the processing capability of the apparatus that executes the processes. Good.

  In the above-described embodiment, an example in which the AD converter 5 is provided has been described. However, the present invention is not limited to this example. For example, digital signal samples may be directly input to the difference signal generation unit 6. In that case, the upper and lower limit values of the digital signal sample correspond to the dynamic range of the collected sound signal.

  When the processing means in the above apparatus is realized by a computer, the processing contents of the functions that each apparatus should have are described by a program. Then, by executing this program on the computer, the processing means in each apparatus is realized on the computer.

  The program describing the processing contents can be recorded on a computer-readable recording medium. As the computer-readable recording medium, for example, any recording medium such as a magnetic recording device, an optical disk, a magneto-optical recording medium, and a semiconductor memory may be used. Specifically, for example, as a magnetic recording device, a hard disk device, a flexible disk, a magnetic tape or the like, and as an optical disk, a DVD (Digital Versatile Disc), a DVD-RAM (Random Access Memory), a CD-ROM (Compact Disc Read Only) Memory), CD-R (Recordable) / RW (ReWritable), etc., magneto-optical recording media, MO (Magneto Optical disc), etc., semiconductor memory, EEP-ROM (Electronically Erasable and Programmable-Read Only Memory), etc. Can be used.

  This program is distributed by selling, transferring, or lending a portable recording medium such as a DVD or CD-ROM in which the program is recorded. Further, the program may be distributed by storing the program in a recording device of a server computer and transferring the program from the server computer to another computer via a network.

  Each means may be configured by executing a predetermined program on a computer, or at least a part of these processing contents may be realized by hardware.

Claims (10)

A difference signal generation unit that generates a transmission signal to be output to the transmission end by subtracting the second pseudo echo signal from the input digital sound pickup signal;
An adaptive filter unit that generates a first pseudo echo signal by using the received signal input to the receiving end and reproduced by the speaker and the transmitted signal as input;
When the sample value of the first pseudo echo signal exceeds a predetermined upper limit value, the predetermined upper limit value is set as a sample value of the second pseudo echo signal corresponding to the sample of the first pseudo echo signal, If the sample value of the first pseudo echo signal exceeds a predetermined lower limit value, the predetermined lower limit value is set as the sample value of the second pseudo echo signal corresponding to the sample of the first pseudo echo signal. In this case, the clip unit that generates the second pseudo echo signal by setting the sample value of the first pseudo echo signal as the sample value of the second pseudo echo signal corresponding to the sample of the first pseudo echo signal. When,
An echo canceling device comprising: A difference signal generation unit that generates a transmission signal to be output to the transmission end by subtracting the second pseudo echo signal from the input digital sound pickup signal;
A transmission-side frequency domain conversion unit that converts the transmission signal into a frequency-domain transmission frequency signal;
A reception-side frequency domain conversion unit that converts a reception signal input to the reception end and reproduced by a speaker into a reception frequency signal in the frequency domain;
A frequency domain adaptive filter unit that receives the reception frequency signal and the transmission frequency signal as input and generates a first pseudo echo signal in the frequency domain;
A time domain conversion unit for converting the first pseudo echo signal in the frequency domain into a first pseudo echo signal in the time domain;
When the sample value of the first pseudo echo signal in the time domain exceeds a predetermined upper limit value, the sample value of the second pseudo echo signal corresponding to the sample of the first pseudo echo signal is set to the predetermined upper limit value. If the value of the sample of the first pseudo echo signal in the time domain exceeds a predetermined lower limit value, the sample of the second pseudo echo signal corresponding to the sample of the first pseudo echo signal is used as the predetermined lower limit value. In other cases, the value of the sample of the first pseudo echo signal in the time domain is set as the value of the sample of the second pseudo echo signal corresponding to the sample of the first pseudo echo signal in the time domain. A clip unit for generating the second pseudo echo signal,
An echo canceling device comprising: In the echo canceling device according to claim 1 or 2,
An AD converter for converting an analog sound pickup signal into a digital sound pickup signal;
The echo cancellation apparatus according to claim 1, wherein the upper limit value and the lower limit value are an upper limit value and a lower limit value of digital signal samples that can be output from the AD converter, respectively. In the echo canceling device according to claim 1 or 2,
The echo canceling apparatus according to claim 1, wherein the upper limit value and the lower limit value are an upper limit value and a lower limit value of a digital signal sample that can be output by an AD converter that generates a digital sound pickup signal, respectively. In the echo canceling method for reducing or reducing the signal component caused by the signal reproduced from the speaker among the signal components included in the transmission signal,
An AD conversion process for converting a signal picked up by a microphone into a digital picked-up signal;
An adaptive filter process for generating a first pseudo-echo signal by using a reception signal input to a reception end and reproduced by a speaker and the transmission signal as input;
When the sample value of the first pseudo echo signal exceeds a predetermined upper limit value, the predetermined upper limit value is set as the sample value of the second pseudo echo signal corresponding to the sample of the first pseudo echo signal, When the sample value of the first pseudo echo signal exceeds a predetermined lower limit value, the predetermined lower limit value is set as the sample value of the second pseudo echo signal corresponding to the sample of the first pseudo echo signal, and other than the above In this case, the clipping process for generating the second pseudo echo signal by setting the sample value of the first pseudo echo signal as the sample value of the second pseudo echo signal corresponding to the sample of the first pseudo echo signal When,
The echo cancellation method characterized by including. A difference signal generating process for generating a transmission signal to be output to the transmission end by subtracting the second pseudo echo signal from the input digital sound pickup signal;
An adaptive filter process for generating a first pseudo-echo signal by using a reception signal input to a reception end and reproduced by a speaker and the transmission signal as input;
When the sample value of the first pseudo echo signal exceeds a predetermined upper limit value, the predetermined upper limit value is set as the sample value of the second pseudo echo signal corresponding to the sample of the first pseudo echo signal, When the sample value of the first pseudo echo signal exceeds a predetermined lower limit value, the predetermined lower limit value is set as the sample value of the second pseudo echo signal corresponding to the sample of the first pseudo echo signal, and other than the above In this case, the clipping process for generating the second pseudo echo signal by setting the sample value of the first pseudo echo signal as the sample value of the second pseudo echo signal corresponding to the sample of the first pseudo echo signal When,
An echo cancellation method comprising: A difference signal generating process for generating a transmission signal to be output to the transmission end by subtracting the second pseudo echo signal from the input digital sound pickup signal;
A transmission side frequency domain conversion process for converting the transmission signal into a frequency domain transmission frequency signal;
A reception side frequency domain conversion process for converting a reception signal input to the reception end and reproduced by a speaker into a reception frequency signal in the frequency domain;
A frequency domain adaptive filter process of receiving the received frequency signal and the transmitted frequency signal as input and generating a first pseudo echo signal in the frequency domain;
A time domain conversion process for converting the first pseudo echo signal in the frequency domain into a first pseudo echo signal in the time domain;
When the sample value of the first pseudo echo signal in the time domain exceeds a predetermined upper limit value, the sample value of the second pseudo echo signal corresponding to the sample of the first pseudo echo signal is set to the predetermined upper limit value. If the value of the sample of the first pseudo echo signal in the time domain exceeds a predetermined lower limit value, the sample of the second pseudo echo signal corresponding to the sample of the first pseudo echo signal is used as the predetermined lower limit value. In other cases, the value of the sample of the first pseudo echo signal in the time domain is set as the value of the sample of the second pseudo echo signal corresponding to the sample of the first pseudo echo signal in the time domain. A clipping process for generating a second pseudo echo signal,
An echo cancellation method comprising: In the echo cancellation method according to any one of claims 5 to 7,
An AD conversion process for converting an analog sound pickup signal into a digital sound pickup signal;
The echo canceling method, wherein the upper limit value and the lower limit value are an upper limit value and a lower limit value, respectively, of digital signal samples that can be output by the AD conversion process. In the echo cancellation method according to any one of claims 5 to 7,
The echo cancellation method, wherein the upper limit value and the lower limit value are an upper limit value and a lower limit value, respectively, of digital signal samples that can be output by an AD converter that generates a digital sound pickup signal.   A program for causing a computer to function as the echo canceling apparatus according to any one of claims 1 to 4.

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