JP5325613B2 - Echo canceller - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve an attenuation amount of an echo canceler by eliminating influence of aliasing distortion. <P>SOLUTION: When a FAX signal is detected from a reception input signal IN1 or an addition signal IN2' by FAX signal detection parts 21, 22, frequencies in frequency bands of a transmission signal and a reception signal outside a frequency band of the FAX signal are cut by LPFs 26, 27. Respective band division parts 12, 13 divide output signals of the respective LPFs 26, 27 into low-frequency signals and high-frequency signals. A low-frequency sub-band echo canceler 15 removes an echo from the divided low-frequency signal. The low-frequency signal with the echo removed therefrom and ground potential (silence) selected by a selector 25 are combined with each other by a band synthesis part 14, and a transmission output signal OUT is output. <P>COPYRIGHT: (C)2010,JPO&amp;INPIT

Description

  The present invention relates to an echo canceller apparatus that improves an echo canceller attenuation amount during facsimile (hereinafter referred to as “FAX”) communication in a broadband network.

  In general, a band division type echo canceller is used for a wideband signal in order to reduce the processing amount.

  FIG. 6 is a schematic configuration diagram showing a conventional band-division echo canceller described in Patent Document 1 below.

  This band division type echo canceller apparatus uses echo signal E in received input signal IN1 (this echo signal E is a line wraparound caused by impedance mismatch in a hybrid circuit among received signals output from the receiver side) And an echo path section (echo path section) 1 to which a transmission input signal IN2 is added again by an acoustic sneak between a microphone and a speaker such as a handset. Yes. A frequency band division unit (hereinafter simply referred to as a “band division unit”) is provided between the input side for receiving the received input signal IN1, the output side of the echo path unit 1, and the output side for outputting the transmission output signal OUT. 2, 3, a frequency band synthesis unit (hereinafter simply referred to as “band synthesis unit”) 4, a low-frequency sub-band echo canceller 5, and a high-frequency sub-band echo canceller 6 are connected.

  The band dividing unit 2 separates the reception input signal IN1 into a low frequency reception signal S2a and a high frequency reception signal S2b, and gives them to the low frequency subband echo canceller 5 and the high frequency subband echo canceller 6, respectively. The echo signal E of the reception input signal IN1 and the transmission input signal IN2 are added by the echo path unit 1, and this addition signal IN2 'is input to the band dividing unit 3. The band dividing unit 3 separates the addition signal IN2 ′ input from the echo path unit 1 into a low-frequency transmission signal S3a and a high-frequency transmission signal S3b, and performs a low-frequency subband echo canceller 5 and a high-frequency subband echo canceller. Give to 6 respectively. The low frequency sub-band echo canceller 5 obtains a low frequency residual signal S5 in which the low frequency component of the echo signal E is eliminated from the low frequency transmission signal S3a by using the low frequency received signal S2a and the low frequency transmission signal S3a. To the band synthesis unit 4. Similarly, the high-frequency subband echo canceller 6 uses the high-frequency received signal S2b and the high-frequency transmitted signal S3b to cancel the high-frequency residual of the echo signal E from the high-frequency transmitted signal S3b. The signal S6 is obtained and given to the band synthesis unit 4. The low band subband echo canceller 5 and the high band subband echo canceller 6 generally use an LMS / NLMS (least mean square / normalized least mean square) algorithm. The band synthesizing unit 4 synthesizes the low-frequency residual signal S5 and the high-frequency residual signal S6, and outputs the transmission output signal OUT on the broadband network.

  When the sampling frequency is 16 kHz, the band dividing units 2 and 3 include ITU-T (International Telecommunication Union-Telecommunication) recommendation G.264. 722 Quadrature Mirror Filter (hereinafter referred to as “QMF”) can be used. Further, an inverse quadrature mirror filter (hereinafter referred to as “IQMF”) can be used for the band synthesizing unit 4. In QMF, after the input signal is separated into a high frequency component and a low frequency component, downsampling is performed to thin out each component, so that each of the subband echo cancellers 5 and 6 can be achieved with a small amount of processing.

JP 2006-203358 A

However, the conventional band division type echo canceller has the following problems.
When the band dividing units 2 and 3 are configured by QMF and the band combining unit 4 is configured by IQMF, if the characteristics of the low frequency subband echo canceller 5 and the high frequency subband echo canceller 6 are not the same at the same time, aliasing ( aliasing) occurs, and the echo signal E in the vicinity of the band boundary is not sufficiently removed, resulting in a residual echo.

  Therefore, in the technique of Patent Document 1, an echo signal near the band boundary is removed from the low-frequency transmission signal S3a output from the band dividing unit 3 by providing a high-pass filter (HPF) that allows only a high-frequency component to pass. I am doing so.

  However, in the technique of Patent Document 1, there is a problem that the echo canceller apparatus cannot perform sufficient learning during FAX communication, and a residual echo is likely to occur. In addition, depending on the amount of residual echo, FAX communication may not be performed, so an echo canceller apparatus that can reduce residual echo even when a FAX signal is input has been desired.

The echo canceller apparatus of the present invention inputs a transmission signal and a reception signal on a broadband network, detects a FAX signal and outputs a detection result, and receives the transmission signal and the reception signal. , and on / off can filter for blocking frequencies within the frequency band of the transmission signal and the received signal in the frequency band of the FAX signals, the detection result based on the on / off control for filter control said filter And a frequency band dividing means configured to divide the output signal of the filter into a plurality of frequency band subband received signals and subband transmitted signals, and the divided subband received signals and subbands. High frequency subband echo key that outputs high frequency subband signal by removing high frequency echo component in transmission signal Based on the detection result, a low-frequency subband echo canceller that outputs a low-frequency subband signal by removing a low-frequency echo component in the divided subband received signal and the subband transmitted signal, Echo canceller control means for controlling the high frequency subband echo canceller and the output of the high frequency subband echo canceller, and IQMF, and synthesizes and transmits the high frequency subband signal and the low frequency subband signal. Frequency band synthesizing means for outputting a speech output signal onto the broadband network.

  According to the present invention, when a FAX signal is detected, a transmission signal outside the frequency band of the FAX signal and a signal obtained by blocking (cutting) a frequency within the frequency band of the reception signal are input to the frequency band dividing unit, Further, the output of the high frequency sub-band echo canceller is controlled. Therefore, the influence of aliasing distortion can be eliminated and the attenuation amount of the echo canceller can be improved.

FIG. 1 is a schematic configuration diagram showing a band-division echo canceller apparatus according to Embodiment 1 of the present invention. FIG. 2 is a diagram showing an example of frequency characteristics in the LPFs 26 and 27 in FIG. FIG. 3 is a schematic configuration diagram showing a band division type echo canceller apparatus according to the second embodiment of the present invention. FIG. 4 is a diagram showing a FAX signal detection result and operation in the echo canceller apparatus of FIG. FIG. 5 is a schematic configuration diagram showing a band division type echo canceller apparatus according to the third embodiment of the present invention. FIG. 6 is a schematic configuration diagram showing a conventional band division type echo canceller.

  Modes for carrying out the present invention will become apparent from the following description of the preferred embodiments when read in light of the accompanying drawings. However, the drawings are only for explanation and do not limit the scope of the present invention.

(Configuration of Example 1)
FIG. 1 is a schematic configuration diagram illustrating a band-division echo canceller apparatus according to a first embodiment of the present invention.

  In the band division type echo canceller of the first embodiment, as in the conventional FIG. 6, it is connected to a broadband network, and the echo signal E and the transmission input signal IN2 of the reception input signal IN1 are added to obtain an addition signal. The echo path unit 11 from which IN2 ′ is output, the frequency band dividing means (for example, the band dividing unit on the reception input signal side and the transmission input signal side) 12, 13, the frequency band synthesizing means (for example, band combining unit) 14, the low A subband echo canceller 15 and a highband subband echo canceller 16 are provided.

  The band dividing unit 12 on the reception input signal side is configured by QMF, and divides the reception input signal IN1 into a subband low-frequency reception signal S12a and a subband high-frequency reception signal S12b of a plurality of frequency bands. The band echo canceller 15 and the high frequency sub-band echo canceller 16 have a function to be given respectively. The band dividing unit 13 on the transmission input signal side is configured by QMF, and divides the addition signal IN2 ′ into a subband low band transmission signal S13a and a subband high band transmission signal S13b of a plurality of frequency bands, It has a function to be given to the low frequency sub-band echo canceller 15 and the high frequency sub-band echo canceller 16, respectively.

  The low frequency sub-band echo canceller 15 uses the low frequency received signal S12a and the low frequency transmitted signal S13a to obtain a low frequency residual signal S15 in which the low frequency component of the echo signal E is eliminated from the low frequency transmitted signal S13a. And a function to be given to the band synthesizing unit 14. The high frequency sub-band echo canceller 16 uses the high frequency received signal S12b and the high frequency transmitted signal S13b to obtain a high frequency residual signal S16 in which the high frequency component of the echo signal E is eliminated from the high frequency transmitted signal S13b. And a function to be given to the band synthesizing unit 14. For these low-frequency subband echo canceller 15 and high-frequency subband echo canceller 16, for example, an LMS / NLMS algorithm is generally used. The band synthesizing unit 4 is composed of IQMF, and has a function of synthesizing the low-frequency residual signal S15 and the high-frequency residual signal S16 and outputting the transmission output signal OUT to the wideband network.

  In the first embodiment, a FAX signal detection unit (for example, a FAX signal detection unit) 21 on the reception input signal side and a FAX signal detection unit (for example, a FAX signal detection unit) on the transmission input signal side are newly added to the conventional apparatus. ) 22, echo canceller control means (for example, echo canceller control section) 23, filter control means (for example, filter control section) 24, selector 25, filter (for example, low-pass filter on the received input signal side (hereinafter referred to as “LPF”) .)) 26 and a filter (for example, LPF on the transmission input signal side) 27 are added.

  The FAX signal detection unit 21 is connected to the reception input signal IN1 side, and the FAX signal detection unit 22 is further connected to the addition signal IN2 'side. The FAX signal detection unit 21 on the reception input signal IN1 side has a function of detecting a FAX signal from the reception input signal IN1 and outputting a detection result. On the output side, an echo canceller control unit 23 and a filter control unit 24 are provided. It is connected. Similarly, the FAX signal detection unit 22 has a function of detecting a FAX signal from the addition signal IN2 ′ given through the echo path unit 11 and outputting a detection result. On the output side, the FAX canceller control unit 23 and A filter control unit 24 is connected.

  The echo canceller controller 23 is connected to the high frequency subband echo canceller 16 and the selector 25 on the output side, and outputs a control signal S23 based on the detection results of the FAX signal detectors 21 and 22, A function of controlling the band echo canceller 16 and a function of controlling the output of the high frequency subband echo canceller 16 (for example, a function of controlling the selector 25 for switching the output of the high frequency subband echo canceller 16). Have. The selector 25 has a band synthesizing unit 14 connected to the output side, and is switched by the control signal S23 to output a high-frequency residual signal S16 output from the high-frequency subband echo canceller 16 or a ground potential (= 0 V) is provided to the band synthesizing unit 14.

  The filter control unit 24 outputs a control signal S24 based on the detection results of the FAX signal detection units 21 and 22, and the control signal S24 turns on / off the LPF 26 on the reception input signal side and the LPF 27 on the transmission input signal side. Function for switching off operation (for example, if the detection result of the FAX signal detection units 21 and 22 is a FAX signal, the LPF 26 and 27 are turned on by the control signal S24, and if the detection result is a non-FAX signal, the control signal S24 A function to turn off the LPFs 26 and 27. The LPF 26 on the reception input signal side is turned on / off by the control signal S24 of the filter control unit 24 and cuts the frequency within the frequency band of the reception input signal IN1 outside the frequency band of the FAX signal (for example, in the ON state). The frequency band of the non-FAX signal is sometimes cut and the input signal is output as it is in the off state), and the band dividing unit 12 is connected to the output side. Similarly, the LPF 27 on the transmission input signal side is turned on / off by the control signal S24 of the filter control unit 24 and cuts the frequency within the frequency band of the addition signal IN2 ′ outside the frequency band of the FAX signal (for example, The function of cutting the frequency band of non-FAX signals in the on state and outputting the input signal as it is in the off state), and the band dividing unit 13 is connected to this output side.

  The echo canceller apparatus according to the first embodiment is configured by, for example, hardware that operates on an electronic circuit, or software that operates on a microcontroller, a digital signal processor (DSP), or the like.

FIG. 2 is a diagram showing an example of frequency characteristics in the LPFs 26 and 27 in FIG.
Each LPF 26, 27 has the same characteristics. It has a filter characteristic that satisfies the 712 recommendation. An example of frequency characteristics of the LPFs 26 and 27 is shown in FIG. The LPFs 26 and 27 include digital filters such as a finite impulse response (hereinafter referred to as “FIR”) filter and an infinite impulse response (hereinafter referred to as “IIR”) filter, for example. Has been.

(Operation of Example 1)
In the echo canceller apparatus of FIG. 1, the reception input signal IN1 is input to the FAX signal detection unit 21 and the LPF 26 and directly becomes a reception output signal. The reception output signal becomes an echo, and this echo signal E is added to the transmission input signal IN2 in the echo path unit 11, and this addition signal IN2 'is given to the FAX signal detection unit 22 and the LPF 27. The FAX signal detection unit 21 on the reception input signal IN1 side and the FAX signal detection unit 22 on the addition signal IN2 ′ side detect 2100 Hz which is a CED (calling terminal identification) response tone of the FAX signal. This may detect a CNG (CalliNG) tone having a frequency of 1300 Hz used for a FAX sequence. The detection results of the FAX signal detection units 21 and 22 are given to the echo canceller control unit 23 and the filter control unit 24, respectively.

  The filter control unit 24 is not a FAX communication but a voice communication (call) when the detection results of the FAX signal detection units 21 and 22 are both non-detection of the FAX signal, so that the LPFs 26 and 27 are controlled by the control signal S24. When the operation is stopped and the input is bypassed and either one is detected, since the FAX communication is performed, the LPFs 26 and 27 are operated by the control signal S24. Each LPF 26, 27 has frequency characteristics as shown in FIG. Since only narrowband signals (300 Hz to 3400 Hz) are used for communication such as FAX, unused signals with a frequency of 4000 Hz or higher are cut by the LPFs 26 and 27.

  In the case of voice communication, since the operation of the LPFs 26 and 27 is stopped, the input is bypassed and sent to the band separation unit 12 on the reception input signal IN1 side and the band separation unit 13 on the addition signal IN2 'side. When the reception input signal IN1 is input via the LPF 26, the band division unit 12 on the reception input signal IN1 side separates the low-frequency reception signal S12a and the high-frequency reception signal S12b into the low-frequency subband echo as in the conventional case. This is given to the canceller 15 and the high frequency sub-band echo canceller 16, respectively. Further, the band dividing unit 13 on the side of the addition signal IN2 ′ receives the addition signal IN2 ′ input from the echo path unit 11 through the LPF 27, as in the conventional case, the low-frequency transmission signal S13a and the high-frequency transmission signal S13b. And are supplied to the low-frequency sub-band echo canceller 15 and the high-frequency sub-band echo canceller 16, respectively.

  The echo canceller control unit 23 enables the high frequency subband echo canceller 16 and makes the selector 25 perform the high frequency subband echo when both the detection results of the FAX signal detection units 21 and 22 indicate that the FAX signal is not detected. The connection selection to the canceller 16 side is selected, but when either one detects the FAX signal, the high frequency sub-band echo canceller 16 is invalidated and the selector 25 is selected to be connected to the ground.

  Therefore, in the case of voice communication, the low frequency subband echo canceller 15 and the high frequency subband echo canceller 16 are effective. Then, as in the conventional case, the low-frequency subband echo canceller 15 uses the low-frequency received signal S12a and the low-frequency transmitted signal S13a to cancel the low-frequency component of the echo signal E from the low-frequency transmitted signal S13a. A band residual signal S15 is obtained and given to the band synthesizing unit 14. Further, the high-frequency sub-band echo canceller 16 uses the high-frequency received signal S12b and the high-frequency transmitted signal S13b to cancel the high-frequency residual signal obtained by eliminating the high-frequency component of the echo signal E from the high-frequency transmitted signal S13b. S16 is obtained and given to the band synthesizing unit 14 via the selector 25. For the low frequency subband echo canceller 15 and the high frequency subband echo canceller 16, for example, an LMS / NLMS algorithm is used. The band synthesizing unit 14 synthesizes the low-frequency residual signal S15 and the high-frequency residual signal S16, and outputs the transmission output signal OUT to the wideband network.

  On the other hand, in the case of FAX communication, the low frequency residual signal S15 output from the low frequency subband echo canceller 15 and the high frequency subband echo canceller 16 are invalidated, and the ground potential connected and selected by the selector 25 is selected. (That is, silence instead of the high-frequency residual signal S16) is provided to the band synthesizing unit 14. Therefore, the band synthesizing unit 14 outputs only the component of the low-frequency residual signal S15 as the transmission output signal OUT.

(Effect of Example 1)
According to the first embodiment, when a FAX signal is detected, a signal obtained by cutting 4 kHz or more is input to the band dividing units 12 and 13, and further, the high frequency residual signal S16 input to the band synthesizing unit 14. Is configured to be silent. Therefore, the influence of aliasing distortion can be eliminated and the attenuation amount of the echo canceller can be improved. In addition, since the high frequency sub-band echo canceller 16 is stopped, the processing amount can be reduced.

(Configuration of Example 2)
FIG. 3 is a schematic configuration diagram illustrating a band-division echo canceller apparatus according to the second embodiment of the present invention. Elements common to those in FIG. 1 illustrating the first embodiment are denoted by common reference numerals. .

  In the band division type echo canceller apparatus according to the second embodiment, the internal configurations of the FAX signal detection units 21A and 22A are changed with respect to the band division type echo canceller apparatus according to the first embodiment. The FAX signal detection units 21A and 22A have a function of discriminating whether the received input signal IN1 and the addition signal IN2 'are each a 2100 Hz signal FAX signal or a 2100 Hz signal FAX signal with a phase inversion of 450 ms. This is the ITU-T Recommendation G. This satisfies the Tone Disabler characteristic of 168 (that is, the characteristic of limiting the echo canceller function by detecting the 2100 Hz signal and detecting the 2100 Hz signal including phase inversion). The detection results of the FAX signal detection units 21A and 22A are non-detection of the FAX signal, 2100 Hz signal detection, or 2100 Hz signal detection including phase inversion, and this detection result is supplied to the echo canceller control unit 23 and the filter control unit 24A. It is configured.

  Further, a selector 28 is added to the output side of the band synthesizing unit 14A, and the control signal S23 output from the echo canceller control unit 23 is also supplied to the low frequency subband echo canceller 15A and the selector 28. The selector 28 selects either the output signal of the band synthesizing unit 14A or the addition signal IN2 'that is the output of the echo path unit 11 based on the control signal S23, and outputs the transmission output signal OUT. The LPFs 26 and 27 are turned on / off by the control signal S24 output from the filter control unit 24A, and the band dividing units 12A and 13A and the band synthesis unit 14A are turned on / off. Other configurations are the same as those of the first embodiment.

(Operation of Example 2)
FIG. 4 is a diagram showing a FAX signal detection result and operation in the echo canceller apparatus of FIG.

  FIG. 4 shows the detection results of the FAX signal detection units 21A and 22A, the band division units 12A and 13A, the band synthesis unit 14A, the low frequency subband echo canceller 15A, the high frequency subband echo canceller 16, and the selectors 25 and 28. , And the operating states of the LPFs 26 and 27 are described.

  The operation of the echo canceller apparatus according to the second embodiment will be described with reference to FIGS. 3 and 4.

  The operations of the band dividing units 12A and 13A, the band synthesizing unit 14A, the low frequency subband echo canceller 15A, and the high frequency subband echo canceller 16 are the same as those in the first embodiment.

  The FAX signal detection units 21A and 22A detect whether the reception input signal IN1 and the addition signal IN2 'are each a 2100 Hz signal FAX signal or a 2100 Hz signal FAX signal including 450 ms phase inversion. The detection result is non-detection of the FAX signal, 2100 Hz signal detection, or 2100 Hz signal detection including phase inversion, and this detection result is given to the echo canceller control unit 23 and the filter control unit 24A.

  When both of the detection results of the FAX signal detection units 21A and 22A indicate that the FAX signal is not detected, the echo canceller control unit 23 normally sets the low frequency subband echo canceller 15A and the high frequency subband echo canceller 16 according to the control signal S23. The selector 25 is operated to select connection to the high frequency sub-band echo canceller 16 side, and the selector 28 is selected to connect to the band synthesizing unit 14A.

  The echo canceller control unit 23 sends a non-linear processor (hereinafter referred to as “NLP”) to the low-frequency subband echo canceller 15A when either or both of the detection results of the FAX signal detection units 21A and 22A detect 2100 Hz signals. .) Stop it when it is used. Further, the high frequency sub-band echo canceller 16 is stopped, the selector 25 is selected to be connected to the ground, and the selector 28 is selected to be connected to the band synthesizing unit 14A.

  The echo canceller controller 23 controls the low-frequency subband echo canceller 15A and the high-frequency subband echo canceller 16 in the case of 2100 Hz signal detection in which either or both of the detection results of the FAX signal detectors 21A and 22A include phase inversion. The selector 28 is stopped, and the selector 28 is selected for connection to the side of the addition signal IN2 ′ that is the output of the echo path unit 11. The selector 25 holds the previous state.

  The filter control unit 24A normally operates the band dividing units 12A and 13A and the band synthesizing unit 14A and stops the LPFs 26 and 27 when both of the detection results of the FAX signal detecting units 21A and 22A indicate that the FAX signal is not detected.

  When either or both of the detection results of the FAX signal detection units 21A and 22A are 2100 Hz signal detection, the filter control unit 24A normally operates the band division units 12A and 13A and the band synthesis unit 14A, and sets the LPFs 26 and 27 to Make it work.

  Further, the filter control unit 24A stops the band dividing units 12A and 13A and the band synthesizing unit 14A in the case of 2100 Hz signal detection including phase inversion in either or both of the detection results of the FAX signal detecting units 21A and 22A. The LPFs 26 and 27 are stopped.

  In the above control content, the 2100 Hz signal detection result including phase inversion has priority over the 2100 Hz signal detection result.

(Effect of Example 2)
According to the second embodiment, the ITU-T recommendation G.I. A wideband echo canceller that operates in accordance with 168 Tone Disabler can be realized.

(Configuration of Example 3)
FIG. 5 is a schematic configuration diagram showing a band-division echo canceller according to the third embodiment of the present invention. Elements common to those in FIG. 1 illustrating the first embodiment are denoted by common reference numerals. .

  The band division type echo canceller apparatus according to the third embodiment is different from the band division type echo canceller apparatus according to the first embodiment in that a sound detection unit (for example, a sound detection unit) 29 and a switching unit (for example, a selector) 30 are used. And are added.

  That is, the echo canceller apparatus according to the third embodiment includes the same band dividing units 12 and 13, the band synthesizing unit 14, the low frequency subband echo canceller 15, the high frequency subband echo canceller 16, and the FAX signal detection unit as in the first exemplary embodiment. 21, an echo canceller control unit 23, a filter control unit 24, a selector 25, and LPFs 26 and 27 are included. The voice detection unit 29 added to this detects whether the received input signal IN1 is voiced or silent, and if this detection result is voiced (that is, during a call), the echo for operating the echo canceller main body 10 is detected. It has a canceller function and a stop function for stopping the operation of the echo canceller main body 10 when the detection result is silent. The selector 30 is switched according to the detection result of the sound detection unit 29. When the detection result is sound, the selector 30 is selected to be connected to the output side of the band synthesis unit 14 and the output signal of the band synthesis unit 14 is transmitted as it is. Output as an output signal OUT, and when the detection result is silent, the connection is selected on the side of the addition signal IN2 ′, which is the output of the echo path unit 11, and the addition signal IN2 ′ is bypassed and output as the transmission output signal OUT It is.

(Operation of Example 3)
In the echo canceller apparatus of the third embodiment, the sound detection unit 29 detects whether the received input signal IN1 is sound or soundless. This can be determined by obtaining an average power value and determining whether the average power value is larger or smaller than a certain threshold. The sound detection unit 29 operates the echo canceller apparatus body 10 in the same manner as in the first embodiment when the detection result is sound, and stops the operation of the echo canceller apparatus body 10 when the detection result is silent. When the detection result is silent, the selector 30 selects the addition signal IN2 ′, which is the output of the echo path unit 11, and the addition signal IN2 ′ is bypassed and output as the transmission output signal OUT.

(Effect of Example 3)
According to the third embodiment, when the reception input signal IN1 is silent, there is no echo (the echo signal E becomes 0). Therefore, by bypassing the transmission input signal IN2 as the addition signal IN2 ′, high quality is achieved. Secure signal. In addition, the processing amount can be reduced by stopping each function and each control in the echo canceller main body 10.

(Modification)
This invention is not limited to the said Examples 1-3, A various utilization form and deformation | transformation are possible. For example, the following forms (a) to (c) are available as usage forms and modifications.

  (A) In the first to third embodiments, the LPFs 26 and 27 are placed on the input side of the band dividing units 12, 12 </ b> A, 13, and 13 </ b> A when signals are detected. The frequency characteristics satisfying 712 are obtained. However, the block function part and the band division function part of “Downsampler satisfying G.712” are simply selected by the selector, and the block function part and band synthesis function part of “Upsampler satisfying G.712” are selected. Even if it changes to the structure which selects with a selector, the effect similar to Examples 1-3 can be acquired.

  (B) In the third embodiment, the sound detection unit 29 is added to the first embodiment. However, even with the configuration added to the second embodiment, substantially the same operational effects as the third embodiment can be obtained.

  (C) In Example 2, the ITU-T recommendation G. The configuration satisfying the Tone Disabler characteristic of 168 has been described. However, the configuration is not limited to the recommendation, and it is possible to change the configuration to satisfy other standards.

DESCRIPTION OF SYMBOLS 11 Echo path 12, 12A, 13, 13A Band division part 14, 14A Band synthesis part 15, 15A Low frequency subband echo canceller 16 High frequency subband echo canceller 21, 21A, 22, 22A FAX signal detection part 23 Echo canceller control part 24, 24A Filter control unit 25, 28, 30 Selector 29 Sound detection unit

Claims (4)

A facsimile signal detection means for inputting a transmission signal and a reception signal on a broadband network, detecting a facsimile signal, and outputting a detection result;
The transmission signal and the reception signal is inputted, and on / off can filter for blocking frequencies within the frequency band of the transmission signal and the received signal in the frequency band of the facsimile signal,
Filter control means for controlling on / off of the filter based on the detection result;
A frequency band dividing means configured by a quadrature mirror filter, and dividing the output signal of the filter into a subband reception signal and a subband transmission signal of a plurality of frequency bands;
A high-frequency subband echo canceller that outputs a high-frequency subband signal by removing a high-frequency echo component in the divided subband received signal and the subband transmitted signal;
A low-frequency sub-band echo canceller that outputs a low-frequency sub-band signal by removing a low-frequency echo component in the divided sub-band received signal and the sub-band transmitted signal;
Based on the detection result, echo canceller control means for controlling the output of the high frequency subband echo canceller and the high frequency subband echo canceller;
A frequency band synthesizing unit configured by an inverse quadrature mirror filter, which synthesizes the high frequency subband signal and the low frequency subband signal and outputs a transmission output signal on the wideband network;
An echo canceller apparatus comprising: The filter cuts off the frequency within the frequency band of the transmission signal and the reception signal outside the frequency band of the facsimile signal when the filter is on, and when the filter is off, the input signal is output as it is.
The filter control means turns the filter on when the detection result is the facsimile signal, and turns the filter off when the detection result is a non-facsimile signal. The echo canceller apparatus described. The facsimile signal detecting means has a function of detecting the facsimile signal and outputting the detection result, and a function of discriminating between a 2100 Hz signal and a 2100 Hz signal accompanied by phase inversion in the facili signal, and outputting a discrimination result. Have
The low frequency sub-band echo canceller is constituted by a non-linear processor,
The filter control means has a function of on / off controlling the filter, the frequency band dividing means, and the frequency band synthesizing means based on the detection result and the discrimination result,
The echo canceller control means has a function of controlling the output of the high frequency subband echo canceller, the low frequency subband echo canceller, and the high frequency subband echo canceller based on the detection result and the discrimination result. The echo canceller according to claim 1 or 2. The echo canceller apparatus according to any one of claims 1 to 3,
The received signal is input to determine whether the received signal is voiced or silent, and a determination result is obtained.If the determination result is the voice, the facsimile signal detection means, the filter, the filter control means, An echo canceller function for operating the frequency band dividing means, the high frequency sub-band echo canceller, the low frequency sub-band echo canceller, the echo canceller control means, and the frequency band synthesizing means, and whether the determination result is the silence. For example, a sound detection means having a stop function for stopping the echo canceller function,
Based on the determination result, if the determination result is the sound, the transmission output signal output from the frequency band synthesizing means is output on the broadband network, and if the determination result is the silence, Switching means for bypassing the input transmission signal and outputting it on the broadband network;
An echo canceller apparatus comprising:

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