JP2000307485A - Echo canceler - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress the rapid increase of processing load on an entire echo canceler when the transfer instruction of an adaptive filter coefficient is generated by inhibiting update processing of the adaptive filter coefficient in an adaptive filter in response to the coefficient transfer instruction. SOLUTION: A series of echo canceling operations are repeated for every cycle when a received code is received, and when an echo cancel characteristic of a semi-fixed filter 5 and an echo cancel characteristic of an adaptive filter 7 have a difference, a coefficient transfer is processed while stopping coefficient update processing of he adaptive filter 7 according to a coefficient transfer instruction. When the echo cancel characteristic of the semi-fixed filter 5 and the echo cancel characteristic of the adaptive filter 7 have no difference, coefficient update processing of the adaptive filter 7 is executed and an optimum filter coefficient at that point of time is calculated. The load increment by the transfer processing can be canceled by the reduction in the update processing of the adaptive filter coefficient.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an echo canceller for removing an echo component contained in a received signal and transferring the same as a transmission signal, and more particularly, to a semi-fixed filter for actually canceling an echo from a transmission signal. The present invention relates to an improvement in an echo canceller including an adaptive filter that outputs a filter coefficient used in the semi-fixed filter, in order to suppress a temporary increase in a processing load accompanying the transfer of the filter coefficient.

[0002]

2. Description of the Related Art FIG. 6 is a block diagram showing a configuration of a conventional echo canceller disclosed in Japanese Patent Publication No. 56-35052. In the figure, reference numeral 1 denotes an input terminal of a received signal;
Is an output terminal of the reception signal, 3 is an input terminal of the transmission signal in which the reception code sequence of the reception signal output from the output terminal 2 and the transmission code sequence are superimposed, and 4 is an output terminal of the corrected transmission signal. .

[0005] Reference numeral 18 denotes a semi-fixed filter for filtering a received signal sequence of the received signal to output a first pseudo echo signal, and 6 denotes a latest pseudo code from the latest transmission code from the input terminal 3. , A first subtractor that outputs the latest first residual code, and 19 is an adaptive filter that performs a filtering process on the received signal sequence of the received signal and outputs a second pseudo echo signal. A second subtractor for subtracting the latest second pseudo echo code from the latest transmission code of the second and outputting the same as the latest second residual code; Is used to compare the echo cancellation performance. If the second residual signal has better echo cancellation performance than the first residual signal, the coefficient transfer instruction signal is transmitted to transfer the adaptive filter coefficient to the semi-fixed filter 18. Comparator for outputting, 20 is a coefficient transfer unit that transfers the adaptive filter coefficients in the semi-fixed filter 18 in accordance with the coefficient transfer instruction signal. The adaptive filter 19 receives the second residual signal as well as the above operation,
An update process of a plurality of adaptive filter coefficients is also performed so that the second residual signal is reduced.

Next, the operation will be described. When the latest received code is input from the input terminal 1, the semi-fixed filter 18
The adaptive filter 19 performs a convolution operation using the plurality of filter coefficients, and the first subtractor 6 and the second subtractor 8 subtract the respective pseudo echo codes from the transmission signal from the input terminal 3. The first residual code output from the first subtractor 6 is output from the output terminal 4 to the transmission code path as a transmission code corresponding to the latest received code.

The adaptive filter 19 updates its own adaptive filter coefficient based on the second residual code.

Further, the comparing section 9 compares the latest first residual code and the second residual code, and if the second residual signal has better echo cancellation performance than the first residual signal. Outputs a coefficient transfer instruction signal to transfer the adaptive filter coefficient to the semi-fixed filter 18, and the coefficient transfer unit 20 transfers the adaptive filter coefficient to the semi-fixed filter 18 according to the input.

The conventional echo canceller repeats the above-described series of echo canceling operations each time the latest received code is input, removes echo components generated in the transmission path of the received signal, and uses this as a transmission signal. Can be output.

Also, as described above, the two filters 18, 1
9 so that the coefficient is updated only on one side and the other is transferred only when the coefficient becomes more appropriate, so that the deterioration of the filter coefficient when double talk or the like occurs. It can be effectively prevented.

Japanese Patent Publication No. 56-31774 discloses a technique for transferring a semi-fixed filter coefficient from a semi-fixed filter 18 to an adaptive filter 19 in reverse.

Further, such an echo canceller estimates an impulse response of an echo path having unknown characteristics by a coefficient adaptive updating algorithm such as a learning identification method, and converts a received signal into an echo signal based on the estimated impulse response. The combined pseudo echo signals are combined, and the pseudo echo signals are subtracted from the transmission signals to thereby eliminate the echo signals included in the transmission signals. The impulse response refers to a response obtained as a transmission signal when a predetermined pulse is passed as a reception signal through an echo path in a situation where there is no communication signal on the transmission side. In general, a pseudo echo signal is an adaptive finite-length impulse response (FIR: Finite Impu) using an impulse response as a filter coefficient.
The signal can be synthesized by passing the received signal through an (lse Response) filter.

[0011]

Since the conventional echo canceller is constructed as described above, when the coefficient transfer instruction signal is output from the comparison unit 9, the coefficient transfer unit 20 is used in addition to the normal processing. Therefore, there is a problem in that the processing load of the filter coefficient is added, and the processing load increases as the processing of the entire echo canceller.

In particular, an acoustic echo canceller used in a video conference system or the like requires several thousands of filter coefficients, and the load of the transfer processing is the same as that of the filter coefficient calculation processing in the adaptive filter 19. It is about a load. Therefore, considering that the processing load of the acoustic echo canceller fluctuates greatly depending on the presence or absence of a transfer instruction, and a series of echo cancellation processes must be performed in real time every time a received code of a received signal is input. In other words, a series of processing must be performed with elements that are so fast that they are excessive.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and the processing load of the entire echo canceller does not suddenly increase when a filter coefficient transfer instruction is issued. It is an object of the present invention to obtain an echo canceller that does not need to execute a series of processing with a device that is so fast as to be excessive even when used as an acoustic echo canceller.

[0014]

An echo canceller according to the present invention receives a received signal and a transmission signal in which the received signal and a transmission code sequence are superimposed, and receives a first pseudo echo obtained from the received signal. In the echo canceller for correcting the transmission signal with a signal, the received signal is input and a plurality of semi-fixed filter coefficients are held, and a convolution of the received signal sequence of the input received signal with the plurality of semi-fixed filter coefficients is performed. A semi-fixed filter that generates the first pseudo echo signal by calculation, a first subtractor that subtracts the first pseudo echo signal from the transmission signal and outputs the result as a first residual signal, and the reception signal is input. And holds a plurality of adaptive filter coefficients, and performs a second convolution operation on the received signal sequence of the input received signal and the plurality of adaptive filter coefficients. And generates an echo signal similar,
An adaptive filter that updates the plurality of adaptive filter coefficients based on a residual obtained by subtracting the second pseudo echo signal from the transmission signal; and subtracting the second pseudo echo signal from the transmission signal to generate a second A second subtractor that outputs a residual signal, and a comparison that compares the echo cancellation performance using the first residual signal and the second residual signal, and outputs a coefficient transfer instruction signal according to the comparison result. Unit, the coefficient transfer instruction signal is input, the update processing of the adaptive filter coefficient in the adaptive filter is inhibited in response to the coefficient transfer instruction, and in this state, the plurality of semi-fixed filter coefficients and the plurality of adaptive filter coefficients And a coefficient transfer processing unit for performing a coefficient transfer process between the two.

In the echo canceller according to the present invention, the coefficient transfer processing unit receives a coefficient transfer instruction signal, and converts a coefficient between a plurality of semi-fixed filter coefficients and the plurality of adaptive filter coefficients according to the coefficient transfer instruction. And a coefficient transfer detector that receives the transfer cycle signal and outputs a coefficient update prohibition signal to the adaptive filter in response to the input of the transfer cycle signal. The adaptive filter is configured to stop updating the adaptive filter coefficient when the coefficient update inhibition signal is input.

In the echo canceller according to the present invention, the coefficient transfer processing unit detects double talk based on the received signal and the transmitted signal or a signal generated based on the signal and outputs a double talk detection signal. When the double talk detection signal and the coefficient transfer instruction signal are input, and when the double talk detection signal is input after the coefficient transfer instruction signal is input, a transfer timing instruction unit that outputs a transfer start signal at that timing; The transfer start signal is input, and when the transfer start signal is input, a coefficient transfer unit that performs a coefficient transfer process between a plurality of semi-fixed filter coefficients and the plurality of adaptive filter coefficients and outputs a transfer cycle signal. Consists of
The adaptive filter stops updating the adaptive filter coefficient when the double talk detection signal is output.

In the echo canceller according to the present invention, the coefficient transfer processing section detects a reception silence state based on a reception signal or a signal generated based on the reception signal and outputs a silence detection signal; When a detection signal and a coefficient transfer instruction signal are input, and a silence detection signal is input after the coefficient transfer instruction signal is input, a transfer timing instruction unit that outputs a transfer start signal at that timing; When the transfer start signal is inputted, the transfer start signal is formed between a plurality of semi-fixed filter coefficients and the plurality of adaptive filter coefficients, and a coefficient transfer unit for outputting a transfer cycle signal is provided. The filter stops updating the adaptive filter coefficient when the silence detection signal is output.

In the echo canceller according to the present invention, the coefficient transfer processing unit detects double talk based on the received signal and the transmitted signal or a signal generated based on the signal and outputs a double talk detection signal. A silence detection circuit that detects a silence state based on a reception signal or a signal generated based on the reception signal and outputs a silence detection signal; and the double talk detection signal and the silence detection signal are input, and And a logic circuit for outputting a detection signal when a detection signal is input, and when the detection signal is input after the coefficient transfer instruction signal is input, a transfer start signal is output at that timing. A transfer timing instructing section to be input and the transfer start signal, and when the transfer start signal is input, a plurality of Performs transfer processing coefficient between the fixed filter coefficient and the plurality of adaptive filter coefficients is composed of a coefficient transfer section for outputting a transfer cycle signal,
The adaptive filter stops updating the adaptive filter coefficient when the detection signal is output.

An echo canceller according to the present invention receives a received signal and a transmitted signal in which the received signal and a transmission code sequence are superimposed, and converts the transmitted signal with a first pseudo echo signal obtained from the received signal. In the echo canceller to be corrected, the received signal is input and a plurality of semi-fixed filter coefficients are held. The first pseudo signal is convoluted with the received signal sequence of the input received signal and the plurality of semi-fixed filter coefficients. A semi-fixed filter that generates an echo signal, and a first subtractor that subtracts the first pseudo echo signal from the transmission signal and outputs the result as a first residual signal,
The received signal is input, and a plurality of adaptive filter coefficients are held, a second pseudo echo signal is generated by a convolution operation of the received signal sequence of the input received signal and the plurality of adaptive filter coefficients, and the transmission is performed. An adaptive filter that updates the plurality of adaptive filter coefficients based on a residual obtained by subtracting the second pseudo echo signal from the signal; and a second residual that subtracts the second pseudo echo signal from the transmission signal. A second subtractor that outputs a signal, a comparison unit that compares the echo cancellation performance using the first residual signal and the second residual signal, and outputs a coefficient transfer instruction signal according to the comparison result. When the coefficient transfer instruction signal is input, and when the coefficient transfer instruction signal is input, the coefficient transfer processing between the plurality of semi-fixed filter coefficients and the plurality of adaptive filter coefficients is repeated. In which the and a coefficient transfer processing unit for performing over input period of the received code.

[0020]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below. Embodiment 1 FIG. FIG. 1 shows A according to Embodiment 1 of the present invention.
FIG. 2 is a block diagram illustrating a configuration of an acoustic echo canceller used in a TM (asynchronous transfer mode) node device, a video conference system, and the like. In the figure, 1 is an input terminal of a reception signal, 2 is an output terminal of the reception signal, 3 is an input terminal of a transmission signal on which a reception code sequence and a transmission code sequence of the reception signal output from the output terminal 2 are superimposed, Reference numeral 4 denotes an output terminal of the corrected transmission signal.

Reference numeral 5 denotes a receiving signal from the input terminal 1 and holding several thousand semi-fixed filter coefficients, and convolution of the received signal sequence of the input received signal with the plurality of semi-fixed filter coefficients. A semi-fixed filter that performs an operation and outputs a first pseudo echo signal as a first pseudo echo code corresponding to the latest input reception code, and 6 is a transmission signal from the input terminal 3 and a first pseudo filter. A first subtractor to which an echo signal is input, subtracts the latest first pseudo echo code from the latest transmission code, and outputs a first residual signal having this as the latest first residual code. Then, the output of the first subtractor 6 is output from the output terminal 4 as a corrected transmission signal.

Reference numeral 7 denotes a receiving signal input from the input terminal 1 and holds the same number of adaptive filter coefficients as the semi-fixed filter 5. The receiving signal sequence of the input receiving signal, the plurality of adaptive filter coefficients, The adaptive filter outputs a second pseudo echo signal, which is the second pseudo echo code corresponding to the latest input reception code, and a transmission signal from the input terminal 3 and a second pseudo echo signal. A second subtractor to which the pseudo echo signal is input, subtracts the latest second pseudo echo code from the latest transmission code, and outputs a second residual signal having this as the latest second residual code. The adaptive filter 7 receives the second residual signal, and updates the plurality of adaptive filter coefficients so that the absolute value of the second residual code becomes small.

Reference numeral 9 denotes a first residual signal and a second residual signal which are input, and uses the latest first residual code of the first residual signal and the latest second residual code of the second residual signal. When the first residual signal has better echo cancellation performance than the second residual signal, a coefficient transfer instruction signal is output to transfer the semi-fixed filter coefficient to the adaptive filter 7. If the second residual signal has better echo cancellation performance than the first residual signal, the comparing unit 10 outputs a coefficient transfer instruction signal so as to transfer the adaptive filter coefficient to the semi-fixed filter 5.
Receives the coefficient transfer instruction signal, outputs a transfer cycle signal in accordance with the input, and then transfers the semi-fixed filter coefficient to the adaptive filter 7 according to the coefficient transfer instruction signal, or transfers the adaptive filter coefficient to the semi-fixed filter 5. A coefficient transfer unit (coefficient transfer processing unit) 11 that receives the transfer cycle signal and outputs a coefficient update prohibition signal to the adaptive filter 7 in response to the input of the transfer cycle signal. Coefficient transfer processing unit). And
When the coefficient update inhibition signal is input, the adaptive filter 7 stops updating the adaptive filter coefficients.

Next, the operation will be described. When the latest received code constituting the received code sequence is input to the input terminal 1, the semi-fixed filter 5 and the adaptive filter 7 perform a convolution operation using a plurality of respective filter coefficients. Specifically, the same number of recent received codes including the latest received code as the filter coefficients are prepared, each received code is multiplied by each filter coefficient, and the sum of a plurality of multiplication results is calculated. This is output as a first pseudo echo code or a second pseudo echo code which can be regarded as an echo component included in the latest received code. Also, the first subtractor 6
And the second subtractor 8 subtracts each pseudo echo code from the transmission signal from the input terminal 3 and outputs this as the latest first residual code or second residual code. The first residual code is output from the output terminal 4 to the transmission code path as a transmission code corresponding to the latest received code.

The comparator 9 to which the latest first residual code and the second residual code are input compares these codes to determine the current echo cancellation performance of the adaptive filter 7 and the semi-fixed filter. 5 is compared with the present echo canceling performance, and when the first residual signal has better echo canceling performance than the second residual signal, coefficient transfer is performed such that the semi-fixed filter coefficient is transferred to the adaptive filter 7. Output an instruction signal,
If the second residual signal has better echo canceling performance than the first residual signal, a coefficient transfer instruction signal is output to transfer the adaptive filter coefficient to the semi-fixed filter 5. In these performance comparisons, for example, the difference between the soft decision result and the hard decision result of each code is compared, and when the difference is equal to or more than a certain value, the coefficient transfer instruction signal is output. Should be compared to

When the coefficient transfer instructing signal is output from the comparing section 9, the coefficient transferring section 10 outputs a transfer cycle signal in accordance with the input, and then applies the semi-fixed filter coefficient to the adaptive filter 7 in accordance with the coefficient transfer instruction. Or the adaptive filter coefficients are transferred to the semi-fixed filter 5, and the coefficient transfer detector 11 outputs a coefficient update prohibition signal to the adaptive filter 7 in response to the input of the transfer cycle signal. Stops the adaptive filter coefficient update process when the coefficient update inhibition signal is input.

The echo canceller according to the first embodiment repeats the above-described series of echo canceling operations each time the latest received code is input. That is, the above-described series of echo canceling operations is repeated for each cycle in which the received code is input, and when a difference occurs between the echo canceling characteristics of the semi-fixed filter 5 and the adaptive filter 7 in that cycle. Performs the coefficient transfer processing while stopping the coefficient update processing in the adaptive filter 7 in accordance with the coefficient transfer instruction, and there is no difference between the echo cancellation characteristics of the semi-fixed filter 5 and the adaptive filter 7. in case of,
The coefficient updating process in the adaptive filter 7 is performed to calculate the optimum filter coefficient at that time.

As described above, according to the first embodiment, the semi-fixed filter 5 and the first subtractor 6 for removing the echo signal from the transmission signal and the semi-fixed filter 5 from the received signal are used. The first residual signal output from the first subtractor 6 and the second residual signal output from the second subtractor 8 are used together with the adaptive filter 7 and the second subtractor 8 that calculate the filter coefficients. And a comparator 9 for outputting a coefficient transfer instruction signal in accordance with the comparison result, and outputting a transfer cycle signal in response to the input of the coefficient transfer instruction signal. A coefficient transfer unit 10 for transferring the semi-fixed filter coefficients to the adaptive filter 7 and for transferring the adaptive filter coefficients to the semi-fixed filter 5 is provided. While changing the coefficients of the constant filter 5 to the optimum semi-fixed filter coefficients according to the state of the receive signal path, there is an effect that can be output as a transmission signal to cancel the echoes in the received signal path.

In addition, when the coefficient transfer instruction signal is output from the comparison unit 9, the coefficient transfer unit 10 simply performs a coefficient transfer process between the plurality of semi-fixed filter coefficients and the plurality of adaptive filter coefficients. Instead of the coefficient transfer detector 11
Correspond to the input of the transfer cycle signal.
, A coefficient update prohibition signal is output, so that the increase in load due to this transfer processing can be offset by the reduction in the adaptive filter coefficient update processing. Therefore, even if the acoustic echo canceller uses several thousands of filter coefficients as in the first embodiment, the processing load is reduced as the processing of the entire echo canceller when the coefficient transfer instruction signal is output from the comparing unit 9. Canceling the echo generated in the reception signal path and outputting it as a transmission signal without performing a series of processing using elements that are so fast that it can be said that it is excessive as it is conventionally, without increasing it There is an effect that can be.

Embodiment 2 FIG. FIG. 2 is a block diagram showing a configuration of an acoustic echo canceller according to Embodiment 2 of the present invention. In the figure, reference numeral 12 denotes a state in which a reception signal, a transmission signal, and a first residual signal are input and a transmission code sequence is output while being received, that is, a so-called double talk state is detected based on these signals. A double-talk detection circuit (coefficient transfer processing unit) 13 for outputting a detection signal receives a coefficient transfer instruction signal together with the double-talk detection signal, and receives a double-talk detection signal after the coefficient transfer instruction signal is input. A transfer timing instruction unit (coefficient transfer processing unit) that outputs a transfer start signal at that timing. The adaptive filter 7 receives the double talk detection signal instead of the coefficient update inhibition signal,
The coefficient transfer unit 10 receives a transfer start signal instead of the coefficient transfer instruction signal. Other configurations are the same as those of the first embodiment, and the same reference numerals are given and the description is omitted.

Next, the operation will be described. When the double talk detection circuit 12 detects a double talk state based on the received signal, the transmission signal and the first residual signal and outputs a double talk detection signal, the adaptive filter 7 stops the operation of updating the filter coefficient. At the same time, if the coefficient transfer instruction signal is input before the double talk detection signal is input, the transfer timing instruction unit 13 transmits the transfer start signal at the timing when the double talk detection signal is input. Output to 10 The coefficient transfer unit 10 transfers the semi-fixed filter coefficient to the adaptive filter 7 or transfers the adaptive filter coefficient to the semi-fixed filter 5 in accordance with the transfer start signal. Performs filtering processing of the received code using the filter coefficient transferred to. Other operations are the same as those in the first embodiment, and a description thereof will be omitted.

As described above, according to the second embodiment, a double-talk detecting circuit for detecting a double-talk and outputting a double-talk detection signal based on a reception signal and a transmission signal or a signal generated based on these signals. 12, a transfer timing instructing unit 13 that receives a double talk detection signal and a coefficient transfer instruction signal, and, when the double talk detection signal is input after the coefficient transfer instruction signal is input, outputs a transfer start signal at that timing. , A transfer start signal is input, and when the transfer start signal is input, the coefficient transfer unit 10 performs coefficient transfer processing between the plurality of semi-fixed filter coefficients and the plurality of adaptive filter coefficients and outputs a transfer cycle signal. The update process of the adaptive filter coefficient is stopped when the double talk detection signal is input. It is possible to stop the updating when Rutoku is unfavorable to update the appropriate adaptive filter coefficients occurs, it is possible to transfer the filter coefficients in the stopped period.

Therefore, compared to the case where the update processing of the adaptive filter coefficient is simply stopped when the coefficient update prohibition signal is input as in the first embodiment, the update processing of the filter coefficient during normal operation is not hindered. The update process can be stopped in the event of an abnormality that has caused double talk, and the transfer can be performed during that period. Therefore, the load increase due to the transfer process can be reduced without impairing the performance of the echo canceller. There is an effect that the offset can be offset by the reduction in the update processing of the adaptive filter coefficient.

Embodiment 3 FIG. 3 is a block diagram showing a configuration of an acoustic echo canceller according to Embodiment 3 of the present invention. In the figure, reference numeral 14 denotes a silence detection circuit (coefficient transfer processing unit) which receives a received signal, detects a silence state of the received signal, and outputs a silence detection signal. Also,
The silence detection signal is input to the adaptive filter 7 instead of the double talk detection signal, and the silence detection signal is input to the transfer timing instruction unit 13 instead of the double talk detection signal. The other configuration is the same as that of the second embodiment, and the same reference numerals are given and the description is omitted.

Next, the operation will be described. When the silence detection circuit 14 detects a silence state based on the received signal and outputs a silence detection signal, the adaptive filter 7 stops the operation of updating the filter coefficient. At the same time, if the coefficient transfer instruction signal is input before the silence detection signal is input, the transfer timing instruction unit 13 sends the transfer start signal to the coefficient transfer unit 1 at the timing when the silence detection signal is input.
Output to 0. The coefficient transfer unit 10 transfers the semi-fixed filter coefficient to the adaptive filter 7 according to the transfer start signal, or transfers the adaptive filter coefficient to the semi-fixed filter 5.
, And in the next cycle, one of the filters executes a received code filtering process using the newly transferred filter coefficients. Other operations are the same as those in the second embodiment, and a description thereof will be omitted.

As described above, according to the third embodiment, the silence detection circuit 14 for detecting the reception silence state based on the reception signal and outputting the silence detection signal, the silence detection signal and the coefficient transfer instruction signal When a silence detection signal is input after the coefficient transfer instruction signal is input, a transfer timing instruction unit 13 that outputs a transfer start signal at that timing, the transfer start signal is input, and the transfer start signal is input. Is input, the coefficient transfer unit 10 performs a coefficient transfer process between the plurality of semi-fixed filter coefficients and the plurality of adaptive filter coefficients, and the adaptive filter 7 is adapted when the silence detection signal is output. Since the update process of the filter coefficient is stopped, the update can be stopped when it is not preferable to update the adaptive filter coefficient due to a silence state. Rutotomoni may forward filter coefficients in the stopped period.

Therefore, compared to the case where the update process of the adaptive filter coefficient is simply stopped when the coefficient update prohibition signal is input as in the first embodiment, the process of updating the filter coefficient during normal operation is not interrupted and the silence is reduced. When the state is reached, the update process can be stopped, and the transfer is performed during that period. Therefore, the load increase due to the transfer process can be reduced by reducing the adaptive filter coefficient update process without impairing the performance as an echo canceller. There is an effect that can be offset by minutes.

Since the silence detection signal is output when the received signal is no longer input, the silence detection signal is output immediately before the transfer is started when an abnormal state such as double talk occurs as in the second embodiment. There is a high possibility that the adaptive filter coefficient appropriately updated based on the received signal can be transferred to the semi-fixed filter 5.

Embodiment 4 FIG. 4 is a block diagram showing a configuration of an acoustic echo canceller according to Embodiment 4 of the present invention. In the figure, reference numeral 15 denotes a logic circuit (coefficient transfer processing unit) which receives a double talk detection signal and a silence detection signal and outputs a detection signal when either of them is inputted. Further, a detection signal is input to the adaptive filter 7 instead of the double talk detection signal or the silence detection signal, and a detection signal is input to the transfer timing instruction unit 13 instead of the double talk detection signal or the silence detection signal. Other configurations are the same as those in FIG. 2 and FIG. 3, and the same reference numerals are given and the description is omitted.

Next, the operation will be described. When the double talk detection circuit 12 detects a double talk state and outputs a double talk detection signal, or the silence detection circuit 14 detects a silence state based on a received signal and outputs a silence detection signal, the logic circuit 15 Output a detection signal, and the adaptive filter 7 stops the update operation of the filter coefficient. At the same time, if a coefficient transfer instruction signal is input before the detection signal is input, the transfer timing instruction unit 13 outputs a transfer start signal to the coefficient transfer unit 10 at the timing when the detection signal is input. . The coefficient transfer unit 10 transfers the semi-fixed filter coefficient to the adaptive filter according to the transfer start signal, or transfers the adaptive filter coefficient to the semi-fixed filter, and in the next cycle, any one of the filters is newly transferred. The received code is subjected to filtering processing using the set filter coefficients. Other operations are the same as those in the third embodiment, and a description thereof will be omitted.

As described above, according to the fourth embodiment, the double talk detection circuit 12 that detects double talk based on a received signal or a transmission signal and outputs a double talk detection signal, A silence detection circuit 14 for detecting a reception silence state and outputting a silence detection signal, a logic circuit 15 for receiving the double talk detection signal and the silence detection signal, and outputting a detection signal when any one of them is inputted. The detection signal and the coefficient transfer instruction signal are input, and when a detection signal is input after the coefficient transfer instruction signal is input, a transfer timing instruction unit 13 that outputs a transfer start signal at that timing; Is input, and when the transfer start signal is input, the coefficient transfer between the plurality of semi-fixed filter coefficients and the plurality of adaptive filter coefficients is performed. The adaptive filter 7 stops the updating process of the adaptive filter coefficient when the detection signal is output, so that the adaptive filter coefficient is updated in a double talk state or a silent state. The updating can be stopped when it is not preferable, and the filter coefficients can be transferred during the stopped period.

Therefore, compared to the case where the update processing of the adaptive filter coefficients is simply stopped when the coefficient update prohibition signal is input as in the first embodiment, the update processing of the filter coefficients during normal operation is not hindered, and When a talk state or a silent state occurs, the update processing can be stopped, and the transfer is performed during that period. Therefore, the load increase due to the transfer processing is reduced by the adaptive filter coefficient without impairing the performance as the echo canceller. There is an effect that the offset can be offset by the reduction in the update processing.

Embodiment 5 FIG. FIG. 5 is a block diagram showing a configuration of an acoustic echo canceller according to Embodiment 5 of the present invention. In the figure, reference numeral 16 denotes a delay circuit (coefficient transfer processing unit) for delaying the coefficient transfer instruction signal by a time equal to the reception cycle of the reception code or a cycle of an integral multiple thereof, and 17 denotes a delay circuit from A division coefficient transfer unit (coefficient transfer processing unit) that receives an output coefficient transfer instruction signal and transfers one or more filter coefficients between the semi-fixed filter 5 and the adaptive filter 7 at the input timing. . The number of the division coefficient transfer units 17 is one more than the number of the delay circuits 16. Other configurations are the same as those of the first embodiment, and the same reference numerals are given and the description is omitted.

Next, the operation will be described. When the coefficient transfer instruction signal is output from the comparison unit 9, the only division coefficient transfer unit 17 transfers one or more filter coefficients between the semi-fixed filter 5 and the adaptive filter 7 in that cycle. Then, also in the next cycle, the first stage delay circuit 1
The only division coefficient transfer unit 17 to which the coefficient transfer instruction signal from 6 is input transfers one or more filter coefficients between the semi-fixed filter 5 and the adaptive filter 7. This operation is repeated, and the transfer of all the filter coefficients is completed in the same number of cycles as the number of the division coefficient transfer units 17. Other operations are the same as those in the first embodiment, and a description thereof will be omitted.

As described above, according to the fifth embodiment, the semi-fixed filter 5 and the first subtractor 6 for removing the echo signal from the transmission signal are used by the semi-fixed filter 5 from the received signal. The first residual signal output from the first subtractor 6 and the second residual signal output from the second subtractor 8 are used together with the adaptive filter 7 and the second subtractor 8 that calculate the filter coefficients. A comparison unit 9 for comparing the echo cancellation performance and outputting a coefficient transfer instruction signal in accordance with the comparison result; and a plurality of delay circuits 16 for delaying the coefficient transfer instruction signal for a period of an integral multiple of the reception cycle of the received code.・ ・
, 16 and a plurality of division coefficient transfers for transferring one or more filter coefficients between the adaptive filter 7 and the semi-fixed filter 5 in accordance with a coefficient transfer instruction signal output from the comparison section 9 or the delay circuit 16 17 are provided, so that the echo of the received signal path is canceled while changing the coefficient of the semi-fixed filter 5 to the optimum semi-fixed filter coefficient according to the state of the received signal path. Thus, there is an effect that the signal can be output as a transmission signal.

Further, when the coefficient transfer instruction signal is output from the comparing section 9, instead of transferring all the filter coefficients in one cycle as in the first embodiment, the input period of a plurality of received codes is not changed. (Cycles), so that the load increase due to this transfer process can be smoothed and reduced. Therefore, even if the acoustic echo canceller uses thousands of filter coefficients, when the coefficient transfer instruction signal is output from the comparison unit 9, the processing load temporarily increases as the processing of the entire echo canceller. Therefore, there is an effect that the echo generated in the reception signal path can be canceled and output as a transmission signal without performing a series of processing using elements that are so fast as to be excessive as in the related art. .

Although the above embodiment has been described in connection with the case where the voice echo canceller is realized by hardware, the same configuration may be realized by software implemented on a central processing unit or a memory. It goes without saying that you can do it. Since the temporary increase in the processing load associated with the transfer of the filter coefficient does not occur as in the present invention, the period of the software is kept constant, and the period is included in the reception period of the reception code, so that the echo cancellation is surely performed. Processing can be performed.

[0048]

As described above, according to the present invention, a semi-fixed filter or first subtractor for removing an echo signal from a transmission signal, and a filter coefficient used in the semi-fixed filter are calculated from a received signal. Along with the adaptive filter and the second subtractor, comparing the echo cancellation performance using the first residual signal output from the first subtractor and the second residual signal output from the second subtractor, A comparing unit that outputs a coefficient transfer instruction signal in accordance with the comparison result, and prohibits update processing of the adaptive filter coefficient in the adaptive filter in response to the coefficient transfer instruction, and in the state, the plurality of semi-fixed filter coefficients and the A coefficient transfer processing unit for performing coefficient transfer processing with a plurality of adaptive filter coefficients is provided, so that the coefficient of the semi-fixed filter is optimally fixed according to the state of the received signal path. While changing the filter coefficient is effective which can output echoes generated in the receive signal path as a cancellation to transmit signals.

Further, when the coefficient transfer instruction signal is output from the comparing section, the coefficient transfer processing section simply performs the coefficient transfer processing between the plurality of semi-fixed filter coefficients and the plurality of adaptive filter coefficients. Instead, the update processing of the adaptive filter coefficient in the adaptive filter is prohibited during the transfer processing, so that the load increase due to the transfer processing can be offset by the reduction in the adaptive filter coefficient update processing. Therefore, even if the acoustic echo canceller uses a filter coefficient of several thousand units, the processing load does not increase as the processing of the entire echo canceller when the coefficient transfer instruction signal is output from the comparing unit. Eventually, without performing a series of processes using elements that are too fast as in the past, Flip echo the effect that can be output as a cancel and transmission signal.

According to the present invention, the coefficient transfer processing unit receives the coefficient transfer instruction signal, and transfers the coefficient between the plurality of semi-fixed filter coefficients and the plurality of adaptive filter coefficients according to the coefficient transfer instruction. A coefficient transfer unit that performs processing and outputs a transfer cycle signal; and a coefficient transfer detection unit that receives the transfer cycle signal and outputs a coefficient update inhibition signal to an adaptive filter in response to the input of the transfer cycle signal. The adaptive filter stops updating the adaptive filter coefficient when the coefficient update prohibition signal is input, so that an increase in load due to the transfer process can be offset by the reduced amount of the adaptive filter coefficient updating process. is there.

According to the present invention, the coefficient transfer processing section detects double talk based on the received signal and the transmitted signal or a signal generated based on the signal and outputs a double talk detection signal, A transfer timing instructing unit that outputs a transfer start signal at the timing when the double talk detection signal and the coefficient transfer instruction signal are input and the double talk detection signal is input after the coefficient transfer instruction signal is input; A start signal is input, and when the transfer start signal is input, a coefficient transfer unit that performs coefficient transfer processing between a plurality of semi-fixed filter coefficients and the plurality of adaptive filter coefficients and outputs a transfer cycle signal. When the adaptive filter outputs the double talk detection signal, the adaptive filter updates the adaptive filter coefficient. Since stop, it is possible to stop the updating when double talk is unfavorable to update the appropriate adaptive filter coefficients occurs, it is possible to transfer the filter coefficients in the stopped period.

Therefore, double talk occurs without hindering the update process of the filter coefficient during normal operation, as compared with the case where the update process of the adaptive filter coefficient is simply stopped when the coefficient update inhibition signal is input. In the event of an abnormality, the updating process can be stopped, and the transfer is performed during that period. Therefore, the load increase due to the transfer process is offset by the reduction in the adaptive filter coefficient update process without impairing the performance as an echo canceller. There is an effect that can be.

According to the present invention, the coefficient transfer processing section detects a reception silence state based on a reception signal or a signal generated based on the reception signal and outputs a silence detection signal, and the silence detection signal And a coefficient transfer instruction signal are input, and if a silence detection signal is input after the coefficient transfer instruction signal is input, a transfer timing instruction unit that outputs a transfer start signal at that timing, and the transfer start signal is input, When the transfer start signal is input, the adaptive filter is configured to perform a coefficient transfer process between a plurality of semi-fixed filter coefficients and the plurality of adaptive filter coefficients, and output a transfer cycle signal. When the silence detection signal is output, the updating process of the adaptive filter coefficient is stopped. It is possible to stop the updating when the unfavorable, it is possible to transfer the filter coefficients in the stopped period.

Therefore, compared with the case where the update processing of the adaptive filter coefficient is simply stopped when the coefficient update prohibition signal is input, the update processing of the filter coefficient during normal operation is not hindered. Since the processing can be stopped and the data is transferred during that period, the increase in load due to the transfer processing can be offset by the reduction in the update processing of the adaptive filter coefficient without impairing the performance as an echo canceller. effective.

According to the present invention, the coefficient transfer processing unit detects double talk based on the received signal and the transmitted signal or a signal generated based on the signal and outputs a double talk detection signal, A silence detection circuit that detects a reception silence state based on a reception signal or a signal generated based on the reception signal and outputs a silence detection signal; and the double talk detection signal and the silence detection signal are input, and one of them is input. A logic circuit that outputs a detection signal when the detection signal is input, and the detection signal and the coefficient transfer instruction signal are input. When the detection signal is input after the coefficient transfer instruction signal is input, a transfer that outputs a transfer start signal at that timing. A timing instructing unit and the transfer start signal are input, and when the transfer start signal is input, a plurality of semi-fixed filter And a coefficient transfer unit for performing a coefficient transfer process between the plurality of adaptive filter coefficients and outputting a transfer cycle signal, wherein the adaptive filter updates the adaptive filter coefficient when the detection signal is output. Since the stop is performed, when it is not preferable to update the adaptive filter coefficient due to a double talk state or a silence state, the update can be stopped, and the filter coefficient can be transferred during the stopped period.

Therefore, the double talk state or the silent state is achieved without hindering the filter coefficient update processing during normal operation as compared with the case where the update processing of the adaptive filter coefficient is stopped simply when the coefficient update inhibition signal is input. In this case, the update processing can be stopped, and the transfer is performed during that period. Therefore, the increase in load due to the transfer processing is offset by the reduction in the update processing of the adaptive filter coefficient without deteriorating the performance as an echo canceller. There is an effect that can be.

According to the present invention, a semi-fixed filter or a first subtractor for removing an echo signal from a transmission signal, an adaptive filter for calculating a filter coefficient used in the semi-fixed filter from a received signal, and a second subtraction Together with the first residual signal output from the first subtractor and the second residual signal output from the second subtractor to compare the echo cancellation performance, the coefficient according to the comparison result A comparison unit that outputs a transfer instruction signal, and when the coefficient transfer instruction signal is input, performs a coefficient transfer process between a plurality of semi-fixed filter coefficients and the plurality of adaptive filter coefficients during an input period of a plurality of reception codes. And a coefficient transfer processing unit for performing the transmission over the semi-fixed filter, the coefficient being generated in the received signal path while changing the coefficient of the semi-fixed filter to an optimal semi-fixed filter coefficient according to the state of the received signal path There is an effect that can be output as a transmission signal to cancel the call.

Further, when the coefficient transfer instruction signal is output from the comparison section, the coefficient transfer processing section simply performs coefficient transfer processing between the plurality of semi-fixed filter coefficients and the plurality of adaptive filter coefficients. Rather, it is performed over the input period of a plurality of received codes, so that the load increase due to this transfer processing can be smoothed and reduced. Therefore, even if the acoustic echo canceller uses a filter coefficient of several thousand units, the processing load does not increase as the processing of the entire echo canceller when the coefficient transfer instruction signal is output from the comparison unit. There is an effect that the echo generated in the reception signal path can be canceled and output as a transmission signal without performing a series of processing using elements that are so fast as to be excessive as in the related art.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of an acoustic echo canceller used in an ATM (asynchronous transfer mode) node device, a video conference system, and the like according to a first embodiment of the present invention.

FIG. 2 is a block diagram showing a configuration of an acoustic echo canceller according to a second embodiment of the present invention.

FIG. 3 is a block diagram showing a configuration of an acoustic echo canceller according to Embodiment 3 of the present invention.

FIG. 4 is a block diagram showing a configuration of an acoustic echo canceller according to a fourth embodiment of the present invention.

FIG. 5 is a block diagram showing a configuration of an acoustic echo canceller according to a fifth embodiment of the present invention.

FIG. 6 is a block diagram showing a configuration of a conventional echo canceller.

[Explanation of symbols]

5 semi-fixed filter, 6 first subtractor, 7 adaptive filter, 8 second subtractor, 9 comparison section, 10 coefficient transfer section (coefficient transfer processing section), 11 coefficient transfer detection section (coefficient transfer processing section), 12 double Talk detection circuit (coefficient transfer processing unit), 13 transfer timing instruction unit (coefficient transfer processing unit), 14 silence detection circuit (coefficient transfer processing unit), 15
Logic circuit (coefficient transfer processing unit), 16 delay circuit (coefficient transfer processing unit), 17 divided coefficient transfer unit (coefficient transfer processing unit).

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 5J023 DA02 DC06 DC07 DD07 5K027 DD10 5K046 AA01 HH11 HH18 HH24 HH37 HH45 HH46 HH56 HH68 HH72

Claims (6)

[Claims] 1. An echo canceller which receives a received signal and a transmission signal on which the received signal and a transmission code sequence are superimposed, and corrects the transmission signal with a first pseudo echo signal obtained from the received signal. The half receiving the received signal and holding a plurality of semi-fixed filter coefficients, and generating the first pseudo echo signal by convolution of the received signal sequence of the input received signal and the plurality of semi-fixed filter coefficients. A fixed filter, a first subtractor for subtracting the first pseudo echo signal from the transmission signal and outputting the same as a first residual signal, and receiving the reception signal and holding a plurality of adaptive filter coefficients; A second pseudo echo signal is generated by convolution of the received signal sequence of the received signal and the plurality of adaptive filter coefficients. An adaptive filter for updating the plurality of adaptive filter coefficients based on a residual obtained by subtracting the second pseudo echo signal from the second pseudo echo signal; and a second residual signal obtained by subtracting the second pseudo echo signal from the transmission signal. A second subtractor that outputs as, a comparison unit that compares the echo cancellation performance using the first residual signal and the second residual signal, and outputs a coefficient transfer instruction signal according to the comparison result, The coefficient transfer instruction signal is input, and in accordance with the coefficient transfer instruction, the update processing of the adaptive filter coefficient in the adaptive filter is prohibited, and in this state, the plurality of semi-fixed filter coefficients and the plurality of adaptive filter coefficients are And a coefficient transfer processing unit for performing a coefficient transfer process. 2. A coefficient transfer processing unit, to which a coefficient transfer instruction signal is input, performs coefficient transfer processing between a plurality of semi-fixed filter coefficients and the plurality of adaptive filter coefficients according to the coefficient transfer instruction, and A coefficient transfer unit that outputs a transfer cycle signal; and a coefficient transfer detection unit that receives the transfer cycle signal and outputs a coefficient update prohibition signal to an adaptive filter in response to the input of the transfer cycle signal. 2. The echo canceller according to claim 1, wherein the updating of the adaptive filter coefficient is stopped when the coefficient update prohibition signal is output. 3. A double talk detection circuit for detecting a double talk based on a received signal and a transmission signal or a signal generated based on the received signal and the transmission signal, and outputting a double talk detection signal; A signal and a coefficient transfer instruction signal are input, and when a double talk detection signal is input after the coefficient transfer instruction signal is input, a transfer timing instruction unit that outputs a transfer start signal at that timing; When the transfer start signal is input, a coefficient transfer unit that performs coefficient transfer processing between a plurality of semi-fixed filter coefficients and the plurality of adaptive filter coefficients and outputs a transfer cycle signal is provided. The filter stops updating the adaptive filter coefficient when the double talk detection signal is output. Echo canceller according to claim 1, symptoms. 4. A silence detection circuit for detecting a silence state on the basis of a received signal or a signal generated based on the received signal or a signal generated based on the received signal, and outputting a silence detection signal; Signal is input,
When a silence detection signal is input after the coefficient transfer instruction signal is input, a transfer timing instructing unit that outputs a transfer start signal at that timing, a plurality of the transfer start signals are input, and when the transfer start signal is input, And a coefficient transfer unit for performing a coefficient transfer process between the semi-fixed filter coefficient and the plurality of adaptive filter coefficients and outputting a transfer cycle signal. The adaptive filter is adapted when the silence detection signal is output. 2. The echo canceller according to claim 1, wherein the updating of the filter coefficients is stopped. 5. A double talk detection circuit for detecting a double talk based on a reception signal and a transmission signal or a signal generated based on the reception signal and the transmission signal and outputting a double talk detection signal; A silence detection circuit that detects a reception silence state based on a signal generated based on the signal and outputs a silence detection signal; and the double talk detection signal and the silence detection signal are input, and a detection signal is output when any one is input. A transfer timing instructing unit that receives the detection signal and the coefficient transfer instruction signal, and receives a detection signal after the coefficient transfer instruction signal is input, and outputs a transfer start signal at that timing. The transfer start signal is input, and when the transfer start signal is input, the plurality of semi-fixed filter coefficients and the plurality of A coefficient transfer unit that performs coefficient transfer processing with the adaptive filter coefficient and outputs a transfer cycle signal. The adaptive filter stops updating the adaptive filter coefficient when the detection signal is output. 2. The echo canceller according to claim 1, wherein: 6. An echo canceller which receives a received signal and a transmitted signal on which the received signal and a transmission code sequence are superimposed, and corrects the transmitted signal with a first pseudo echo signal obtained from the received signal. The half receiving the received signal and holding a plurality of semi-fixed filter coefficients, and generating the first pseudo echo signal by convolution of the received signal sequence of the input received signal and the plurality of semi-fixed filter coefficients. A fixed filter, a first subtractor for subtracting the first pseudo echo signal from the transmission signal and outputting the same as a first residual signal, and receiving the reception signal and holding a plurality of adaptive filter coefficients; A second pseudo echo signal is generated by convolution of the received signal sequence of the received signal and the plurality of adaptive filter coefficients. An adaptive filter for updating the plurality of adaptive filter coefficients based on a residual obtained by subtracting the second pseudo echo signal from the second pseudo echo signal; and a second residual signal obtained by subtracting the second pseudo echo signal from the transmission signal. A second subtractor that outputs as, a comparison unit that compares the echo cancellation performance using the first residual signal and the second residual signal, and outputs a coefficient transfer instruction signal according to the comparison result, When the coefficient transfer instruction signal is input and the coefficient transfer instruction signal is input, the coefficient transfer between the plurality of semi-fixed filter coefficients and the plurality of adaptive filter coefficients over the input period of the plurality of received codes. An echo canceller comprising: a coefficient transfer processing unit that performs processing.