Echo canceller

[Detailed Description of the Invention]

Field of the Invention The present invention eliminates the echo signal which occurs by a long-distance call circuit etc., and relates to the echo canceller used in order to aim at improvement in telephone speech quality. PRIOR ART In recent years, the echo signal which occurs by the communication meeting system etc. which connect a long-distance call circuit or a remote place point is eliminated, An example of the conventional echo canceller mentioned above while referring to below O drawing in which the echo canceller that the echo canceller which aims at improvement in telephone speech quality is indicated to Open Proc, ICASSP 83.PP, 466-469, and Apri11983 is developed is explained. Drawing 6 is a lineblock diagram of the conventional echo canceller. In Drawing 6, 23 is a receiving side input signal terminal, and 24 is a receiving side output signal terminal, The adaptation filter which comprises the coefficient-of-variable-capacitance transversal filter for creating the estimate (false echo signal) of the echo signal which 26 is based on a transmitting side input signal terminal, 26 is based on a transmitting side output signal terminal, and 27 is based on a receiving side input signal and a transmitting side output signal, and is included in a transmitting side input signal, When 28 deducts the above-mentioned false echo signal from the above-mentioned transmitting side input signal, it is an echo course which the subtraction machine which creates the above-mentioned transmitting side output signal with which the echo signal was eliminated, and 29 generate an echo canceller, and 30 makes generate the echo signal from the above-mentioned receiving side input signal to the above-mentioned transmitting side input signal. About the echo canceller constituted as mentioned above, the operation is explained below. Although the signal inside an echo canceller is dealt with in the following explanation as a discrete time signal sampled about time therefore, it is common knowledge about a required analog digital converter and a digital analog converter, and omits in the following explanation. Receiving side input signal Xj and transmitting side output signal J It is based and is impulse response [ of echo course 30 ] (in filter factor of adaptation filter) h, [ in / in echo canceller 29, it is with adaptation filter 2 A, and / time j ] (t=o, 1. ... N--1 and N presume sample number) of an impulse response, It is transmitting side input signal Zl by what impulse response Ri, and (△ is a sign showing an estimate) and the above-mentioned receiving side input signal which were presumed are collapsed for as shown in a The (1) type (a receiving side input signal is filtered with the above-mentioned filter factor). False echo signal 11 included is created. next -- it is with subtraction machine 28 -- a The (2) type -- [ -- the transmitting side output signal with which the echo signal was eliminated is created by deducting the above-mentioned false echo signal from the above-mentioned transmitting side input signal so that it may be shown. ei="j -yj Presumption of fill * Coefficient of a ""° * * *'° * * * Law adaptation filter factor, It carries out by correcting a filter factor for every sample cycle according to the algorithm of the learning identification method which is performed when the above-mentioned transmitting side input signal has arisen only according to the above-mentioned receiving side input signal, for example, is shown in a The (3) type. ............... (3) However, alpha is a becoming constant 0<alpha To 2. It becomes possible by being in long-distance call mouth # or a communication meeting system with an echo canceller as mentioned above to perform the natural telephone call from which the echo signal was eliminated. The problem which an invention tends to solve However, in the echo canceller of the above composition, when a receiving side input signal was a narrow band region signal like a modem signal, when presumption of the prolonged echo course was continued, operation became unstable, and it had the problem of causing large degradation of the amount of echo elimination. That is, it is although it is what is in echo canceller 29 with adaptation filter 27, and presumes the impulse response of echo course 30, When the useless receiving side input signal which presumes is a narrow band region signal, since presumption of an echo course cannot be performed, the right impulse response cannot be presumed out of the frequency band of a receiving side input signal. They are actually literature 2 Yamamoto and Kiyama. the algorithm and the characteristic of the echo canceller using rice field material, Chihara, Sakurai, and a '' high-speed Kalman filter -- " . 'rl Child consecutive (according to iir society paper magazine (") +"" and '6'-By A 4 *PP and 318-325.1978, when a receiving side input signal is an audio signal, it has been reported that presumption of an echo course is made during [ which has little correlativity ] the broadband correlativity mainly voiceless sound.) An operation error is produced at the time of presumption of an echo course by mixing of the noise to the limited register length and the echo course at the time of realizing an echo canceller by hardware, etc. Therefore, when a receiving side input signal was a narrow band region signal and presumption of the prolonged echo course was continued, the above-mentioned operation error accumulated gradually, it became unstable operating it, and there was a problem of causing large degradation of the amount of echo elimination. The present invention provides the echo canceller which operates stably also to a narrow band region signal not only like an audio signal but a modem signal in view of the above-mentioned problem. The means for solving a problem it is solution about the above-mentioned problem -- " -- in order to carry out -- the echo canceller of the present invention, The adaptation filter which creates a false echo signal based on a receiving side input signal and a transmitting side output signal, It comprises a subtraction machine which creates the above-mentioned transmitting side output signal, and a narrow band region signal detector which measures the narrow band Regionality of the above-mentioned receiving side input signal, and forbids correction of the coefficient of the above-mentioned adaptation filter based on the above-mentioned narrow band Regionality by deducting the above-mentioned false echo signal from a transmitting side input signal. OPERATION When a receiving side input signal is a narrow band region signal by the composition which the echo canceller of the present invention described above, Since presumption of an echo course is stopped when a narrow band region signal detector detects the narrow band Regionality and forbids correction of the coefficient of an adaptation filter, it operates stably, without the operation error mentioned above accumulating. Therefore, even if the echo canceller of the present invention inputs a narrow band region signal not only like an audio signal but a modem signal for a long time, it can always operate stably. EXAMPLE It explains, while referring to drawings for the echo canceller of one example of the present invention below. Drawing 1 shows the lineblock diagram of the echo canceller in one example of the present invention. In Drawing 1, 1 is a receiving side input signal terminal, and 2 is a receiving side output signal terminal, The adaptation filter which comprises the useless variable transversal filter which 3 is based on a transmitting side input signal terminal, 4 is based on a transmitting side output signal terminal, and 6 is based on a receiving side input signal and a transmitting side output signal, and creates a false echo signal, The subtraction machine which creates the account transmitting side output signal of front - with which the echo signal was eliminated when 6 deducted the above-mentioned false echo signal from a transmitting side input signal, It is an echo course which 7 measures the narrow band Regionality of the above-mentioned receiving side input signal, the narrow band region signal detector which forbids correction of the coefficient of the above-mentioned adaptation filter based on the above-mentioned narrow band Regionality, and 8 generate an echo canceller, and 9 makes generate the echo signal from the above-mentioned receiving side input signal to the above-mentioned transmitting side input signal. About the echo canceller constituted as mentioned above, the operation is explained below. First, a false echo signal is created by being with adaptation filter 6 which has memorized the presumed impulse response of echo course 9 as the filter factor, and filtering a receiving side input signal. Next, a transmitting side output signal is created by being with subtraction machine 6 and deducting the above-mentioned false echo signal from a transmitting side input signal. In narrow band region signal detector 7, when the narrow band Regionality of the above-mentioned receiving side input signal is measured and it is judged with a narrow band region signal based on the above-mentioned narrow band Regionality, the signal (it is called below a filter factor correction prohibition signal) which forbids correction of the filter factor of adaptation filter 5 is outputted. Presumption of the filter factor of adaptation filter 6 is performed when the above-mentioned transmitting side input signal has arisen only with the echo signal of the above-mentioned receiving side input signal in the time of the As mentioned above filter factor correction prohibition signal not being outputted for narrow band region signal detector 7, For example, according to the algorithm of the learning identification method mentioned above, it carries out by correcting a filter factor one by one. Still more detailed explanation about narrow band region signal detector 7 which is [ following ] the feature of the present invention is performed. Drawing 2 shows the internal configuration figure in the 1st example of narrow band region signal detector 7. A band-pass filter for 10 to divide a receiving side input signal into the zone signal of a frequency band [ two or more (n piece) ] a receiving side input signal terminal and 111-11n in Drawing 2, The short-time energy calculation machine for computing 121 to 12 n of energies from the above-mentioned zone signal for a short time [ the ], The narrow band Regionality judging machine which 13 measures the narrow band Regionality based on the short-time energy of the n above-mentioned zone signals, is judged to be a narrow band region signal, and outputs a filter factor correction prohibition signal to a case at adaptation filter 5, and 14 are filter factor correction prohibition signal output terminals. The operation is explained below about the narrow band region signal detector constituted as mentioned above. If a receiving side input signal is inputted from receiving side input signal terminal 10, n zone signals will be acquired with n band-pass filters 111-11n which have a frequency characteristic as shown in Drawing 3. Next, the short-time energy of each zone signal is computed by being with energy calculation machines 121-12n for a short time, and it outputs to narrow band Regionality judging machine 13. When a receiving side input signal is a narrow band region signal, the distribution map of energy is obtained for a short time [ as shown, for example in Drawing 4 ]. With narrow band Regionality judging machine 13, while computing total of the short-time energy of the above-mentioned zone signal and asking for energy for a short time [ all the ], the ratio of the short-time energy of the above-mentioned zone signal to all the above-mentioned energies is calculated, When the value of the above-mentioned ratio exceeds a predetermined threshold, it judges with the narrow band region signal which energy is concentrating on the specific frequency band, and outputs a filter factor correction prohibition signal to filter factor correction prohibition signal 14. According to this example, the narrow band region signal detector which measures the narrow band Regionality of the above-mentioned receiving side input signal from the short-time energy distribution on the frequency axis of a receiving side input signal, and forbids correction of the coefficient of an adaptation filter based on the above-mentioned narrow band Regionality is formed as mentioned above, A Touched echo canceller of operation can be provided stably, without the operation error at the time of echo course presumption accumulating, even if it inputs a narrow band region signal as a receiving side input signal for a long time. Drawing 5 shows the internal configuration figure in the 2nd example of a narrow band region signal detector. The number-of-times calculation machine of zero intersection with which 15 computes a receiving side input signal terminal, and 16 computes the number of times of zero intersection of a receiving side input signal in Drawing 5, A maximum detector for a memory for 17 to memorize the above-mentioned number of times of zero intersection and 18 to detect the maximum of the number of times of zero intersection memorized by the above-mentioned memory 17, The useless minimum detector with which 19 detects the minimum of the number of times of zero intersection memorized by the above-mentioned memory, A subtraction machine for 20 to search for the difference of the maximum of the above-mentioned number of times of zero intersection, and the minimum, When 21 judges the narrow band Regionality of the above-mentioned receiving side input signal based on the difference of the maximum of the above-mentioned number of times of zero intersection, and the minimum and it is judged with a narrow band region signal, the narrow band Regionality judging machine which outputs a filter factor correction prohibition signal to an adaptation filter, and 22 are filter factor correction prohibition signal output terminals. The operation is explained below about the narrow band region signal detector constituted as mentioned above. If a receiving side input signal is inputted from receiving side input signal terminal 15, with number-of-times calculation machine 16 of zero intersection, the number of times of zero intersection of predetermined time (this time is called a frame below) will be computed, and it will write in memory 17 for memorizing the newest number of times of zero intersection of a predetermined frame number. Next, the contents which are with maximum detector 18 and minimum detector 19, and are memorized by memory 17 are read, and the maximum and the minimum of the number of times of zero intersection are detected, respectively. Subsequently, it is with subtraction machine 2o, and searches for the difference of the maximum of the above-mentioned number of times of zero intersection, and the minimum. threshold going up predetermined with narrow band Regionality judging machine 21 in the difference of the maximum of the above-mentioned number of times of zero intersection, and the minimum -- case it is small That is, when the number of times of zero intersection continues with a predetermined time predetermined value within the limits, it judges with a receiving side input signal being a narrow band region signal, and outputs a filter factor correction prohibition signal to filter factor correction prohibition signal output terminal 22. According to this example, the narrow band region detector which measures the narrow band Regionality of the above-mentioned receiving side input signal from the parameter on a time-axis called the number of times of zero intersection of a receiving side input signal, and forbids correction of the coefficient of an adaptation filter based on the above-mentioned narrow band Regionality is formed as mentioned above, The echo canceller which operates stably can be provided, without the operation error at the time of echo course presumption accumulating, even if it inputs a narrow band region signal as a receiving side input signal for a long time. In the 2nd example, since it is with a parameter called the easy number of times of zero intersection of calculation and narrow band Regionality is judged, it has the feature that few amounts of A 1-Dwarf and amounts of operations may be as compared with the 1st example. EFFECT OF THE INVENTION The narrow band region detector which the echo canceller of the present invention measures the narrow band Regionality of a receiving side input signal on a frequency axis or a time-axis, and forbids correction of the coefficient of an adaptation filter based on the above-mentioned narrow band Regionality is formed as mentioned above, It can operate stably also not only to an audio signal but to a narrow band region signal, and can extend the scope.

[Brief Description of the Drawings]

Drawing 1 is a lineblock diagram of the echo canceller in the 1st example of the present invention, It is a figure in which Drawing 2 shows the internal configuration figure of the narrow band region signal detector of the 1st example, and Drawing 3 shows the frequency characteristic of the band-pass filter, The short-time energy distribution figure of a zone signal when Drawing 4 makes a narrow band region signal an input signal, and Drawing 6 are an internal configuration figure of the narrow band region signal detector of the 2nd example, and a lineblock diagram of the echo canceller of the former [ Drawing / 6 ]. 1 ...... A receiving side input signal terminal, 2 ...... A receiving side output signal terminal, 3 ...... A transmitting side input signal terminal, 4 ...... A transmitting side output signal terminal, 6 ...... An adaptation filter, 6 ...... A subtraction machine, 7 ...... A narrow band region signal detector, 8 ...... An echo canceller, 9 ...... An echo course, 1o- -.... A receiving side input signal terminal, 111~11n ...... A band-pass filter, 121~12n ...... A short-time energy calculation machine, 13 ...... A narrow band Regionality judging machine, 14 ...... A filter factor correction prohibition signal output terminal, 15 ...... A receiving side input signal terminal and 16 ...... the number-of-times calculation machine of zero intersection, and 17 ...... a memory and 18 ...... a maximum detector and 19 ...... a minimum detector and 20 ...... a subtraction machine and 21 ...... a narrow band Regionality judging machine and 22 ...... a filter factor correction prohibition signal output terminal. A representative's name Patent attorney One-person wJ1 figure figure 2 besides Toshio Nakao