JP2002152093A - Device and method for canceling echo - Google Patents

Abstract

PROBLEM TO BE SOLVED: To perform a processing such as the cancel of much more echoes in multiple lines, sound synthesis and sound recognition with the same operation quantity in a communication line including multiple echo cancellors. SOLUTION: An obtained estimated echo is deducted from an echo multiplex call signal by using a filtering means generating the estimated echo by folding a filtering coefficient simulating the echo and a reference signal in order to cancel the echo generated in the communication line including 2-wires/4-wires transforming units. The attenuation rate of the filter coefficient and a reverberation curve are calculated from a filter coefficient estimated by a filter means. The level of the reference signal is calculated from the reference signal and the filter coefficient attenuation rate. Filter length satisfying a designated permissible echo level and/or a request filter length reduction rate is calculated. A filter length variation filter means is used as the filter means and the filter means receives calculated filter length. Only a part corresponding to filter length performs a folding operation.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a reverberation canceling apparatus and method for canceling reverberation (echo) occurring in a communication line including a two-wire / four-wire converter.

[0002]

2. Description of the Related Art FIG. 4 shows a communication line including a two-wire / four-wire converter. In such a communication line, a voice transmitted from a terminal 11 is transmitted by a two-wire / four-wire converter 13 for transmission. It is transferred to the terminal 12 on the other side via the transmission network 10 via the transmission network 10 via the two-wire / four-wire converter 14.
A part of the transmitted voice is reflected by the two-wire / four-wire converter 14 and returns to the terminal 11 via the transmission network 10 and the two-wire / four-wire converter 13 due to the impedance mismatching of 4. This terminal 11
The transmitted voice returning to is called reverberation or echo and significantly interferes with the call. Similarly, an echo of the sound transmitted from the terminal 12 occurs.

In order to solve such a problem of echo or echo, conventionally, as shown in FIG. 5, echo cancellers or echo cancellers 20 and 21 are installed in a line, and these echo cancellers 20 and 21 are installed. This cancels the echoes generated by the two-wire / four-wire converters 13 and 14, respectively.

The operation of these conventional echo cancellers will be described with reference to FIG. FIG. 6 shows the echo canceller 20.
The configuration of the echo canceller 21 is the same. The echo canceller 20 has two lines 4 that generate an echo.
The impulse response of the line converter 13 is estimated by the filter updating unit 32, and a signal input to the two-wire / four-wire converter 13 is used as a reference signal x, and the reference signal x and a filter coefficient simulating the estimated impulse response are filtered. The convolution unit 30 generates an estimated echo y ^, and the adder 31 subtracts the estimated echo y ^ from the echo superimposed transmission signal d to generate a residual signal e from which the echo has been eliminated. The suppressor 33 suppresses the amplitude of the residual echo component in the residual signal e,
Generate a transmission signal s.

The filters in the filter section 30 are usually finite response length (FIR) filters or infinite response length filters. F
In the case of the IR filter, the estimated echo y ^ (k) at the discrete time k is obtained by the following equation. y ^ (k) = Σ _{i = 0} ^L-1 x (ki) h _i where Σ _{i = 0} ^L-1 is the sum of i = 0,1, ..., L-1
L is the filter length, x (ki) is the reference signal at time ki, h _i denotes the i th filter coefficient.

The suppressor 33 is advantageous in that the amount of computation is much smaller than the generation of an estimated echo. However, the suppressor 33 distorts a transmission signal or echo, causes a sense of intermittent communication due to turning on and off suppression, and reduces the communication quality. There is a disadvantage to lower,
If a sufficient amount of calculation can be secured, it is desirable to cancel the echo by subtracting the estimated echo.

Although the impulse response of the two-wire / four-wire converter 13 that produces an echo differs for each call, once the call is established, the change in the impulse response is small. After that, only the operation of generating the estimated echo and subtracting the estimated echo from the echo-superimposed transmission signal is performed.

In a local exchange or a PBX accommodating a large number of 2-wire 4-wire converters, a large number of echo cancellers are required. As a conventional installation method of an echo canceller, there is a method of allocating one echo canceller to one two-wire / four-wire converter. However, in this method, not all the 2-wire 4-wire converters are used at the same time, but an unnecessary echo canceller is required, so that there is a problem that the cost is unnecessarily high.

A conventional method partially solving this problem will be described with reference to FIG. In FIG. 7, six lines are shown in three rows and two columns in the left, right, upper, middle, and lower stages. Of these lines, the upper and lower lines on the right are not used, and other lines are busy. The line in the middle stage on the left shows the state immediately after the call is established. In this state, the echo canceller of this line has the same configuration as in FIG. 4, and the impulse response is being estimated. The upper left and lower lines and the right middle line show a state where a certain time has passed since the call was established. In this state, the filter update unit 32 of the echo canceller of these lines is stopped or removed, and the impulse response The estimation is finished and only filtering is performed. As described above, when a call is generated, the echo canceller 20 including the filter unit 30, the adder 31, and the filter update unit 32 is connected to the 4-wire side in order to estimate the impulse response. , The filter updating unit 32 is stopped or removed, and when the call is disconnected,
By stopping or removing the filter unit 30 and the adder 31, the storage device and the amount of calculation are reduced.

[0010]

In the above conventional method, the number of calls that can be handled simultaneously is limited by the number of echo cancellers prepared in advance or the number of filterings that can be executed simultaneously. In other words, in order to handle a sufficiently large number of calls, it is necessary to prepare a large number of echo cancellers and arithmetic devices, and there is a problem that the device becomes expensive. In addition, when performing other processing such as voice recognition and voice synthesis with a plurality of echo cancellers on a single calculation resource, it is not possible to allocate a sufficient calculation amount to operations other than echo cancellation. There was also a problem that operation was delayed. SUMMARY OF THE INVENTION An object of the present invention is to eliminate the problems of the above-mentioned conventional method, and to execute processing such as elimination of echoes of more lines, voice synthesis, and voice recognition with the same amount of calculation.

[0011]

According to the present invention, the impulse response of the two-wire / four-wire converter estimated by the filter updating unit rises after a delay time as shown in FIG. 6, and then attenuates by an exponential envelope. (1) The contribution of the filter coefficient to the estimated echo is large at the initial rise and then attenuates.
(2) Consideration that when the reference signal level is low, the echo level is also low, so that if some error is allowed in the estimated echo, it is not necessary to use all of the filters to generate the estimated echo. It is based on. Here, the delay time part of this impulse response is
When a delay equivalent to the delay time is inserted into the reference input signal,
Since it does not appear in the filter, the rise of the impulse response can start at the beginning of the filter, and it is assumed that this is the case below. The error level allowed for the estimated echo is such that the echo is not perceived as an echo after suppression by the suppressor 33.

The present invention has been made in order to solve the above problems.
Based on the above considerations, in order to eliminate the reverberation occurring in a communication line including a two-wire / four-wire converter, a filtering means for generating an estimated reverberation by convolving a reference signal with a filtering coefficient simulating the reverberation is provided. An echo canceller comprising an adding unit for subtracting the estimated echo from the echo multiplex transmission signal to generate a residual signal, and a suppressing unit for suppressing an echo component in the residual signal, the device further comprising: Attenuation characteristic calculating means for calculating an attenuation rate and a reverberation curve of the filter coefficient from the filter coefficient estimated by the filter means; level calculation means for calculating the level of the reference signal from the reference signal and the filter coefficient attenuation rate; Filter length calculation means for calculating a filter length that satisfies the specified allowable echo level based on the reverberation curve,
The filter means is a filter length variable filter means, receives the calculated filter length, and performs only the convolution operation on a portion corresponding to the filter length.

[0013]

As described above, according to the present invention, an estimated echo having a required accuracy is calculated with a minimum necessary filter length in consideration of the attenuation characteristic of the filter coefficient and the level of the reference signal, so that unnecessary filtering is eliminated. Thus, the amount of calculation can be reduced. As a result, other processes such as echo cancellation, voice synthesis, and voice recognition of more lines can be performed with the same operation amount without increasing the echo level compared to the related art.

[0014]

FIG. 1 is a diagram showing a basic configuration of an echo canceller according to the present invention. Reference numeral 101 denotes a level calculator for calculating an input level P of a reference signal (received signal) x;
Attenuation characteristic calculation unit for calculating an attenuation characteristic of the filter coefficient h _i is 102 filter length calculating unit that determines a filter length Ls used for filtering from said reference signal input level P and the attenuation characteristic of the filter coefficient h _i, 104 is This is a filter length variable filtering unit that convolves the reference signal x and the filter coefficient h _i by the filter length calculated by the filter length calculation unit 102. The estimated echo y obtained by the convolution is subtracted from the echo-superposed transmission signal d by the adder 31 to generate a residual signal e in which the echo is eliminated, and the residual echo component in the residual signal is suppressed by the suppressor 33.

The level calculator 101 calculates the level of the reference signal. When the level at time k is expressed as P (k), P (k) = λ (k) P (k−1) + (1−λ (k)) × ² (k) or P (k) = λ ( k) P (k-1) + (1-λ (k)) | x (k) | Here, λ (k) is a forgetting coefficient of P (k), and is set to be approximately equal to the attenuation factor of the filter coefficient obtained by the attenuation characteristic calculator 103. Although the forgetting coefficient λ (k) is described as a function of time, it may take a fixed value.

The attenuation characteristic calculating unit 103 calculates the attenuation from the filter coefficient h _i in the filter length variable filter unit 104. A reverberation curve is calculated as one of the attenuation characteristics. The reverberation curve is given by the following equation. Y (n) = Σ _{i = n} ^L (h _i ) ² = Y (n + 1) + (h _n ) ² where the filter length L is long enough to calculate a highly accurate estimated echo. It is assumed that Y (n) means the ratio of the residual signal to the reference signal level P when filtering is stopped at the n-th coefficient. For example, if Y (50) is 1/10, if filtering is stopped at 50 taps, the level of the residual signal is 1/10 of P (k).
become. The attenuation characteristic calculation unit 103 further obtains the attenuation coefficient λ of the filter coefficient from the slope of the reverberation curve by the following equation, and supplies the attenuation coefficient λ to the level calculation unit 101 as a forgetting coefficient. λ = E _n [exp ({ln Y (n + nd) −ln Y (n)} / dn)] = E _n [{Y (n + nd) / Y (n)} ^{1 / dn} ] where E _n [] refers to the average on n. dn is about several tens to 100 in the case of a line echo.

The filter length calculation unit 102 calculates the reverberation curve Y obtained from the attenuation characteristic calculation unit 103 and the level calculation unit 101.
The filter length Ls is obtained from the reference signal level P obtained from the above, the specified allowable echo level Q and / or the required filter length reduction rate ρ. Here, the required filter length reduction rate ρ is a reduction rate of the filter length for the purpose of reducing the amount of calculation or the storage capacity when the amount of calculation or storage capacity is exhausted. If the allowable echo level is Q (k) and the reference signal level is P (k), the residual signal level Pe (k, n) when the filter length is n is Pe (k, n) = Y (n ) P (k), and the condition regarding the echo level is Pe (k, n) <Q (k), so that the filter length is Lq = min (n | Y (n) P (k) <Q (k) )). Here, the right side means the minimum n that satisfies Y (n) P (k) <Q (k). On the other hand, the filter length based on the required filter length reduction rate ρ is (1-ρ) L, and the filter length L
s is determined from Lq and (1-ρ) L. For example, L
s and (1-ρ) L, or Lq and (1-ρ)
L can be set as an internal dividing point.

The filter length variable filtering unit 104 receives the filter length Ls from the filter length calculation unit 102, filters only the portion corresponding to the filter length Ls, and generates an estimated echo y ^ (k) according to the following equation. y ^ (k) = Σ _{i = 0} ^Ls-1 x (ki) h _i

The filter length calculation unit 102 further calculates a residual signal level increase rate g by truncating the filter length corresponding to the filter length Ls according to g = Y (L) / Y (Ls). Control unit 105
Inform The control unit of the suppressor controls the suppression rate of the suppressor according to the increase rate g. Although the operation of the suppressor control unit differs depending on the type of suppressor, it is generally controlled so that the suppression rate of the suppressor is proportional to the residual signal level increase rate g.

FIG. 2 is a diagram showing a processing procedure of the reverberation elimination method according to the present invention. The attenuation characteristic calculator 103 calculates the filter coefficient attenuation rate λ and the reverberation curve Y from the filter coefficients.
(Step S11). Thereafter, the level calculation unit 101 calculates the reference signal level P (step S12), and the filter length calculation unit 102 calculates the filter length L from the reference signal level P, the reverberation curve Y and the allowable echo level Q, and the filter length reduction rate ρ.
s and the residual level increase rate g are calculated (step S13), the filter is operated by the filter length variable filtering unit 104 by the filter length Ls to calculate an estimated echo, and the obtained estimated echo is superimposed on an echo in the adder 31. The echo is eliminated by subtracting it from the transmission signal (step S14), and the suppressor control unit 105 adjusts the residual signal suppression rate of the suppressor based on the residual signal increase rate g (step S15),
The suppressor 33 suppresses the residual echo component in the residual signal (step S16), and repeats the above operation until the call is disconnected (step S17).

When there is a sufficient amount of calculation, the allowable echo level Q and the required filter length reduction rate ρ are reduced, echo suppression by the suppressor is reduced, and communication quality can be maintained. When the amount of computation that can be used is reduced due to an increase in calls or the like, the suppression by the suppressor is increased, and at the same time, the allowable echo level Q and the required filter length reduction rate ρ are increased to shorten the filter length Ls, thereby reducing the filtering. The required amount of calculation can be reduced.

FIG. 3 is a diagram for explaining an embodiment in which the present invention is applied to a multiplex echo canceller that operates a plurality of echo cancellers on computer resources that can be shared. First, when the occurrence of a call is detected in step S1, step S1
In step 2, an operating system that calls the echo canceller secures computer resources for operating the echo canceller. Next, in step S3, the echo canceller performs generation of the estimated echo and elimination of the echo using a filter length L0 that is long enough to cancel the echo, and then sets the filter length to L1 in step S4. Perform an update. Next, step S
In step 5, after calculating the reference signal level, generation of the estimated echo, elimination of the echo, update of the filter, and calculation of the reference level are repeated until it is determined that the learning of the filter has been completed. Whether the learning of the filter has been completed can be determined based on the time average value of the amount of echo cancellation ε = (e / d) ² and the minimum value within a certain time being equal to or more than a certain value.

If it is determined that the learning of the filter has been completed, the above-described echo canceling step S1 of the present invention is performed.
-Execute S6. That is, the attenuation calculator 103 calculates the attenuation factor λ of the filter coefficient and the reverberation curve Y from the filter coefficient in step S11, the level calculator 101 calculates the reference signal level in step S12, and the filter length calculator 102
Step S13 of calculating the filter length Ls and the residual level increase rate g in Step S1. The filter length variable filtering section 104 operates the filter by the filter length Ls to calculate the estimated echo, and the adder 31 eliminates the echo.
4. The control unit 104 of the suppressor repeats the step S15 of adjusting the residual signal suppression rate based on the residual level increase rate and the step S16 of suppressing the echo component in the residual signal until the call is disconnected.

[0024]

As is apparent from the above description, according to the present invention, an estimated echo having a required accuracy is calculated with a minimum necessary filter length in consideration of the attenuation characteristic of the filter coefficient and the level of the reference signal. Therefore, unnecessary filtering is eliminated, and the amount of calculation can be saved, so that many echoes can be eliminated on one shared computer resource as in the embodiment of FIG. It is possible to dedicate an operation amount to operations other than echo cancellation such as voice and voice synthesis.

[Brief description of the drawings]

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

FIG. 2 is a diagram showing a processing procedure of an echo cancellation method according to the present invention.

FIG. 3 is a diagram showing a processing procedure of an embodiment in which the present invention is applied to a multiple echo canceller that operates a plurality of echo cancellers on a computer resource that can be shared.

FIG. 4 is a diagram illustrating generation of an echo in a communication line.

FIG. 5 is a diagram illustrating a communication line including an echo canceller.

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

FIG. 7 is a diagram illustrating the operation of an existing multiple echo canceller.

FIG. 8 is a diagram showing characteristics of an impulse response of a two-wire / four-wire converter.

[Explanation of symbols]

 31 Adder 33 Suppressor 101 Level Calculator 102 Filter Length Calculator 103 Attenuation Characteristic Calculator 104 Filter Length Variable Filtering 105 Suppressor Control

 ────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yoichi Haneda 2-3-1 Otemachi, Chiyoda-ku, Tokyo Nippon Telegraph and Telephone Corporation F-term (reference) 5K027 BB03 DD10 5K046 AA01 BA01 HH24 HH60 HH69

Claims (4)

[Claims] 1. Filtering means for generating an estimated reverberation by convolving a reference signal and a filtering coefficient for simulating the reverberation in order to eliminate reverberation occurring in a communication line including a two-wire / four-wire converter, and the obtained estimation An echo canceller including an adding unit that generates a residual signal by subtracting an echo from the echo multiplex transmission signal, and a suppressing unit that suppresses a residual echo component in the residual signal, the device further includes:
Attenuation characteristic calculating means for calculating an attenuation rate and a reverberation curve of the filter coefficient from the filter coefficient estimated by the filter means; level calculating means for calculating the level of the reference signal from the reference signal and the filter coefficient attenuation rate; And a filter length calculation means for calculating a filter length that satisfies a specified allowable reverberation level and / or a required filter length reduction rate based on the reverberation curve, and the filter means is a filter length variable filter means, A reverberation canceller characterized by receiving the calculated filter length and performing only the convolution operation on a portion corresponding to the filter length. 2. The filter length calculating means also calculates a residual signal level increase rate, and the suppressing means comprises means for adjusting a residual signal suppression rate based on the calculated residual signal level increase rate. 2. The reverberation canceling apparatus according to claim 1, wherein: 3. A filtering means for generating an estimated reverberation by convolving a reference signal with a filtering coefficient simulating the reverberation to eliminate reverberation occurring in a communication line including a two-wire / four-wire converter. A reverberation elimination method in which a residual signal is generated by subtracting the estimated reverberation from the reverberation multiplex transmission signal and a residual reverberation component in the residual signal is suppressed by a suppressor, a filter coefficient is calculated from a filter coefficient estimated by the filter. Calculating the attenuation level and reverberation curve of the reference signal, calculating the level of the reference signal from the reference signal and the filter coefficient attenuation rate, and specifying the specified allowable reverberation level and / or requirement based on the reference signal level and the reverberation curve. Calculating a filter length that satisfies a filter length reduction rate; and a filter length variable filter means as the filter means. Used, reverberation erasing method characterized by comprising the steps of performing only the convolution operation portion corresponding to the calculated filter length. 4. A step of calculating a residual signal level increase rate in the step of calculating the filter length, and adjusting a suppression rate of the residual signal of the suppressor based on the calculated residual signal level increase rate. The method according to claim 3, further comprising: