CN1691716A - Echo eliminator - Google Patents

Abstract

A echo elimination device comprises adaptive filter, used to simulate echo signal in work window; delay estimator with long-term energy, used to estimate time delay of echo path and transmit work signal of adaptive filter in effective coverage to adaptive filter according to time delay simultaneous; echo elimination device is used to echo signal; nonlinear processor decides whether to set zero or pass entirely for output signal of echo elimination device. It can decrease amount of calculation of adaptive filter by the method. Compared with delay T1 by traditional delay estimation method, the invention can decide more accurately the delay T2 of echo path, more approach to real delay T3, and then avoid utility imperfection of effective zone of filter parameter, solve echo elimination imperfection by traditional method and the divergence problem in real system.

Description

Echo cancelling device

Technical field

The present invention relates to a kind of device in novel estimated echo path and Echo Canceller of algorithm of utilizing, relate in particular to a kind of apparatus and method that adopt energy budget echo delay time when long, be used for eliminating such as sneaking into the leakage voice signal that send the language tone signal to produce because of a part that is subjected to the language tone signal at communication equipments such as telephonic communication systems.

Background technology

In public switched telephone network, echoing is that the impedance mismatching by the four line two wires converters that are called as hybrid circuit causes.The combination of this echo and network delay is the reason that causes speech quality to descend.In order to eliminate this echoing, generally all can be equipped with Echo Canceller to prevent the decline of speech quality.

Existing Echo Canceller is to utilize one to be called as the estimation of normalization minimum mean-square (NLMS) sef-adapting filter and to remove the echo of returning from hybrid circuit.But,, as IP telephony technology, make the echo delay time become longer, so the amount of calculation of sef-adapting filter is increasing along with the development of voice communication technology.Suppose that sample frequency is 8KHz, echo path is 128ms, and the exponent number of sef-adapting filter is 1024 rank so.According to the ITU-T standard code, the effective coverage of the impulse response of echo path is 128 rank to the maximum, in other inactive area, except time delay without any other information, only just have the information of echo transfer function in the effective coverage.Therefore, if can the estimated echo delay time, then Echo Canceller can be by the amount of calculation estimated echo on 128 rank, and like this, Echo Canceller can be ignored the echo path time-delay and carry out its operation by smaller calculation.

The weak point that conventional echo is eliminated is that the amount of calculation that filter needs is very big.For example, if when sample rate is 8KHz, each sampling point of the sef-adapting filter in then traditional Echo Canceller just needs the coefficient on filter 1024 rank to participate in calculating.According to the ITU-T standard code, the filter effective coverage outside the pure time of echo delay is generally less than 128 rank, almost less than the 128/8000=16 millisecond, can not surpass 128 rank so in fact participate in the effective coverage of the coefficient on 1024 rank of calculating.In addition, because the value of actual effective coverage is near a constant, so when whole time of echo delay becomes longer, utilize the echo estimating device can be very effective.

Recently the time-delay estimation approach of using mainly contains cross-correlation method and searches the method for the absolute value maximum of filter coefficient, these two kinds of methods all be finally with the peaked position of the absolute value of filter coefficient as the echo path delay time.According to the echo path in the ITU-T standard, the echo path delay time also is not equal to the peaked position of the absolute value of filter coefficient, but preceding about 5 milliseconds in maximum, if the peaked position with absolute value is time of delay, can make the echo path that estimates inaccurate, thereby make not thorough that echo is eliminated in the real system, even cause Echo Canceller to disperse.

Summary of the invention

The purpose of this invention is to provide a kind of Echo Canceller, adopt novel time delay estimation approach, can estimate more accurately that the real time of echo path postpones.For realizing above-mentioned order ground, a kind of echo cancelling device comprises:

Sef-adapting filter is used for simulating echo signal in operation window;

Adopt the time delay estimator of energy when long, be used for the time delay in estimated echo path, the operation window of the effective coverage of the sef-adapting filter that will obtain according to time delay sends sef-adapting filter to simultaneously;

Echo Canceller is used to eliminate echo signal;

Nonlinear processor, whether decision is carried out zero setting to the output signal of Echo Canceller or is passed through fully.

According to another aspect of the present invention, the echo delay evaluation method in a kind of echo eliminator comprises step:

Energy during initialization filter long;

Read filter device coefficient;

Energy during calculating filter coefficient long;

Whether energy is greater than threshold value when judging filter coefficient long;

Acquisition obtains the delay of echo path greater than the position of threshold value;

Adjust the operation window of filter, and give filter.

By time-delay method of estimation of the present invention, can reduce the amount of calculation of sef-adapting filter.The time-delay T1 that obtains than traditional time-delay estimation approach, the present invention can judge the time-delay T2 of echo path more accurately, more near the actual time delay T3 of echo path, thereby avoid filter coefficient the effective coverage utilization not exclusively, solved traditional time-delay and estimated to cause echo and eliminate not exclusively and the problem of in real system, dispersing easily.

Description of drawings

Fig. 1 represents the structured flowchart of echo cancelling device of the present invention;

Fig. 2 illustrates a block diagram according to echo path delay estimating device of the present invention;

Fig. 3 illustrates a flow chart according to echo path delay evaluation method of the present invention.

Fig. 4 illustrates the advantage that the present invention compares with previous methods.

Embodiment

With reference to the accompanying drawings the specific embodiment of the present invention is elaborated.

As shown in Figure 1, echo cancelling device is at the hybrid circuit of callee and send that the form with 4 terminal structures links together between the hybrid circuit of words end.In this echo cancelling device, the language tone signal R that send of ' A ' end is sent to ' B ' end by hybrid circuit 510.The echo of sending the language tone signal of ' A ' end that produces from the input speech signal of ' B ' end with by this hybrid coil forms that B holds send language tone signal S, and this signal is transferred to Echo Canceller 550.' A ' end the input that send language tone signal R to be sent to sef-adapting filter 520 simultaneously by hybrid circuit, as sef-adapting filter 520 input.

Simultaneously, the coefficient of sef-adapting filter 520 outputs to the time delay estimation unit 530 of energy when adopting length, the time delay in these time delay estimation unit 530 estimated echo paths sends the operation window of the effective coverage of the sef-adapting filter 520 that obtains according to time delay to sef-adapting filter 520 simultaneously.Sef-adapting filter 520 carries out filtering according to this operation window.

The output of sef-adapting filter 520 is sent to Echo Canceller 550, and Echo Canceller 550 is to constitute for the operation of sending the echo among the language tone signal S that elimination is superimposed upon B end.

The output signal Err of Echo Canceller 550 receives the input of sef-adapting filter 520 and nonlinear processor 540 simultaneously.

Sef-adapting filter 520 is adjusted relevant parameter according to the output signal Err of Echo Canceller 550.

Whether input has the voice signal input according to ' B ' end for nonlinear processor 540, and whether decision is carried out zero setting (or output comfort noise) to the output signal Err of Echo Canceller 550 and still passed through fully.

Fig. 2 illustrate one according to employing of the present invention the block diagram of the time delay estimation unit 530 of energy when long.With reference to figure 2, time delay estimating device 530 comprises 630, one operation window adjustment units 640 of 620, one judging units of energy calculation unit when 610, one of filter coefficient reading units are long.

With reference now to Fig. 1 and Fig. 2, the operating process of adopting echo cancelling device of the present invention is described.

Reasons such as sound feedback when the conversion of four-wire circuit and two-wire channel on employed hybrid circuit 510 and end user's the terminal, the part of sending language tone signal R of ' A ' end, be superimposed upon sending among the language tone signal S of B end and form echo, and be imported into Echo Canceller 550.In sef-adapting filter 520, according to inferring that from the output of sending language tone signal R and Echo Canceller 550 of ' A ' end the pulsion phase that echo path should, convolution ' A ' end send language tone signal R and impulse response, generate artificial echo, deduct artificial echo from sending of B end the language tone signal S by Echo Canceller 550 and eliminate echo.

Filter coefficient reading unit 610 when adopting length in the time delay estimation unit 530 of energy reads the coefficient of sef-adapting filter, this coefficient is all values that comprise effective coverage and inactive area, because in the system of reality, echo path usually takes place gradual, if all coefficients are all read, will follow the tracks of this variation.

Energy when energy calculation unit 620 is used for calculating filter coefficient long when long, energy can reflect the conversion of filter coefficient in inactive area and effective coverage when growing.The coefficient of energy can be adjusted when the calculating of different echo paths was long, to obtain optimum efficiency.

Can calculate energy when long according to following formula.

en(n)＝(1-α)en(n-1)+α*g(n)g(n) (1)

Wherein α can get 0.01.

Whether energy was above predetermined threshold value D when judging unit 630 was mainly judged filter coefficient long, and this threshold value can be adjusted according to the echo path of reality, can be set at peaked 0.1～0.5 times of filter coefficient absolute value.When energy surpassed this threshold value D when filter coefficient long, judging unit 630 just judged that filter coefficient is in the effective coverage, inactive area before this with regard to the time echo path time delay.

Operation window adjustment unit 640 is set the operation window of filter according to the effective coverage of filter coefficient, if the window of testing simultaneously is near the situation on both sides.This adjustment unit is chosen the operation window W of sef-adapting filter according to the effective coverage, and W is delivered to sef-adapting filter with this operation window, and sef-adapting filter utilizes operation window to calculate the estimated value Err of echo.In obtaining echo estimated value Err process, corresponding that a series of coefficients are used to calculate the echo estimated value with operation window, and a series of coefficients outside operation window often are set to ' 0 '.

Sef-adapting filter 520 receives effective operation window of the filter that send language tone signal R and 640 settings of operation window adjustment unit of ' A ' end, calculates echo estimated value Err, and echo estimated value Err is sent to Echo Canceller 550.Echo Canceller 550 is removed the end value that obtains behind the echo estimated value Err from sending of B end and is sent to Nonlinear Processing device 540 the language tone signal S.If the voiceless sound signal is from ' B ' end input, then Nonlinear Processing device 540 becomes ' 0 ' or become comfort noise with input signal, and the signal that is changed is sent to ' A ' end.

Fig. 3 illustrates one according to the flow chart of estimated echo of the present invention road through the process of time delay, illustrates according to the method for estimated echo of the present invention road through time delay below with reference to Fig. 3.

In step 710, the energy initialization is made as a minimum positive number to its initial value, for example: 0.0001 during to the coefficient of sef-adapting filter 520 long.

In step 720, read the coefficient of filter from sef-adapting filter 520.

In step 730, energy during coefficient long of calculating sef-adapting filter 520 according to formula 1.

In step 740, the point greater than threshold value of energy carries out following operation when finding sef-adapting filter long.

Relatively energy and pre-set threshold during filter coefficient long, if when long energy in certain some beginning greater than preset threshold, this point N under the record carry out step 750 so.If energy never greater than the point of threshold value, then carry out step 760 when long.

In step 750,, calculate the time delay of echo path according to the some N under 740 records.

In step 760, the most current time delay of time delay of the echo path that last computation is obtained.

In step 770,, the operation window of sef-adapting filter 520 is adjusted according to the time delay of the time delay of the echo path that estimates.

Fig. 4 is the curve chart that the present invention compares with conventional method, as can be seen from Figure 4 the present invention's advantage compared with prior art.

Claims (5)

1. echo cancelling device comprises:

Sef-adapting filter is used for simulating echo signal in operation window;

Adopt the time delay estimator of energy when long, be used for the time delay in estimated echo path, the operation window of the effective coverage of the sef-adapting filter that will obtain according to time delay sends sef-adapting filter to simultaneously;

Echo Canceller is used to eliminate echo signal;

Nonlinear processor, whether decision is carried out zero setting to the output signal of Echo Canceller or is passed through fully.

2. by the described device of claim 1, it is characterized in that described time delay estimator comprises:

The reading unit of filter coefficient is used to read the coefficient of sef-adapting filter;

The energy calculation unit is used for calculating filter coefficient when long;

Judging unit, whether energy surpasses threshold value when being used to judge filter coefficient long;

Adjustment unit utilizes the time delay that obtains to determine the operation window of filter coefficient.

3. by the described device of claim 2, it is characterized in that described threshold value is the peaked 0.1-0.5 of filter absolute value times.

4. the echo delay evaluation method in the echo eliminator comprises step:

Energy during initialization filter long;

Read filter device coefficient;

Energy during calculating filter coefficient long;

Whether energy is greater than threshold value when judging filter coefficient long;

Acquisition obtains the delay of echo path greater than the position of threshold value;

Adjust the operation window of filter, and give filter.

5. by the described method of claim 4, energy is calculated by following formula when it is characterized in that described calculating filter long:

en(n)＝(1-α)en(n-1)+α*g(n)g(n)，

Wherein α gets 0.01.

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