WO2007109949A1

WO2007109949A1 - A method and a device for generating comfort noise in echo cancellation

Info

Publication number: WO2007109949A1
Application number: PCT/CN2007/000166
Authority: WO
Inventors: Dailin Jiang
Original assignee: Huawei Technologies Co., Ltd.
Priority date: 2006-03-27
Filing date: 2007-01-17
Publication date: 2007-10-04
Also published as: CN101046965A; CN101046965B

Abstract

A method and a device for generating comfort noise in echo cancellation, in which the method includes the steps of: obtaining amplitude of residual echo and absolute value of amplitude of background noise (S20); comparing the amplitude of residual echo and the absolute value of the amplitude of background noise (S22); if the amplitude of the residual echo is larger than the absolute value of the amplitude of the background noise, clipping the amplitude of the residual echo to make the amplitude of the residual echo equal to the amplitude of the background noise (S23,S24) or make the difference between the amplitude of the residual echo and the amplitude of the background noise is smaller than a presetting threshold value (S25), and making the residual echo serve as the comfort noise.

Description

Method and device for generating comfort noise in echo cancellation

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a background noise control method in a communication device, and more particularly to a method and apparatus for generating comfort noise in echo cancellation.

Background technique

"Echo, is a phenomenon that occurs in the telephone system when the energy of a portion of the transmitted speech signal is reflected back to the transmitter. These reflections are caused by impedance mismatch in the analog portion of the telephone network, for example, in public switched telephones. In the network (PSTN) user interface, the 4-wire is converted into a 2-wire hybrid circuit, or the acoustic crosstalk in a mobile radiotelephone. The echo generally includes electrical echoes and acoustic echoes, and electrical echoes often occur in long-distance signal transmission. In applications where long-distance signal transmissions involve excessive propagation delays (due to the incompleteness of the hybrid line that converts the twisted pair connections to a four-wire system). The "signal leakage" or cause of the incompleteness of such hybrid lines Signal reflection caused by impedance mismatch, known as network electrical echo. Sound waves from the receiver (headphones), reflected by a solid object located on the sound path into the microphone (microphone) of the phone, or in the speakerphone, An acoustic echo is formed. The echo accompanying the basic delay can severely degrade the quality of the processed speech signal.

The structure of the echo canceller is now often used to eliminate the above-mentioned echoes in the communication system. As shown in Fig. 1, a schematic diagram of an echo canceller in the ITU G.168 standard is shown. Wherein, Rin/Rout is the far-end input/output signal, Sin/Sout is the near-end input/output signal, and the far-end output signal (Rout) to the near-end input signal (Sin) is the echo path, and the near-end input signal (Sin) contains echo signals; linear convolution processing (subtraction) is performed with the near-end input signal (Sin) and the estimated echo to obtain residual echoes. When the cancellation effect is good, the residual echoes are in the residual echoes. The echo component is very small, which can improve the call effect; but for some reason, when the cancellation effect is not good, the echo component in the residual echo is large, and the call effect is not good (or worse), then usually The residual echo is nonlinearly processed by a nonlinear processor (LP) to further reduce the echo component. At this time (when the LP is operating), the residual echo is replaced by comfort noise (CN). To improve the performance of the call. Among them, the standard definition of comfort noise: pseudo noise or background noise or idle channel inserted during silence when NLP is working Noise, the purpose of which is to prevent the effects of mute on background noise, where background noise is part of the speech.

Two methods are now used to generate comfort noise: One is to use white noise (or HOTH noise) as comfort noise, and its amplitude is comparable to background noise. This method is easy to implement, but when the background noise is large, the background noise is The comfort noise switching is obvious, the call is unnatural; the other method is to use complex algorithms to simulate the background noise. This method works well, that is, the background noise and the comfort noise are also very close when the background noise is large. Naturally, but this method is complicated in algorithm and costly to implement.

Summary of the invention

It is an object of the present invention to provide a method and apparatus for generating comfort noise in echo cancellation, which is capable of generating natural comfort noise.

One embodiment of the present invention provides a method of generating comfort noise in echo cancellation, the method comprising the steps of:

Obtaining the absolute value of the amplitude of the residual echo and the amplitude of the background noise;

Comparing the amplitude of the residual echo and the absolute value of the amplitude of the background noise;

If the amplitude of the residual echo is greater than the absolute value of the amplitude of the background noise, limiting the amplitude of the residual echo such that the amplitude of the residual echo is equal to the amplitude of the background noise or the residual echo The amplitude difference between the amplitude and the background noise is less than a set threshold, making the residual echo a comfort noise.

An embodiment of the apparatus for generating comfort noise in echo cancellation provided by the present invention, comprising: a signal input unit for obtaining an absolute value of a magnitude of a residual echo and a magnitude of a background noise;

a comparison unit, configured to compare an amplitude of the residual echo and an absolute value of a magnitude of the background noise; and if the amplitude of the residual echo is greater than an absolute value of the amplitude of the background noise, output the comparison result to the comfort noise Generating unit;

a comfort noise generating unit, configured to limit an amplitude of the residual echo according to an indication of the comparing unit, such that an amplitude of the residual echo is equal to an amplitude of the background noise or a magnitude of the residual echo The amplitude difference of the background noise is less than a set threshold, making the residual echo a comfort noise. According to the above embodiment provided by the present invention, when the amplitude of the residual echo is greater than the absolute value of the amplitude of the background noise, the amplitude of the residual echo is limited, that is, the residual echo is performed by using the background noise amplitude. Limiting, the amplitude of the residual echo is equal to the amplitude of the background noise or the amplitude difference between the amplitude of the residual echo and the background noise is less than a set threshold, making the residual echo a comfort noise , thus providing natural comfort noise with background noise switching.

DRAWINGS

1 is a schematic diagram of a model of a conventional echo canceler;

2 is a flow chart of an embodiment of the method of the present invention;

3 is a block diagram of an embodiment of the apparatus of the present invention.

detailed description

The present invention provides a method of generating comfort noise in echo cancellation. Here echoes include, but are not limited to, electrical echoes and acoustic echoes. The invention utilizes the obtained near-end background noise to limit the residual echo, and then appropriately processes the clipped echo as comfort noise (the definition reference background technology), that is, when the nonlinear processor works, the background is utilized. The noise amplitude limits the residual echo, and then the residual echo after clipping can be filtered to reduce the low frequency component of the speech to achieve comfort noise. When the nonlinear processor is not working, the residual echo is not performed. deal with.

2 is a flow chart of a method of generating comfort noise in echo cancellation in accordance with the present invention. In the method provided by the present invention, the method for estimating the amplitude of the background noise and the specific implementation of the condition for judging whether the nonlinear processor is working or not are explained (can be realized by many prior art), but by using the prior art amplitude estimation The method, the amplitude of the comfort noise produced by the present invention should be comparable to the background noise amplitude, as in the ITU G.168 standard, the required difference between the two does not exceed ± 2 dB. In the present invention, it is assumed that the background noise amplitude obtained by the prior art amplitude estimation method is a non-negative value, expressed by AMP; suitable comfort noise can ensure the comfort noise and background output when the nonlinear processor operates. The connection of the noise is natural, the voice heard at the far end has no switching sense (or is not obvious), the comfort noise is represented by CN; the residual echo is represented by RES.

The processing of the comfort noise of the present invention will be described with reference to FIG.

First, the amplitude of the residual echo (RES) and the amplitude of the background noise are obtained in step S20, and the process of obtaining the residual echo (RES) can be referred to the description of the background art, the background noise The magnitude (AMP) can be obtained using the amplitude estimation method of prior art background noise. Next, it is determined in step S21 whether the current non-linear processor is working. If the non-linear processor needs to work at this time (that is, the remote party is unilaterally talking at this time), the flow goes to step S22; When the device does not need to work (that is, the call is not unilaterally unilaterally), the flow goes to step S29, and the remote output signal (Sout) is a residual echo (RES), that is, no residual echo (RES) is needed. ) for processing. In step S22, it is necessary to compare the amplitude of the residual echo and the amplitude of the background noise to determine whether the amplitude of the residual echo (RES) exceeds the background noise amplitude (AMP), if the amplitude of the residual echo (RES) is smaller than the background. a negative value of the noise amplitude (-AMP), in step S23, the amplitude of the residual echo is equal to the negative value of the background noise amplitude (-AMP) by clipping processing, thereby generating comfort noise (CN), The amplitude of the comfort noise (CN) is equal to the negative value of the background noise amplitude (-AMP); in this embodiment, the "equal to" is relative, which has two meanings of exact equality and ambiguity, the fuzzy Equivalence is both "equal, or substantially equal" as described above. In the comparison of the amplitudes of residual echo and background noise as described above, the "less than" or "exceeded" means that the difference is not equal or the difference is large; The amplitude of the echo (RES) is greater than the positive value (AMP) of the background noise amplitude, and in step S24, the amplitude of the residual echo is equal to the positive value (AMP) of the background noise amplitude by clipping processing, thereby Residual The residual echo becomes comfort noise (CN), and the amplitude of the comfort noise (CN) is equal to the positive value of the background noise amplitude (AMP). If the amplitude of the residual echo (RES) is within the background noise amplitude ( - AMP<RES <AMP), that is, when the amplitude of the residual echo is less than or equal to the absolute value of the amplitude of the background noise, then in step S25, the residual echo (RES) is not limited, then the residual echo (RES) Directly as comfort noise (CN), ie the amplitude of the comfort noise is equal to the amplitude of the residual echo. The output processed by step S23, S24 or S25 is comfort noise (CN); in step S26, Comfort noise (CN) performs filtering, such as high-pass filtering, to filter out components with low frequency components or relatively low frequencies to improve residual echo effects; and in step S27, moderate amount in comfort noise (CN) Mixed with white noise or HOTH noise, the mixing ratio can be adjusted, and can start from a preset ratio, where white noise is filtered to remove white noise of high frequency components, and the filtering process can be 4th pass filtering. Li, so that more natural conversation. No fixed order between the steps S26 and S27, wherein, in other embodiments, the step can also be omitted S26 and/or step S27. After the above processing, the final comfort noise is obtained; then in step S29, the far-end output signal (Sout) is the comfort noise (CN); this completes the processing of the comfort noise, which is heard from the far end. Voice is more natural than pure HOTH noise.

By using the method of the present invention to generate comfort noise in echo cancellation, the residual echo is limited by the background noise amplitude, thereby providing a natural comfort noise when the background noise is large;

And by using a non-linear processor to work, the residual echo is limited by the obtained background noise amplitude to achieve comfort noise; when the nonlinear processor is not working, the residual echo is not processed, The invention solves the problem that the white noise (or HOTH noise) is used as the comfort noise (ie, the noise during the call) when the background noise is large, and the switching is obvious and the call is unnatural, and the prior art utilizes complicated The algorithm to simulate background noise has complex algorithms and high cost, and achieves the purpose of natural call, small amount of calculation, easy implementation and low cost.

In addition, the filtering process is used to filter out the low-frequency components of the residual echo, which can reduce the influence of the residual echo; and the residual echo after clipping can be mixed with white noise that is filtered to remove high-frequency components, so that the call is made. More natural.

The apparatus for generating comfort noise in echo cancellation provided by the present invention includes: a signal input unit 31 for obtaining the absolute value of the amplitude of the residual echo and the amplitude of the background noise, and a comparison unit 32, For comparing the amplitude of the residual echo and the absolute value of the amplitude of the background noise; if the amplitude of the residual echo is greater than the absolute value of the amplitude of the background noise, the comparison result is output to the comfort noise generating unit 33;

a comfort noise generating unit 33, configured to limit an amplitude of the residual echo according to an indication of the comparing unit 32, such that an amplitude of the residual echo is equal to an amplitude of the background noise or a magnitude of the residual echo The amplitude difference from the background noise is less than a set threshold, making the residual echo a comfort noise.

In order to further improve the performance of the above apparatus, in another embodiment of the present invention, a filtering unit 35 is further provided for filtering the comfort noise output by the comfort noise generating unit. In addition, in another embodiment, a noise mixing unit 34 is further provided for mixing a predetermined proportion of white noise or noise in the comfort noise output from the comfort noise generating unit 33. In the comfort noise described, the comfort noise mixed with white noise or HOTH noise is filtered by the filtering unit 35. This embodiment refers to FIG. 3.

In the embodiment of Figure 3, the comparison unit 32 employs a non-linear processor.

It should be noted that, in another embodiment of the present invention, the noise mixing unit 34 may also be used to mix a predetermined proportion of white noise or HOTH noise into the comfort noise in the filtered comfort noise output by the filtering unit. in.

Since the specific implementation manner of the present invention has been described in detail above, it will not be further described herein.

Claims

Rights request

What is claimed is: 1. A method of generating comfort noise in echo cancellation, comprising the steps of: obtaining an amplitude of a residual echo and an absolute value of a magnitude of background noise;

2. A method of generating comfort noise in echo cancellation as claimed in claim 1 wherein the non-linear processor is used to compare the amplitude of said residual echo with the absolute value of the amplitude of the background noise.

3. The method of generating comfort noise in echo cancellation according to claim 2, further comprising the steps of:

When the non-linear processor is not operating, the residual echo is output as a remote output signal.

4. The method of generating comfort noise in echo cancellation according to claim 1, further comprising:

The comfort noise is filtered.

5. The method of generating comfort noise in echo cancellation according to claim 1, further comprising:

A predetermined proportion of white noise or HOTH noise is mixed into the comfort noise.

A method of generating comfort noise in echo cancellation according to claim 5, wherein said white noise is white noise that filters out high frequency components.

7. The method of generating comfort noise in echo cancellation according to claim 1, further comprising:

Filtering the comfort noise;

Mix a certain percentage of white noise or HOTH noise into the filtered comfort noise.

8. The method of generating comfort noise in echo cancellation according to any one of claims 1 or 2 or 4 or 5 or 6 or 7, further comprising: using said comfort noise as a remote output Signal output.

9. A method of generating comfort noise in echo cancellation, comprising the steps of: obtaining an amplitude of a residual echo and an absolute value of a magnitude of background noise;

If the amplitude of the residual echo is less than or equal to the absolute value of the amplitude of the background noise, comfort noise is generated, the amplitude of the comfort noise being equal to the amplitude of the residual echo.

10. The method of generating comfort noise in echo cancellation according to claim 9, further comprising:

11. The method of generating comfort noise in echo cancellation according to claim 9, further comprising: filtering said comfort noise.

12. A device for generating comfort noise in echo cancellation, comprising: a signal input unit for obtaining an absolute value of a magnitude of a residual echo and a magnitude of background noise;

a comparison unit, configured to compare an amplitude of the residual echo and an absolute value of a magnitude of the background noise, and if the amplitude of the residual echo is greater than an absolute value of the amplitude of the background noise, output the comparison result to comfort noise generation Unit

a comfort noise generating unit, configured to limit an amplitude of the residual echo according to an indication of the comparing unit, such that an amplitude of the residual echo is equal to an amplitude of the background noise or a magnitude of the residual echo The amplitude difference of the background noise is less than the set threshold, making the residual echo a comfortable noise.

13. Apparatus for generating comfort noise in echo cancellation as claimed in claim 12, further comprising:

A filtering unit is configured to filter the comfort noise output by the comfort noise generating unit.

14. Apparatus for generating comfort noise in echo cancellation according to claim 12 or claim 13 further comprising:

A noise mixing unit for mixing a predetermined proportion of white noise or noise into the comfort noise in the comfort noise output by the comfort noise generating unit.

15. Apparatus for generating comfort noise in echo cancellation as claimed in claim 14 wherein said comparing unit is a non-linear processor.