# US 2012/0084085 A1 · Method and device for tracking background noise in communication system

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- Number: US 2012/0084085 A1
- Document ID: US20120084085A1
- Status: Published application
- Kind: A1
- Application number: 13/325,985
- Filed: 2011-12-14
- Published: 2012-04-05
- Earliest claimed: 2009-10-15
- Assignees: Huawei Technologies Co., Ltd.
- Inventors: Zhe Wang
- Web page: https://patentgrep.com/patent/US20120084085A1

## CPC

- G10L 21/0208: Noise filtering
- G10L 25/84: for discriminating voice from noise
- G10L: SPEECH ANALYSIS TECHNIQUES OR SPEECH SYNTHESIS; SPEECH RECOGNITION; SPEECH OR VOICE PROCESSING TECHNIQUES; SPEECH OR AUDIO CODING OR DECODING

## Abstract

A method and a device for tracking background noise in a communication system are provided. The method includes: calculating a SNR of a current frame according to input audio signals; increasing a frame counter, and calculating tone features and signal steadiness features of the current frame if the SNR of the current frame is not less than a first threshold; determining the possibility of a time window including a noise interval according to the calculated tone feature values and signal steadiness feature values of each frame of the time window when the frame counter is increased to the length of the time window; and extracting noise features in the time window. Existence of background noise is analyzed continuously in a time window, so that background noise that changes frequently.

## Claims

### Claim 1

A method for tracking background noise in a communication system, comprising:
calculating a Signal to Noise Ratio (SNR) of a current frame according to input audio signals;
increasing a frame counter cnt2 and calculating values for tone feature and signal steadiness features of the current frame if the SNR of the current frame is greater than or equal to a first threshold;
determining the possibility of a time window comprising a noise interval according to the tone feature value and the signal steadiness feature values of each frame of the time window when the frame counter cnt2 is increased to the length of the time window; and
extracting noise features in the time window according to the determined possibility of the time window comprising a noise interval.

### Claim 2 (depends on 1)

The method according to claim 1, wherein calculating values for tone features and signal steadiness features of the current frame comprises: calculating the tone feature values of the current frame, a spectrum fluctuation value spdev of the current frame, a spectrum peak position fluctuation value of the current frame, and a spectrum maximum Peak to Valley Ratio (PVR) position fluctuation value of the current frame.

### Claim 3 (depends on 2)

The method according to claim 2, wherein calculating the tone feature value of the current frame comprises: calculating a sum of the largest three normalized PVRs of the spectrum according to a formula of tonal=PVRmax1+PVRmax2+PVRmax3, where PVRmax1, PVRmax2, and PVRmax3 represent the largest three normalized PVRs of the spectrum of the current frame, each normalized PVR satisfies PVR=[(peak−vall)+(peak−valr)]/Eavg, where peak represents a local peak of a Fast Fourier Transform (FFT) spectrum, vall represents a minimum value found within a range of 4 frequency points to the left of the FFT spectrum peak, valr represents a minimum value found within a range of 4 frequency points to the right of the FFT spectrum peak, vall and valr represent local valleys that are on the two sides of peak and are the nearest to peak, and Eavg represents an average value of the FFT spectrum energy,
wherein calculating the spectrum fluctuation value spdev of the current frame comprises: calculating the spectrum fluctuation value spdev according to the formula of
spdev
=
1
N

∑
i

(
E
w

(
i
)
-
M
)
2
,
where M is an average value of Ew(i), Ew(i) is energy of an ith sub-band after spectral subtraction according to Ew(i)=Es(i)/Eavg(i), where Es(i) represents energy of the ith sub-band of the current frame, Eavg(i) represents an energy slide average of the ith sub-band; and Eavg is calculated according to the formula of Eavg(i)=α·Eavg(i)+(1−α)·Es(i), where α is a for getting coefficient,
wherein calculating the spectrum peak position fluctuation value pflux of the current frame comprises: calculating the spectrum peak position fluctuation value pflux of the current frame according to the formula of pflux=idxpmax(0)−idxpmax(−1), where idxpmax (0) represents an FFT frequency point index of the spectrum maximum peak of the current frame, and idxpmax(−1) represents an FFT frequency point index of the spectrum maximum peak of a previous frame,
wherein calculating the spectrum maximum PVR position fluctuation value Mpflux of the current frame comprises: calculating the spectrum maximum PVR position fluctuation value Mpflux of the current frame a ccording to the formula of Mpflux=idxpvrmax(0−idxpvrmax(−1), where idxpvrmax(0) represents an FFT frequency point index with the maximum PVR of the current frame, and idxpvrmax(−1) represents an FFT frequency point index with the maximum PVR of a previous frame, and
wherein idxpvrmax(0) and idxpvrmax(−1) are determined according to pvr values which are calculated by: pvr=4·Eidx—peak(Eidx—peak−1+Eidx—peak−2+Eidx—peak+1+Eidx—peak+2), where Eidx—peak represents energy of the local peak peak, Eidx—peak−i represents energy of an ith FFT frequency point to the left of peak, and Eidx—peak+i represents energy of an ith FFT frequency point to the right of peak.

### Claim 4 (depends on 2)

The method according to claim 2, wherein before determining the possibility of the time window comprising a noise interval, the method further comprises:
increasing a weak spectrum fluctuation counter cnt3 if the spectrum fluctuation value of the current frame is less than a third threshold;
increasing a weak tone counter cnt4 if the tone feature values of the current frame are less than a fourth threshold;
increasing a steady maximum PVR position counter cnt5 if the spectrum maximum PVR position fluctuation value of the current frame is less than a fifth threshold;
increasing a spectrum peak position fluctuation counter cnt6 if the spectrum peak position fluctuation value of the current frame is greater than a sixth threshold; and
determining whether the time window comprises a noise frame according to the spectrum fluctuation value, the tone feature values, the spectrum maximum PVR position fluctuation value, the spectrum peak position fluctuation value of the current frame, and all of a plurality of counters, wherein the plurality of counters comprise the frame counter cnt2, the weak spectrum fluctuation counter cnt3, the weak tone counter cnt4, the steady maximum PVR position counter cnt5, and the spectrum peak position fluctuation counter cnt6, and
wherein determining whether the time window comprises a noise frame when the frame counter cnt2 is increased to the length of the time window comprises:
if the weak tone counter cnt4 is less than or equal to a seventh threshold, determining that the time window does not comprise a noise frame;
if the weak tone counter cnt4 is greater than the seventh threshold, determining that the current frame is a noise frame if the weak spectrum fluctuation counter cnt3 is greater than an eighth threshold, the steady maximum PVR position counter cnt5 is less than a ninth threshold, the spectrum peak position fluctuation counter cnt6 is greater than a tenth threshold, and the spectrum fluctuation value of the current frame is less than an eleventh threshold; and
if the weak tone counter cnt4 is greater than the seventh threshold, determining that the time window comprises a noise frame if the steady maximum PVR position counter cnt5 is less than the ninth threshold and the spectrum peak position fluctuation counter cnt6 is greater than the tenth threshold;
otherwise determining that the time window does not comprise a noise frame.

### Claim 5 (depends on 4)

The method according to claim 4, wherein if the time window comprises a noise frame, determining the possibility of the time window comprising a noise interval comprises:
determining that all intervals in the time window are noise intervals if the weak spectrum fluctuation counter cnt3 is equal to the length of the time window; and
determining that most of the intervals in the time window are noise intervals and a small number of the intervals in the time window are non-noise intervals if the weak spectrum fluctuation counter cnt3 is less than the length of the time window but greater than a preset length.

### Claim 6 (depends on 5)

The method according to claim 5, wherein if most of the intervals in the time window comprising the noise intervals are noise intervals, and a small number of the intervals in the time window comprising the noise intervals are non-noise intervals, the method further comprises:
determining a type of position of the small number of the non-noise intervals in the time window, wherein the type of position comprises: a front end of the time window, a rear end of the time window, or both,
wherein determining the type of the position of the small number of the non-noise intervals in the time window comprises:
obtaining a frame that cannot make the weak spectrum fluctuation counter cnt3 increase;
obtaining a position of the frame according to the obtained frame; and
obtaining the type of the position of the small number of the non-noise intervals in the time window according to the position, and
wherein extracting the noise features of the time window according to the determined possibility of the time window comprising a noise interval comprises:
if the intervals in the time window are all the noise intervals, extracting feature values of the noise interval at the very rear end of the time window; or, extracting average values of the features of all of the noise intervals in the time window; or, extracting weighted feature values of a part of or all of the noise intervals in the time window; and
if most of the intervals in the time window are noise intervals and a small number of the intervals are non-noise intervals, performing any one of the steps exposed as: extracting feature values of the noise interval at the very rear end of the time window; or, extracting weighted feature values of a part of the noise intervals close to the rear end in the time window if the non-noise intervals are not at the rear end of the time window; or, extracting a smallest value of the noise features in the time window; or, extracting weighted feature values of a part of the noise intervals if the non-noise intervals are at the rear end of the time window.

### Claim 7 (depends on 1)

The method according to claim 1, wherein before determining the possibility of the time window comprising a noise interval, the method further comprises:
increasing one or more counters corresponding to the tone feature value and the signal steadiness feature values that meet their respective requirements according to a result obtained by comparing the tone feature value and the signal steadiness feature values with one or more thresholds corresponding to the tone feature values and/or the signal steadiness feature values.

### Claim 8 (depends on 7)

The method according to claim 7, wherein increasing the one or more counters corresponding to the tone feature value and the signal steadiness feature values that meet their respective requirements according to the comparison performed between the tone feature value and the signal steadiness feature values, and the thresholds corresponding to the tone feature value and/or the signal steadiness feature values comprises:
increasing a weak spectrum fluctuation counter cnt3, if the spectrum fluctuation value of the current frame is less than a third threshold;
increasing a weak tone counter cnt4 if the tone feature value of the current frame are less than a fourth threshold;
increasing a steady maximum PVR position counter cnt5 if the spectrum maximum PVR position fluctuation value of the current frame is less than a fifth threshold;
increasing a spectrum peak position fluctuation counter cnt6 if the spectrum peak position fluctuation value of the current frame is greater than a sixth threshold; and
determining whether the time window comprises a noise frame according a spectrum fluctuation value, the tone feature value, a spectrum maximum PVR position fluctuation value, a spectrum peak position fluctuation value of the current frame, and all of the one or more counters.

### Claim 9 (depends on 8)

The method according to claim 8, wherein determining the possibility of the time window comprising a noise interval according to the calculated tone feature value and the signal steadiness feature values of each frame of the time window when the frame counter cnt2 is increased to the length of the time window comprises:
determining whether the time window comprises a noise frame according to the tone feature value, the signal steadiness feature values, and the counters corresponding to the tone feature value and the signal steadiness feature values when the frame counter cnt2 is increased to the length of the time window; and
determining the possibility of the time window comprising a noise interval if the time window comprises a noise frame.

### Claim 10 (depends on 9)

The method according to claim 9, wherein determining whether the time window comprises a noise frame when the frame counter cnt2 is increased to the length of the time window comprises:
if the weak tone counter cnt4 is not greater than a seventh threshold, determining that the time window does not comprise a noise frame;
if the weak tone counter cnt4 is greater than the seventh threshold, determining that the current frame is a noise frame if the weak spectrum fluctuation counter cnt3 is greater than a eighth threshold, the steady maximum PVR position counter cnt5 is less than a ninth threshold, and the spectrum peak position fluctuation counter cnt6 is greater than a first threshold, and the spectrum fluctuation value of the current frame is less than a eleventh threshold, determining that the time window comprises a noise frame if the steady maximum PVR position counter cnt5 is less than the ninth threshold and the spectrum peak position fluctuation counter cnt6 is greater than the tenth threshold, otherwise determining that the time window does not comprise a noise frame,
wherein if the time window comprises a noise frame, determining the possibility of the time window comprising a noise interval comprises:
determining that all intervals in the time window are noise intervals if the weak spectrum fluctuation counter cnt3 is equal to the length of the time window; and
determining that most of the intervals in the time window are noise intervals and a small number of the intervals in the time window are non-noise intervals if the weak spectrum fluctuation counter cnt3 is less than the length of the time window and greater than a preset length,
wherein if most of the intervals in the time window comprising the noise intervals are noise intervals, and a small number of the intervals in the time window comprising the noise intervals are non-noise intervals, the method further comprises: determining a type of position of the small number of the non-noise intervals in the time window, wherein the type of position comprises: a front end of the time window, a rear end of the time window, or both, wherein determining the type of position of the small number of the non-noise intervals in the time window comprises:
obtaining a frame that cannot make the weak spectrum fluctuation counter cnt3 increase according to the weak spectrum fluctuation counter cnt3;
obtaining a position of the frame according to the obtained frame; and
obtaining the type of the position of the small number of the non-noise intervals in the time window according to the position.

### Claim 11 (depends on 10)

The method according to claim 10, wherein extracting the noise features of the time window according to the determined possibility of the time window comprising a noise interval comprises:
if the intervals in the time window are all the noise intervals, extracting feature values of the noise interval at the very rear end of the time window; or, extracting average values of the features of all of the noise intervals in the time window; or, extracting weighted feature values of a part of or all of the noise intervals in the time window; and
if most of the intervals in the time window are noise intervals and a small number of the intervals are non-noise intervals, extracting feature values of the noise interval at the very rear end of the time window; or extracting weighted feature values of a part of the noise intervals close to the rear end in the time window if the non-noise intervals are not at the rear end of the time window; or extracting a smallest value of the noise features in the time window; or extracting weighted feature values of a part of the noise intervals if the non-noise intervals are at the rear end of the time window.

### Claim 12 (depends on 1)

The method according to claim 1, wherein when the frame counter cnt2 is greater than the length of the time window, the method further comprises:
obtaining a spectrum fluctuation value of the current frame;
determining that the current frame is a noise frame if the spectrum fluctuation value of the current frame is less than a eleventh threshold; and
determining that the current frame is a non-noise frame if the spectrum fluctuation value of the current frame is greater than or equal to the eleventh threshold.

### Claim 13

A device for tracking background noise in a communication system, comprising:
a first processing module, configured to calculate a Signal to Noise Ratio (SNR) of a current frame according to input audio signals;
a second processing module, configured to increase a frame counter cnt2, and calculate values for tone features and signal steadiness features of the current frame if the SNR of the current frame is greater than or equal to a first threshold;
a third processing module, configured to determine the possibility of a time window comprising a noise interval according to the tone feature values and the signal steadiness feature values of each frame of the time window when the frame counter cnt2 is increased to the length of the time window; and
a fourth processing module, configured to extract noise features in the time window according to the determined possibility of the time window comprising a noise interval.

### Claim 14 (depends on 13)

The device according to claim 13, wherein the second processing module comprises:
a threshold determining unit, configured to determine whether the SNR of the current frame is greater than the first threshold;
a frame counter increasing unit, configured to increase the frame counter cnt2 if a determining result of the threshold determining unit indicates that the SNR of the current frame is less than or equal to the first threshold; and
a calculating unit, configured to calculate a spectrum fluctuation value of the current frame, the tone feature values of the current frame, a spectrum peak position fluctuation value of the current frame, and a spectrum maximum Peak to Valley Ratio (PVR) position fluctuation value of the current frame.

### Claim 15 (depends on 14)

The device according to claim 14, wherein the third processing module further comprises:
an increasing unit, configured to:
increase a weak spectrum fluctuation counter cnt3 if the spectrum fluctuation value of the current frame is less than a third threshold;
increase a weak tone counter cnt4 if the tone feature values of the current frame are less than a fourth threshold;
increase a steady maximum PVR position counter cnt5 if the spectrum maximum PVR position fluctuation value of the current frame is less than a threshold value 5; and
increase a spectrum peak position fluctuation counter cnt6 if the spectrum peak position fluctuation value of the current frame is greater than a threshold value 6; and
a determining unit, configured to:
determine whether the time window comprises a noise frame according to the spectrum fluctuation value, the tone feature values, the spectrum maximum PVR position fluctuation value, the spectrum peak position fluctuation value of the current frame, and one or more counters, wherein the determining unit is configured to determine that the time window does not comprise a noise frame if the weak tone counter cnt4 is greater than a seventh threshold;
determine that the current frame is a noise frame if the weak tone counter cnt4 is greater than the seventh threshold, the weak spectrum fluctuation counter cnt3 is greater than a eighth threshold, the steady maximum PVR position counter cnt5 is less than a ninth threshold, the spectrum peak position fluctuation counter cnt6 is greater than a tenth threshold, and the spectrum fluctuation value of the current frame is less than a eleventh threshold; and
determine that the time window comprises a noise frame if the steady maximum PVR position counter cnt5 is less than the ninth threshold, and the spectrum peak position fluctuation counter cnt6 is greater than the tenth threshold;
otherwise determine that the time window does not comprise a noise frame.

### Claim 16 (depends on 15)

The device according to claim 15, wherein the third processing module is configured to:
determine that all intervals in the time window are noise intervals if the weak spectrum fluctuation counter cnt3 is equal to the length of the time window; and
determine that most of the intervals in the time window are noise intervals and a small number of the intervals in the time window are non-noise intervals if the weak spectrum fluctuation counter cnt3 is less than the length of the time window and greater than a preset length;
otherwise determine that the time window does not comprise a noise frame.

### Claim 17 (depends on 16)

The device according to claim 16, wherein if most of the intervals in the time window are noise intervals and a small number of the intervals in the time window are non-noise intervals, then the third processing module further comprises:
a position type determining unit, configured to determine a type of position of the small number of the non-noise intervals in the time window, wherein the type of position comprises: a front end of the time window, a rear end of the time window, or both.

### Claim 18 (depends on 17)

The device according to claim 17, wherein the position type determining unit is configured to:
obtain a frame that cannot make the weak spectrum fluctuation counter cnt3 increase according to the weak spectrum fluctuation counter cnt3;
obtain a position of the frame according to the obtained frame; and
obtain the type of position of the small number of the non-noise intervals in the time window according to the position of the frame.

### Claim 19 (depends on 17)

The device according to claim 17, wherein if the intervals in time window are all the noise intervals, the fourth processing module is configured to extract feature values of the noise interval at the very rear end of the time window; or extract average values of the features of all of the noise intervals in the time window; or extract weighted feature values of a part of or all of the noise intervals in the time window,
wherein if most of the intervals in the time window are noise intervals and a small number of the intervals are non-noise intervals, the fourth processing module is configured to extract the feature values of the noise interval at the very rear end of the time window; or extract weighted feature values of a part of the noise intervals near the rear end in the time window if the non-noise intervals are not at the rear end of the time window; or extract a smallest value of the noise features in the time window; or extract weighted feature values of a part of the noise intervals if the non-noise intervals are at the rear end of the time window.

### Claim 20 (depends on 14)

The device according to claim 14, wherein if the frame counter cnt2 is greater than the length of the time window, the third processing module is further configured to:
determine that the current frame is a noise frame if the spectrum fluctuation value of the current frame is less than the eleventh threshold; and
determine that the current frame is a non-noise frame if the spectrum fluctuation value of the current frame is greater than or equal to the first threshold.