Weighted frequency-channel background noise suppressor

• US 6,826,528 B1
• Filed: 10/18/2000
• Issued: 11/30/2004
• Est. Priority Date: 09/09/1998
• Status: Expired due to Fees

• Current Assignee: Sony Corporation (Sony Group Corp.), Sony Electronics Inc. (Sony Group Corp.)
• Original Assignee: Sony Corporation (Sony Group Corp.), Sony Electronics Inc. (Sony Group Corp.)
• Inventors: Wu, Duanpei, Menendez-Pidal, Xavier, Tanaka, Miyuki
• Primary Examiner(s): Dorvil, Richemond
• Assistant Examiner(s): Storm, Donald L.
• Application Number:
  US09/691,878
• Time in Patent Office: 1,504 Days
• Field of Search: 704/233, 704/226, 704/227, 704/204
• US Class Current: 704/226
• CPC Class Codes: G10L 21/0208 Noise filtering
• CPC Class Codes: G10L 21/0232 Processing in the frequency domain
• CPC Class Codes: G10L 25/18 the extracted parameters being spectral information of each sub-band
• CPC Class Codes: G10L 25/78 Detection of presence or absence of voice signals switching of direction of transmission by voice frequency in two-way loud-speaking telephone systems H04M9/10

Abstract

A method for implementing a noise suppressor in a speech recognition system comprises a filter bank for separating source speech data into discrete frequency sub-bands to generate filtered channel energy, and a noise suppressor for weighting the frequency sub-bands to improve the signal-to-noise ratio of the resultant noise-suppressed channel energy. The noise suppressor preferably includes a noise calculator for calculating background noise values, a speech energy calculator for calculating speech energy values for each channel of the filter bank, and a weighting module for applying calculated weighting values to the projected channel energy to generate the noise-suppressed channel energy.

Claims

1. A system for suppressing background noise in audio data, comprising:

a detector configured to perform a manipulation process on said audio data, said detector including a filter bank that generates filtered channel energy by separating said audio data into discrete frequency channels, said detector including a weighting module that weights selected components of said audio data to suppress said background noise, said weighting module generating noise-suppressed channel energy by applying separate weighting values directly to each of said discrete frequency channels of said filtered channel energy, said separate weighting values being related to background noise values of said discrete frequency channels; and

a processor coupled to said system to control said detector for suppressing said background noise.

2. The system of claim 1 wherein said audio data includes speech information.

3. The system of claim 2 wherein said detector comprises a speech detector that includes program instructions which are stored in a memory device coupled to said processor, said speech detector weighting said selected components of said audio data to suppress said background noise.

4. The system of claim 3 wherein said speech information includes digital source speech data that is provided to said speech detector by an analog sound sensor and an analog-to-digital converter.

5. The system of claim 4 wherein said speech detector comprises a noise suppressor, said noise suppressor including a noise calculator, a speech energy calculator, and said weighting module.

8. The system of claim 5 wherein said noise calculator derives a channel average background noise value “

N_i(m)”

for a channel m at a frame i by using an iterative equation

9. The system of claim 8 wherein A system for suppressing background noise in audio data, comprising:

a detector configured to perform a manipulation process on said audio data that includes digital source speech data provided to said speech detector by an analog sound sensor and an analog-to-digital converter, said detector including a filter bank that generates filtered channel energy by separating said digital source speech data into discrete frequency channels, said detector including a speech detector with program instructions that are stored in a memory device, said speech detector including a noise suppressor with a noise calculator, a speech energy calculator, and a weighting module, said speech detector weighting selected components of said audio data to suppress said background noise, said noise calculator deriving a channel average background noise value “

N_i(m)”

for a channel m at a frame i by using an iterative equation

10. The system of claim 5 wherein A system for suppressing background noise in audio data, comprising:

a detector configured to perform a manipulation process on said audio data that includes digital source speech data provided to said speech detector by an analog sound sensor and an analog-to-digital converter, said detector including a filter bank that generates filtered channel energy by separating said digital source speech data into discrete frequency channels, said detector including a speech detector with program instructions that are stored in a memory device, said speech detector including a noise suppressor with a noise calculator, a speech energy calculator, and a weighting module, said speech detector weighting selected components of said audio data to suppress said background noise, said noise calculator utilizing a non-linear spectrum subtraction procedure that removes a mean value and produces a channel average background noise variance value “

V_i(m)”

for a channel m at a frame i, said channel average background noise variance value “

V_i(m)”

for said channel m at said frame i being calculated using an iterative equation

11. The system of claim 10 wherein said a is equal to 0.985 which is equivalent to a window size of 145 frames.

6. A system for suppressing background noise in audio data, comprising:

a detector configured to perform a manipulation process on said audio data that includes digital source speech data provided to said speech detector by an analog sound sensor and an analog-to-digital converter, said detector including a filter bank that generates filtered channel energy by separating said digital source speech data into discrete frequency channels, said detector including a speech detector with program instructions that are stored in a memory device, said speech detector including a noise suppressor with a noise calculator, a speech energy calculator, and a weighting module, said speech detector weighting selected components of said audio data to suppress said background noise, said noise calculator calculating background noise values during a silent segment of said audio data, said silent segment being located below an ending noise-calculation threshold that is expressed by the formula;

7. A system for suppressing background noise in audio data, comprising:

a detector configured to perform a manipulation process on said audio data that includes digital source speech data provided to said speech detector by an analog sound sensor and an analog-to-digital converter, said detector including a filter bank that generates filtered channel energy by separating said digital source speech data into discrete frequency channels, said detector including a speech detector with program instructions that are stored in a memory device, said speech detector including a noise suppressor with a noise calculator, a speech energy calculator, and a weighting module, said speech detector weighting selected components of said audio data to suppress said background noise, said noise calculator calculating background noise values during a silent segment of said audio data, said silent segment being located below a beginning noise-calculation threshold that is expressed by the formula;

12. A system for suppressing background noise in audio data, comprising:

a detector configured to perform a manipulation process on said audio data that includes digital source speech data provided to said speech detector by an analog sound sensor and an analog-to-digital converter, said detector including a filter bank that generates filtered channel energy by separating said digital source speech data into discrete frequency channels, said detector including a speech detector with program instructions that are stored in a memory device, said speech detector including a noise suppressor with a noise calculator, a speech energy calculator, and a weighting module, said speech detector weighting selected components of said audio data to suppress said background noise, said weighting module generating noise-suppressed channel energy by applying separate weighting values to each of said discrete frequency channels of said filtered channel energy, said separate weighting values being related to background noise values of said discrete frequency channels; and

a processor coupled to said system to control said detector for suppressing said background noise.

13. The system of claim 12 wherein said noise-suppressed channel energy “

E_T”

equals a summation of said filtered channel energy from each of said discrete frequency channels “

E_i”

multiplied by a corresponding one of said weighting values “

w_i”

.

14. The system of claim 13 wherein said noise-suppressed channel energy “

E_T”

is defined by a formula;

15. The system of claim 12 wherein said weighting module calculates a weighting value “

w_i(m)”

for said channel “

i”

using a formula

16. The system of claim 12 wherein said weighting module calculates a weighting value “

w_i(m)”

for said channel “

i”

using a formula

17. The system of claim 16 wherein said MINV is equal to one of a value between 0.0001 and 0.0002, and a value equal to 0.00013.

18. The system of claim 12 wherein an endpoint detector analyzes said noise-suppressed channel energy to generate an endpoint signal.

19. The system of claim 18 wherein said endpoint detector calculates endpoint detection parameters according to a formula $\mathrm{DTF}$

(i)=∑

m=0M-1

 



yi

(m)

wi

(m)

where said w_i(m) is a respective weighting value, said y_i(m) is a channel signal energy value of said channel m at said frame i, and said M is a total number of said channels of said filter bank.

20. The system of claim 19 wherein a recognizer analyzes said endpoint signals and feature vectors from a feature extractor to generate a speech detection result for said speech detector.

21. A method for suppressing background noise in audio data, comprising:

performing a manipulation process on said audio data using a detector that includes a filter bank that generates filtered channel energy by separating said audio data into discrete frequency channels, said detector including a weighting module that weights selected components of said audio data to suppress said background noise, said weighting module generating noise-suppressed channel energy by applying separate weighting values directly to each of said discrete frequency channels of said filtered channel energy, said separate weighting values being related to background noise values of said discrete frequency channels; and

controlling said detector with a processor to thereby suppress said background noise.

22. The method of claim 21 wherein said audio data includes speech information.

23. The method of claim 22 wherein said detector comprises a speech detector that includes program instructions which are stored in a memory device coupled to said processor, said speech detector weighting selected said components of said audio data to suppress said background noise.

24. The method of claim 23 wherein said speech information includes digital source speech data that is provided to said speech detector by an analog sound sensor and an analog-to-digital converter.

25. The method of claim 24 wherein said speech detector comprises a noise suppressor, said noise suppressor including a noise calculator, a speech energy calculator, and said weighting module.

26. The system of claim 25 wherein A method for suppressing background noise in audio data, comprising:

performing a manipulation process on said audio data using a detector, said audio data including digital source speech data provided to said speech detector by an analog sound sensor and an analog-to-digital converter, said detector including a filter bank that generates filtered channel energy by separating said digital source speech data into discrete frequency channels, said detector including a speech detector with program instructions that are stored in a memory device, said speech detector including a noise suppressor with a noise calculator, a speech energy calculator, and a weighting module, said speech detector weighting selected components of said audio data to suppress said background noise, said noise calculator calculating background noise values during a silent segment of said audio data, said silent segment being located below an ending noise-calculation threshold that is expressed by the formula;

28. The method of claim 25 wherein said noise calculator derives a channel average background noise value “

N_i(m)”

for a channel m at a frame i by using an iterative equation

27. A method for suppressing background noise in audio data, comprising:

performing a manipulation process on said audio data using a detector, said audio data including digital source speech data provided to said speech detector by an analog sound sensor and an analog-to-digital converter, said detector including a filter bank that generates filtered channel energy by separating said digital source speech data into discrete frequency channels, said detector including a speech detector with program instructions that are stored in a memory device, said speech detector including a noise suppressor with a noise calculator, a speech energy calculator, and a weighting module, said speech detector weighting selected components of said audio data to suppress said background noise, said noise calculator calculating background noise values during a silent segment of said audio data, said silent segment being located below an ending noise-calculation threshold that is expressed by the formula;

29. A method for suppressing background noise in audio data, comprising:

performing a manipulation process on said audio data using a detector, said audio data including digital source speech data provided to said speech detector by an analog sound sensor and an analog-to-digital converter, said detector including a filter bank that generates filtered channel energy by separating said digital source speech data into discrete frequency channels, said detector including a speech detector with program instruction s that are stored in a memory device, said speech detector including a noise suppressor with a noise calculator, a speech energy calculator, and a weighting module, said speech detector weighting selected components of said audio data to suppress said background noise, said noise calculator deriving a channel average background noise value “

N_i(m)”

for a channel m at a frame i by using an iterative equation

30. A method for suppressing background noise in audio data, comprising:

performing a manipulation process on said audio data using a detector, said audio data including digital source speech data provided to said speech detector by an analog sound sensor and an analog-to-digital converter, said detector including a filter bank that generates filtered channel energy by separating said digital source speech data into discrete frequency channels, said detector including a speech detector with program instructions that are stored in a memory device, said speech detector including a noise suppressor with a noise calculator, a speech energy calculator, and a weighting module, said speech detector weighting selected components of said audio data to suppress said background noise, said noise calculator utilizing a non-linear spectrum subtraction procedure that removes a mean value and produces a channel average background noise variance value “

V_i(m)”

for a channel m at a frame i, said channel average background noise variance value “

V_i(m)”

for said channel m at said frame i being calculated using an iterative equation

31. The method of claim 30 wherein said α

is equal to 0.985 which is equivalent to a window size of 145 frames.

32. A method for suppressing background noise in audio data, comprising:

performing a manipulation process on said audio data using a detector, said audio data including digital source speech data provided to said speech detector by an analog sound sensor and an analog-to-digital converter, said detector including a filter bank that generates filtered channel energy by separating said digital source speech data into discrete frequency channels, said detector including a speech detector with program instructions that are stored in a memory device, said speech detector including a noise suppressor with a noise calculator, a speech energy calculator, and a weighting module, said speech detector weighting selected components of said audio data to suppress said background noise, said weighting module generating noise-suppressed channel energy by applying separate weighting values to each of said discrete frequency channels of said filtered channel energy, said separate weighting values being related to background noise values of said discrete frequency channels; and

controlling said detector with a processor to thereby suppress said background noise.

33. The method of claim 32 wherein said noise-suppressed channel energy “

E_T”

equals a summation of said filtered channel energy from each of said discrete frequency channels “

E_i”

multiplied by a corresponding one of said weighting values “

w_i”

.

34. The method of claim 33 wherein said noise-suppressed channel energy “

E_T”

is defined by a formula;

35. The method of claim 32 wherein said weighting module calculates a weighting value “

w_i(m)”

for said channel “

i”

using a formula

36. The method of claim 32 wherein said weighting module calculates a weighting value “

w_i(m)”

for said channel “

i”

using a formula

37. The method of claim 36 wherein said MINV is equal to one of a value between 0.0001 and 0.0002, and a value equal to 0.00013.

38. The method of claim 32 wherein an endpoint detector analyzes said noise-suppressed channel energy to generate an endpoint signal.

39. The method of claim 38 wherein said endpoint detector calculates endpoint detection parameters according to a formula $\mathrm{DTF}$

(i)=∑

m=0M-1

 



yi

(m)

wi

(m)

where said w_i(m) is a respective weighting value, said y_i(m) is a channel signal energy value of said channel m at said frame i, and said M is a total number of said channels of said filter bank.

40. The method of claim 39 wherein a recognizer analyzes said endpoint signals and feature vectors from a feature extractor to generate a speech detection result for said speech detector.

41. A computer-readable medium comprising program instructions for suppressing background noise by:

performing a manipulation process on said audio data using a detector that includes a filter bank that generates filtered channel energy by separating said audio data into discrete frequency channels, said detector including a weighting module that weights selected components of said audio data to suppress said background noise, said weighting module generating noise-suppressed channel energy by applying separate weighting values directly to each of said discrete frequency channels of said filtered channel energy, said separate weighting values being related to background noise values of said discrete frequency channels; and

controlling said detector with a processor to thereby suppress said background noise.

42. A system for suppressing background noise in audio data, comprising:

means for performing a manipulation process on said audio data, said means for performing including a filter bank that generates filtered channel energy by separating said audio data into discrete frequency channels, said means for performing also including a weighting module that weights selected components of said audio data to suppress said background noise, said weighting module generating noise-suppressed channel energy by applying separate weighting values directly to each of said discrete frequency channels of said filtered channel energy, said separate weighting values being related to background noise values of said discrete frequency channels;

means for controlling said means for performing to thereby suppress said background noise.