Reverberation estimation and suppression system

• US 8,284,947 B2
• Filed: 12/01/2004
• Issued: 10/09/2012
• Est. Priority Date: 12/01/2004
• Status: Active Grant

• Current Assignee: Blackberry Limited
• Original Assignee: QNX Software Systems Limited (Canada) (Blackberry Limited)
• Inventors: Giesbrecht, David, Hetherington, Phillip
• Primary Examiner(s): Chin, Vivian
• Assistant Examiner(s): Tran, Con P
• Application Number:
  US11/002,328
• Publication Number:
  US 20060115095A1
• Time in Patent Office: 2,869 Days
• Field of Search: 381/61, 381/63, 381/66, 381/86, 381/94.1, 381/94.2, 381/94.3, 381/71.8, 381/71.14, 381/93, 381/83, 379/406.01, 379/406.14, 379/406.12, 379/406.06, 704/E21.007, 704/E21.003, 704/E21.002, 84D/IG.26, 847/07, 847/01
• US Class Current: 381/66
• CPC Class Codes: H04M 9/08 Two-way loud-speaking telephone systems with means for conditioning the signal, e.g. for suppressing echoes for one or both directions of traffic

Abstract

A signal processing system detects reverberation. The system may suppress the reverberation and improve signal quality. The system analyzes frequency bands of an input signal to determine whether reverberation characteristics are present. When reverberation is detected, the system may attenuate the reverberant frequency band to reduce or eliminate the reverberation.

Claims

1. A reverberation suppression system comprising:

signal analysis logic operative to analyze a signal decay rate in a first frequency band of a signal, where the signal analysis logic is operative to identify a first reverberant characteristic in the first frequency band of the signal based on a comparison between the signal decay rate in the first frequency band and a first reverberation decay rate threshold, where the signal analysis logic is operative to adapt the first reverberation decay rate threshold over time based on an identification of a linear signal decay characteristic, and where the signal analysis logic comprises a processor that executes instructions stored in a memory; and

attenuation logic responsive to identification of the first reverberant characteristic to attenuate the signal in the first frequency band to generate a reverberation suppressed signal.

2. The system of claim 1, where the signal analysis logic is operable to identify the first reverberant characteristic when the signal decay rate is an approximately linear decay rate in the first frequency band.

3. The system of claim 2, where the first reverberant characteristic is an approximately linear decay in dB over Time in the first frequency band.

4. The system of claim 1, where the signal analysis logic is operable to identify the first reverberant characteristic when the signal decay rate in the first frequency band approximately meets the first reverberation decay rate threshold.

5. The system of claim 4, where the first reverberation decay threshold is an enclosed space reverberation decay rate threshold.

6. The system of claim 4, where the first reverberation decay threshold is a vehicle interior reverberation decay rate threshold.

7. The system of claim 4, where:

the signal analysis logic is further operable to identify, in a second frequency band, a second reverberant characteristic when a second decay rate approximately meets a second reverberation decay rate threshold; and

the attenuation logic is also operable to attenuate the signal in the second, frequency band in response to identification of the second reverberant characteristic.

8. The system of claim 7, where the first reverberation decay rate threshold and the second reverberation decay rate threshold are frequency band thresholds.

9. The system of claim 1, where:

the signal analysis logic is further operable to analyze a signal decay rate in a second frequency band of the signal to identify a second reverberant characteristic in the second frequency band; and

the attenuation logic is also operable to attenuate the signal in the second frequency band in response to identification of the second reverberant characteristic.

10. The system of claim 1, further comprising signal-to-noise ratio logic, where the analysis logic identifies the reverberant characteristic when the signal-to-noise ratio logic determines a positive signal-to-noise ratio.

11. The system of claim 1, further comprising adaptive filter logic operable to provide an estimate of an expected reverberation decay rate in the first frequency band, where the signal analysis logic is operative to determine whether the first frequency band is a reverberant frequency band based on a comparison between the expected reverberation decay rate and the signal decay rate measured in the first frequency band.

12. The system of claim 1, further comprising signal-to-noise ratio estimation logic operable to determine a signal-to-noise ratio of the signal in the first frequency band;

where the attenuation logic is responsive to the signal-to-noise ratio estimation logic, and where the attenuation logic is operable to attenuate the signal in the first frequency band by a higher amount when the signal-to-noise ratio is relatively high and the first reverberant characteristic is identified than when the signal-to-noise ratio is relatively low and the first reverberant characteristic is identified.

13. The system of claim 1, where the signal analysis logic is operable to monitor a signal-to-noise ratio in the first frequency band and the signal decay rate to determine when to adapt the first reverberation decay rate threshold, and where the signal analysis logic is operable to adapt the first reverberation decay rate threshold upon determination that a signal-to-noise ratio in the first frequency band is positive and the signal in the first frequency band has a linear decay rate.

14. A reverberation analysis system comprising:

a signal input;

signal analysis logic coupled to the signal input and operable to estimate a first decay rate for signal content of a first frequency band, where the signal analysis logic is operable to adapt a first reverberation decay rate threshold over time based on an identification of a linear signal decay characteristic, and where the signal analysis logic comprises a processor that executes instructions stored in a memory;

comparison logic coupled to the signal analysis logic and operable to perform a comparison between the first decay rate and the first reverberation decay rate threshold;

characterization logic coupled to the comparison logic and operable to identify whether the first frequency band is a reverberant frequency band based on the comparison between the first decay rate and the first reverberation decay rate threshold;

attenuation logic operable to attenuate the first frequency band to generate a reverberation suppressed signal in response to a characterization of the first frequency band as the reverberant frequency band; and

a signal output coupled to the attenuation logic and operable to output the reverberation suppressed signal.

15. The system of claim 14, where:

the signal analysis logic is further operable to estimate a second decay rate for signal content of a second frequency band; and

the comparison logic is further operable to compare the second decay rate to a second reverberation decay rate threshold.

16. The system of claim 15, where the first and second frequency bands comprise Bark frequency bands.

17. The system of claim 15, where the first and second frequency bands comprise MeI frequency bands.

18. The system of claim 14, where the signal input couples a speech signal to the signal analysis logic.

19. The system of claim 14, where the signal analysis logic is operable to fit a line to signal decay over time in the first frequency band to estimate the first decay rate.

20. The system of claim 14, where the characterization logic comprises a digital signal processor that executes instructions stored in a memory.

21. A method for suppressing reverberation, comprising:

adapting a reverberation decay rate threshold over time based on an identification of a linear signal decay characteristic;

determining a division of a signal into multiple frequency bands;

determining a signal decay rate in at least one frequency band of the multiple frequency bands;

identifying the at least one frequency band as being a reverberant frequency band based on a comparison between the signal decay rate in the at least one frequency band and the reverberation decay rate threshold; and

attenuating the signal in the reverberant frequency band to generate a reverberation suppressed signal.

22. The method of claim 21, where identifying comprises;

comparing the signal decay rate to the reverberation decay rate threshold; and

characterizing the at least one frequency band as being the reverberant frequency band based on a use of the reverberation decay rate threshold as a hard threshold or as part of a soft decision logic that includes a smooth transition between characterizing the at least one frequency band as reverberant or non-reverberant.

23. The method of claim 22, where the reverberation decay rate threshold is an enclosed space reverberation decay rate threshold.

24. The method of claim 22, where the reverberation decay threshold is a vehicle interior reverberation decay rate threshold.

25. The method of claim 21, where determining comprises:

determining the signal decay rate in each of the frequency bands;

determining whether each frequency band is a reverberant frequency band based on its signal decay rate; and

attenuating each reverberant frequency band.

26. The method of claim 21, where identifying comprises:

determining whether the signal decay rate is linear.

27. The method of claim 26, where identifying further comprises:

determining whether the signal decay rate approximately meets the reverberation decay rate threshold.

28. The method of claim 21, further comprising determining a signal-to-noise ratio for the reverberant frequency band;

and

where attenuating comprises attenuating the signal in the reverberant frequency band by a higher amount when the signal-to-noise ratio is relatively high than when the signal-to-noise ratio is relatively low.

29. The method of claim 21, further comprising:

monitoring a signal-to-noise ratio in the first frequency band and the signal decay rate to determine when to adapt the reverberation decay rate threshold; and

adapting the reverberation decay rate threshold upon determination that a signal-to-noise ratio in the first frequency band is positive and the signal in the first frequency band has a linear decay rate.

30. The method of claim 21, where attenuating comprises attenuating the signal by attenuation logic that comprises a digital signal processor that executes instructions stored in a memory.

31. A product comprising:

a non-transitory machine readable medium; and

machine readable instructions embodied on the machine readable medium that;

adapt a reverberation decay rate threshold over time based on an identification of a linear signal decay characteristic;

determine a signal decay rate in a frequency band of an input signal;

identify a reverberant frequency band based on a comparison between the signal decay rate and the reverberation decay rate threshold; and

attenuate the signal in the reverberant frequency band to generate a reverberation suppressed signal.

32. The product of claim 31, where the instructions that determine the signal decay rate comprise instructions that:

fit a line to signal decay over time in the frequency band.

33. The product of claim 31, where the input signal is a speech signal.

34. The product of claim 31, further comprising instructions that:

determine a division of the input signal into Bark frequency bands.

35. The product of claim 31, further comprising instructions that:

determine a division of the input signal into MeI frequency bands.

36. The product of claim 31, where the instructions that identify the reverberant frequency band comprise instructions that:

compare the signal decay rate to an office space reverberation decay rate threshold.

37. The product of claim 31, where the instructions that identify the reverberant frequency band comprise instructions that:

compare the signal decay rate to a vehicle interior reverberation decay rate threshold.

38. The product of claim 31, where the instructions that identify the reverberant frequency band comprise instructions that:

compare the signal decay rate to a mobile phone speakerphone reverberation decay rate threshold.

39. The product of claim 31, where the determination instructions, identification instructions, and attenuation instructions are responsive to detecting speech in the input signal.

40. The product of claim 31, where the determination instructions, identification instructions, and attenuation instructions are responsive to SNR in the input signal being above an SNR threshold.

41. The product of claim 31, where the instructions that attenuate the signal comprises instructions that attenuate multiple reverberant frequency bands.

42. A reverberation suppression system comprising:

signal analysis hardware operative to identify a first reverberant characteristic in a first frequency band of a signal;

signal-to-noise ratio estimation hardware operable to determine a signal-to-noise ratio of the signal in the first frequency band; and

attenuation hardware responsive to the signal analysis hardware and the signal-to-noise ratio estimation hardware, where the attenuation hardware is operable to attenuate the signal in the first frequency band to generate a reverberation suppressed signal, where the attenuation hardware is operable to set an attenuation level for the signal in the first frequency band based on the signal-to-noise ratio of the signal in the first frequency band, and where the attenuation hardware is operable to attenuate the signal in the first frequency band to a greater extent when the signal-to-noise ratio is relatively high and the first reverberant characteristic is identified than when the signal-to-noise ratio is relatively low and the first reverberant characteristic is identified;

where the signal analysis hardware is operative to identify the first reverberant characteristic in the first frequency band based on a comparison between a signal decay rate in the first frequency band and a reverberation decay rate threshold, and where the signal analysis hardware is operative to adapt the reverberation decay rate threshold over time based on an identification of a linear signal decay characteristic.

43. The system of claim 42, where the attenuation hardware comprises a maximum allowed attenuation level, and where the maximum allowed attenuation level is set to a higher level when the signal-to-noise ratio is relatively high and the first reverberant characteristic is identified than when the signal-to-noise ratio is relatively low and the first reverberant characteristic is identified.

44. The system of claim 42, where the attenuation hardware comprises a digital signal processor that executes instructions stored in a memory.