SUB-BAND PERIODIC SIGNAL ENHANCEMENT SYSTEM

• US 20080004868A1
• Filed: 06/04/2007
• Published: 01/03/2008
• Est. Priority Date: 10/26/2004
• Status: Active Grant

• Current Assignee: Blackberry Limited
• Original Assignee: QNX Software Systems Limited (Canada) (Blackberry Limited)
• Inventors: Hetherington, Phillip, Nongpiur, Rajeev
• Granted Patent: US 8,306,821 B2
• Time in Patent Office: Days
• US Class Current: 704/207
• CPC Class Codes: G10L 21/0364 for improving intelligibility
• CPC Class Codes: G10L 25/90 Pitch determination of speech signals
• CPC Class Codes: H03H 21/0012 Digital adaptive filters
• CPC Class Codes: H03H 2220/08 Variable filter length

Abstract

A signal enhancement system reinforces signal content and improves the signal-to-noise ratio of a signal. The system detects, tracks, and reinforces non-stationary periodic signal components of a signal. The periodic signal components may represent vowel sounds or other voiced sounds. The system may detect, track, and attenuate quasi-stationary signal components in the signal.

Claims

1. A signal enhancement system, comprising:

a plurality of sub-band analysis filters configured to separate an input signal into a plurality of sub-band input signals;

a plurality of delay logic circuits configured to receive the respective sub-band input signals and generate respective delayed sub-band signals;

a plurality of adaptive filter circuits configured to receive the respective delayed sub-band signals;

a plurality of reinforcement logic circuits coupled to the respective adaptive filter circuits and to the respective sub-band input signals; and

a plurality of sub-band synthesis filters configured to receive an output from the respective reinforcement logic circuits and synthesize an output signal.

2. The signal enhancement system of claim 1, where the sub-band analysis filters divide a frequency spectrum of the input signal into the plurality of sub-bands.

4. The signal enhancement system of claim 1, where the sub-band synthesis filters comprise Gammatone filters.

6. The signal enhancement system of claim 2, where at least one sub-band has a bandwidth different than an adjacent sub-band.

7. The signal enhancement system of claim 1, where the input signal is separated into a plurality of sub-bands by down-sampling.

11. The signal enhancement system of claim 1, where the sub-band analysis filtersperform a fast Fourier transform.

13. The signal enhancement system of claim 2, further comprising a multiplier circuit for each sub-band that control an amount of enhancement applied to an output of the respective reinforcement logic circuit.

14. The signal enhancement system of claim 13, where the amount of enhancement applied is a multiplier factor having a value between about zero and about one.

16. The signal enhancement system of claim 1, where the respective tonal noise detector monitors coefficients corresponding to the respective adaptive filter circuit to detect tonal noise.

18. The signal enhancement system of claim 16, where the respective tonal noise detector inhibits adaptation of the respective adaptive filter circuit when tonal noise is detected.

19. The signal enhancement system of claim 16, where the respective tonal noise detector minimizes the tonal noise by applying a negative component of the tonal noise to an output of the respective reinforcement logic circuit.

3. (canceled)

5. (canceled)

8. (canceled)

9. (canceled)

10. (canceled)

12. (canceled)

15. (canceled)

17. (canceled)

20. A method for enhancing a signal, comprising:

separating an input signal into a plurality of sub-band input signals;

delaying the respective sub-band input signals and generating respective delayed sub-band signals;

adaptively filtering the respective delayed sub-band signals and generating respective adaptively filtered signals;

reinforcing the respective sub-band input signals with the respective adaptively filtered signal and generating respective reinforced signals; and

synthesizing an output signal based on the respective reinforced signals.

21. The method of claim 20, comprising dividing a frequency spectrum of the input signal into a plurality of sub-bands.

22. The method of claim 20, comprising providing a Gammatone filter to separate the input signal.

24. The method of claim 21, comprising dividing a frequency spectrum of the input signal into a plurality of equal bandwidth sub-bands.

25. The method of claim 21, where at least one sub-band has a bandwidth different than an adjacent sub-band,

26. The method of claim 20, comprising down-sampling the input signal.

30. The method of claim 20, performing a fast Fourier transform to facilitate separation of the input signal.

32. The method of claim 21, further comprising controlling an amount of enhancement applied to the respective reinforced signal.

33. The method of claim 32, where the amount of enhancement applied comprises a multiplier factor having a value between zero and one.

35. The method of claim 20, further comprising monitoring coefficients of corresponding adaptive filters to detect tonal noise.

36. The method of claim 35, further comprising detecting tonal noise based on a maximum value of one or more coefficients.

37. The method of claim 35, further comprising inhibiting adaptation of a respective adaptive filter when tonal noise is detected.

38. The method of claim 35, further comprising minimizing tonal noise by applying a negative component of the tonal noise to the respective reinforced signal.

23. (canceled)

27. (canceled)

28. (canceled)

29. (canceled)

31. (canceled)

34. (canceled)

39. A computer-readable storage medium having processor-executable instructions to enhance a signal by performing the acts of:

separating an input signal into a plurality of sub-band input signals;

delaying the respective sub-band input signal and generating respective delayed sub-band signals;

adaptively filtering the respective delayed sub-band signals and generating respective adaptively filtered signals;

reinforcing the respective sub-band input signal with the respective adaptively filtered signal and generating respective reinforced signals; and

synthesizing an output signal based on the respective reinforced signals.