Periodic signal enhancement system

• US 8,170,879 B2
• Filed: 04/08/2005
• Issued: 05/01/2012
• Est. Priority Date: 10/26/2004
• Status: Active Grant

• Current Assignee: Blackberry Limited
• Original Assignee: QNX Software Systems Limited (Canada) (Blackberry Limited)
• Inventors: Nongpiur, Rajeev, Giesbrecht, David, Hetherington, Phillip
• Primary Examiner(s): COLUCCI, MICHAEL C
• Application Number:
  US11/101,796
• Publication Number:
  US 20060098809A1
• Time in Patent Office: 2,580 Days
• Field of Search: 708/300, 708/322, 704/267, 704/228, 704/207, 704/222, 704/225, 704/226, 704/230, 704/500, 375/240.25, 375/232, 846/61, 333/300
• US Class Current: 704/268
• CPC Class Codes: G10L 21/0364 for improving intelligibility
• CPC Class Codes: G10L 25/90 Pitch determination of speech signals

Abstract

A signal enhancement system improves the understandability of speech or other audio signals. The system reinforces selected parts of the signal, may attenuate selected parts of the signal, and may increase SNR. The system includes delay logic, a partitioned adaptive filter, and signal reinforcement logic. The partitioned adaptive filter may track and enhance the fundamental frequency and harmonics in the input signal. The partitioned filter output signals may approximately reproduce the input signal, delayed by an integer multiple of the period of the fundamental frequency of the input signal. The reinforcement logic combines the input signal and the filtered signals to produce an enhanced output signal.

Claims

1. A signal enhancement system comprising:

a processor;

a signal input;

partitioned delay logic coupled to the signal input;

a partitioned adaptive filter coupled to the partitioned delay logic and comprising multiple adaptive filter outputs;

gain logic coupled to the adaptive filter outputs, where the gain logic is configured to receive an adaptive filter output signal from at least one of the adaptive filter outputs and generate a gain-weighted adaptive filter output signal from the adaptive filter output signal; and

signal reinforcement logic comprising an enhanced signal output, and where the processor is configured to execute the signal reinforcement logic to add the gain-weighted adaptive filter output signal to an input signal received on the signal input to increase a first periodic signal component in the input signal that is at least partially in-phase with a second periodic signal component in the gain-weighted adaptive filter output signal.

2. The signal enhancement system of claim 1, where the partitioned adaptive filter comprises multiple adaptive filters, each adaptive filter comprising filter coefficients.

3. The signal enhancement system of claim 2, where the gain logic comprises multiple gain parameters determined as a function of the filter coefficients.

4. The signal enhancement system of claim 3, where the gain parameters are further determined based on a normalizing constant.

5. The signal enhancement system of claim 2, where the gain logic comprises multiple gain parameters, and where at least one of the gain parameters is dependent upon the magnitude of the positive filter coefficients.

6. The signal enhancement system of claim 1, where the gain logic comprises a gain parameter that increases with decreasing signal-to-noise ratio.

7. The signal enhancement system of claim 1, where the gain logic comprises a gain parameter that decreases with increasing signal-to-noise ratio.

8. The signal enhancement system of claim 1, where the partitioned delay logic implements an adaptation pitch range including that of human voice.

9. The signal enhancement system of claim 1, further comprising a first stage filter coupled between the signal input and the delay logic, the first stage filter comprising quasi-stationary frequency tracking and attenuation logic.

10. The signal enhancement system of claim 1, where the signal reinforcement logic is configured to add an output of the filter reinforcement logic to a signal received at the signal input to generate reinforced periodic signal content in the enhanced signal output.

11. A method for signal enhancement comprising:

receiving an input signal;

delaying the input signal by multiple delays;

processing the multiply delayed input signal in a partitioned adaptive filter comprising multiple adaptive filter outputs;

biasing an adaptive filter output signal received from at least one of the adaptive filter outputs to generate a gain-weighted adaptive filter output signal from the adaptive filter output signal;

generating a summed adaptive filter output signal after biasing, where the summed adaptive filter output signal comprises a sum of the gain-weighted adaptive filter output signal and at least one other adaptive filter output signal; and

reinforcing periodic signal content in the input signal with the summed adaptive filter output signal by adding the summed adaptive filter output signal to the input signal to increase a first periodic signal component in the input signal that is at least partially in-phase with a second periodic signal component in the summed adaptive filter output signal, where the act of reinforcing is performed by a processor executing signal reinforcement logic.

12. The method of claim 11, where the adaptive filter outputs comprise:

a first adaptive filter output; and

a second adaptive filter output, and where the partitioned adaptive filter comprises;

a first adaptive filter comprising the first adaptive filter output; and

a second adaptive filter comprising the second adaptive filter output;

and further comprising;

generating a first error signal based on the input signal and a first adaptive filter output signal from the first adaptive filter output;

generating a second error signal based on the input signal and a second adaptive filter output signal from the second adaptive filter output; and

updating the first adaptive filter based on the first error signal and updating the second adaptive filter based on the second error signal.

13. The method of claim 11, where the partitioned adaptive filter comprises multiple adaptive filters, each adaptive filter comprising filter coefficients, and further comprising:

determining gain parameters as a function of the filter coefficients and biasing adaptive filter output signals from the adaptive filter outputs using the gain parameters.

14. The method of claim 13, further comprising adjusting a gain parameter based upon the magnitude of a positive filter coefficient.

15. The method of claim 13, further comprising determining the gain parameters based on signal-to-noise ratio.

16. The method of claim 13, further comprising increasing or decreasing at least one of the gain parameters based on signal-to-noise ratio.

17. The method of claim 11, where delaying comprises delaying the input signal by a number of samples that establishes a maximum adaptation pitch that includes a human voice pitch.

18. The method of claim 11, further comprising filtering the input signal through a first stage filter coupled between the signal input and the delay logic, the first stage filter comprising quasi-stationary frequency tracking and attenuation logic.

19. The method of claim 11, where reinforcing the periodic signal content comprises adding the summed adaptive filter output to the input signal to generate an enhanced signal output with reinforced periodic signal content.

20. A product comprising:

a machine readable storage medium; and

machine readable instructions encoded on the medium that;

delay an input signal by multiple delays;

process the multiply delayed input signal in a partitioned adaptive filter comprising multiple adaptive filter outputs;

bias an adaptive filter output signal received from at least one of the adaptive filter outputs to generate a gain-weighted adaptive filter output signal from the adaptive filter output signal;

generate a summed adaptive filter output signal after biasing, where the summed adaptive filter output signal comprises a sum of the gain-weighted adaptive filter output signal and at least one other adaptive filter output signal; and

reinforce periodic signal content in the input signal with the summed adaptive filter output signal by adding the summed adaptive filter output signal to the input signal to increase a first periodic signal component in the input signal that is at least partially in-phase with a second periodic signal component in the summed adaptive filter output signal.

21. The product of claim 20, further comprising instructions that:

determine multiple gain parameters as a function of filter coefficients in the partitioned adaptive filter.

22. The product of claim 21, further comprising determining the gain parameters based on a normalizing constant.

23. The product of claim 20, further comprising instructions that filter a quasi-stationary signal component in the input signal prior to processing with the partitioned adaptive filter.

24. The product of claim 20, further comprising instructions that:

update filter coefficients in the partitioned adaptive filter;

determine a gain parameter for biasing an adaptive filter output signal from at least one of the adaptive filter outputs; and

estimate the gain parameter based on the magnitude of a positive filter coefficient.

25. The product of claim 20, where the biasing instructions:

increase bias with decreasing signal-to-noise ratio.

26. The product of claim 20, where the biasing instructions:

decrease bias with increasing signal-to-noise ratio.

27. The product of claim 20, where the adaptive filter outputs comprise:

a first adaptive filter output; and

a second adaptive filter output, and where the processing instructions implement;

a first adaptive filter comprising the first adaptive filter output; and

a second adaptive filter comprising the second adaptive filter output;

and where the instructions;

generate a first error signal based on the input signal and a first adaptive filter output signal from the first adaptive filter output;

generate a second error signal based on the input signal and a second adaptive filter output signal from the second adaptive filter output; and

update the first adaptive filter based on the first error signal and updating the second adaptive filter based on the second error signal.

28. The product of claim 20, where the reinforcement instructions comprise instructions that add the summed adaptive filter output to the input signal to generate an enhanced signal output with reinforced periodic signal content.

29. A pitch detector comprising:

a processor;

a signal input;

an adaptive filter coupled to the signal input, the adaptive filter comprising filter coefficients and operable to adapt based on an error signal;

pitch detection logic coupled to the adaptive filter, where the processor is configured to execute the pitch detection logic and find a peak in the filter coefficients and produce a pitch estimate based on the position of the peak; and

a pitch estimate output coupled to the pitch detection logic.

30. The pitch detector of claim 29, where the pitch detection logic is operable to determine a pitch estimate according to:

31. The pitch detector of claim 30, where the peak is the first peak in the adaptive filter coefficients.

32. The pitch detector of claim 29, further comprising an error estimator coupled to the adaptive filter and operable to determine the error signal based on an input signal and a filter output signal.

33. The pitch detector of claim 29, where the pitch estimate is a non-voice pitch estimate.

34. The pitch detector of claim 29, where the pitch estimate is a male or a female voice pitch estimate.

35. A method for pitch detection comprising:

receiving an input signal;

filtering the input signal through an adaptive filter;

updating filter coefficients in the adaptive filter based on an error signal;

determining a peak in the filter coefficients by a pitch detector comprising a non-transitory computer-readable medium or circuit;

producing a pitch estimate based on the position of the peak.

36. The method of claim 35, where producing the pitch estimate comprises producing the pitch estimate based on a sampling frequency and a filter length of the adaptive filter.

37. The method of claim 35, where producing the pitch estimate comprises determining the pitch estimate according to:

38. The method of claim 35, where the peak is the first peak in the adaptive filter coefficients.

39. The method of claim 35, where the pitch estimate is a non-voice pitch estimate.

40. The method of claim 35, where the pitch estimate is a male or a female voice pitch estimate.

41. A voice detector comprising:

a processor;

a signal input;

an adaptive filter coupled to the signal input, the adaptive filter comprising filter coefficients and operable to adapt based on an error signal;

voice detection logic coupled to the adaptive filter, where the processor is configured to execute the voice detection logic to analyze the filter coefficients of the adaptive filter to determine a detection measure based on the filter coefficients of the adaptive filter, where the voice detection logic is operable to analyze the detection measure to detect whether voiced speech is present in a signal received on the signal input;

a voice detection output coupled to the voice detection logic.

42. The voice detector of claim 41, where the voice detection logic is configured to assert the voice detection output based on a determination that the detection measure exceeds a threshold.

43. The voice detector of claim 41, where the voiced speech is a vowel sound component.

44. The voice detector of claim 41, further comprising an error estimator coupled to the adaptive filter and operable to determine the error signal based on an input signal and a filter output signal.

45. The voice detector of claim 41, where the detection measure comprises a sum of magnitudes of positive filter coefficients, and where the voice detection logic is operable to identify that the signal contains voiced speech and assert the voice detection output based on a determination that the sum of magnitudes of positive filter coefficients exceeds a threshold.

46. A method for voice detection comprising:

receiving an input signal;

filtering the input signal through an adaptive filter;

updating filter coefficients in the adaptive filter based on an error signal;

analyzing the filter coefficients of the adaptive filter to determine a detection measure based on the filter coefficients of the adaptive filter, where the act of analyzing the filter coefficients is performed by a voice detector comprising a non-transitory computer-readable medium or circuit;

analyzing the detection measure to detect whether periodic components are present in the input signal; and

asserting a voice detection output based on a determination that the detection measure is above a threshold.

47. The method of claim 46, where the threshold is based on the SNR level, the background noise level, and the shape of the background noise spectrum.

48. The method of claim 46, where the periodic input signal component is a vowel sound component.

49. The method of claim 46, further comprising determining the error signal based on an input signal and a filter output signal.

50. The voice detector of claim 46, where the detection measure comprises a sum of magnitudes of positive filter coefficients, and where asserting the voice detection output comprises identifying that the signal contains periodic components and asserting the voice detection output based on a determination that the sum of magnitudes of positive filter coefficients exceeds the threshold.