Sub-band periodic signal enhancement system

• US 8,306,821 B2
• Filed: 06/04/2007
• Issued: 11/06/2012
• 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, Hetherington, Phillip A.
• Primary Examiner(s): Han, Qi
• Assistant Examiner(s): Villena, Mark
• Application Number:
  US11/757,768
• Publication Number:
  US 20080004868A1
• Time in Patent Office: 1,982 Days
• Field of Search: 379/406.14, 379/406.01, 704/207, 370/290
• 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
• 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 delay logic circuit configured to receive an input signal and generate a delayed signal;

an adaptive filter circuit coupled with the delay logic circuit and configured to receive the delayed signal and generate an output signal based on the delayed signal and filter coefficients of the adaptive filter circuit, where the adaptive filter circuit is configured to adapt the filter coefficients based on a difference between the output signal and the input signal; and

a reinforcement logic circuit coupled to the adaptive filter circuit, where the reinforcement logic circuit is configured to add the input signal and the output signal from the adaptive filter circuit 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 output signal.

2. The signal enhancement system of claim 1, where the delay logic circuit is a first delay logic circuit, the adaptive filter circuit is a first adaptive filter circuit, and the reinforcement logic circuit is a first reinforcement logic circuit, the system further comprising:

a filter bank configured to divide an input signal frequency spectrum into a plurality of sub-bands, where the input signal processed by the first delay logic circuit, the first adaptive filter circuit, and the first reinforcement logic circuit is a first sub-band input signal of the plurality of sub-bands;

a second delay logic circuit configured to receive a second sub-band input signal of the plurality of sub-bands and generate a delayed second sub-band signal;

a second adaptive filter circuit coupled with the second delay logic circuit and configured to receive the delayed second sub-band signal and generate a sub-band output signal based on the delayed second sub-band signal and filter coefficients of the second adaptive filter circuit; and

a second reinforcement logic circuit coupled to the second adaptive filter circuit, where the second reinforcement logic circuit is configured to add the second sub-band input signal and the sub-band output signal from the adaptive filter circuit to increase a first periodic signal component in the second sub-band input signal that is at least partially in-phase with a second periodic signal component in the sub-band output signal.

3. The signal enhancement system of claim 2, further comprising a synthesis filter bank configured to receive a first reinforced sub-band signal from the first reinforcement logic circuit, receive a second reinforced sub-band signal from the second reinforcement logic circuit, and reconstruct a reinforced output signal from the first reinforced sub-band signal and the second reinforced sub-band signal.

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

5. The signal enhancement system of claim 2, further comprising a multiplier circuit coupled between the second adaptive filter circuit and the second reinforcement logic circuit, where the multiplier circuit is configured to control an amount of enhancement applied to the sub-band output signal.

6. The signal enhancement system of claim 5, where the amount of enhancement applied is a multiplier factor having a value between about zero and about one.

7. The signal enhancement system of claim 2, where the filter bank comprises a plurality of Gammatone-type band-pass filters.

8. The signal enhancement system of claim 2, where the filter bank is configured to generate the plurality of sub-bands by down-sampling.

9. The signal enhancement system of claim 2, further comprising a tonal noise detector in communication with the first adaptive filter circuit, where the tonal noise detector is configured to monitor the filter coefficients of the first adaptive filter circuit to detect tonal noise.

10. The signal enhancement system of claim 9, where the tonal noise detector is configured to inhibit adaptation of the first adaptive filter circuit when tonal noise is detected.

11. The signal enhancement system of claim 9, where the tonal noise detector is configured to minimize the tonal noise by applying a negative component of the tonal noise to an output of the first reinforcement logic circuit.

12. The signal enhancement system of claim 1, where the input signal comprises an audio signal, and where the output signal from the adaptive filter circuit that is added together with the input signal is a delayed and filtered version of the input signal.

13. A method for enhancing a signal, comprising:

delaying an input signal to generate a delayed signal;

adaptively filtering the delayed signal, by an adaptive filter implemented in hardware or executed by a processor, to generate an output signal based on the delayed signal and filter coefficients of the adaptive filter;

adapting the filter coefficients of the adaptive filter based on a difference between the output signal and the input signal; and

reinforcing the input signal with the output signal to generate a reinforced signal, where the act of reinforcing comprises adding the input signal and the output signal from the adaptive filter 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 output signal.

14. The method of claim 13, where the adaptive filter is a first adaptive filter, the method further comprising:

dividing an input signal frequency spectrum into a plurality of sub-bands, where the input signal processed by the first adaptive filter is a first sub-band input signal of the plurality of sub-bands;

delaying a second sub-band input signal of the plurality of sub-bands to generate a delayed second sub-band signal;

adaptively filtering the delayed second sub-band signal, by a second adaptive filter implemented in hardware or executed by a processor, to generate a sub-band output signal based on the delayed second sub-band signal and filter coefficients of the second adaptive filter;

reinforcing the second sub-band input signal with the sub-band output signal to generate a reinforced signal, where the act of reinforcing comprises adding the second sub-band input signal and the sub-band output signal from the second adaptive filter to increase a first periodic signal component in the second sub-band input signal that is at least partially in-phase with a second periodic signal component in the sub-band output signal.

15. The method of claim 14, where at least one sub-band of the plurality of sub-bands has a bandwidth different than an adjacent sub-band.

16. The method of claim 14, where the act of dividing the input signal frequency spectrum comprises providing a Gammatone filter to separate the input signal.

17. The method of claim 14, further comprising monitoring the filter coefficients of the first adaptive filter to detect tonal noise.

18. The method of claim 17, further comprising detecting tonal noise based on a maximum value of the filter coefficients of the first adaptive filter.

19. The method of claim 17, further comprising inhibiting adaptation of the first adaptive filter when tonal noise is detected.

20. The method of claim 13, where the input signal comprises an audio signal, and where the output signal that is added together with the input signal is a delayed and filtered version of the input signal.

21. A machine-readable non-transitory medium having processor-executable instructions to enhance a signal by performing the acts of:

delaying an input signal to generate a delayed signal;

adaptively filtering the delayed signal to generate an output signal based on the delayed signal and filter coefficients of an adaptive filter;

adapting the filter coefficients of the adaptive filter based on a difference between the output signal and the input signal; and

reinforcing the input signal with the output signal to generate a reinforced signal, where the act of reinforcing comprises adding the input signal and the output signal from the adaptive filter 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 output signal.

22. The machine-readable non-transitory medium of claim 21, where the adaptive filter is a first adaptive filter, where the processor-executable instructions further perform the acts of:

dividing an input signal frequency spectrum into a plurality of sub-bands, where the input signal processed by the first adaptive filter is a first sub-band input signal of the plurality of sub-bands;

delaying a second sub-band input signal of the plurality of sub-bands to generate a delayed second sub-band signal;

adaptively filtering the delayed second sub-band signal to generate a sub-band output signal based on the delayed second sub-band signal and filter coefficients of a second adaptive filter;

reinforcing the second sub-band input signal with the sub-band output signal to generate a reinforced signal, where the act of reinforcing comprises adding the second sub-band input signal and the sub-band output signal from the second adaptive filter to increase a first periodic signal component in the second sub-band input signal that is at least partially in-phase with a second periodic signal component in the sub-band output signal.

23. The machine-readable non-transitory medium of claim 21, where the input signal comprises an audio signal, and where the output signal that is added together with the input signal is a delayed and filtered version of the input signal.