Adaptive filter pitch extraction

• US 20060095256A1
• Filed: 12/09/2005
• Published: 05/04/2006
• Est. Priority Date: 10/26/2004
• Status: Active Grant

• Current Assignee: Blackberry Limited
• Original Assignee: QNX Software Systems Company (Blackberry Limited)
• Inventors: Hetherington, Phillip A., Nongpiur, Rajeev
• Granted Patent: US 7,949,520 B2
• Time in Patent Office: Days
• US Class Current: 704/207
• CPC Class Codes: G06Q 20/108 Remote banking, e.g. home banking
• CPC Class Codes: G10L 2021/02085 Periodic noise
• CPC Class Codes: G10L 25/90 Pitch determination of speech signals
• CPC Class Codes: H03H 21/0012 Digital adaptive filters

Abstract

An enhancement system extracts pitch from a processed speech signal. The system estimates the pitch of voiced speech by deriving filter coefficients of an adaptive filter and using the obtained filter coefficients to derive pitch. The pitch estimation may be enhanced by using various techniques to condition the input speech signal, such as spectral modification of the background noise and the speech signal, and/or reduction of the tonal noise from the speech signal.

Claims

1. A system for extracting pitch from a speech signal having voiced and unvoiced segments, the system comprising:

a discrete input;

a delay unit that digitally delays a speech signal received through the discrete input; and

an adaptive filter coupled to the delay unit, where filter coefficients derived from the adaptive filter are used to estimate the pitch of the speech signal.

2. The system of claim 1 further comprising a low-pass filter coupled between the delay unit and the adaptive filter.

3. The system of claim 1 further comprising spectral modification logic coupled between the delay unit and the adaptive filter.

4. The system of claim 1 where the delay unit comprises a programmable delay that delays passing the input signal to the adaptive filter.

5. The system of claim 1 further comprising a programmable filter coupled to the delay unit, where the programmable filter comprises a transfer function functionally related to a transfer function of the adaptive filter.

6. The system of claim 5 where the delay unit comprises a programmable delay that delays passing the input signal to the programmable filter.

7. The system of claim 1 where the system is configured to calculate a leaky average vector of the filter coefficients, and then subtract the leaky average from a total estimate of the adaptive filter coefficients.

8. The system of claim 1 where the system is configured to add a noise to the speech signal before passing the signal through the adaptive filter.

9. The system of claim 8 where the noise comprises a white noise.

10. A system for extracting pitch from a speech signal having voiced and unvoiced segments, the system comprising:

a discrete input;

a delay unit that digitally delays a signal received through the discrete input;

an adaptive filter coupled to the delay unit, where filter coefficients derived from the adaptive filter are used to estimate the pitch of the speech signal; and

a spectral modification logic coupled between the delay unit and the adaptive filter, where the spectral modification logic is configured to modify the spectrum of the signal prior to filtering of the signal by the adaptive filter.

11. The system of claim 10 further comprising a programmable filter coupled to the delay unit, where the programmable filter comprises a transfer function functionally related to a transfer function of the adaptive filter.

12. The system of claim 11 where the delay unit comprises a programmable delay that delays passing the input signal to the programmable filter.

13. The system of claim 10 where the system is configured to calculate a leaky average vector of the filter coefficients and subtract the leaky average from an estimate of the adaptive filter coefficients.

14. The system of claim 10 where the system is configured to add a noise to the reference input signal before passing the signal through the adaptive filter.

15. A method for extracting pitch from a speech signal, the method comprising:

delaying a speech signal;

passing the delayed speech signal through an adaptive filter;

obtaining filter coefficients of the adaptive filter; and

utilizing the filter coefficients to estimate pitch in the speech signal.

16. The method of claim 15 further comprising enhancing the periodic components of the speech signal.

17. The method of claim 15 further comprising reducing the tonal noise in the speech signal.

18. The method of claim 17, where reducing the tonal noise in the speech signal comprises:

calculating a leaky average of the filter coefficients that corresponds to a tonal noise; and

subtracting the leaky average vector from the total estimate of the filter coefficients.

19. The method of claim 15 further comprising passing the speech signal through a low-pass filter before passing the signal through the adaptive filter.

20. The method of claim 15 further comprising spectrally flattening the speech signal before passing the signal through the adaptive filter.

21. The method of claim 15 further comprising adding noise to the speech signal to enhance an estimation of the filter coefficients.