Advanced periodic signal enhancement

• US 7,716,046 B2
• Filed: 12/23/2005
• Issued: 05/11/2010
• Est. Priority Date: 10/26/2004
• Status: Active Grant

• Current Assignee: Blackberry Limited
• Original Assignee: QNX Software Systems Company (Blackberry Limited)
• Inventors: Nongpiur, Rajeev, Heterington, Phillip A.
• Primary Examiner(s): Wozniak; James S
• Application Number:
  US11/317,762
• Publication Number:
  US 20060136199A1
• Time in Patent Office: 1,600 Days
• Field of Search: 704/200, 704/201, 704/226, 704/233, 381/71.1, 381/94.1, 381/94.2
• US Class Current: 704/226
• CPC Class Codes: G10L 19/26 Pre-filtering or post-filtering
• CPC Class Codes: G10L 21/0364 for improving intelligibility
• CPC Class Codes: G10L 25/90 Pitch determination of speech signals
• CPC Class Codes: H03H 2021/0083 Shadow filter, i.e. one of two filters which are simultaneously adapted, wherein the results of adapting the shadow filter are used for adapting the other filter
• CPC Class Codes: H03H 21/0012 Digital adaptive filters
• CPC Class Codes: H03H 2220/08 Variable filter length

Abstract

An enhancement system improves the perceptual quality of a processed speech. The system includes a delay unit that delays a signal received through a discrete input. A spectral modifier linked to the delay unit is programmed to substantially flatten the spectral character of a background noise. An adaptive filter linked to the spectral modifier adapts filter characteristics to match a response of a non-delayed signal. A programmable filter is linked to the delay unit. The programmable filter has a transfer function functionally related to a transfer function of the adaptive filter.

Claims

1. An enhancement speech system that improves the perceptual quality of a processed speech segment, comprising:

a discrete input;

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

a spectral modifier coupled to the delay unit programmed to substantially flatten the spectral character of a background noise;

an adaptive filter coupled to the spectral modifier that adapts filter characteristics to match a response to the signal received through the discrete input before the signal is delayed;

a programmable filter coupled to the delay unit having a transfer function functionally related to a transfer function of the adaptive filter; and

an adder comprising circuitry, a non-transitory computer-readable storage medium with program instructions stored thereon, or both, where the adder sums an output signal of the programmable filter and the signal received through the discrete input to increase a first periodic signal component in the signal received through the discrete input that is at least partially in-phase with a second periodic signal component in the output signal of the programmable filter.

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

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

5. The system of claim 1 where the spectral modifier is coupled to a circuit that allows frequencies below a predetermined frequency or frequency range to pass.

6. The speech system of claim 1 where the spectral modifier is coupled to an adder that adds a high frequency band of a delayed signal to a low frequency band comprising a signal having a spectrally flattened background noise.

7. The speech system of claim 1 where the spectral modifier is coupled to a spectral mask.

8. The speech system of claim 7 where the spectral mask is configured to substantially dampen signals lying outside an aural pass-band.

9. The speech system of claim 1 where the transfer function of the programmed filter is substantially the same as the transfer function of the adaptive filter at discrete points in time.

10. The speech system of claim 1 where the transfer function of the programmed filter and the transfer function of the adaptive filter change with the response of the input signal.

11. The speech system of claim 1 where coefficients of the programmable filter are functionally related to the coefficients of the adaptive filter, respectively.

12. The speech system of claim 11, where the functional relationship between the coefficients of the programmable filter and coefficients of the adaptive filter comprises a moving average, and where the coefficients of the programmable filter comprise a difference between a moving average of the coefficients of the adaptive filter and an instantaneous estimate of the coefficients of the adaptive filter.

13. The speech system of claim 12 where the functional relationship between the coefficients of the programmable filter and coefficients of the adaptive filter comprises a leaky average, and where the coefficients of the programmable filter comprise a difference between a leaky average of the coefficients of the adaptive filter and an instantaneous estimate of the coefficients of the adaptive filter.

14. The system of claim 1, where an input of the programmable filter is coupled to an output of the delay unit, where an input of the spectral modifier is coupled to the output of the delay unit, and where the delay unit outputs the same signal to the programmable filter and the spectral modifier.

15. The system of claim 1, where the adder sums the output signal of the programmable filter and the signal received through the discrete input to decrease a first non-periodic signal component in the signal received through the discrete input that is at least partially out of phase with a second non-periodic signal component in the output signal of the programmable filter.

16. The system of claim 1, further comprising:

a low-pass filter coupled with the spectral modifier, where the low-pass filter and the spectral modifier produce a low-pass filtered and spectrally-modified signal with a spectrally flattened background noise level;

a high-pass filter coupled with an output of the delay unit; and

a second adder coupled with an output of the high-pass filter and an output of the low-pass filter, where the second adder adds the low-pass filtered and spectrally-modified signal with an output signal of the high-pass filter to obtain a summed signal at an output of the second adder, and where the output of the second adder is coupled with an input of the adaptive filter.

17. An enhancement speech system that improves the perceptual quality of a processed speech segment, comprising:

a discrete input;

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

a spectral modifier coupled to the delay unit programmed to substantially flatten a portion of the spectral character of a detected background noise;

an adaptive filter coupled to the spectral modifier that adapts coefficients to match a response to the signal received through the discrete input before the signal is delayed;

a programmable filter coupled to the delay unit having a transfer function functionally related to a transfer function of the adaptive filter; and

an adder comprising circuitry, a non-transitory computer-readable storage medium with program instructions stored thereon, or both, where the adder sums an output signal of the programmable filter and the signal received through the discrete input to increase a first periodic signal component in the signal received through the discrete input that is at least partially in-phase with a second periodic signal component in the output signal of the programmable filter, and where the adder amplifies a harmonic structure of the signal received through the discrete input based on the output signal of the programmable filter.

18. The system of claim 17, where the delay unit comprises a programmable delay that delays passing the input signal to the adaptive filter and the programmable filter.

19. The system of claim 17 where the spectral modifier is coupled to a circuit that allows frequencies below a predetermined frequency or frequency range to pass.

20. The system of claim 17, further comprising:

a low-pass filter coupled with the spectral modifier, where the low-pass filter and the spectral modifier produce a low-pass filtered and spectrally-modified signal with a spectrally flattened background noise level;

a high-pass filter coupled with an output of the delay unit; and

a second adder coupled with an output of the high-pass filter and an output of the low-pass filter, where the second adder adds the low-pass filtered and spectrally-modified signal with an output signal of the high-pass filter to obtain the summed signal at an output of the second adder, and where the output of the second adder is coupled with an input of the adaptive filter.

21. The system of claim 17, where the adder sums the output signal of the programmable filter and the discrete signal to decrease a first non-periodic signal component in the discrete signal that is at least partially out of phase with a second non-periodic signal component in the output signal of the programmable filter.

22. A method of enhancing the perceptual quality of a processed speech segment, comprising:

delaying an input signal;

modifying the spectral characteristic of the input signal by substantially flattening the spectral characteristics of a background noise;

adapting the coefficients of a filter to match the response of the input signal;

adapting the coefficients of a programmable filter so that the transfer function of the programmable filter is functionally related to the transfer function of the filter; and

adding an output signal from the programmable filter 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 output signal from the programmable filter.

23. The method of claim 22 further comprising adjusting the gain of the input signal based on the output of the programmable filter.