Estimation of excitation parameters

• US 5,826,222 A
• Filed: 04/14/1997
• Issued: 10/20/1998
• Est. Priority Date: 01/12/1995
• Status: Expired due to Term

• Current Assignee: Digital Voice Systems, Inc.
• Original Assignee: Digital Voice Systems, Inc.
• Inventors: Griffin, Daniel Wayne
• Primary Examiner(s): Hudspeth, David R.
• Assistant Examiner(s): Chawan, Vijay B.
• Application Number:
  US08/834,145
• Time in Patent Office: 554 Days
• Field of Search: 704/207, 704/208, 704/209, 704/226, 704/229
• US Class Current: 704/207
• CPC Class Codes: G10L 19/0204 using subband decomposition
• CPC Class Codes: G10L 19/08 Determination or coding of the excitation function; Determination or coding of the long-term prediction parameters
• CPC Class Codes: G10L 2025/937 Signal energy in various frequency bands
• CPC Class Codes: G10L 25/03 characterised by the type of extracted parameters
• CPC Class Codes: G10L 25/90 Pitch determination of speech signals
• CPC Class Codes: G10L 25/93 Discriminating between voiced and unvoiced parts of speech signals G10L25/90 takes precedence

Abstract

A method of encoding speech by analyzing a digitized speech signal to determine excitation parameters for the digitized speech signal is disclosed. The method includes dividing the digitized speech signal into at least two frequency bands, determining a first preliminary excitation parameter by performing a nonlinear operation on at least one of the frequency band signals to produce a modified frequency band signal and determining the first preliminary excitation parameter using the modified frequency band signal, determining a second preliminary excitation parameter using a method different from the first method, and using the first and second preliminary excitation parameters to determine an excitation parameter for the digitized speech signal. The method is useful in encoding speech. Speech synthesized using the parameters estimated based on the invention generates high quality speech at various bit rates useful for applications such as satellite voice communication.

Claims

1. A method of analyzing a digitized speech signal to determine excitation parameters for the digitized speech signal, comprising:

dividing the digitized speech signal into one or more frequency band signals;

determining a first preliminary excitation parameter using a first method that includes performing a nonlinear operation on at least one of the frequency band signals to produce at least one modified frequency band signal and determining the first preliminary excitation parameter using the at least one modified frequency band signal;

determining at least a second preliminary excitation parameter using at least a second method different from the said first method; and

using the first and at least a second preliminary excitation parameters to determine an excitation parameter for the digitized speech signal.

2. The method of claim 1, wherein the determining and using steps are performed at regular intervals of time.

3. The method of claim 1, wherein the digitized speech signal is analyzed as a step in encoding speech.

4. The method of claim 1, wherein the excitation parameter comprises a voiced/unvoiced parameter for at least one frequency band.

5. The method of claim 4, further comprising determining a fundamental frequency for the digitized speech signal.

6. The method of claim 4, wherein the first preliminary excitation parameters comprises a first voiced/unvoiced parameter for the at least one modified frequency band signal, and wherein the first determining step includes determining the first voiced/unvoiced parameter by comparing voiced energy in the modified frequency band signal to total energy in the modified frequency band signal.

7. The method of claim 6, wherein the voiced energy in the modified frequency band signal corresponds to the energy associated with an estimated fundamental frequency for the digitized speech signal.

8. The method of claim 6, wherein the voiced energy in the modified frequency band signal corresponds to the energy associated with an estimated pitch period for the digitized speech signal.

9. The method of claim 6, wherein the second preliminary excitation parameter includes a second voiced/unvoiced parameter for the at least one frequency band signal, and wherein the second determining step includes determining the second voiced/unvoiced parameter by comparing sinusoidal energy in the at least one frequency band signal to total energy in the at least one frequency band signal.

10. The method of claim 6, wherein the second preliminary excitation parameter includes a second voiced/unvoiced parameter for the at least one frequency band signal, and wherein the second determining step includes determining the second voiced/unvoiced parameter by autocorrelating the at least one frequency band signal.

11. The method of claim 4, wherein the voiced/unvoiced parameter has values that vary over a continuous range.

12. The method of claim 1, wherein the using step emphasizes the first preliminary excitation parameter over the second preliminary excitation parameter in determining the excitation parameter for the digitized speech signal when the first preliminary excitation parameter has a higher probability of being correct than does the second preliminary excitation parameter.

13. The method of claim 1, further comprising smoothing the excitation parameter to produce a smoothed excitation parameter.

14. A method of synthesizing speech using the excitation parameters, where the excitation parameters were estimated using the method in claim 1.

15. The method of claim 1, wherein at least one of the second methods uses at least one of the frequency band signals without performing the said nonlinear operation.

16. A method of analyzing a digitized speech signal to determine excitation parameters for the digitized speech signal, comprising the steps of:

dividing the digitized speech signal into one or more frequency band signals;

determining a preliminary excitation parameter using a method that includes performing a nonlinear operation on at least one of the frequency band signals to produce at least one modified frequency band signal and determining the preliminary excitation parameter using the at least one modified frequency band signal; and

smoothing the preliminary excitation parameter to produce an excitation parameter.

17. The method of claim 16, wherein the digitized speech signal is analyzed as a step in encoding speech.

18. The method of claim 16, wherein the preliminary excitation parameters include a preliminary voiced/unvoiced parameter for at least one frequency band and the excitation parameters include a voiced/unvoiced parameter for at least one frequency band.

19. The method of claim 18, wherein the excitation parameters include a fundamental frequency.

20. The method of claim 18, wherein the digitized speech signal is divided into frames and the smoothing step makes the voiced/unvoiced parameter of a frame more voiced than the preliminary voiced/unvoiced parameter when voiced/unvoiced parameters of frames that precede or succeed the frame by less than a predetermined number of frames are voiced.

21. The method of claim 18, wherein the smoothing step makes the voiced/unvoiced parameter of a frequency band more voiced than the preliminary voiced/unvoiced parameter when voiced/unvoiced parameters of a predetermined number of adjacent frequency bands are voiced.

22. The method of claim 18, wherein the digitized speech signal is divided into frames and the smoothing step makes the voiced/unvoiced parameter of a frame and frequency band more voiced than the preliminary voiced/unvoiced parameter when voiced/unvoiced parameters of frames that precede or succeed the frame by less than a predetermined number of frames and voiced/unvoiced parameters of a predetermined number of adjacent frequency bands are voiced.

23. The method of claim 18, wherein the voiced/unvoiced parameter is permitted to have values that vary over a continuous range.

24. The method of claim 16, wherein the smoothing step is performed as a function of time.

25. The method of claim 16, wherein the smoothing step is performed as a function of both time and frequency.

26. A method of synthesizing speech using the excitation parameters, where the excitation parameters were estimated using the method in claim 16.

27. A method of analyzing a digitized speech signal to determine excitation parameters for the digitized speech signal, comprising the steps of:

estimating a fundamental frequency for the digitized speech signal;

evaluating a voiced/unvoiced function using the estimated fundamental frequency to produce a first preliminary voiced/unvoiced parameter;

evaluating the voiced/unvoiced function at least using one other frequency derived from the estimated fundamental frequency to produce at least one other preliminary voiced/unvoiced parameter; and

combining the first and at least one other preliminary voiced/unvoiced parameters to produce a voiced/unvoiced parameter.

28. The method of claim 27, wherein the said at least one other frequency is derived from the said estimated fundamental frequency as a multiple or submultiple of the said estimated fundamental frequency.

29. The method of claim 27, wherein the digitized speech signal is analyzed as a step in encoding speech.

30. A method of synthesizing speech using the excitation parameters, where the excitation parameters were estimated using the method in claim 27.

31. The method of claim 27, wherein the combining step includes choosing the first preliminary voiced/unvoiced parameter as the voiced/unvoiced parameter when the first preliminary voiced/unvoiced parameter indicates that the digitized speech signal is more voiced than does the second preliminary voiced/unvoiced parameter.

32. A method of analyzing a digitized speech signal to determine a fundamental frequency estimate for the digitized speech signal, comprising the steps of:

determining a predicted fundamental frequency estimate from previous fundamental frequency estimates;

determining an initial fundamental frequency estimate;

evaluating an error function at the initial fundamental frequency estimate to produce a first error function value;

evaluating the error function at at least one other frequency derived from the initial fundamental frequency estimate to produce at least one other error function value;

selecting a fundamental frequency estimate using the predicted fundamental frequency estimate, the initial fundamental frequency estimate, the first error function value, and the at least one other error function value.

33. The method of claim 32, wherein the said at least one other frequency is derived from the said estimated fundamental frequency as a multiple or submultiple of the said estimated fundamental frequency.

34. The method of claim 32, wherein the predicted fundamental frequency is determined by adding a delta factor to a previous predicted fundamental frequency.

35. The method of claim 34, wherein the delta factor is determined from previous first and at least one other error function values, the previous predicted fundamental frequency, and a previous delta factor.

36. A method of synthesizing speech using a fundamental frequency, where the fundamental frequency was estimated using the method in claim 32.

37. A system for analyzing a digitized speech signal to determine excitation parameters for the digitized speech signal, comprising:

means for dividing the digitized speech signal into one or more frequency band signals;

means for determining a first preliminary excitation parameter using a first method that includes performing a nonlinear operation on at least one of the frequency band signals to produce at least one modified frequency band signal and determining the first preliminary excitation parameter using the at least one modified frequency band signal;

means for determining a second preliminary excitation parameter using a second method that is different from the above said first method; and

means for using the first and second preliminary excitation parameters to determine an excitation parameter for the digitized speech signal.

38. A system for analyzing a digitized speech signal to determine excitation parameters for the digitized speech signal, comprising:

means for dividing the digitized speech signal into one or more frequency band signals;

means for determining a preliminary excitation parameter using a method that includes performing a nonlinear operation on at least one of the frequency band signals to produce at least one modified frequency band signal and determining the preliminary excitation parameter using the at least one modified frequency band signal; and

means for smoothing the preliminary excitation parameter to produce an excitation parameter.

39. A system for analyzing a digitized speech signal to determine modified excitation parameters for the digitized speech signal, comprising:

means for estimating a fundamental frequency for the digitized speech signal;

means for evaluating a voiced/unvoiced function using the estimated fundamental frequency to produce a first preliminary voiced/unvoiced parameter;

means for evaluating the voiced/unvoiced function using another frequency derived from the estimated fundamental frequency to produce a second preliminary voiced/unvoiced parameter; and

means for combining the first and second preliminary voiced/unvoiced parameters to produce a voiced/unvoiced parameter.

40. A system for analyzing a digitized speech signal to determine a fundamental frequency estimate for the digitized speech signal, comprising:

means for determining a predicted fundamental frequency estimate from previous fundamental frequency estimates;

means for determining an initial fundamental frequency estimate;

means for evaluating an error function at the initial fundamental frequency estimate to produce a first error function value;

means for evaluating the error function at at least one other frequency derived from the initial fundamental frequency estimate to produce a second error function value;

means for selecting a fundamental frequency estimate using the predicted fundamental frequency estimate, the initial fundamental frequency estimate, the first error function value, and the second error function value.

41. A method of analyzing a digitized speech signal to determine a voiced/unvoiced function for the digitized speech signal, comprising:

dividing the digitized speech signal into at least two frequency band signals;

determining a first preliminary voiced/unvoiced function for at least two of the frequency band signals using a first method;

determining a second preliminary voiced/unvoiced function for at least two of the frequency band signals using a second method which is different from the above said first method; and

using the first and second preliminary excitation parameters to determine a voiced/unvoiced function for at least two of the frequency band signals.