Voiced speech preprocessing employing waveform interpolation or a harmonic model

• US 6,738,739 B2
• Filed: 02/15/2001
• Issued: 05/18/2004
• Est. Priority Date: 02/15/2001
• Status: Expired due to Term

• Current Assignee: MACOM Technology Solutions Holdings, Inc.
• Original Assignee: Mindspeed Technologies Inc. (MACOM Technology Solutions Holdings, Inc.)
• Inventors: Gao, Yang
• Primary Examiner(s): Dorvil, Richemond
• Assistant Examiner(s): Nolan, Daniel A
• Application Number:
  US09/784,360
• Publication Number:
  US 20020111797A1
• Time in Patent Office: 1,188 Days
• Field of Search: 704/207, 704/208, 704/211, 704/227, 704/230, 704/265, 704/275
• US Class Current: 704/207
• CPC Class Codes: G10L 19/02 using spectral analysis, e.g. transform vocoders or subband vocoders
• CPC Class Codes: G10L 19/0204 using subband decomposition
• CPC Class Codes: G10L 19/0212 using orthogonal transformation

Abstract

Voiced speech preprocessing employs waveform interpolation or a harmonic model circuit to smooth a transition region and simplify speech coding. At low bit rates, the speech is coded by a system that maintains a high perceptual quality in the transition region from a voiced (quasi-periodic) portion of the speech signal to an unvoiced (non-periodic) portion of the speech signal. Similarly, the transition region from an unvoiced portion to a voiced portion is conditioned to maintain a high perceptual quality at a low bandwidth. The transition region from one type of voiced region to another type of voiced region is also smoothed. The transition region is smoothed to create a quasi-periodic speech signal.

Claims

1. A speech codec comprising

a failure detection circuit configured to initiate a frequency transformation of a speech signal using a harmonic model circuit when said failure detection circuit detects at least one of a long term pre-processing circuit failure, a long term processing circuit failure, and an irregular voice speech portion of the speech signal;

a classifier configured to process parameters that identify a transition region between at least two portions of the speech signal, one of the at least two portions of the speech signal being a voiced portion; and

a periodic smoothing circuit configured to smooth the transition region represented by at least one of a weighted representation of the speech signal, a residual signal, and the speech signal using at least one of an interpolated pitch lag and a constant pitch lag, the interpolated pitch lag being derived from a pitch track corresponding to the voiced portion of the speech signal,

wherein the periodic smoothing circuit is configured to use at least one of a forward pitch extension and a backward pitch extension.

2. The speech codec of claim 1 wherein the other one of the at least two portions of the speech signal is a periodic portion.

3. The speech codec of claim 1 wherein the transition region extends through a plurality of frames of the speech signal.

4. The speech codec of claim 1 wherein at least one of the portions of the speech signal is an unvoiced portion.

5. The speech codec of claim 1 wherein the periodic smoothing circuit is configured to smooth the transition region using the harmonic model circuit.

6. A speech coding system comprising:

a failure detection circuit configured to initiate a frequency transformation of a speech signal using a harmonic model circuit when said failure detection circuit detects at least one of a long term pre-processing circuit failure, a long term processing circuit failure, and an irregular voice speech portion of the speech signal;

a classifier that is configured to detect a transition region between at least two portions of the speech signal, at least one portion of the speech signal being a periodic portion; and

a periodic smoothing circuit that is configured to smooth the transition region using at least one of a forward pitch extension and a backward pitch extension, with either being derived from a pitch track corresponding to the periodic portion of the speech signal.

7. The speech coding system of claim 6 wherein the at least two portions of the speech signal are periodic portions.

8. The speech coding system of claim 6 wherein the periodic smoothing circuit is configured to smooth the transition region in a frequency domain using the harmonic model circuit.

9. The speech coding system of claim 6 wherein the classifier is configured to use at least one of a pitch lag, a linear prediction coefficient parameter, an energy level, and a normalized pitch correlation to classify the speech signal.

10. A method of smoothing a transition region comprising:

initiating a frequency transformation of a speech signal using a harmonic model circuit when at least one of a long term pre-processing circuit failure, a long term processing circuit failure, and an irregular voice speech portion of the speech signal is detected;

detecting a transition region between a periodic portion and a second portion of the speech signal; and

smoothing the transition region using at least one of a forward pitch extension and a backward pitch extension, with either being derived from a pitch track corresponding to the periodic portion of the speech signal.

11. The method of claim 10 wherein the second portion of the speech signal is a periodic portion.

12. The method of claim 10 wherein the second portion of the speech signal is a voiced portion.

13. The method of claim 10 wherein the forward pitch extension is derived by calculating a pitch from a previous frame of the speech signal.

14. The method of claim 10 wherein the backward pitch extension is calculated from at least one of a current frame and a second frame of the speech signal.

15. A speech codec comprising

a failure detection circuit configured to initiate a waveform interpolation of a speech signal in the time domain when said failure detection circuit detects at least one of a long term pre-processing circuit failure, a long term processing circuit failure, and an irregular voice speech portion of the speech signal;

a classifier configured to process parameters that identify a transition region between at least two portions of the speech signal, one of the at least two portions of the speech signal being a voiced portion; and

a periodic smoothing circuit configured to smooth the transition region represented by at least one of a weighted representation of the speech signal, a residual signal, and the speech signal using at least one of an interpolated pitch lag and a constant pitch lag, the interpolated pitch lag being derived from a pitch track corresponding to the voiced portion of the speech signal,

wherein the periodic smoothing circuit is configured to use at least one of a forward pitch extension and a backward pitch extension.

16. The speech codec of claim 15 wherein the other one of the at least two portions of the speech signal is a periodic portion.

17. The speech codec of claim 15 wherein the transition region extends through a plurality of frames of the speech signal.

18. The speech codec of claim 15 wherein at least one of the portions of the speech signal is an unvoiced portion.

19. The speech codec of claim 15 wherein the failure detection circuit is further configured to initiate a frequency domain smoothing of the speech signal using a harmonic circuit.

20. A speech coding system comprising:

a failure detection circuit configured to initiate a waveform interpolation of a speech signal in the time domain when said failure detection circuit detects at least one of a long term pre-processing circuit failure, a long term processing circuit failure, and an irregular voice speech portion of the speech signal;

a classifier that is configured to detect a transition region between at least two portions of the speech signal, at least one portion of the speech signal being a periodic portion; and

a periodic smoothing circuit that is configured to smooth the transition region using at least one of a forward pitch extension and a backward pitch extension, with either being derived from a pitch track corresponding to the periodic portion of the speech signal.

21. The speech coding system of claim 20 wherein the at least two portions of the speech signal are periodic portions.

22. The speech coding system of claim 20 wherein the periodic smoothing circuit is configured to smooth the transition region in a time domain using a waveform interpolation circuit.

23. The speech coding system of claim 20 wherein the periodic smoothing circuit is configured to smooth the transition region in a frequency domain using a harmonic model circuit.

24. The speech coding system of claim 20 wherein the classifier is configured to use at least one of a pitch lag, a linear prediction coefficient parameter, an energy level, and a normalized pitch correlation to classify the speech signal.

25. A method of smoothing a transition region comprising:

initiating a waveform interpolation of a speech signal in the time domain when at least one of a long term pre-processing circuit failure, a long term processing circuit failure, and an irregular voice speech portion of the speech signal is detected;

detecting a transition region between a periodic portion and a second portion of the speech signal; and

smoothing the transition region using at least one of a forward pitch extension and a backward pitch extension, with either being derived from a pitch track corresponding to the periodic portion of the speech signal.

26. The method of claim 25 wherein the second portion of the speech signal is a periodic portion.

27. The method of claim 25 wherein the second portion of the speech signal is a voiced portion.

28. The method of claim 25 wherein the forward pitch extension is derived by calculating a pitch from a previous frame of the speech signal.

29. The method of claim 25 wherein the backward pitch extension is calculated from at least one of a current frame and a second frame of the speech signal.