Voiced speech preprocessing employing waveform interpolation or a harmonic model

• US 20020111797A1
• Filed: 02/15/2001
• Published: 08/15/2002
• Est. Priority Date: 02/15/2001
• Status: Active Grant

• Current Assignee: MACOM Technology Solutions Holdings, Inc.
• Original Assignee: Mindspeed Technologies Inc. (MACOM Technology Solutions Holdings, Inc.)
• Inventors: Gao, Yang
• Granted Patent: US 6,738,739 B2
• Time in Patent Office: Days
• 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 classifier configured to process parameters that identify a transition region between at least two portions of a speech signal, at least one of the 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 a 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.

2. The speech codec of claim 1 wherein the second portion of the speech signal is a periodic portion.

3. The speech codec of claim 1 wherein the periodic smoothing circuit is configured to use at least one of a forward pitch extension and a backward pitch extension.

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

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

6. The speech codec of claim 1 wherein the periodic smoothing circuit is configured to smooth the transition region using a waveform interpolation circuit.

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

8. The speech codec of claim 1 further comprising at least one of a long term pre-processing circuit and a long term processing circuit, wherein the periodic smoothing circuit is initiated upon at least one of a failure of the long term pre-processing circuit, a failure of the long term processing circuit, and a detection of an irregular voiced speech portion.

9. A speech coding system comprising:

a classifier that is configured to detect a transition region between at least two portions of a 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 that is derived from a pitch track corresponding to the periodic portion of the speech signal.

10. The speech coding system of claim 9 wherein the at least two portions of the speech signal are periodic portions.

11. The speech coding system of claim 9 wherein the periodic smoothing circuit is configured to smooth the transition region in a time domain using a waveform interpolation circuit.

12. The speech coding system of claim 9 wherein the periodic smoothing circuit is configured to smooth the transition region in a frequency domain using a harmonic model circuit.

13. The speech codec of claim 9 further comprising at least one of a long term pre-processing circuit and a long term processing circuit, wherein the periodic smoothing circuit is initiated upon a detection of at least one of a failure of the long term pre-processing circuit, a failure of the long term processing circuit, and a detection of an irregular voiced speech portion.

14. The speech coding system of claim 9 further comprising a failure detection circuit coupled to a long term processing circuit, wherein the periodic smoothing circuit is configured to smooth the transition region when a failure of the long term processing circuit is detected by the failure detection circuit.

15. The speech coding system of claim 9 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.

17. The method of claim 16 wherein the second portion of the speech signal is a periodic portion.

18. The method of claim 16 wherein the second portion of the speech signal is a voiced portion.

19. The method of claim 16 wherein the forward pitch extension is derived by calculating a pitch from a previous frame of the speech signal.

20. The method of claim 16 wherein the backward pitch extension is calculated from at least one of a current frame and a second frame of the speech signal.

16. A method of smoothing a transition region comprising:

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

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