Short-term enhancement in CELP speech coding

• US 6,678,651 B2
• Filed: 01/25/2001
• Issued: 01/13/2004
• Est. Priority Date: 09/15/2000
• 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): To, Doris H.
• Assistant Examiner(s): Nolan, Daniel A.
• Application Number:
  US09/771,293
• Publication Number:
  US 20030004710A1
• Time in Patent Office: 1,083 Days
• Field of Search: 704/219, 704/220, 704/222, 704/201, 704/204, 704/209, 704/211, 704/262
• US Class Current: 704/219
• CPC Class Codes: C07K 16/1282 from Clostridium (G)
• CPC Class Codes: G01N 33/56911 Bacteria
• CPC Class Codes: G10L 19/12 the excitation function being a code excitation, e.g. in code excited linear prediction [CELP] vocoders
• CPC Class Codes: G10L 19/26 Pre-filtering or post-filtering
• CPC Class Codes: G10L 25/15 the extracted parameters being formant information

Abstract

A speech-coding device includes a fixed codebook, an adaptive codebook, a short-term enhancement circuit, and a summing circuit. The short-term enhancement circuit connects an output of the fixed codebook to a summing circuit. The summing circuit adds an adaptive codebook contribution to a fixed codebook contribution. The short-term enhancement circuit can also be connected to a synthesis filter to emphasize the spectral formants in an encoder and a decoder.

Claims

1. A speech communication system comprising:

an adaptive codebook that characterizes a speech segment;

a fixed codebook that characterizes the speech segment and generates an excitation, wherein said excitation is scaled by an adaptive factor to generate a scaled signal;

a filter configured to filter the scaled signal by an enhancement that emphasizes the formants of a Linear Prediction Coding spectrum to generate a filtered signal;

a summer configured to sum the filtered signal with an output of the adaptive codebook to generate a summed signal;

a convolver configured to convolve the summed signal to generate a convoluted signal; and

a synthesizer configured to filter the convoluted signal.

2. The system of claim 1, wherein the convolver comprises a spectral filter having a transfer function of 1/A(z/α

).

3. The system of claim 1, wherein the system comprises an extended Code Excited Linear Prediction System.

4. The system of claim 1, wherein the convolver emphasizes the formant structure convolving two time domain signals.

18. The system of claim 1 wherein α

is less than about 0.1.

5. A speech communication system comprising:

an excitation that characterizes a speech segment;

a convolver having an input configured to receive the excitation; and

a synthesizer coupled to an output of the convolver, the convolver being configured to emphasize a formant structure of a spectral envelope of the speech segment in a closed-loop of an encoder;

wherein the convolver comprises a spectral filter configured to modify an input signal by a transfer function of the form 1/A(z/α

).

6. The system of claim 5 wherein the excitation is derived from an output of a first codebook and a second codebook.

7. The system of claim 6 wherein the first codebook comprises an adaptive codebook.

8. The system of claim 7 wherein the second codebook comprises a fixed codebook.

9. The system of claim 8 further comprising a minimizing circuit coupled to the fixed codebook.

10. The system of claim 9 further comprising a weighting filter coupled to the minimizing circuit.

11. The system of claim 10 further comprising a subtracting circuit coupled to the synthesizer and the weighting filter.

12. The system of claim 6 wherein the convolver generates a convoluted result of an enhancement signal and at least an output signal of the second codebook.

13. The system of claim 5 wherein the convolver is electrically coupled to an output of a summing circuit.

14. The system of claim 5 wherein the system comprises a Code Excited Linear Prediction System.

15. The system of claim 5 wherein the system comprises an eXtended Code Excited Linear Prediction System.

16. The system of claim 5 wherein the convolver comprises a short-term enhancement circuit configured to enhance at least one of the formants of the spectral envelope.

17. The system of claim 5 wherein the convolver comprises a short-term enhancement circuit configured to enhance the formant structure of the spectral envelope.

19. The system of claim 5 wherein the convolver is configured to emphasize the formant structure of the spectral envelope of the speech segment in a decoder.

20. A speech communication system comprising:

a fixed codebook that characterizes a speech segment;

an adaptive codebook that characterizes the speech segment;

means for emphasizing a formant structure of an envelope of the speech segment connected to an output of the fixed codebook; and

a synthesizer connected to an output of the means for emphasizing;

wherein the means for emphasizing emphasizes the formant structure by convolving two time domain signals.

21. The system of claim 20 wherein the means for emphasizing comprises a filter.

22. The system of claim 20 wherein the means for emphasizing comprises a convolver.

23. The system of claim 20 wherein the means for emphasizing is connected to an output of a summing circuit.

24. A method that improves speech coding comprising:

generating a fixed codebook index to select an excitation;

scaling the excitation by an adaptive factor; and

filtering the scaled excitation by an enhancement that emphasizes the formants of a Linear Prediction Coding spectrum in a closed-loop of an encoder;

summing the filtered and scaled excitation with an output of an adaptive codebook; and

convolving the summed signal and filtering the convoluted signal by a synthesizing filter.

25. The method of claim 24 wherein the act of filtering comprises a device having a transfer function of the form 1/A(z/α

).

26. The method of claim 25 wherein α

is less than about 0.1.

27. The method of claim 24 wherein the filtering of the scaled excitation by the enhancement that emphasizes the formants of the Linear Prediction Coding spectrum occurs in a decoder.

28. The method of claim 24 wherein the fixed codebook index is derived by subtracting a reconstructed speech signal from a speech signal;

filtering the difference between the reconstructed speech signal and the speech signal through a weighting function; and

minimizing the filtered difference.

29. A speech coding method comprising:

generating a fixed codebook index to select an excitation;

convolving the excitation by an enhancement that emphasizes the formants of a Linear Prediction Coding spectrum;

scaling the convolved excitation by an adaptive factor;

summing the scaled and convolved excitation with an output of an adaptive codebook; and

synthesizing the summed signal by a synthesizing filter.

30. The method of claim 29, wherein the convolving uses a spectral filter configured to modify an input signal by a transfer function of the form 1/A(z/α

).

31. The method oil claim 29, wherein the method is performed in an eXtended Code Excited Linear Prediction system.

32. The method of claim 29, wherein the convolving emphasizes the formant structure by convolving two time domain signals.