CELP-based to CELP-based vocoder packet translation

• US 6,260,009 B1
• Filed: 02/12/1999
• Issued: 07/10/2001
• Est. Priority Date: 02/12/1999
• Status: Expired due to Term

• Current Assignee: Qualcomm, Inc.
• Original Assignee: Qualcomm, Inc.
• Inventors: Dejaco, Andrew P.
• Primary Examiner(s): Dorvil, Richemond
• Assistant Examiner(s): Nolan, Daniel A.
• Application Number:
  US09/249,060
• Time in Patent Office: 879 Days
• Field of Search: 704/201-223
• US Class Current: 704/221
• 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 19/173 Transcoding, i.e. converting between two coded representations avoiding cascaded coding-decoding

Abstract

A method and apparatus for CELP-based to CELP-based vocoder packet translation. The apparatus includes a formant parameter translator and an excitation parameter translator. The formant parameter translator includes a model order converter and a time base converter. The method includes the steps of translating the formant filter coefficients of the input packet from the input CELP format to the output CELP format and translating the pitch and codebook parameters of the input speech packet from the input CELP format to the output CELP format. The step of translating the formant filter coefficients includes the steps of converting the model order of the formant filter coefficients from the model order of the input CELP format to the model order of the output CELP format and converting the time base of the resulting coefficients from the input CELP format time base to the output CELP format time base.

Claims

1. An apparatus for converting a compressed speech packet from one code excited linear prediction (CELP) format to another, comprising:

a formant parameter translator that translates input formant filter coefficients having an input CELP format and corresponding to a speech packet to an output CELP format to produce output formant filter coefficients; and

an excitation parameter translator that translates input pitch and codebook parameters having an input CELP format and corresponding to said speech packet to said output CELP format to produce output pitch and codebook parameters, wherein said excitation parameter translator comprises;

a model order converter that converts the model order of said input formant filter coefficients from a model order of said input CELP format to a model order of said output CELP format;

a time base converter that converts the time base of said input formant filter coefficients from a time base of said input CELP format to a time base of said output CELP format;

a speech synthesizer that produces a target signal using said input pitch and codebook parameters and said output formant filter coefficients; and

a searcher that searches for said output codebook and pitch parameters using said target signal and said output formant filter coefficients.

2. The apparatus of claim 1, wherein said formant parameter translator comprises:

a model order converter that converts the model order of said input formant filter coefficients from a model order of said input CELP format to a model order of said output CELP format; and

a time base converter that converts the time base of said input formant filter coefficients from a time base of said input CELP format to a time base of said output CELP format.

3. The apparatus of claim 1, wherein said searcher comprises:

a further speech synthesizer that generates a guess signal using guess excitation parameters and said output formant filter coefficients;

a combiner that generates an error signal based on said guess signal and said target signal; and

a minimization element that varies said guess excitation parameters to minimize said error signal.

4. The apparatus of claim 1, wherein said model order converter further comprises:

a formant filter coefficient translator that translates said input formant filter coefficients to a third CELP format prior to use by said speech synthesizer to produce third coefficients.

5. The apparatus of claim 4, wherein said model order converter further comprises:

an interpolator that interpolates said third coefficients to produce order corrected coefficients when said model order of said input CELP format is lower than said model order of said output CELP format; and

a decimator that decimates said third coefficients to produce said order corrected coefficients when said model order of said input CELP format is higher than said model order of said output CELP format.

6. The apparatus of claim 1, wherein said speech synthesizer comprises:

a codebook using said input codebook parameters to produce a codebook vector;

a pitch filter using said input pitch filter parameters and said codebook vector to produce a pitch signal; and

a formant filter using said output formant filter coefficients and said pitch signal to produce said target signal.

7. The apparatus of claim 6, wherein said guess excitation parameters include guess pitch filter parameters and guess codebook parameters, wherein said further speech synthesizer comprises:

a further codebook using said guess codebook parameters to produce a further codebook vector;

a pitch filter using said guess pitch filter parameters and said further codebook vector to produce a further pitch signal; and

a formant filter using said output formant filter coefficients and said further pitch signal to produce said guess signal.

8. The apparatus of claim 2, further comprising:

a first formant filter coefficient translator that translates said input formant filter coefficients to a fourth CELP format before use by said time base converter.

9. The apparatus of claim 2, further comprising:

a second formant filter coefficient translator that translates the output of said time base converter from said fourth CELP format to said output CELP format.

10. The apparatus of claim 4, wherein said third CELP format is a reflection coefficient CELP format.

11. The apparatus of claim 8, wherein said fourth CELP format is a line spectral pair CELP format.

12. A method for converting a compressed speech packet from one CELP format to another, comprising the steps of:

(a) translating input formant filter coefficients corresponding to a speech packet from an input CELP format to an output CELP format to produce output formant filter coefficients; and

(b) translating input pitch and codebook parameters corresponding to said speech packet from said input CELP format to said output CELP format to produce output pitch and codebook parameters, comprising;

(i) synthesizing speech using said input pitch and codebook parameters in said input CELP format and said output formant filter coefficients to produce a target signal; and

(ii) searching for said output pitch and codebook parameters using said target signal and said output formant filter coefficients.

13. The method of claim 12, wherein step (a) comprises the steps of:

(i) converting the model order of said input formant filter coefficients from a model order of said input CELP format to a model order of said output CELP format; and

(ii) converting the time base of said input formant filter coefficients from a time base of said input CELP format to a time base of said output CELP format.

14. The method of claim 13, wherein step (i) comprises the steps of:

translating said input formant filter coefficients from said input CELP format to a third CELP format to produce third coefficients; and

converting the model order of said third coefficients from a model order of said input CELP format to a model order of said output CELP format to produce order corrected coefficients.

15. The method of claim 14, wherein step (ii) comprises the steps of:

translating said order corrected coefficients t o a fourth format to produce fourth coefficients;

converting the time base of said fourth coefficients form a time base of said input CELP format to a time base of said output CELP format to produce time base corrected coefficients; and

translating said time base corrected coefficients from said fourth format to said output CELP format to produce said output formant filter coefficients.

16. The method of claim 12, wherein said searching step (ii) comprises the steps of:

generating a guess signal using guess codebook and pitch parameters and said output coefficients;

generating an error signal based on said guess signal and said target signal; and

varying said guess codebook and pitch parameters to minimize said error signal.

17. The method of claim 14, wherein step (i) further comprises the steps of:

interpolating said third coefficients to produce said order corrected coefficients when said model order of said input CELP format is lower than said model order of said output CELP format; and

decimating said third coefficients to produce said order corrected coefficients when said model order of said input CELP format is higher than said model order of said output CELP format.

18. The method of claim 14, wherein said third CELP format is a reflection coefficient CELP format.

19. The method of claim 15, wherein said fourth CELP format is a line spectral pair CELP format.