Method and apparatus for transcoding between different speech encoding/ decoding systems and recording medium

• US 20050240400A1
• Filed: 07/01/2005
• Published: 10/27/2005
• Est. Priority Date: 07/24/2002
• Status: Active Grant

• Current Assignee: NEC Corporation
• Original Assignee: NEC Corporation
• Inventors: Murashima, Atsushi
• Granted Patent: US 7,319,953 B2
• Time in Patent Office: Days
• US Class Current: 704/225
• CPC Class Codes: G10L 19/083 the excitation function being an excitation gain G10L25/90 takes precedence
• 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

Disclosed is a code converting apparatus for converting a first code sequence conforming to a first system to a second code sequence conforming to a second system, in which a speech decoding circuit acquires a first linear prediction coefficient and the information on an excitation signal from the first code sequence, and actuates a filter having the aforementioned first linear prediction coefficient with the excitation signal obtained from the information on the excitation signal, to generate a first speech signal. A gain code generating circuit calculates a gain minimizing the distance between a second speech signal, generated from the information, obtained from the second code sequence, and the first speech signal (optimum gain), and corrects the optimum gain and the gain code generating circuit then finds the gain information in the second code sequence, based on the optimum gain as corrected (optimum gain corrected), the above optimum gain and a gain read out from a gain codebook of the second system. The gain is found at this time, in a non-speech segment, based on a speech decision value, using an evaluation function which will reduce time variations of the gain of the second system.

Claims

1. A code converting method for converting a first code sequence conforming to a first system to a second code sequence conforming to a second system, comprising the steps of:

decoding the gain information from said first code sequence;

correcting the gain decoded (termed ‘

decoding gain’

); and

finding the gain information in said code sequence based on the decoding gain corrected (termed ‘

corrected decoded gain’

), said decoded gain and the gain read out from the codebook in said second system.

2. The code converting method according to claim 1, further comprising the steps of:

calculating a first square error from the corrected decoded gain and from the gain read out from said gain codebook;

calculating a second square error from said decoded gain and from the gain read out from said gain codebook; and

selecting a gain minimizing an evaluation function which is based on said first square error and said second square error from said gain codebook to find the gain information in said second code sequence.

3. The code converting method according to claim 1, wherein said corrected decoded gain is based on the long-term average value of said decoded gain.

4. The code converting method according to claim 2, wherein said evaluation function is composed of said first square error, said second square error and weighting coefficients.

5. The code converting method according to claim 1, further comprising the steps of:

determining a speech decision value, discriminating the speech segment/non-speech segment, based on said first linear prediction coefficient; and

finding the gain information in said second code sequence, using an evaluation function which will decrease a temporal variation of the gain in said second code sequence, when said speech decision value indicates the non-speech segment.

6. The code converting method according to claim 2, further comprising the steps of:

determining a speech decision value, discriminating the speech segment/non-speech segment, based on said first linear prediction coefficient;

said evaluation function being found by taking a weighted average value of said first and second square errors by weighting coefficients; and

setting said weighting coefficients to respective preset values, based on said speech decision value, depending on the speech segment and the non-speech segment, to calculate said evaluation function.

7. A code converting apparatus for converting a first code sequence conforming to a first system to a second code sequence conforming to a second system, said apparatus comprising:

a gain decoding circuit for decoding the gain information from said first code sequence;

a decoded gain correcting circuit for correcting the gain decoded (termed ‘

decoded gain’

); and

a gain encoding circuit for finding the gain information in said code sequence based on the decoded gain corrected (‘

corrected decoded gain’

), said decoded gain and the gain read out from the codebook in said second system.

8. The code converting apparatus according to claim 7, wherein said gain encoding circuit includes a unit for calculating a first square error from the corrected decoded gain and from the gain read out from said gain codebook, calculating a second square error from said decoded gain and from the gain read out from said gain codebook, and selecting a gain minimizing an evaluation function which is based on said first square error and said second square error from said gain codebook to find the gain information in said second code sequence.

9. The code converting apparatus according to claim 7, wherein said corrected decoded gain is based on the long-term average value of said decoded gain.

10. The code converting apparatus according to claim 8, wherein said evaluation function is composed of said first square error, said second square error and weighting coefficients.

11. The code converting apparatus according to claim 7, further comprising:

a speech/non-speech discriminating circuit for discriminating a speech decision value, discriminating the speech segment/non-speech segment, based on said first linear prediction coefficient;

said gain encoding circuit finding the gain information in said second code sequence, using an evaluation function which will decrease temporal variations of the gain in said second code sequence, when said speech decision value indicates the non-speech segment.

12. The code converting apparatus according to claim 8, further comprising;

a speech/non-speech discriminating circuit for outputting a speech decision value, discriminating the speech segment/non-speech segment, based on said first linear prediction coefficient;

said gain encoding circuit finding said evaluation function by taking a weighted average value of said first and second square errors by weighting coefficients; and

setting said weighting coefficients to respective preset values, based on said speech decision value, depending on the speech segment and the non-speech segment, to calculate said evaluation function.

13. A computer program product in a medium used by a computer, that composes a code converting apparatus for converting a first code sequence, into a second code sequence conforming to a second system, comprising a program to cause said computer to execute:

(a) the processing of decoding the gain information from said first code sequence;

(b) the processing of correcting the gain decoded (decoded gain); and

(c) the processing of finding the gain information in said code sequence based on the decoded gain corrected (corrected decoded gain), said decoded gain and the gain read out from the codebook in said second system.

14. The computer program product according to claim 13, further comprising a program to cause said computer to execute the processing of calculating a first square error from the corrected decoded gain and from the gain read out from said gain codebook, calculating a second square error from said decoded gain and from the gain read out from said gain codebook, and selecting a gain minimizing an evaluation function which is based on said first square error and said second square error from said gain codebook to find the gain information in said second code sequence.

15. The computer program product according to claim 13, wherein said corrected decoded gain is based on a long-term average value of said decoded gain.

16. The computer program product according to claim 14, wherein said evaluation function is composed of said first square error, said second square error and weighting coefficients.

17. The computer program product according to claim 13, further comprising a program to cause the computer to execute:

the processing of outputting a speech decision value, discriminating the speech segment/non-speech segment, based on said first linear prediction coefficient; and

the processing of finding the gain information in said second code sequence, using an evaluation function which will decrease temporal variations of the gain in said second code sequence, when said speech decision value indicates the non-speech segment.

18. The computer program product according to claim 14, further comprising a program to cause the computer to execute:

the processing of outputting a speech decision value, discriminating the speech segment/non-speech segment, based on said first linear prediction coefficient; and

the processing of finding said evaluation function by taking a weighted average value of said first and second square errors by weighting coefficients, and setting said weighting coefficients to respective preset values, based on said speech decision value, depending on the speech segment and the non-speech segment, to calculate said evaluation function.

19. A recording medium that may be read out by a computer, said recording medium having recorded thereon said program as defined in claim 13.