Apparatus and method for speech coding

• US 20050197833A1
• Filed: 04/01/2005
• Published: 09/08/2005
• Est. Priority Date: 08/23/1999
• Status: Active Grant

• Current Assignee: III Holdings 12, LLC (Intellectual Ventures LLC)
• Original Assignee: Matsushita Electric Industrial Company Limited (Panasonic Holdings Corporation)
• Inventors: Morii, Toshiyuki, Yasunaga, Kazutoshi
• Granted Patent: US 7,383,176 B2
• Time in Patent Office: Days
• US Class Current: 704/223
• CPC Class Codes: G10L 19/083 the excitation function being an excitation gain G10L25/90 takes precedence
• CPC Class Codes: G10L 19/09 Long term prediction, i.e. removing periodical redundancies, e.g. by using adaptive codebook or pitch predictor
• CPC Class Codes: G10L 19/16 Vocoder architecture

Abstract

CELP-based speech encoder that performs encoding by decomposing one frame into a plurality of subframes, includes an LPC synthesizer that obtains synthesized speech by filtering an adaptive excitation vector and a stochastic excitation vector stored in an adaptive codebook and in an stochastic codebook using LPC coefficients obtained from input speech. A gain calculator calculates gains of the adaptive excitation vector and the stochastic excitation vector. A parameter coder performs vector quantization of the adaptive excitation vector and the stochastic excitation vector obtained by comparing distortions between the input speech and the synthesized speech. A pitch analyzer performs pitch analyses of a plurality of subframes in the frame respectively, before performing an adaptive codebook search for the first subframe, calculating correlation values and finding a value most approximate to the pitch period using the correlation values.

Claims

1. CELP-based speech encoder that performs encoding by decomposing one frame into a plurality of subframes, comprising:

an LPC synthesizer that obtains synthesized speech by filtering an adaptive excitation vector and a stochastic excitation vector stored in an adaptive codebook and in an stochastic codebook using LPC coefficients obtained from input speech;

a gain calculator that calculates gains of said adaptive excitation vector and said stochastic excitation vector;

a parameter coder that performs vector quantization of the adaptive excitation vector and the stochastic excitation vector obtained by comparing distortions between said input speech and said synthesized speech, and

a pitch analyzer that performs pitch analyses of a plurality of subframes in the frame respectively, before performing an adaptive codebook search for the first subframe, calculating correlation values and finding a value most approximate to the pitch period using said correlation values.

2. The speech encoder according to claim 1, further comprising a search range setter that determines a lag search range of a plurality of subframes based on the correlation value and the value most approximate to the pitch period obtained by said pitch analyzer.

3. The speech encoder according to claim 2, wherein said search range setter determines a provisional pitch that becomes the center of the search range using the correlation values and the values most approximate to the pitch period obtained by said pitch analyzer.

4. The speech encoder according to claim 3, wherein the search range setter sets a lag search section in a specified range around the provisional pitch.

5. The speech encoder according to claim 2, wherein the search range setter sets a lag search section by reducing a number of candidates for short pitch periods.

6. The speech encoder according to claim 2, wherein the search range setter performs a lag search within a set range during an adaptive codebook search.

7. A computer-readable recording media storing a speech encoding program, an adaptive codebook storing part used for synthesizing excitation vector signals and a stochastic codebook storing a plurality of stochastic excitation vectors, said speech encoding program comprising:

obtaining a synthesized speech by filtering an adaptive excitation vector and by filtering a stochastic excitation vector stored in said adaptive codebook and in said stochastic codebook using decoded LPC coefficients obtained from an input speech;

calculating gains of said adaptive excitation vector and said stochastic excitation vector;

performing vector quantization on the adaptive excitation vector and the stochastic excitation vector determined by comparing distortions between said input speech and said synthesized speech, wherein said vector quantization further comprising;

determining a quantization target vector based on comparing distortions between a plurality of quantization target vectors and prediction coefficients used for predictive coding; and

adjusting said prediction coefficients according to one or more states of one or more previous subframe.

8. A computer-readable recording medium storing a speech encoding program, an adaptive codebook storing part used for synthesizing an excitation vector signal and a stochastic codebook storing a plurality of stochastic excitation vectors, said speech coding program comprising:

obtaining a synthesized speech by filtering an adaptive excitation vector and a stochastic excitation vector stored in said adaptive codebook and said in stochastic codebook using decoded LPC coefficients obtained from an input speech;

calculating gains of said adaptive excitation vector and said stochastic excitation vector;

performing vector quantization on the adaptive excitation vector and the stochastic excitation vector determined by comparing distortions between said input speech and said synthesized speech; and

calculating correlation values by performing pitch analyses of a plurality of subframes in the processing frame before performing an adaptive codebook search of the first subframe and calculating a value most approximate to the pitch period using said correlation values.