Vector quantinizer with distance measure calculated by using correlations

• US 5,761,632 A
• Filed: 05/16/1997
• Issued: 06/02/1998
• Est. Priority Date: 06/30/1993
• Status: Expired due to Fees

• Current Assignee: NEC Corporation
• Original Assignee: NEC Corporation
• Inventors: Serizawa, Masahiro
• Primary Examiner(s): MacDonald, Allen R.
• Assistant Examiner(s): Opsasnick, Michael N.
• Application Number:
  US08/857,653
• Time in Patent Office: 382 Days
• Field of Search: 704/216-222
• US Class Current: 704/218
• CPC Class Codes: G10L 19/038 Vector quantisation, e.g. TwinVQ audio
• CPC Class Codes: G10L 19/04 using predictive techniques

Abstract

A vector quantizer for a speech coder for coding speech signals at low bit rates. The vector quantizer includes an auto-correlation calculation circuit for calculating an impulse response of a weighting function for each sub-interval of an input signal vector. The vector quantizer also includes a weighted cross-correlation calculation circuit for calculating a weighted cross-correlation of the weighted input signal vector and the weighted codevector having a code length equal to that of the input signal vector. The vector quantizer further includes a weighted auto-correlation calculation circuit for calculating an auto-correlation of the weighted codevectors, by using respective auto-correlations of the impulse responses, the codevectors and the cross-correlations. A distance between the input signal vector and the codevector is calculated by using the cross-correlations of the weighted input signal vector and the weighted codevectors, and the auto-correlation of the weighted codevector, and an index of a codevector corresponding to the minimum distance is obtained by an inspection circuit.

Claims

1. A speech coder for coding speech signals, said speech coder including a vector quantizer, said vector quantizer comprising:

a plurality of auto-correlation calculation means each of which calculates an auto-correlation of an impulse response signal of a weighting function for a corresponding sub-interval of a plurality of sub-intervals of an input signal vector which corresponds to the input speech signal;

a signal codebook means for storing a plurality of codevectors produced in advance, each of said codevectors having a length equal to a code length of said input signal vector;

a plurality of auto-correlation codebook means for respectively storing a corresponding one of the plurality of auto-correlations calculated by a corresponding one of said plurality of auto-correlation calculation means;

a first auto-correlation calculation circuit for calculating an auto-correlation of a first impulse response signal, said first impulse response signal corresponding to a weighting function for a first time interval of an input signal vector which corresponds to the input speech signal;

a second auto-correlation calculation circuit for calculating an auto-correlation of a second impulse response signal, said second impulse response signal corresponding to said weighting function for a second time interval of said input signal vector, wherein said second time interval has a same time length as said first time interval and wherein said second time interval starts immediately after said first time interval ends;

a signal codebook for storing a plurality of codevectors, each of said codevectors having a length equal to a code length of said input signal vector;

a first auto-correlation codebook for storing the auto-correlation of the first impulse response signal as calculated by said first auto-correlation calculation circuit;

a second auto-correlation codebook for storing the auto-correlation of the second impulse response signal as calculated by said second auto-correlation calculation circuit;

a cross-correlation codebook for storing a cross-correlation of the first and second sub-intervals for each of the codevectors;

a weighted cross-correlation calculation circuit for calculating a weighted cross-correlation of the input signal vector and each of the codevectors, with both the input signal vector and said each codevector being weighted by the weighting function, the weighted cross-correlation being performed for each codevector with respect to the input signal vector, the auto-correlations of the first and second impulse response signals, and the cross-correlation for said each codevector that is stored in the cross-correlation codebook;

a weighted auto-correlation calculation circuit for calculating a weighted auto-correlation for said each codevector,

a cross-correlation codebook means for storing a plurality of cross-correlations of the respective sub-intervals for each of the codevectors;

a weighted cross-correlation calculation means for calculating a weighted cross-correlation of the input signal vector and each of the codevectors by weighting the input signal vector and said each codevector by the weighting function corresponding to each of the sub-intervals, and calculating the weighted cross-correlation by using the input signal vector, the plurality of codevectors and the plurality of impulse response signals;

a weighted auto-correlation calculation means for calculating an auto-correlation of each of the weighted codevectors, as a weighted auto-correlation, by using the auto-correlations of the plurality of impulse response signals, the plurality of codevectors, and the cross-correlations;

a distance calculation means for calculating a corresponding distance between the input signal vector and each of the codevectors, by using the cross-correlations of the weighted input signal vector and weighted codevectors, and the auto-correlation of the weighted codevectors; and

a distance inspection means for supplying an index of one of the codevectors corresponding to a minimum distance of the distances calculated by the distance calculation means,

wherein the one of the codevectors is used to quantize the input speech vector.

2. A speech coder for coding speech signals said speech coder including a vector quantizer, said vector quantizer comprising:

a plurality of auto-correlation calculation means each of which calculates an auto-correlation of an impulse response signal of a weighting function for a corresponding sub-interval of a plurality of sub-intervals of an input signal vector which corresponds to the input speech signal;

a signal codebook means for storing a plurality of codevectors produced in advance, each of said codevectors having a length equal to a code length of said input signal vector;

a plurality of auto-correlation codebook means for respectively storing a corresponding one of the plurality of auto-correlations calculated by a corresponding one of said plurality of auto-correlation calculation means;

a weighted cross-correlation calculation means for calculating a weighted cross-correlation of the input signal vector and each of the codevectors by weighting the input signal vector and said each codevector by the weighting function corresponding to each of the sub-intervals, the weighted cross-correlation being calculated by using the input signal vector, the plurality of codevectors and the plurality of impulse response signals;

a weighted auto-correlation calculation means for calculating an auto-correlation of each of the weighted codevectors, as a weighted auto-correlation, by using the auto-correlations of the plurality of impulse response signals and the plurality of codevectors;

a distance calculation means for calculating a corresponding distance between the input signal vector and each of the codevectors, by using the cross-correlations of the weighted input signal vector and weighted codevectors, and the auto-correlation of the weighted codevectors; and

a distance inspection means for supplying an index of one of the codevectors corresponding to a minimum distance of the distances calculated by the distance calculation means,

wherein the one of the codevectors is used to quantize the input speech signal.

3. A speech coder for coding speech signals, said speech coder including a vector quantizer, said vector quantizer comprising:

the weighted auto-correlation for said each codevector being weighted by the weighting function, the weighted auto-correlations being calculated using the auto-correlations of the first and second impulse response signals respectively retrieved from the first and second auto-correlation codebooks, together with the cross-correlations retrieved from the cross-correlation codebook;

a distance calculating circuit for calculating a distance for said each codevector with respect to the input signal vector, the corresponding distance being calculated by using the weighted cross-correlations of said codevector and the weighted auto-correlations of said each codevector; and

a distance inspection circuit for supplying an index of a particular one of the codevectors which has a minimum distance among the distances calculated by the distance calculating circuit,

wherein the particular one of the codevectors is used to quantizer the input speech signal.

4. A vector quantizer according to claim 3, wherein the distance inspection circuit outputs an output command flag to each of the signal codebook, the first auto-correlation codebook, the second auto-correlation codebook, and the cross-correlation codebook,

wherein the output command flag is used by the signal codebook to output one of the codevectors stored therein together with a first index designation, with one of the codevectors being output for every receipt of the output command flag, wherein an index number for the signal codebook is incremented by one for every receipt of the output command flag;

wherein the output command flag is used by the first and second auto-correlation codebooks to respectively output the auto-correlation of one of the first impulse response signal and the second impulse response signal that are stored therein together with a second index designation, wherein an index number for the respective first and second auto-correlation codebooks is incremented by one for every receipt of the output command flag, and

wherein the output command flag is used by the cross-correlation codebook to output the cross-correlations stored therein together with a third index designation, wherein an index number for the cross-correlation codebook is incremented by one for every receipt of the output command flag.

5. A vector quantizer according to claim 4, wherein the first, second and third index designation are identical, such that information related to a particular one of the codevectors is output substantially simultaneously from the signal codebook, the first auto-correlation codebook, the second auto-correlation codebook, and the cross-correlation codebook.