Method of encoding and decoding speech using modified logarithmic transformation with offset of line spectral frequency
First Claim
1. A speech encoding method of encoding speech parameters representing the spectral envelope of an input speech signal comprising the steps of:
- obtaining an autocorrelation coefficient from the input speech signal;
obtaining first LSF (line spectral frequency) parameters represented by F(k) (k=1, 2, . . . , N;
N is the order of the LSF parameters) on the basis of the autocorrelation coefficient;
obtaining second LSF parameters f(k) by performing on the first LSF parameters a transformation defined by
space="preserve" listing-type="equation">f(k)=log C(1+A×
F(k))(A, C=positive constant);
quantizing the second LSF parameters to obtain third quantized LSF parameters fq(k) and first codes representing the third LSF parameters; and
obtaining fourth LSF parameters Fq(k) by performing on the third LSF parameters an inverse transformation defined by
space="preserve" listing-type="equation">Fq(k)=(C.sup.fq(k) -1)/A.
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Abstract
On the basis of an autocorrelation coefficient calculated by an autocorrelation coefficient computation section from an input speech signal, an LSF computation section computes LSF parameters F(k) (k=1, 2, . . . , N). A modified logarithmic transformation section performs on the LSF parameters a logarithmic transformation with offset defined by f(k)=logC (1+A×F(k)) to obtain modified logarithmic LSF parameters f(k). The resulting modified logarithmic LSF parameters are quantized by a quantization section to provide quantized LSF parameters fq(k). Codes representing the quantized LSF parameters fq(k) are outputted. An inverse transformation defined by Fq(k)=(Cfq(k) -1)/A is performed on the LSF parameters fq(k) to output LSF parameters Fq(k) on the general frequency scale.
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Citations
16 Claims
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1. A speech encoding method of encoding speech parameters representing the spectral envelope of an input speech signal comprising the steps of:
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obtaining an autocorrelation coefficient from the input speech signal; obtaining first LSF (line spectral frequency) parameters represented by F(k) (k=1, 2, . . . , N;
N is the order of the LSF parameters) on the basis of the autocorrelation coefficient;obtaining second LSF parameters f(k) by performing on the first LSF parameters a transformation defined by
space="preserve" listing-type="equation">f(k)=log C(1+A×
F(k))(A, C=positive constant); quantizing the second LSF parameters to obtain third quantized LSF parameters fq(k) and first codes representing the third LSF parameters; and obtaining fourth LSF parameters Fq(k) by performing on the third LSF parameters an inverse transformation defined by
space="preserve" listing-type="equation">Fq(k)=(C.sup.fq(k) -1)/A. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 12, 13)
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9. A speech encoding method comprising the steps of:
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obtaining autocorrelation coefficients for an input speech signal; obtaining first LSF parameters represented by F(k) (k=1, 2, . . . , N) on the basis of the autocorrelation coefficients; obtaining second LSF parameters f(k) by performing on the first LSF parameters a transformation defined by
space="preserve" listing-type="equation">f(k)=log C(1+A×
F(k))(A, C=positive constant); obtaining weights for the second LSF parameters on the basis of their distance to adjacent second LSF parameters; quantizing the second LSF parameters using the weights to obtain third LSF parameters represented by fq(k) and first codes representing the third LSF parameters; and obtaining fourth LSF parameters represented by Fq(k) by performing an inverse transformation defined by
space="preserve" listing-type="equation">Fq(k)=(C.sup.fq(k) -1)/A. - View Dependent Claims (10, 11)
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14. A speech encoding method of encoding speech parameters representing the spectral envelope of an input speech signal comprising the steps of:
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obtaining autocorrelation coefficients from the input speech signal; obtaining first LSF (line spectral frequency) parameters on the basis of the autocorrelation coefficients; obtaining second LSF parameters f(k) by performing on the first LSF parameters a modified logarithmic transformation with offset; quantizing the second LSF parameters to obtain third quantized LSF parameters and first codes representing the third LSF parameters; and obtaining fourth LSF parameters by performing on the third LSF parameters an inverse transformation against the modified logarithmic transformation. - View Dependent Claims (15, 16)
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Specification