LPC vector quantization apparatus
First Claim
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1. An LPC parameter vector quantization apparatus comprising:
- a distortion calculator that calculates distortion between a plurality of codevectors successively read from an LSF codebook storing a plurality of LSF codevectors and a target quantization using a first distortion evaluation measure;
an LPC code pre-selector that preliminarily selects indices of codevectors that reduce the amount of distortion according to said first distortion evaluation measure, from said plurality of LSF codevectors, and that generates decoded LSF parameters corresponding to the respective preliminarily selected indices;
a first parameter convertor that converts said decoded LSF parameters to first distortion calculation parameters, respectively, with which distance of a spectrum can be calculated;
a second parameter convertor that converts an LSF parameter comprising said quantization target to a second distortion calculation parameter with which distance of a spectrum can be calculated; and
an LPC code final searcher that calculates distortion between said second distortion calculation parameter, obtained by converting said quantization target and supplied from said second parameter convertor, and said first distortion calculation parameters, obtained by converting said decoded LSF parameters and supplied from said first parameter convertor, using a second distortion evaluation measure that is different from said first distortion evaluation measure, and that outputs, as an LPC code, an index of an LSF codevector corresponding to said first distortion calculation parameter that minimizes the amount of distortion according to said second distortion evaluation measure.
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Abstract
The present invention carries out pre-selection on many LPC codevectors stored in an LSF codebook 101 using a weighted Euclidean distortion as a measure and carries out a full-code selection on the LPC codevectors left after the pre-selection using an amount of distortion in a spectral space as a measure. This makes it possible to improve the quantization performance of the LPC parameter vector quantizer and improve the quality of synthesized speech of the speech coder/decoder.
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Citations
22 Claims
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1. An LPC parameter vector quantization apparatus comprising:
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a distortion calculator that calculates distortion between a plurality of codevectors successively read from an LSF codebook storing a plurality of LSF codevectors and a target quantization using a first distortion evaluation measure; an LPC code pre-selector that preliminarily selects indices of codevectors that reduce the amount of distortion according to said first distortion evaluation measure, from said plurality of LSF codevectors, and that generates decoded LSF parameters corresponding to the respective preliminarily selected indices; a first parameter convertor that converts said decoded LSF parameters to first distortion calculation parameters, respectively, with which distance of a spectrum can be calculated; a second parameter convertor that converts an LSF parameter comprising said quantization target to a second distortion calculation parameter with which distance of a spectrum can be calculated; and an LPC code final searcher that calculates distortion between said second distortion calculation parameter, obtained by converting said quantization target and supplied from said second parameter convertor, and said first distortion calculation parameters, obtained by converting said decoded LSF parameters and supplied from said first parameter convertor, using a second distortion evaluation measure that is different from said first distortion evaluation measure, and that outputs, as an LPC code, an index of an LSF codevector corresponding to said first distortion calculation parameter that minimizes the amount of distortion according to said second distortion evaluation measure. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13)
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14. An LPC parameter vector quantization apparatus comprising:
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a Euclidean distortion calculator that calculates a Euclidean distortion between codevectors successively read from an LSF codebook storing a plurality of LSF codevectors and a quantization target; an LPC code pre-selector that preliminarily selects codevector indices that reduce said Euclidean distortion and that generates decoded LSF parameters corresponding to the respective preliminarily selected indices; a first LSF/LPC coefficient convertor that converts said decoded LSF parameters to the respective decoded LPC coefficients; a first LPC coefficient/LPC cepstrum convertor that converts said decoded LPC coefficients to the respective LPC cepstra; a second LSF/LPC coefficient converter that converts an LSF parameter comprising said quantization target to an LPC coefficient; a second LPC coefficient/LPC cepstrum convertor that converts said LPC coefficient, obtained by converting said quantization target, to an LPC cepstrum; an LPC code final searcher that calculates cepstrum distortion (CD) between LPC cepstra obtained by converting said quantization target and supplied from said first and second LPC coefficient/LPC cepstrum converters and the LPC cepstra obtained by converting said decoded LSF parameters, and that outputs, as an LPC code, the index of the LSF codevector corresponding to an LPC cepstrum that minimizes said cepstrum distortion. - View Dependent Claims (15)
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16. An LPC parameter vector quantization apparatus comprising:
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a Euclidean distortion calculator that calculates a Euclidean distortion between codevectors successively read from an LSF codebook storing a plurality LSF codevectors and a quantization target; an LPC code pre-searcher that preliminarily selects codevector indices that reduce said Euclidean distortion and that generates decoded LSF parameters corresponding to the respective preliminarily selected indices; an LSF/LPC coefficient convertor that converts said decoded LSF parameters to their respective decoded LPC coefficients; a first LPC coefficient/FFT power spectrum calculator that calculates FFT power spectra from said decoded LPC coefficients; an LSF/LPC coefficient convertor that converts an LSF parameter comprising said quantization target to an LPC coefficient; a second LPC coefficient/FFT power spectrum calculator that calculates an FFT power spectrum from said LPC coefficient obtained by converting said quantization target; and an LPC code final searcher that calculates spectrum distortion (SD) between FFT power spectra obtained by converting said quantization target and supplied from said first and second LPC coefflcient/FFT power spectrum calculators and the FFT power spectra obtained by converting said decoded LSF parameters, and that outputs, as an LPC code, the LSF codevector index corresponding to an FFT power spectrum that minimizes said spectrum distortion.
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17. An LSF parameter vector quantization apparatus having a two-stage split configuration that calculates a differential vector by differentiating a prestored average LSF parameter from an input LSF parameter, that calculates a predictive vector corresponding to said differential vector, that calculates a predictive residual vector by further differentiating said predictive vector from said differential vector, that vector- quantizes said predictive residual vector and outputs an LPC code, said quantization apparatus comprising:
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a first stage vector quantization section that vector-quantizes said predictive residual vector using a plurality of predictive residual vectors stored in a first stage codebook and using a weighted Euclidean distortion as a distortion evaluation measure; and a second stage vector quantization section that vector-quantizes a first stage VQ residual vector generated by said first stage vector quantization section using a plurality of first stage VQ residual vector lower frequency components stored in a second stage lower frequency codebook and first stage VQ residual vector higher frequency components stored in a second stage higher frequency codebook and using cepstrum distortion (CD) as a distortion evaluation measure. - View Dependent Claims (18, 19)
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20. An LSF parameter vector quantization apparatus having a two-stage split configuration that calculates a differential vector by differentiating a prestored average LSF parameter from an input LSF parameter, that calculates a predictive vector corresponding to said differential vector, that calculates a predictive residual vector by further differentiating said predictive vector from said differential vector, vector- quantizes said predictive residual vector and that outputs an LPC code, said quantization apparatus compnsing:
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a first stage vector quantization section that vector-quantizes said predictive residual vector using a plurality of predictive residual vectors stored in a first stage codebook and using a weighted Euclidean distortion as a distortion evaluation measure; and a second stage vector quantization section that vector-quantizes a first stage VQ residual vector generated by said first stage vector quantization section using the same number of entries of lower frequency scaling factors as predictive residual vectors stored in a lower frequency scaling factor codebook, the same number of entries of higher frequency scaling factors as predictive residual vectors stored in the first stage codebook stored in a higher frequency scaling factor codebook and higher frequency codevectors stored in the second stage higher frequency codebook and using cepstrum distortion (CD) as a distortion evaluation measure. - View Dependent Claims (21, 22)
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Specification