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US 6,073,092 AGranted
Method for speech coding based on a code excited linear prediction (CELP) model
AssigneeTelogy Networks, Inc.
InventorSoon Y. Kwon
Life of this patent
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Abstract
The invention provides a method for speech coding using Code-Excited Linear Prediction (CELP) producing toll-quality speech at data rates between 4 and 16 Kbit/s. The invention uses a series of baseline, implied and adaptive codebooks, comprised of pulse and random codebooks, with associated gain vectors, to characterize the speech. Improved quantization and search techniques to achieve real-time operation, based on the codebooks and gains, are also provided.
Claims24
A method for speech coding based on a code excited linear prediction (CELP) model comprising:
- (a) dividing speech at a sending station into discrete speech samples;
- (b) digitizing the discrete speech samples;
- (c) forming a mixed excitation function by selecting a combination of two codevectors from two fixed codebooks, each having a plurality of codevectors, and selecting a combination of two codebook gain vectors from a plurality of codebook gain vectors;
- (d) selecting an adaptive codevector from an adaptive codebook, and selecting a pitch gain in combination with the mixed excitation function to represent the digitized speech;
- (e) encoding one of the two selected codevectors, both of the selected codebook gain vectors, the adaptive codevector and the pitch gain as a digital data stream;
- (f) sending the digital data stream from the sending station to a receiving station using transmission means;
- (g) decoding the digital data stream at the receiving station to reproduce the selected codevector, the two codebook gain vectors, the adaptive codevector, the pitch gain, and LPC filter parameters;
- (h) reproducing a digitized speech sample at the receiving station using the selected codevector, the two codebook gain vectors, adaptive codevector, the pitch gain, and the LPC filter parameters;
- (i) converting the digitized speech sample at the receiving station into an analog speech sample;
- and
- (j) combining a series of analog speech samples to reproduce the coded speech;
- and
- wherein encoding one of the two selected codevectors, both of the selected codebook gain vectors, the adaptive codevector and pitch gain as a digital data stream further comprises:
- adjusting the baseline codevector by the baseline gain and adjusting the implied codevector by the implied gain to form a mixed excitation function;
- using the mixed excitation function as an input to a pitch filter;
- using the output of the pitch filter as an input of a linear predictive coding synthesis filter;
- and
- subtracting the output from the linear predictive coding synthesis filter from the speech to form an input to a weighting filter.
15 more elements
A method for speech coding based on a code excited linear prediction (CELP) model comprising:
- (a) dividing speech at a sending station into discrete speech samples;
- (b) digitizing the discrete speech samples;
- (c) forming a mixed excitation function by selecting a combination of two codevectors from two fixed codebooks, each having a plurality of codevectors, and selecting a combination of two codebook gain vectors from a plurality of codebook gain vectors;
- (d) selecting an adaptive codevector from an adaptive codebook, and selecting a pitch gain in combination with the mixed excitation function to represent the digitized speech;
- (e) encoding one of the two selected codevectors, both of the selected codebook gain vectors, the adaptive codevector and the pitch gain as a digital data stream;
- (f) sending the digital data stream from the sending station to a receiving station using transmission means;
- (g) decoding the digital data stream at the receiving station to reproduce the selected codevector, the two codebook gain vectors, the adaptive codevector, the pitch gain, and LPC filter parameters;
- (h) reproducing a digitized speech sample at the receiving station using the selected codevector, the two codebook gain vectors, adaptive codevector, the pitch gain, and the LPC filter parameters;
- (i) converting the digitized speech sample at the receiving station into an analog speech sample;
- and
- (j) combining a series of analog speech samples to reproduce the coded speech wherein the two fixed codebooks further comprise:
- selecting the first of the combination of two codevectors from a baseline codebook with a plurality of baseline codevectors;
- and
- selecting the second of the combination of two codevectors from an implied codebook with a plurality of implied codevectors,
- wherein reproducing a digitized speech sample at the receiving station using the selected codevector, the two codebook gain vectors, adaptive codevector, the pitch gain, and the LPC filter parameters further comprises:
- adjusting the baseline codevector by the baseline gain and adjusting the implied codevector by the implied gain to form the mixed excitation function;
- using the mixed excitation function as an input to a pitch filter;
- using the output from the pitch filter as an input to an LPC filter;
- postfiltering the output of the LPC filter;
- and
- producing a digitized speech sample from the output from the LPC filter.
18 more elements
The method for speech coding based on a code excited linear prediction (CELP) model of claim 14 wherein post filtering the output of the LPC filter further comprises:
- (a) inverse filtering the output of the LPC filter with a zero filter to produce a residual signal;
- (b) operating on the residual signal outpt of the zero filter with a pitch post filter;
- (c) operating on the output of the pitch post filter with an all-pole filter;
- (d) operating on the output of the all-pole filter with a tilt compensation filter to generate post-filtered speech;
- (e) operating on the output of the tilt compensation filter with a gain control to match the energy of the postfilter input;
- and
- (f) operating on the output of the gain control with a highpass filter to produce perceptually enhanced speech.
4 more elements
A method of encoding a speech signal comprising:
- adjusting a baseline codevector by a baseline gain and adjusting an implied codevector by an implied gain to form a mixed excitation function;
- using the mixed excitation function as an input to a pitch filter;
- using the output of the pitch filter as an input of a linear predictive coding synthesis filter;
- and
- producing an encoded speech signal based on an output of the predictive coding synthesis filter.
2 more elements
A method for speech coding comprising:
- forming a mixed excitation function by selecting a first of a combination of codevectors from a baseline codebook having a plurality of baseline codevectors and by selecting a second of the combination of codevectors from an implied codebook having a plurality of implied codevectors;
- extracting mixed excitation function parameters from the baseline codebook and the implied codebook;
- and
- producing an encoded speech signal based on the mixed excitation function parameters.
1 more element
Dependencies are inferred from the claim text.