Method for speech coding based on a code excited linear prediction (CELP) model
First Claim
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1. 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.
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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.
142 Citations
24 Claims
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1. A method for speech coding based on a code excited linear prediction (CELP) model comprising:
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(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. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12)
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13. A method for speech coding based on a code excited linear prediction (CELP) model comprising:
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(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.
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14. 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:
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(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.
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15. A method of encoding a speech signal comprising:
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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. - View Dependent Claims (16, 17, 18, 19, 20)
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21. A method for speech coding comprising:
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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. - View Dependent Claims (22, 23, 24)
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Specification