Analysis-by-synthesis speech coding method with truncation of th

Details Analysis-by-synthesis speech coding method with truncation of th Analysis-by-synthesis speech coding method with truncation of th

1997-10-22

1999-10-05

Hudspeth, David R.

Data processing: speech signal processing, linguistics, language

Speech signal processing

For storage or transmission

704219, G10L 302

Patent

active

059638982

DESCRIPTION:

BRIEF SUMMARY
BACKGROUND OF THE INVENTION

The present invention relates to analysis-by-synthesis speech coding.
The applicant company has particularly described such speech coders, which it has developed, in its European patent applications 0 195 487, 0 347 307 and 0 469 997.
In an analysis-by-synthesis speech coder, linear prediction of the speech signal is performed in order to obtain the coefficients of a short-term synthesis filter modelling the transfer function of the vocal tract. These coefficients are passed to the decoder, as well as parameters characterising an excitation to be applied to the short-term synthesis filter. In the majority of present-day coders, the longer-term correlations of the speech signal are also sought in order to characterise a long-term synthesis filter taking account of the pitch of the speech. When the signal is voiced, the excitation in fact includes a predictable component which can be represented by the past excitation, delayed by TP samples of the speech signal and subjected to a gain g.sub.p. The long-term synthesis filter, also reconstituted at the decoder, then has a transfer function of the form 1/B(z) with B(z)=1-g.sub.p.z.sup.-TP. The remaining, unpredictable part of the excitation is called stochastic excitation. In the coders known as CELP ("Code Excited Linear Prediction") coders, the stochastic excitation consists of a vector looked up in a predetermined dictionary. In the coders known as MPLPC ("Multi-Pulse Linear Prediction Coding") coders, the stochastic excitation includes a certain number of pulses the positions of which are sought by the coder. In general, CELP coders are preferred for low data transmission rates, but they are more complex to implement than MPLPC coders.
In order to determine the long-term prediction delay, a closed-loop analysis is frequently used, contributing directly to minimising the perceptually weighted difference between the speech signal and the synthetic signal. The drawback of this closed-loop analysis is that it is demanding in terms of the amount of calculation, since the selection of a delay implies the evaluation of a certain number of candidate delays, and each evaluation of a delay requires calculations of products of convolution between the delayed excitation and the impulse response of the perceptually weighted synthesis filter. The above drawback also exists for the search for the stochastic excitation, which is also a closed-loop process in which products of convolution with this impulse response are involved. The excitation varies more rapidly than the spectral parameters characteristic of the short-term synthesis filter. The excitation (predictable and stochastic) is typically determined once per 5 ms sub-frame, whereas the spectral parameters are determined once per 20 ms frame. The complexity and the frequency of the closed-loop search for the excitation make this stage the most critical one as far as the speed of the necessary calculations in a speech coder is concerned.
A main object of the invention is to propose a speech coding method of reduced complexity as far as the closed-loop analysis or analyses are concerned.


SUMMARY OF THE INVENTION

Hence, the invention proposes an analysis-by-synthesis method of coding a speech signal digitised into successive frames which are subdivided into sub-frames including a defined number of samples wherein a linear prediction analysis of the speech signal is performed for each frame in order to determine the coefficients of a short-term synthesis filter, and an open-loop analysis is performed for each frame in order to determine a degree of voicing of the frame, and at least one closed-loop analysis is performed for each sub-frame in order to determine an excitation sequence which, submitted to the short-term synthesis filter, produces a synthetic signal representative of the speech signal. Each closed-loop analysis uses the impulse response of a composite filter consisting of the short-term synthesis filter and of a perceptual weighting filter. During each closed-loop analysis, s

REFERENCES:
patent: 4802171 (1989-01-01), Rasky
patent: 4831624 (1989-05-01), McLaughlin et al.
patent: 4964169 (1990-10-01), Ono
patent: 5060269 (1991-10-01), Zinser
patent: 5097507 (1992-03-01), Zinser et al.
patent: 5142584 (1992-08-01), Ozawa
patent: 5253269 (1993-10-01), Gerson et al.
patent: 5265219 (1993-11-01), Gerson et al.
patent: 5293448 (1994-03-01), Honda
patent: 5473727 (1995-12-01), Nishiguchi et al.
patent: 5633980 (1997-05-01), Ozawa
patent: 5642465 (1997-06-01), Scott et al.
patent: 5644679 (1997-07-01), Scott et al.
patent: 5699477 (1997-12-01), McCree
patent: 5717825 (1998-02-01), Lablin
patent: 5732389 (1998-03-01), Kroon et al.
patent: 5751903 (1998-05-01), Swaminathan et al.
patent: 5765127 (1998-06-01), Nishiguchi et al.
patent: 5778334 (1998-07-01), Ozawa et al.
patent: 5787390 (1998-07-01), Quinquis et al.
patent: 5799271 (1998-08-01), Byun et al.
patent: 5828996 (1998-10-01), Iijima et al.
Database INSPEC, Institute of Elect. Engineers, Stevenage, GB, Inspec No. 4917063 A. Kataoka et al, "Implementation and performance of an 8-kbit/s conjugate structure speech coder", Abstract.
IEEE Trans, on Acoustics, Speech and Signal Processing, vol. 37, No. 3, Mar. 1989, pp. 317-327, S. Signhal et al, "Amplitude Optimization and Pitch Prediction in Multipulse Coders".
Xiongwei et al, "A New Excitation Model for LPC Vocoder at 2.4 Kb/s", ICASSP '92.
Goalic et al, "An Intrinsically Reliable and Fast Algorithm to Compute the Line Spectrum Pairs (LSP) in Low bit CELP Coding", ICASSP '95.
Nishiguchi et al, "Harmoni and Noise coding of LPC Residuals with Classified Vector Quantization", ICASSP '95.
Ramalingam et al, "Voiced-Speech Analysis Based on the Residual Interfering Signal Canceler (RISC) Algorithm", ICASSP '94.

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