Algebraic code-excited linear prediction speech coding method

Details Algebraic code-excited linear prediction speech coding method Algebraic code-excited linear prediction speech coding method

1996-08-26

1998-02-10

MacDonald, Allen R.

395 228, 395 209, 395 21, 395 229, G10L 700

Patent

active

057178259

DESCRIPTION:

BRIEF SUMMARY
The present invention relates to a method of digital coding, in particular of speech signals.


BACKGROUND OF THE INVENTION

One of the best current methods of compressing signals in order to reduce the bit rate while still maintaining good quality is the technique of code-excited linear prediction CELP. This type of coding is widely used, essentially in terrestrial or satellite transmission systems, or in storage applications. However, the first generation of CELP coders which used stochastic codebooks was very complex to implement and required large memory capacities. A second generation of CELP coders then appeared: algebraic codebook CELP coders. They are less complex to implement and require less memory, but the savings are still inadequate.
The technology of algebraic codebook CELP coding has been further improved by the introduction of ACELP (Algebraic Code Excited Linear Prediction) coders which use an algebraic codebook associated with a focused search with adaptive thresholds allowing the complexity of the calculation to be adjusted. However, the amount of random-access memory required is still substantial.
The CELP coders belong to the family of analysis-by-synthesis coders, in which the synthesis model is used at the coder. The signals to be coded may be sampled at the telephone frequency (Fe=8 kHz) or a higher frequency, for example 16 kHz for wideband coding (passband from 0 to 7 kHz). Depending on the application and the quality desired, the compression factor varies from 1 to 16: CELP coders operate at bit rates of from 2 to 16 kbits/s in the telephone band, and at bit rates of from 16 to 32 kbits/s in wideband.
In a digital coder of CELP type, the speech signal is sampled and converted into a string of frames of L samples. Each frame is synthesized by filtering a waveform extracted from a codebook (also referred to as a dictionary), and multiplied by a gain through two time-varying filters. The excitation codebook is a set of K codes or waveforms of L samples. The waveforms are numbered by an integer index k, k ranging from 0 to K-1, K being the size of the codebook. The first filter is the long-term prediction filter. An "LTP" (Long Term Prediction) analysis allows evaluation of the parameters of this long-term predictor and thus exploitation of the periodicity of the voiced sounds (for example: the vowels); this long-term correlation is due to the vibration of the vocal chords. The second filter is the short-term prediction filter. The methods of analysis by linear prediction "LPC" (Linear Prediction Coding) make it possible to obtain these short-term prediction parameters representative of the transfer function of the vocal tract and characteristic of the spectrum of the signal. The method used to determine the innovation sequence is the method of analysis by synthesis: at the coder, all the innovation sequences of the excitation codebook are filtered by the two filters, LTP and LPC, and the waveform selected is that producing the synthetic signal closest to the original speech signal, according to a perceptual weighting criterion.
In a CELP coder, the excitation of the synthesis model therefore consists of waveforms extracted from a codebook. Depending on the type of this codebook, two kinds of CELP coders are distinguished. The codebooks of the first CELP coders consisted of stochastic waveforms. These codebooks are obtained either by learning or by random generation. Their major drawback is their lack of structure which makes it necessary to store them and gives rise to a high complexity of implementation. The excitation codebook of the first CELP coder was a stochastic dictionary, made up of a set of 1024 waveforms of 40 Gaussian samples. This CELP coder did not operate in real time on the most powerful computers of that era. Other stochastic dictionaries allowing a reduction in the necessary memory and computation time have been introduced; however, both the complexity and the memory capacity required remained substantial.
To remedy this drawback, another category of codebooks has

REFERENCES:
patent: 4868867 (1989-09-01), Davidson et al.
patent: 4899385 (1990-02-01), Ketchum et al.
patent: 4910781 (1990-03-01), Ketchum et al.
patent: 4945565 (1990-07-01), Ozawa et al.
patent: 4945567 (1990-07-01), Ozawa et al.
patent: 5195137 (1993-03-01), Swaminathan
patent: 5230036 (1993-07-01), Akamine et al.
patent: 5265167 (1993-11-01), Akamine et al.
patent: 5444816 (1995-08-01), Adoul et al.
patent: 5495555 (1996-02-01), Swaminathan
patent: 5583963 (1996-12-01), Lozach
Laflamme et al, "16 KBPS Wideband Speech Coding Technique Based on Algebraic Celp", ICASSP 1991: acoustics, Speech and Signal Processing, pp. 13-16, Jul. 1991.
Lamblin et al, "Fast Celp Coding Based on the Barnes-Wall Lattice in 16 Dimensions", ICASSP 1989: Acoustics, Speech and Signal Processing, pp. 61-64, Feb. 1989.
Menez et al, "A 2 ms-Delay adaptive Code Excited Predictive Coder", ICASSP 1990, Acoustics, Speech and Signal Processing Conference, pp. 457-460, Feb. 1990.
Laflamme et al, "On Reducing Computational Complexity of Codebook Search in CELP Coder Through the Use of Algebraic Codes", ICASSP 1990: Acoustics, Speech and Signal Procecssing, pp. 177-180, Feb. 1990.
U.S. Ser. No. 296,764, Ketchum et al., filed Dec. 1988.
U.S. Ser. No. 497,479, Swaminathan, filed Aug. 1992.
U.S. Ser. No. 379,296, Chen, filed Apr. 1991.
Steger, "On the Use of a Constant Autocorrelation Codebook for CELP Coding", Signal Processing VI, Proceeding of EUSIPCO 92, vol. 1, Aug. 1992, pp. 467-470, Aug. 1992.
Delprat et al, "A 6 KBPS Regular Pulse Celp Coder for Mobile Radio Communications", Advances in Speech Coding, Jan. 1991, pp. 179-188, Jan. 1991.
Gersho, "Advances in Speech and Audio Compression", Proceedings of the IEEE, vol. 82, Jun. 1994, pp. 900-918, Jun. 1994.

Affiliated with

Also associated with

Rating

Algebraic code-excited linear prediction speech coding method does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Algebraic code-excited linear prediction speech coding method, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Algebraic code-excited linear prediction speech coding method will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-2084951