Topic
Code-excited linear prediction
About: Code-excited linear prediction is a research topic. Over the lifetime, 2025 publications have been published within this topic receiving 28633 citations. The topic is also known as: CELP.
Papers published on a yearly basis
Papers
More filters
TL;DR: In this article, an improved vector generation and search technique was described for a code-excited linear prediction (CELP) speech coder using a codebook of excitation code vectors.
Abstract: An improved excitation vector generation and search technique (FIG. 1) is described for a code-excited linear prediction (CELP) speech coder (100) using a codebook of excitation code vectors. A set of M basis vectors Vm (n) are used along with the excitation signal codewords (i) to generate the codebook of excitation vectors ui (n) according to a "vector sum" technique (120) of converting the selector codewords into a plurality of interim data signals, multiplying the set of M basis vectors by the interim data signals, and summing the resultant vectors to produce the set of 2M codebook vectors. The entire codebook of 2M possible excitation vectors is efficiently searched by using the vector sum generation technique with the M basis vectors--without ever having to generate and evaluate each of the 2M code vectors themselves. Furthermore, only M basis vectors need to be stored in memory (114), as opposed to all 2M code vectors.
123 citations
07 Apr 1986
TL;DR: The best quality and the lowest transmission rates were achieved by a residually excited subband coded vector quantization system coupled with a three-way classifier with design parameters: LPC order P=14; 32-band complete binary tree QMF filter bank implementation of SBC and VQ waveform encoding with dimension K=32 at an overall bitrate of 3,100 bps.
Abstract: Vector quantization (VQ), subband coding (SBC) and linear predictive coding (LPC) are three of the most effective data compression schemes used for medium-to-narrow band speech coding. In this study, we have attempted to improve the quality of encoded speech by using various combinations of these three coding methods. Waveform coders with rates 2400-9600 bits per second resulted in overall signal-to-distortion ratios of 6-12 dB. We have obtained somewhat lower values for segmented SNR's in the case of straight waveform encoding and higher values for the residually excited subband coded VQ quantizers as expected. However, informal listening tests yielded noticeable improvements over those of straight waveform VQ results. The best quality and the lowest transmission rates were achieved by a residually excited subband coded vector quantization system coupled with a three-way classifier with design parameters: LPC order P=14; 32-band complete binary tree QMF filter bank implementation of SBC and VQ waveform encoding with dimension K=32 at an overall bitrate of 3,100 bps.
120 citations
14 Apr 1991
TL;DR: An efficient procedure for searching such a large codebook deploying a focused search strategy, where less than 0.1% of the codebook is searched with performance very close to that of a full search is described.
Abstract: The application of algebraic code excited linear prediction (ACELP) coding to wideband speech is presented An algebraic codebook with a 20 bit address can be used without any storage requirements and, more importantly, with a very efficient search procedure which allows for real-time implementation The authors describe an efficient procedure for searching such a large codebook deploying a focused search strategy, where less than 01% of the codebook is searched with performance very close to that of a full search High-quality speech at a bit rate of 13 kbps was obtained >
114 citations
Patent•
25 Jun 1992
TL;DR: In this article, a low-bit-rate speech decoder is proposed, which operates in two modes depending on the received mode bit, pitch prefiltering and global post-filtering are employed for enhancement of the synthesized speech.
Abstract: Code excited linear prediction (CELP) is performed using two voiced and unvoiced sets of windows, each set is used both for linear prediction and pitch determination. The accompanying degradation in voice quality is comparable to the IS54 standard 8.0 Kbps voice coder employed in U.S. digital cellular systems. This is accomplished by using the same parametric model used in traditional CELP coders but determining, quantizing, encoding, and updating these parameters differently. The low bit rate speech decoder is like most CELP decoders except that it operates in two modes depending on the received mode bit. Both pitch prefiltering and global postfiltering are employed for enhancement of the synthesized speech. In addition, built-in error detection and error recovery schemes are used that help mitigate the effects of any uncorrectable transmission errors.
113 citations
TL;DR: A robust linear prediction (LP) algorithms is proposed that minimizes the sum of appropriately weighted residuals and takes into account the non-Gaussian nature of the excitations for voiced speech and gives a more efficient and less biased estimate for the prediction coefficients than conventional methods.
Abstract: A robust linear prediction (LP) algorithms is proposed that minimizes the sum of appropriately weighted residuals. The weight is a function of the prediction residual, and the cost function is selected to give more weight to the bulk of small residuals while deemphasizing the small portion of large residuals. In contrast, the conventional LP procedure weights all prediction residuals equally. The robust algorithm takes into account the non-Gaussian nature of the excitations for voiced speech and gives a more efficient (less variance) and less biased estimate for the prediction coefficients than conventional methods. The algorithm can be used in the front-end features extractor for a speech recognition system and as an analyzer for a speech coding system. Testing on synthetic vowel data demonstrates that the robust LP procedure is able to reduce the formant and bandwidth error rate by more than an order of magnitude compared to the conventional LP procedures and is relatively insensitive to the placement of the LPC (LP coding) analysis window and to the value of the pitch period, for a given section of speech signal. >
112 citations