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.

Direct linear conversion of LSP parameters for perceptual control in speech and audio coding

Abstract: We have devised a direct and simple scheme for linear conversion of line spectrum pairs (LSP) with low computational complexity aiming at weighting or inverse weighting spectral envelopes for noise control in speech and audio coders. Using optimally prepared coefficients, we can perform the conversion directly in the LSP domain, which ensures low computational costs and also simplifies the check or the modification of unstable parameters. We show that this method performs the same as the weighting in the linear prediction coding domain but with lower complexity in a low-bit-rate situation. The devised method is therefore expected to be useful for lowbit-rate speech and audio coders for mobile communications.

Methods and systems for celp-based speech coding with fine grain scalability

Abstract: Methods and systems for providing a CELP-based speech coding with fine grain scalability include a parameter encoder that generates a basic bit-stream from LPC coefficients for a frame, pitch-related information for all the sub-frames obtained by searching an adaptive codebook, and first pulse-related information for even sub-frames obtained by searching an fixed codebook. The parameter encoder also generates enhancement bits, which are preceded by the basic bit-stream, from second pulse-related information for odd sub-frames. The quality of synthesized speech is improved on a basis of one additional odd sub-frame pulse, as more of the second pulse-related information in the enhancement bits is received by a decoder.

Efficient methods for high quality low bit rate wideband speech coding

Abstract: This paper describes efficient encoding and decoding methods for achieving high quality wideband speech at low rates. CELP-based technologies have been successful in achieving high quality speech at low bit rates, however, new efficient techniques are needed to maintain high speech quality when the model is applied to wideband signals. This article discusses some techniques that improve the performance of the CELP model including efficient perceptual weighting and pitch codebook, and decoding techniques such as gain smoothing, periodicity enhancement, and high frequency generation. These techniques have been incorporated in the AMR-WB (adaptive multi-rate wideband) codec selected by 3GPP and ITU-T, where high quality wideband speech can be maintained at bit rates around 13 kbit/s.

Reduced real-time processing in stochastic celp encoding

Abstract: Methods are presented for reducing the processing required for CELP speech encoders which have multiple fixed stochastic codebook subframes corresponding to a single adaptive codebook subframe. The search for the optimum excitation vector in the fixed stochastic codebook requires calculating terms involving correlation of the target speech sample and the fixed stochastic codebook excitation vector as well as energy terms involving only the fixed stochastic codebook excitation vector, and for this class of CELP encoders it is possible to simplify the calculations to reduce their complexity and to make advantageous use of an adaptive energy lookup table. In addition, linear interpolation may be employed to estimate values for the adaptive energy lookup table and further reduce the computational burden.

An embedded scheme for regular pulse excited (RPE) linear predictive coding

Abstract: The feasibility and performance of an embedded RPE (ERPE) scheme based on multistage coding is investigated. The coding efficiency of second and subsequent stages depends on the spectral envelope difference between the original speech and the error signal at each stage whereas re-use of LPC parameters derived from the original speech depends on the corresponding LPC spectral difference. Suitable measures of spectral difference are defined and simulation shows that both decrease with the perceptual weighting factor. The ERPE system requires little extra coding complexity and can be simplified further by using a partial phase adaptation procedure with marginal loss of SNR performance. The simulated ERPE system shows graceful reduction of reconstructed speech quality for bit rates from 14.8 to 6.4 kb/s in 4.2 kb/s steps.