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.

A mixed sinusoidally excited linear prediction coder at 4 kb/s and below

Abstract: There is currently a great deal of interest in the development of speech coding algorithms capable of delivering toll quality at 4 kb/s and below. For synthesizing high quality speech, accurate representation of the voiced portions of speech is essential. For bit rates of 4 kb/s and below, conventional code excited linear prediction (CELP) may likely not provide the appropriate degree of periodicity. It has been shown that good quality low bit rate speech coding can be obtained by frequency domain techniques such as sinusoidal transform coding (STC), multi-band excitation (MBE), mixed excitation linear prediction (MELP), and multi-band LPC (MB-LPC) vocoders. In this paper, a speech coding algorithm based on an improved version of MB-LPC is presented. Main features of this algorithm include a multi-stage time/frequency pitch estimation and an improved mixed voicing representation. An efficient quantization scheme for the spectral amplitudes of the excitation, called formant weighted vector quantization, is also used. This improved coder, called mixed sinusoidally excited linear prediction (MSELP), yields an unquantized model with speech quality better than the 32 kb/s AD-PCM quality. Initial efforts towards a fully quantized 4 kb/s coder, although not yet successful in achieving the toll quality goal, have produced good output speech quality.

Apparatus and method for speech encoding based on short-term prediction valves

Abstract: Foe executing the code excitation linear prediction (CELP) coding, for example, α-parameters are taken out from the input speech signal by a linear prediction coding (LPC) analysis circuit 12. The α-parameters are then converted by an α-parameter to LSP converting circuit 13 into linear spectral pair (LSP) parameters and a vector of these line spectral pair (LSP) parameters is vector-quantized by a quantizer 14. The changeover switch 16 is controlled depending upon the pitch value detected by a pitch detection circuit 22 for selecting and using one of the codebook 15M for male voice and the codebook 15F for female voice for improving quantization characteristics without increasing the transmission bit rate.

Stable 1-norm error minimization based linear predictors for speech modeling

Abstract: In linear prediction of speech, the 1-norm error minimization criterion has been shown to provide a valid alternative to the 2-norm minimization criterion. However, unlike 2-norm minimization, 1-norm minimization does not guarantee the stability of the corresponding all-pole filter and can generate saturations when this is used to synthesize speech. In this paper, we introduce two new methods to obtain intrinsically stable predictors with the 1-norm minimization. The first method is based on constraining the roots of the predictor to lie within the unit circle by reducing the numerical range of the shift operator associated with the particular prediction problem considered. The second method uses the alternative Cauchy bound to impose a convex constraint on the predictor in the 1-norm error minimization. These methods are compared with two existing methods: the Burg method, based on the 1-norm minimization of the forward and backward prediction error, and the iteratively reweighted 2-norm minimization known to converge to the 1-norm minimization with an appropriate selection of weights. The evaluation gives proof of the effectiveness of the new methods, performing as well as unconstrained 1-norm based linear prediction for modeling and coding of speech.

High-quality digital speech at 4 kb/s

Abstract: A speech coder based on a single-pulse excitation code-excited linear predictive coding (SPE-CELP) model of linear-predictive coding (LPC) is proposed. An algorithm for determining the time instants of pitch periods within a short interval of periodic speech, which results in a time sequence of marker points that indicate the beginning of the pitch periods in the analyzed speech interval, is described. The LPC excitation is generated by a stochastic codebook for nonperiodic speech and by a single pulse per pitch period for periodic speech. The proper alignment of the excitation pulse is efficiently computed using dynamic programming. It is concluded that, at overall bit rates of around 3 kb/s, the coder produces significantly better speech quality than LPC10E, though the synthesized speech still sounds slightly buzzy for certain speakers. >

Perceptual enhancement of CELP speech coders

Abstract: The dominant technique in present day low bit rate speech coders is based on the use of voice production models in which vocal tract filters are excited by vectors chosen from fixed and adaptive codebooks. It has long been recognized that to improve the perceptual quality of such coders it is necessary to also allow for the psychoacoustic properties of the human ear. The weighting filter traditionally used for this purpose is sub-optimal as it doesn't explicitly evaluate auditory characteristics. In this paper we replace the weighting filter with an auditory model which enables the search for the optimum stochastic code vector in the psychoacoustic domain. The algorithm, which has been termed PERCELP (for perceptually enhanced random codebook excited linear prediction), produces speech that is of considerably better quality than obtained with a weighting filter. The computational overhead is low enough to warrant the use of this approach in new speech coders. >