Code-excited linear prediction

Code-excited linear prediction (CELP) is a speech coding algorithm originally proposed by M. R. Schroeder and B. S. Atal in 1985. At the time, it provided significantly better quality than existing low bit-rate algorithms, such as residual-excited linear prediction and linear predictive coding vocoders (e.g., FS-1015). Along with its variants, such as algebraic CELP, relaxed CELP, low-delay CELP and vector sum excited linear prediction, it is currently the most widely used speech coding algorithm. It is also used in MPEG-4 Audio speech coding. CELP is commonly used as a generic term for a class of algorithms and not for a particular codec.

Introduction

The CELP algorithm is based on four main ideas:

Using the source-filter model of speech production through linear prediction (LP) (see the textbook "speech coding algorithm");

Using an adaptive and a fixed codebook as the input (excitation) of the LP model;

Performing a search in closed-loop in a “perceptually weighted domain”.

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