'''Code-excited linear prediction''' ('''CELP''') is a [[speech coding]] algorithm originally proposed by [[Manfred_RManfred R._Schroeder Schroeder|M. R. Schroeder]] and [[Bishnu S. Atal|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{{Citation needed|reason=No sources to back this claim up.|date=November 2016}}. 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.
Before exploring the complex encoding process of CELP we introduce the decoder here. Figure 1 describes a generic CELP decoder. The excitation is produced by summing the contributions from an adaptive (akaa.k.a. pitch) codebook and a stochastic (akaa.k.a. innovation or fixed) codebook:
