Code-Excited Linear Prediction

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Basic structure of the CELP decoder

Code (-book) Excited Linear Prediction ( CELP ) is a hybrid method for audio data compression that combines the advantages of signal shape coding using vector quantization and the parametric method. The result is good voice quality , whichroughly corresponds tothat of pulse code modulation ,even at low data transmission rates of 4 to 16 k bit / s. The procedure is described in Part 3 of the MPEG-4 standard ( ISO / IEC 14496-3).

Most hybrid coding methods are based on coding using linear predictive coding (LPC), the remaining signal of which is compressed by "looking up" ( quantization ) in a table - usually 40 samples (5 ms signal) are converted into 10 bits (Table with 1024 entries). The table search means that compression is more time-consuming and resource-intensive than decompression.

The greatest disadvantage of CELP, a signal delay of around 50 ms, was reduced to less than 2 ms in the 1992 standardized G.728 " low-delay CELP codec ". The Algebraic Code Excited Linear Prediction (ACELP) is a patented further development of the process .

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