4-542: Algebraic code-excited linear prediction ( ACELP ) is a speech coding algorithm in which a limited set of pulses is distributed as excitation to a linear prediction filter. It is a linear predictive coding (LPC) algorithm that is based on the code-excited linear prediction (CELP) method and has an algebraic structure. ACELP was developed in 1989 by the researchers at the Université de Sherbrooke in Canada . The ACELP method
8-478: Is widely employed in current speech coding standards such as AMR , EFR , AMR-WB (G.722.2), VMR-WB , EVRC , EVRC-B , SMV , TETRA , PCS 1900, MPEG-4 CELP and ITU-T G-series standards G.729 , G.729.1 (first coding stage) and G.723.1 . The ACELP algorithm is also used in the proprietary ACELP.net codec. Audible Inc. use a modified version for their speaking books. It is also used in conference-calling software, speech compression tools and has become one of
12-479: The 3GPP formats. The ACELP patent expired in 2018 and is now royalty-free. The main advantage of ACELP is that the algebraic codebook it uses can be made very large (> 50 bits) without running into storage ( RAM / ROM ) or complexity ( CPU time) problems. The ACELP algorithm is based on that used in code-excited linear prediction (CELP), but ACELP codebooks have a specific algebraic structure imposed upon them. A 16-bit algebraic codebook shall be used in
16-440: The innovative codebook search, the aim of which is to find the best innovation and gain parameters. The innovation vector contains, at most, four non-zero pulses. In ACELP, a block of N speech samples is synthesized by filtering an appropriate innovation sequence from a codebook, scaled by a gain factor g c , through two time-varying filters. The long-term (pitch) synthesis filter is given by: The short-term synthesis filter
#566433