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'''Algebraic code-excited linear prediction''' ('''ACELP''') is a [[patent]]ed<ref>US Patent 5717825 Algebraic code-excited linear prediction speech coding method</ref> [[speech coding]] algorithm by [[ VoiceAge | VoiceAge Corporation]] in which a limited set of pulses is distributed as excitation to a [[Linear predictive coding|linear prediction]] filter.

The ACELP method is widely employed in current speech coding standards such as [[Adaptive Multi-Rate|AMR]], [[Enhanced Full Rate|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]].<ref>[http://web.archive.org/web/20071014224013/www.voiceage.com/image/ACELPMAP.jpg ACELP map], VoiceAge Corporation, Archive.org</ref><ref>[http://web.archive.org/web/20071014095716/www.voiceage.com/relatedstandards.php VoiceAge Corporation - related standards]</ref><ref name="archive-voiceage-technologies">{{cite web |author=VoiceAge Corporation |url=http://www.voiceage.com/technologies.php |title=Codec Technologies |date=2007-10-13 |accessdate=2009-09-20 |archiveurl=http://web.archive.org/web/20071013162836/http://www.voiceage.com/technologies.php |archivedate=2007-10-13}}</ref><ref name="voiceage-technologies">{{cite web |author=VoiceAge Corporation |publisher=VoiceAge Corporation |url=http://www.voiceage.com/technologies.php |title=Codec Technologies |date= |accessdate=2009-09-20| archiveurl= http://web.archive.org/web/20091018020920/http://www.voiceage.com/technologies.php| archivedate= 18 October 2009 <!--DASHBot-->| deadurl= no}}</ref> The ACELP algorithm is also used in the proprietary ACELP.net codec.<ref>{{cite web |url=http://www.voiceage.com/acelpnet.php |title=ACELP.net — Beyond the Standards |author=VoiceAge Corporation |accessdate=2010-01-03 |archiveurl=http://web.archive.org/web/20071014035312/http://www.voiceage.com/acelpnet.php |archivedate=2007-10-14}}</ref>

ACELP is a patented technology and registered trademark of [http://www.voiceage.com VoiceAge Corporation]<ref>[http://www.voiceage.com/trademarks.php Trademarks<!-- Bot generated title -->]</ref> in Canada and/or other countries and was developed in 1989 by the [[Université de Sherbrooke]] in [[Canada]].<ref>[http://www.usherbrooke.ca/recherche/fr/partenariats/pour-les-entreprises/transfert-de-technologie/exemples-de-transferts/technologie-de-compression-de-la-parole-acelpr/ Transfer of technology]</ref>

==Features==
The main advantage of ACELP is that the algebraic codebook it uses can be made very large (> 50 bits) without running into storage ([[RAM]]/[[Read-only memory|ROM]]) or complexity ([[CPU]] time) problems.

==Technology==
The ACELP algorithm is based on that used in [[code-excited linear prediction]], but ACELP codebooks have a specific algebraic structure imposed upon them.

A 16-bit algebraic codebook shall be used in 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:

:<math>\frac1{B(z)} = \frac1{ 1 - g_p z^{-T} }</math>

The short-term synthesis filter is given by: 
:<math>\frac1{A(z)} = \frac1{ 1 + \sum_{i=1}^P a_i z^{-i} }</math>

==References==
{{Reflist}}

{{Compression Methods}}

[[Category:Speech codecs]]

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