ACELP
Encyclopedia
Algebraic code-excited linear prediction (ACELP) is a patent
Patent
A patent is a form of intellectual property. It consists of a set of exclusive rights granted by a sovereign state to an inventor or their assignee for a limited period of time in exchange for the public disclosure of an invention....

ed speech coding
Speech coding
Speech coding is the application of data compression of digital audio signals containing speech. Speech coding uses speech-specific parameter estimation using audio signal processing techniques to model the speech signal, combined with generic data compression algorithms to represent the resulting...

 algorithm by VoiceAge Corporation in which a limited set of pulses is distributed as excitation to linear prediction
Linear predictive coding
Linear predictive coding is a tool used mostly in audio signal processing and speech processing for representing the spectral envelope of a digital signal of speech in compressed form, using the information of a linear predictive model...

 filter.

The ACELP method is widely employed in current speech coding standards such as AMR
Adaptive Multi-Rate
The Adaptive Multi-Rate audio codec is a patented audio data compression scheme optimized for speech coding. AMR was adopted as the standard speech codec by 3GPP in October 1999 and is now widely used in GSM and UMTS...

, EFR
Enhanced Full Rate
Enhanced Full Rate or EFR or GSM-EFR or GSM 06.60 is a speech coding standard that was developed in order to improve the quite poor quality of GSM-Full Rate codec. Working at 12.2 kbit/s the EFR provides wirelike quality in any noise free and background noise conditions...

, AMR-WB
AMR-WB
Adaptive Multi-Rate Wideband is a patented speech coding standard developed based on Adaptive Multi-Rate encoding, using similar methodology as Algebraic Code Excited Linear Prediction...

 (G.722.2), VMR-WB
VMR-WB
Variable-Rate Multimode Wideband is a source-controlled variable-rate multimode codec designed for robust encoding/decoding of wideband/narrowband speech. The operation of VMR-WB is controlled by speech signal characteristics and by traffic condition of the network...

, EVRC
EVRC
Enhanced Variable Rate CODEC is a speech codec used in CDMA networks. It was developed in 1995 to replace the QCELP vocoder which used more bandwidth on the carrier's network, thus EVRC's primary goal was to offer the mobile carriers more capacity on their networks while not increasing the amount...

, EVRC-B
EVRC-B
Enhanced Variable Rate Codec B is a speech codec used by CDMA networks. EVRC-B is an enhancement to EVRC and compresses each 20 milliseconds of 8000 Hz, 16-bit sampled speechinput into output frames of one of the four different sizes:...

, SMV
SMV
Selectable Mode Vocoder is variable bitrate speech coding standard used in CDMA2000 networks. SMV provides multiple modes of operation that are selected based on input speech characteristics....

, TETRA
Tetra
thumb|right|250px|Pristella tetra — [[Pristella maxillaris]].thumb|right|250px|Golden Pristella tetra, a [[morph |morph]] of [[Pristella maxillaris]].thumb|right|250px|[[Silvertip tetra]] — Hasemania nana....

, PCS 1900, MPEG-4
MPEG-4
MPEG-4 is a method of defining compression of audio and visual digital data. It was introduced in late 1998 and designated a standard for a group of audio and video coding formats and related technology agreed upon by the ISO/IEC Moving Picture Experts Group under the formal standard ISO/IEC...

 CELP and ITU-T
ITU-T
The ITU Telecommunication Standardization Sector is one of the three sectors of the International Telecommunication Union ; it coordinates standards for telecommunications....

 G-series standards G.729
G.729
G.729 is an audio data compression algorithm for voice that compresses digital voice in packets of 10 milliseconds duration. It is officially described as Coding of speech at 8 kbit/s using conjugate-structure algebraic code-excited linear prediction .Because of its low bandwidth requirements,...

, G.729.1
G.729.1
G.729.1 is an 8-32 kbit/s embedded speech and audio codec providing bitstream interoperability with G.729, G.729 Annex A and G.729 Annex B. Its official name is G.729-based embedded variable bit rate codec: An 8-32 kbit/s scalable wideband coder bitstream interoperable with G.729.This codec has...

 (first coding stage) and G.723.1
G.723.1
G.723.1 is an audio codec for voice that compresses voice audio in 30 ms frames. An algorithmic look-ahead of 7.5 ms duration means that total algorithmic delay is 37.5 ms...

. The ACELP algorithm is also used in the proprietary ACELP.net codec.

ACELP is a patented technology and registered trademark of VoiceAge Corporation in Canada and/or other countries and was developed in 1989 by the Université de Sherbrooke
Université de Sherbrooke
The Université de Sherbrooke is a large university with campuses located in Sherbrooke, Quebec, Canada and Longueuil, a suburb of Montreal approximately west of Sherbrooke. It is one of two universities, and the only French language university, in the Estrie region of Quebec.In 2007, the...

 in Canada
Canada
Canada is a North American country consisting of ten provinces and three territories. Located in the northern part of the continent, it extends from the Atlantic Ocean in the east to the Pacific Ocean in the west, and northward into the Arctic Ocean...

.

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/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 or pitch, synthesis filter is given by: 1/B(z) = 1/(1 − gpzT)

The short-term synthesis filter is given by: H(z) = 1/A(z) = 1/(1 + ZIGMAi = 1 to Paizi)
The source of this article is wikipedia, the free encyclopedia.  The text of this article is licensed under the GFDL.
 
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