View source for Vector sum excited linear prediction

{{short description|Audio compression standard}}
'''Vector sum excited linear prediction''' ('''VSELP''') is a [[speech coding]] method used in several cellular standards. The VSELP algorithm is an analysis-by-synthesis coding technique and belongs to the class of speech coding algorithms known as [[CELP]] (Code Excited Linear Prediction).<ref>ETSI, [http://webapp.etsi.org/workprogram/Report_WorkItem.asp?WKI_ID=10142 EN 300 969 - Half rate speech transcoding (GSM 06.20 version 8.0.1 Release 1999)], Retrieved on 2009-07-11</ref>
Variations of this [[codec]] have been used in several [[2G]] cellular telephony standards, including [[IS-54]], [[IS-136]] (D-AMPS), [[GSM]] ([[Half Rate]] speech) and [[Integrated Digital Enhanced Network|iDEN]]. It was also used in the first version of [[RealAudio]] for audio over the [[Internet]]. The IS-54 VSELP standard was published by the [[Telecommunications Industry Association]] in 1989.
D-AMPS (IS-54 and IS-136) VSELP specifies an encoding of each 20 [[millisecond|ms]] of speech into 159-bit frames, thus achieving a raw data rate of 7.95&nbsp;kbit/s. In an actual TDMA cell phone, the [[vocoder]] output is packaged with error correction and signaling information, resulting in an over-the-air data rate of 16.2&nbsp;kbit/s. For internet audio, each 159-bit frame is stored in 20 bytes, leaving 1 bit unused. The resulting file thus has a data rate of exactly 8&nbsp;kbit/s.
GSM half-rate VSELP (GSM 06.20) uses 20 ms frames with 112 bits per frame, giving a raw data rate of 5.6&nbsp;kbit/s. The iDEN VSELP coder has three modes:
* 30 ms frames at 126 bits per frame with a raw data rate of 4.2&nbsp;kbit/s,
* 22.5 ms frames at 99 bits per frame with a raw data rate of 4.4&nbsp;kbit/s and
* 22.5 ms frames at 180 bits per frame with a raw data rate of 8.0&nbsp;kbit/s.
A major drawback of VSELP is its limited ability to encode non-speech sounds, so that it performs poorly when encoding speech in the presence of background noise. For this reason, use of VSELP has been gradually phased out in favor of newer codecs.
VSELP is also the proprietary digital vocoder used in early Motorola ASTRO products. It was phased out in favor of the newer [[IMBE]] method used for P25.
==References==
* Ira A. Gerson and Mark A. Jasiuk, ''Vector Sum Excited Linear Prediction (VSELP),'' IEEE Workshop on Speech Coding for Telecommunications, September 1989, pp. 66–68
* Ira A. Gerson and Mark A. Jasiuk, ''Vector sum excited linear prediction (VSELP) speech coding at 8&nbsp;kbps,'' Proceedings of the 1990 IEEE [[International Conference on Acoustics, Speech, and Signal Processing]] (ICASSP-90), April 1990, pp. 461–464
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==External links==
* [http://www.tiaonline.org/ Telecommunications Industry Association web site]
[[Category:Speech codecs]]