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Vector Sum Excited Linear Prediction (VSELP)

Complete Definition

Vector Sum Excited Linear Prediction (VSELP) is a speech coding method used   in the IS-54 standard. This codec was used in early TDMA cell phones in the   United States. 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.

IS-54 VSELP specifies an encoding of each 20 ms of speech into 159-bit   frames, thus achieving a raw data rate of 7.95 kbps. 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  kbps. 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 kbps.

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 encoding method used in some early Motorola Type II   trunking systems. It was phased out in favor of the newer IMBE method.

Wikipedia CELP  Definition

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