Enhanced Variable Rate CODEC (EVRC) is aspeech codec used inCDMA networks. It was developed in 1995 to replace theQCELP 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 of bandwidth or wireless spectrum needed.[1] EVRC usesRCELP technology.
EVRC compresses each 20 milliseconds of 8000 Hz, 16-bit sampled speech input into output frames of one of three different sizes: full rate – 171 bits (8.55 kbit/s), half rate – 80 bits (4.0 kbit/s), eighth rate – 16 bits (0.8 kbit/s). A quarter rate was not included in the original EVRC specification and eventually became part ofEVRC-B.
EVRC was replaced bySMV. Recently, however,SMV itself has been replaced by the newCDMA2000 4GV codecs.4GV is the next generation3GPP2 standards-basedEVRC-B codec. 4GV is designed to allow service providers to dynamically prioritize voice capacity on their network as required.
EVRC can be also used in 3GPP2 container file format -3G2.
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