Enhanced Variable Rate Codec B (EVRC-B) is a speech codec used by
CDMA
Code-division multiple access (CDMA) is a channel access method used by various radio communication technologies. CDMA is an example of multiple access, where several transmitters can send information simultaneously over a single communication ...
networks. EVRC-B is an enhancement to
EVRC Enhanced Variable Rate CODEC (EVRC) 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 ca ...
and compresses each 20 milliseconds of 8000 Hz, 16-bit sampled speech
input into output frames of one of the four different sizes:
Rate 1 - 171 bits,
Rate 1/2 - 80 bits,
Rate 1/4 - 40 bits,
Rate 1/8 - 16 bits.
In addition, there are two zero bit codec frame types: null frames and erasure frames, similar to EVRC. One significant enhancement in EVRC-B is the use of 1/4 rate frames that were not used in EVRC. This provides lower average data rates (ADRs) compared to EVRC, for a given voice quality.
The new
4GV
Qualcomm's (4G) is a suite of voice speech codecs used by CDMA networks that allows the network operators to dynamically prioritize voice quality to increase network capacity while maintaining voice quality. Currently, the 4GV suite offers EVR ...
Codecs used in
CDMA2000
CDMA2000 (also known as C2K or IMT Multi‑Carrier (IMT‑MC)) is a family of 3G mobile technology standards for sending voice, data, and Signaling (telecommunication), signaling data between mobile phones and cell sites. It is developed by 3GP ...
are based on EVRC-B. 4GV is designed to allow service providers to dynamically prioritize voice capacity on their network as required.
The
Enhanced Variable Rate Coder (EVRC) is a speech codec used for cellular telephony in cdma2000 systems. EVRC provides excellent speech quality using variable rate coding with 3 possible rates, 8.55, 4.0 and 0.8 kbit/s. However, the Quality of Service (QoS) in cdma2000 systems can significantly benefit from a codec which allows tradeoffs between voice quality and network capacity, which cannot be achieved efficiently with the EVRC.
An upgrade of the EVRC
vocoder
A vocoder (, a portmanteau of ''voice'' and ''encoder'') is a category of speech coding that analyzes and synthesizes the human voice signal for audio data compression, multiplexing, voice encryption or voice transformation.
The vocoder was ...
, known as EVRC-B, was recently introduced by