Enhanced Variable Rate Codec B

Enhanced Variable Rate Codec B (EVRC-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 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 Codecs used in CDMA2000 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.