codec). IS-641 is the TIA/EIA IS-641 TDMA Enhanced Full Rate Speech Codec. PDC-EFR is the ARIB 6.7 kbps Enhanced Full Rate Speech Codec. extensively use Adaptive Multirate Coding (AMR) vocoder while EVRC (Enhanced Variable Rate Codec) is commonly used in cdma2000 systems. The AMR speech coder consists of the multi-rate speech coder, a source controlled rate scheme including a voice activity detector and a comfort noise generation system, and an error concealment mechanism to combat the effects of transmission errors and lost packets. The multi-rate speech coder is a single integrated speech codec with eight source rates from 4.75 to 12.2 kbps, and a low rate background noise encoding mode as shown in Table 10.2. The speech coder is capable of switching its bit-rate every 20 ms speech frame upon command [16]. The evolution of AMR resulted in the standardization of AMR-WB and AMR-WB- AMR-Wideband is codified as G.722.2, an ITU-T standard speech codec and operates like AMR with nine different bit rates. AMR-Wideband+ is an audio codec that extends AMR-WB by adding support for stereo signals and higher sampling rates. The AMR-WB operates at an internal sampling rate of 12.8 kHz, whereas the AMR-WB- supports multiple internal sampling frequencies range from 12.8 to 38.4 kHz. The EVRC vocoder encodes narrowband speech on a frame by frame basis at a bit-rate of 8.55, 4.0, or 0.8 kbps depending on the characteristics (voiced and unvoiced, transients, or silence) of the current speech frame (20ms in duration). In May 2006, a new source-controlled narrowband variable rate vocoder called EVRC-B that encodes a 20 ms speech frame at one of 8.55, 4.0, 2.0, or 0.8 kbps bit-rate (designated full, half, quarter and eighth rate modes, respectively) modes was standardized. Then, in January 2007 3GPP2 approved the EVRC-WB standard. The EVRC-WB is based on a split-band coding approach in which the wideband input speech signal is separated into a low frequency band (0-4 KHz) signal and the high frequency band (3.5-7 KHz) signal using 