AMR (Adaptive Multi-Rate)
The AMR (Adaptive Multi-Rate) standard is a speech coding algorithm operating at eight bit rates in the range of 4.75 to 12.2 kbps and was specifically designed to improve link robustness. This technology was initially developed for GSM systems, the single most deployed 2G mobile telecommunication standard worldwide. The AMR narrowband codec was standardized by the European Telecommunications Standards Institute (ETSI) and adopted by the 3GPP as the mandatory codec for 2.5G and 3G wireless systems based on the evolved GSM core network (WCDMA, EDGE, GPRS). It was also recently included in the CableLabs® PacketCable™ 2.0 specification.
Designed to allow transcoder-free connectivity between GSM, US-TDMA and PDC networks, AMR is the 3GPP mandatory standard codec for narrowband speech and multimedia messaging services over GSM and evolved GSM (WCDMA, GPRS and EDGE) networks.
AMR supports dynamic adaptation to network conditions, using lower bit rates during network congestion or degradation while preserving audio quality. By trading off the speech bit rate to channel coding, AMR maximizes the likelihood of receiving the signal at the far end. Adding this channel protection has proved more successful than allowing frame losses.
AMR provides toll quality speech starting at 7.4 kbps, with near-toll quality at lower rates and greater robustness and better reproduction of non-speech sounds at higher rates. Because it consists of 8 rates, AMR can be considered to be the most widely deployed codec in the world today, operating in 2 billion wireless handsets as well as in base stations and other network equipment.
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