AMR

• company: VoiceAge
• samples: http://samples.mplayerhq.hu/A-codecs/amr/
• specification: http://www.3gpp.org/ftp/Specs/html-info/26-series.htm
• Wikipedia article: http://en.wikipedia.org/wiki/Adaptive_Multi-Rate

AMR (Adaptive Multi-Rate) is a vocoder employed in low-bitrate applications like mobile phones. There are narrowband and wideband variants of this codec.