High Quality Content by WIKIPEDIA articles! The Adaptive Multi-Rate (AMR or AMR-NB) audio codec is a patented audio data compression scheme optimized for speech coding. AMR speech codec consists of a multi-rate narrowband speech codec, that encodes narrowband (200-3400 Hz) signals at variable bit rates ranging from 4.75 to 12.2 kbps with toll quality speech starting at 7.4 kbps.