What is a AMR file?
Speech-optimized mobile audio format
AMR was adopted as the standard speech codec by the 3rd Generation Partnership Project Group (3GPP)and is now widely used in GSM and UMTS for 3G mobile phones and devices.
The Adaptive Multi-Rate (AMR) audio file format that is optimized for speech coding. Thus, most audio saved in the AMR file format is compressed and optimized for human speech frequency ranges. Thus, the 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 kbit/s with normal quality speech starting at 7.4 kbit/s. Since it is used mainly for mobile speech communication, it chooses between the 8 different bit rates based on link conditions.
