This is a proprietary format (with a paid license) developed by Matthew T. Ashland. Sound is stored without any loss, but the format isn’t too common because of license restrictions and because the official codecs works only on the Windows platform.

This format was originally intended for voice compression and is able to change the bit rates of encoded audio data. AMR is actively used for encoding and decoding voice while its being transmitted over network channels. The format allows one to consider network capacity and adapt it to channel loads. Due to this, the voice quality is practically undiminished.