AMR is a sound file format with a specific focus. Created a long time ago, before the advent of MP3. some sources call the developer Ericsson. The name of the format is an abbreviation for Adaptive Multi Rate. Sound files of this format are intended for mobile devices and in GSM cellular networks. Using this format provides a small file size due to the technology of signal coding in the speech frequency range. Effectively compressing audio recordings of human speech makes this format often used in voice recorders on mobile phones, for voice recordings, and for MMS messages.
MP3 is the most common music (sound) file format. This format was developed by Fraunhofer IIS and Thomson. This format for storing and transmitting music (sound) files in digital form uses signal compression technology. That is why, unlike the previously widespread WAV format, MP3 files (full name - MPEG Audio Layer-3) are much smaller in size, and their sound quality is much higher. The MP3 format was one of the first and most successful sound compression methods. One of the important characteristics of this process is the degree of compression, that is, how much data is transferred per unit of time. Standard MP3 encoding is from 64 to 320 kb / s.