AMR is a speech coder standard introduced by the 3rd Generation Partnership Project (3GPP), a partnership project of various standards organizations, developed to preserve high speech quality under a wide range of transmission conditions. The theory behind AMR is to lower the codec rate as the interference increases, thus enabling the application of more error correction. The AMR codec is also used to harmonize the codec standards amongst different cellular systems.
Synchronisation Analog
Synchronisation 
Analog