.amr File — Adaptive Multi-Rate Audio

AMR (Adaptive Multi-Rate) is a speech audio codec originally developed for GSM mobile telephony by Ericsson. The codec dynamically adapts its bitrate between 4.75 and 12.2 kbps based on network conditions — using lower bitrates when the channel is poor and higher bitrates when conditions improve. AMR-WB (Wideband), also known as G.722.2, extends the frequency range to 50-7000 Hz for HD Voice quality. AMR was widely used for voice recording on older mobile phones, particularly Nokia and Samsung feature phones, where it served as the default format for voice memo and call recording applications. The codec is optimized for speech and performs poorly with music or other audio content. AMR files are extremely compact — a one-minute voice recording is typically only 50-100 KB. The format saw extensive use in MMS messaging and mobile voicemail systems. While newer smartphones have moved to AAC, Opus, or proprietary formats for voice recording, AMR files remain common in archives of mobile recordings. The codec is part of the 3GPP standard and is supported by most media players.