AMR (Adaptive Multi-Rate Audio)
AMR is a speech-optimized audio codec used primarily in mobile phone voice recordings and 3G cellular networks. It dynamically adjusts its bitrate between 4.75 and 12.2 kbps to adapt to network conditions, prioritizing intelligible speech at very low bitrates.
MIME Type
audio/amr
Type
Binary
Compression
Lossy
Advantages
- + Excellent speech quality at very low bitrates
- + Adaptive bitrate adjusts to network conditions in real time
- + Standard in GSM and 3G voice networks worldwide
Disadvantages
- − Poor quality for music — optimized only for speech
- − 8 kHz narrowband sounds telephony-quality, not natural
- − Limited playback support outside mobile and VoIP contexts
When to Use .AMR
Use AMR for voice memos and mobile phone recordings where speech clarity at minimal file size is the priority.
Technical Details
AMR uses algebraic code-excited linear prediction (ACELP) with 8 bitrate modes. The codec operates on 20 ms frames at 8 kHz sampling. AMR-WB extends this to 16 kHz for wideband speech.
History
The European Telecommunications Standards Institute (ETSI) adopted AMR in 1999 as the mandatory speech codec for GSM and 3G (UMTS) networks. AMR-WB (Wideband) was later standardized for HD Voice.