Adaptive Multi-Rate audio codec

Adaptive Multi-Rate (AMR)
Filename extension
.amr, .3ga
Internet media type
audio/amr, audio/3gpp, audio/3gpp2
Initial release23 June 1999 (1999-06-23)[1][2]
Latest release
14.0.0
17 March 2017; 7 years ago (2017-03-17)
Type of formatLossy audio
Open format?Yes
Free format?No

The Adaptive Multi-Rate (AMR, AMR-NB or GSM-AMR) audio codec is an audio compression format optimized for speech coding. AMR is a multi-rate narrowband speech codec that encodes narrowband (200–3400 Hz) signals at variable bit rates ranging from 4.75 to 12.2 kbit/s with toll quality[3] speech starting at 7.4 kbit/s.[4]

AMR was adopted as the standard speech codec by 3GPP in October 1999 and is now widely used in GSM[5] and UMTS. It uses link adaptation to select from one of eight different bit rates based on link conditions.

AMR is also a file format for storing spoken audio using the AMR codec. Many modern mobile telephone handsets can store short audio recordings in the AMR format, and both free and proprietary programs exist (see Software support) to convert between this and other formats, although AMR is a speech format and is unlikely to give ideal results for other audio. The common filename extension is .amr. There also exists another storage format for AMR that is suitable for applications with more advanced demands on the storage format, like random access or synchronization with video. This format is the 3GPP-specified 3GP container format based on ISO base media file format.[6]

  1. ^ "3GPP TS 26.090 - Mandatory Speech Codec speech processing functions; Adaptive Multi-Rate (AMR) speech codec; Transcoding functions". 3GPP. Retrieved 2010-07-21.
  2. ^ "3GPP TS 26.071 - Mandatory speech CODEC speech processing functions; AMR speech Codec; General description". 3GPP. Retrieved 2010-07-21.
  3. ^ "What's toll-quality voice?". ITworld. 13 December 2000. Retrieved 26 July 2019.
  4. ^ RFC 4867 - RTP Payload Format and File Storage Format for the Adaptive Multi-Rate (AMR) and Adaptive Multi-Rate Wideband (AMR-WB) Audio Codecs Page 35
  5. ^ "Sorting Through GSM Codecs: A Tutorial". 11 July 2003.
  6. ^ RFC 4867 - RTP Payload Format and File Storage Format for the Adaptive Multi-Rate (AMR) and Adaptive Multi-Rate Wideband (AMR-WB) Audio Codecs Page 35