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AMR, Adaptive Multi-Rate Codec File (.amr)
The AMR Audio file format
AMR is a compression format to optimize speech coding consisting of multi-rate narrowband speech codecs. AMR files can be recorded with mobile phones. To accomplish random access or synchronization of audio and video the 3GPP format can be utilized. AMR uses ACELP, DTX, VAD, and CNG to code the 160 20-millisecond samples contained in each frame. AMR files are used for voice recording though the format is usually converted into other files for use and distribution.
Technical details of AMR files
AMR is capable of encoding 200-3400 Hz signals from 4.75 to 12.2 kbit/s with quality starting at 7.4 kbit/s. Adopted in 1999 by 3GPP, this method is used by GSM and UMTS, using link adaptation to choose from the 8 different bit rates. AMR optimizes link adaptation with the best codec available in order to be utilized with radio channel and capacity requirements. This is only possible if a good connection is provided to prevent the loss of the audio's quality.
More information about the AMR file format
| File extension | .amr |
| File category | Audio |
| Example file |
Download example.amr file (55.16 KiB) |
| Associated programs | Audacity Android Open Source software AMR Player QuickTime Real Player VLS Media Player Apple iPhone |
| Useful links | More information on AMR |
| Developer | 3rd Generation Partnership Project (3GPP) |