Adaptive Multi-Rate Audio Codec

Adaptive Multi-Rate Audio Codec

The Adaptive Multi-Rate (AMR or AMR-NB) audio codec is a patented audio data compression scheme optimized for speech coding. AMR speech codec consists of a multi-rate narrowband speech codec, that encode narrowband (200-3400 Hz) signals at variable bit rates ranging from 4.75 to 12.2 kbps with toll quality speech starting at 7.4 kbps.

AMR was adopted as the standard speech codec by 3GPP in October 1999 and is now widely used in GSM 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.

Read more about Adaptive Multi-Rate Audio Codec:  Usage, Features, Licensing and Patent Issues, Software Support

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