About AMR, description of the AMR format
Adaptive Multi-Rate (AMR or AMR-NB) audio codec is a patented audio data compressionscheme optimized for speech coding. AMR was adopted as the standard speech codec by 3GPPin October 1998 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.This open standard format involves compressing of audio data to allow more storage on voice files. Originally developed for GSM (Global System for Mobile), a circuit-switched telecommunication system, it has now been adopted by most cellular companies all over the world.
AMR audio is a file storing spoken audio using the AMR codec. Many modern mobile telephone handsets can store short audio recordings in the AMR format.The common filename extension is .amr. And with the development of technology and science, both free and proprietary programs are developed to convert between this and other formats.
AMR operates on narrow-band signals (200-3400 Hz) at eight different bit rates – 12.2, 10.2, 7.95, 7.40, 6.70, 5.90, 5.15 and 4.75 kb/s – which are based on frames containing 160 samples and are 20 milliseconds long. AMR is optimized for link adaptation, which enables it to select the best coding technique for better reproduction. The coding techniques that AMR uses are ACELP (Algebraic Code Excited Linear Prediction), DTX (Discontinuous Transmission), VAD (Voice Activity Detection), and CNG (Comfort Noise Generation). Hence the name Adaptive Multi-Rate.
The benefits of AMR are:
AMR provides the best end-to-end solution to various applications, its flexible bit rate enables error correction
AMR can be used in multi-media applications after being encapsulated in 3GP or MPEG-4 file formats
AMR can easily be applied in low bit rate speech coding
AMR has the most consistent performance across all major languages
AMR’s applications include multi-media services for cellular communication systems, Wi-Fi telephony, digital radio broadcasting, conferencing, voice over IP, internet applications, streaming, content downloads, unified messaging, and in portable audio devices.
AMR is also a file format used for storing spoken audio. The main use of this file format is in storing short recordings in mobile telephones using the AMR codec. AMR is said to have more bits available for speech coding than any other speech codec, thus giving the most natural sounding voice quality to a recording than any other codec.
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