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Adaptive Multi-Rate audio codec

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Adaptive Multi-Rate (AMR) is a lossy data compression scheme optimized for speech. AMR is adopted as the standard speech codec by 3GPP.

The codec has eight bit rates, 12.2, 10.2, 7.95, 7.40, 6.70, 5.90, 5.15 and 4.75 Kbps. The bitstream is based on frames which contain 160 samples and are 20 milli-seconds longs. AMR uses different techniques, such as Algebraic Code Excited Linear Prediction (ACELP), Discontinuous Transmission (DTX), Voice Activity Detection (VAD) and Comfort Noise Generation (CNG).