Adaptive Multi-Rate audio codec: Difference between revisions

Revision as of 04:57, 10 February 2015

Revision as of 07:24, 23 February 2015

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* Sampling frequency 8 kHz/13-bit (160 samples for 20 ms frames), filtered to 200–3400 Hz.

* The AMR codec uses eight source codecs with bit-rates of 12.2, 10.2, 7.95, 7.40, 6.70, 5.90, 5.15 and 4.75 kbit/s.

* Generates frame length of 95, 103, 118, 134, 148, 159, 204, or 244 samplesbits for AMR FR bit rates 4.75, 5.15, 5.90, 6.70, 7.40, 7.95, 10.2, or 12.2 kbit/s, respectively. AMR HR frame lengths are different.

* AMR utilizes [[Discontinuous Transmission]] (DTX), with [[Voice Activity Detection]] (VAD) and [[Comfort noise|Comfort Noise Generation]] (CNG) to reduce bandwidth usage during silence periods

* Algorithmic delay is 20 ms per frame. For bit-rates of 12.2, there is no 'algorithm' look-ahead delay. For other rates, look-ahead delay is 5 ms. Note that there is 5 ms 'dummy' look-ahead delay, to allow seamless frame-wise mode switching with the rest of rates.