Adaptive Multi-Rate audio codec: Difference between revisions

Revision as of 11:43, 7 April 2015

Revision as of 01:50, 7 November 2015

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* Generates frame length of 95, 103, 118, 134, 148, 159, 204, or 244 bits 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.

* AMR is a hybrid speech coder, and as such transmits both speech parameters and a waveform signal

** [[Linear predictive coding]] (LPC) is used to synthesize the speech from a residual waveform. The LPC parameters are encoded as [[Line spectral pairs]] (LSP).