Features
- 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 samples for bit rates 4.75, 5.15, 5.90, 6.70, 7.40, 7.95, 10.2, or 12.2 kbit/s, respectively
- AMR utilizes Discontinuous Transmission (DTX), with Voice Activity Detection (VAD) and 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 which uses Algebraic Code Excited Linear Prediction (ACELP)
- The complexity of the algorithm is rated at 5, using a relative scale where G.711 is 1 and G.729a is 15.
- PSQM testing under ideal conditions yields Mean Opinion Scores of 4.14 for AMR (12.2 kbit/s), compared to 4.45 for G.711 (u-law)
- PSQM testing under network stress yields Mean Opinion Scores of 3.79 for AMR (12.2 kbit/s), compared to 4.13 for G.711 (u-law)
Read more about this topic: Adaptive Multi-Rate Audio Codec
Famous quotes containing the word features:
“However much we may differ in the choice of the measures which should guide the administration of the government, there can be but little doubt in the minds of those who are really friendly to the republican features of our system that one of its most important securities consists in the separation of the legislative and executive powers at the same time that each is acknowledged to be supreme, in the will of the people constitutionally expressed.”
—Andrew Jackson (1767–1845)
““It looks as if
Some pallid thing had squashed its features flat
And its eyes shut with overeagerness
To see what people found so interesting
In one another, and had gone to sleep
Of its own stupid lack of understanding,
Or broken its white neck of mushroom stuff
Short off, and died against the windowpane.””
—Robert Frost (1874–1963)
“Each reader discovers for himself that, with respect to the simpler features of nature, succeeding poets have done little else than copy his similes.”
—Henry David Thoreau (1817–1862)