Adaptive Multi-Rate Audio Codec - Features

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:

    “The features of our face are hardly more than gestures which force of habit made permanent. Nature, like the destruction of Pompeii, like the metamorphosis of a nymph into a tree, has arrested us in an accustomed movement.”
    —Marcel Proust (1871–1922)

    “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)

    “It is a tribute to the peculiar horror of contemporary life that it makes the worst features of earlier times—the stupefaction of the masses, the obsessed and driven lives of the bourgeoisie—seem attractive by comparison.”
    —Christopher Lasch (b. 1932)