Analysis/Synthesis Audio Coding (MPEG-4 HILN Parametric Audio Coding)

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Standardization activities within MPEG-4 have been started which aim at the developement of a coding standard for transmitting audio signals at bit rates below 16 kbit/s.

Currently available general purpose audio codecs operate at bit rates above 16 kbit/s. On the other hand speech codecs operating in the desired range of bit rates are not suited for encoding audio signals.

A coding scheme is to be developed wich allows the transmission of audio signals with a bandwidth of 4 ... 8 kHz at bit rates between 6 and 16 kbit/s.

The concept of an object based analysis/synthesis scheme is applied.

In the encoder the input signal is first decomposed into audio objects which can be described by appropriate source models and represented by corresponding sets of model parameters. For each object the model parameters are estimated, coded, and transmitted. Additionally a signal is synthesized from the derived parameters which assists the decomposition of the residual. Quantization and coding of the model parameters is controlled by a psychoacoustic model which exploits the input signal dependent sensitivity of the human ear to reconstruction errors.

In the decoder for each audio object a signal is synthesized from the decoded model parameters. The decoder output is the sum of all object signals.

This coding scheme was adopted as parametric audio coder in the MPEG-4 Audio Standard, where it is referred to as HILN ("Harmonic and Individual Lines plus Noise").

Further details about this coding scheme are available from numerous publications. For general information, see the Parametric Audio Coding Bibliography.

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  • Nicolle van Schijndel, Julien Bensa, Mads Christensen, Catherine Colomes, Bernd Edler, Richard Heusdens, Jesper Jensen, Jensen Søren, Bastiaan Kleijn, Valery Kot, Balazs Kovesi, Jonas Lindblom, Dominique Massaloux, Omar Niamut, Frederik Norden, Jan Plasberg, Renat Vafin, Steven van de Par, David Virette, Oliver Wübbolt
    Adaptive RD Optimized Hybrid Sound Coding
    J. Audio Eng. Soc., Audio Engineering Society, Vol. 56, No. 10, pp. 787-809, October 2008
  • Bernd Edler
    Audiocodierung in MPEG-4
    Telekommunikation Aktuell, Verlag für Wissenschaft und Leben, Erlangen, July 2004
  • Heiko Purnhagen, Nikolaus Meine, Bernd Edler
    Sinusoidal Coding Using Loudness-Based Component Selection
    Int. Conf. on Acoustics, Speech, and Signal Processing, Orlando, May 2002