Proceedings of the International Conference
I W S S I P   2005
12th INTERNATIONAL WORKSHOP ON SYSTEMS, SIGNALS & IMAGE PROCESSING

22 - 24 September 2005, Chalkida Greece
 
(from Chapter 1: Invited Addresses and Tutorials on Signals, Coding, Systems and Intelligent Techniques)

 Full Citation and Abstract

0 Title: Recent developments in audio coding
  Author(s): Maciej Bartkowiak
  Address: Pozna University of Technology, Div. Multimedia Telecommunications and Radioelectronics ul. Piotrowo 3a,60-965 Pozna
mbartkow @ et.put.poznan.pl
  Reference: SSIP-SP1, 2005  pp. 45 - 45
  Abstract/
Summary
A tremendous progress has taken place in audio coding technologies in recent years. Perceptual coding paradigm became ubiquitous among standard and proprietary techniques for compressed audio storage and delivery in applications ranging from narrowband internet streaming of music and speech to high definition multichannel home theatre. Coding scenarios make heavy use of psychoacoustics, especially masking phenomena that render some components of the sound inaudible in the presence of other strong components with similar spectra. Departing from 1st generation basic subband coding scheme with perceptually controlled uniform scalar quantization, modern algorithms of 2nd and 3rd generation have evolved into sophisticated forms of transform coding with switched time and frequency resolution and temporal shaping of quantization noise. Several additional tools have been introduced to model and remove the redundant and perceptually irrelevant components of audio signal, thus increasing the coding efficiency. These tools include variants of prediction in time and frequency domain, perceptual substitution of noise components, diverse quantization schemes (including vector quantization) and refined entropy coding. Although the original 1st and 2nd generation techniques were aimed at near-CD or broadcast quality, there was a strong demand for codecs offering decent quality at reduced bit rate. At very low bit rates however, traditional waveform coding methods are no longer able to hide the quantization noise below the threshold of audibility and coding artefacts become apparent because the masking conditions of the perceptual models are heavily violated. The 4th generation audio codec recently standardized by ISO uses two new model-based tools to describe parametrically the high frequency content and spatial information instead of coding them. Spectral band replication and parametric stereo encoding allow reducing the bit rate required for good quality audio down to a range wh...
 

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