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41 Digital Audio Coding: Dolby AC-3

In order to more efficiently transmit or store high-quality audio signals, it is often desirable to reduce the amount of information required to represent them. | Davidson G.A. Digital Audio Coding Dolby AC-3 Digital Signal Processing Handbook Ed. Vijay K. Madisetti and Douglas B. Williams Boca Raton CRC Press LLC 1999 1999 by CRC Press LLC 41 Digital Audio Coding Dolby AC-3 Grant A. Davidson Dolby Laboratories Inc. 41.1 Overview 41.2 Bit Stream Syntax 41.3 Analysis Synthesis Filterbank Window Design Transform Equations 41.4 Spectral Envelope 41.5 Multichannel Coding Channel Coupling Rematrixing 41.6 Parametric Bit Allocation Bit Allocation Strategies Spreading Function Shape Algorithm Description 41.7 Quantization and Coding 41.8 Error Detection References 41.1 Overview In order to more efficiently transmit or store high-quality audio signals it is often desirable to reduce the amount of information required to represent them. In the case of digital audio signals the amount of binary information needed to accurately reproduce the original pulse code modulation PCM samples may be reduced by applying compression algorithm. A primary goal of audio compression algorithms is to maximally reduce the amount of digital information bit-rate required for conveyance of an audio signal while rendering differences between the original and decoded signals inaudible. Digital audio compression is useful wherever there is an economic benefit realized by reducing the bit-rate. Typical applications are in satellite or terrestrial audio broadcasting delivery of audio over electrical or optical cables or storage of audio on magnetic optical semiconductor or other storage media. One application which has received considerable attention in the United States is digital television DTV . Audio and video compression are both necessary in DTV to meet the requirement that one high-definition DTV channel fit within the 6 MHz transmission bandwidth occupied by one preexisting NTSC analog channel. In December 1996 the United States Federal Communications Commission adopted the ATSC standard for DTV which is consistent with a consensus agreement developed