Perceptual audio coder
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Perceptual Audio Coder (PAC) is an algorithm, like MPEG's MP3 standard, used to compress digital audio by removing extraneous information not perceived by most people. It is used by Sirius Satellite Radio for their DARS service, and iBiquity has been testing it for their IBOC digital radio upgrade for FM and AM. PAC is very similar to Advanced Audio Coding, the latter sharing many design elements.
The PAC originally developed by Elemedia, a subsidiary of Bell Labs, has a flexible format and bitrate. It provides efficient compression of high-quality audio over a variety of formats from 16 kb/s for a monophonic channel to 1024 kb/s for a 5.1 format with four or six auxiliary audio channels, and provisions for an ancillary (fixed rate) and auxiliary (variable rate) side data channel. For stereo audio signals, it is claimed that it provides near compact disc (CD) quality at about 56-64 kb/s, with transparent coding at bit rates approaching 128 kb/s[citation needed]. In the 1993, ISO-MPEG-2 5-channel test, PAC demonstrated the best decoded audio signal quality available from any algorithm at 320 kb/s, far outperforming all algorithms, including the layer-II and layer-III backward compatible algorithms.[citation needed]
Over the years PAC has evolved considerably. A known software implementation of this codec is CelestialTech's AudioLib. Later, it was considerably improved and renamed to ePAC (enhanced Perceptual Audio Coder) by Lucent. It's available in the AudioVeda music library manager.
The non-capitalized term is used to describe lossy compression codecs that utilize perceptual coding techniques for audio.
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