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42 The Perceptual Audio Coder (PAC)

With the overwhelming success of the compact disc (CD) in the consumer audio marketplace, the public’s notion of “high quality audio” has become synonymous with “compact disc quality”. | Deepen Sinha et. Al. The Perceptual Audio Coder PAC . 2000 CRC Press LLC. http www.engnetbase.com . The Perceptual Audio Coder PAC Deepen Sinha Bell Laboratories Lucent Technologies James D. Johnston AT T Research Labs Sean Dorward Bell Laboratories Lucent Technologies Schuyler R. Quackenbush AT T Research Labs 42.1 Introduction 42.2 Applications and Test Results 42.3 Perceptual Coding PAC Structure The PAC Filterbank The EPAC Filterbank and Structure Perceptual Modeling MS vs. LR Switching Noise Allocation Noiseless Compression 42.4 Multichannel PAC Filterbank and Psychoacoustic Model The Composite Coding Methods Use of a Global Masking Threshold 42.5 Bitstream Formatter 42.6 Decoder Complexity 42.7 Conclusions References PAC is a perceptual audio coder that is flexible in format and bitrate and provides high-quality audio compression 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. In all of its forms it provides efficient compression of high-quality audio. For stereo audio signals it provides near compact disk CD quality at about 56 to 64 kb s with transparent coding at bit rates approaching 128 kb s. PAC has been tested both internally and externally by various organizations. 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. PAC is the audio coder in most of the submissions to the U.S. Digital Audio Radio DAR standardization project at bit rates of 160 kb s or 128 kb s for two-channel audio compression. It has been adapted by various vendors for the delivery of high quality music over the Internet as well as ISDN links. Over the years PAC has evolved considerably. In this paper we present an overview for