Perceptual coding of digital audio

During the last decade, CD-quality digital audio has essentially replaced analog audio. Emerging digital audio applications for network, 'wireless, and multimedia computing systems face a series of constraints suck as reduced channel bandwidth, limited storage capacity, and low cost. These new applications have created a demand for high-quality digital audio delivery at tow bit rates. In response to this need, considerable research has been devoted to 'he development of algorithms for perceptually transparent coding of high-fidelity (CD-quality) digital audio. As a result, many algorithms have been proposed, and several have now become international and!or commercial product standards. This paper reviews algorithms for perceptually transparent coding of CD-quality digital audio, including both research and standardization activities. This paper is organized as follows. First, psychoacoustic principles are described, with the MPEG psychoacoustic signal analysis model 1 discussed in some detail. Next, filler bank design issues and algorithms are addressed, with a particular emphasis placed on the modified discrete cosine transform, a perfect reconstruction cosine-modulated filter bank that has become of central importance in perceptual audio coding. Then, we review methodologies that achieve perceptually transparent coding of FM- and CD-quality audio signals, including algorithms that manipulate transform components, subband signal decompositions, sinusoidal signal components, and linear prediction parameters, as well as hybrid algorithms that make use of more than one signal model. These discussions concentrate on architectures and applications of those techniques that utilize psychoacoustic models to exploit efficiently masking characteristics of the human receiver. Several algorithms that have become international andor commercial standards receive in-depth treatment, including the ISOIEC MPEG family (-1, -2. -4), the Lucent Technologies PACEPACMPAC, the Dolby' AC-21 AC-3, and the Sony ATRACSDDS algorithms. Then, we describe subjective evaluation methodologies in some detail, including the ITU-R BSJ1I6 recommendation on subjective measurements of small impairments. This paper concludes with a discussion of future research directions.