Perceptual Coding of Digital Audio

Description

Proceedings of the IEEE, 2000. — 63 p.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 such as reduced channel bandwidth, limited storage capacity, and low cost. These new applications have created a demand for high-quality digital audio delivery at low bit rates. In response to this need, considerable research has been devoted to the 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, filter 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 and/or commercial standards receive in-depth treatment, including the ISO/IEC MPEG family (-1, -2, -4), the Lucent Technologies PAC/EPAC/MPAC, the Dolby1 AC-2/AC-3, and the Sony ATRAC/SDDS algorithms. Then, we describe subjective evaluation methodologies in some detail, including the ITU-R BS.1116 recommendation on subjective measurements of small impairments. This paper concludes with a discussion of future research directions.IntroductionGeneric Perceptual Audio Coding ArchitecturePaper OrganizationPsychoacoustic PrinciplesAbsolute Threshold of HearingCritical BandsSimultaneous Masking, Masking Asymmetry, and the Spread of MaskingNonsimultaneous MaskingPerceptual EntropyExample Codec Perceptual Model: ISO 11172-3 (MPEG-1) Psychoacoustic ModelTime-Frequency Analysis: Filter Banks and TransformsFilter Banks for Audio Coding: Design ConsiderationsCosine Modulated Pseudo —QMF M-Band BanksCosine Modulated PR M-Band Banks and the MDCTPre-Echo DistortionPre-Echo Control StrategiesTransform CodersOptimum Coding in the Frequency Domain (OCF-1, OCF-2, OCF-3)Perceptual Transform Coder (PXFM)Brandenburg–Johnston Hybrid CoderCNET CoderASPECDPACDFT Noise SubstitutionDCT with Vector QuantizationMDCT with Vector QuantizationSubband CodersMASCAMMUSICAMWavelet DecompositionsAdapted Wavelet Packet DecompositionsHybrid Harmonic/Wavelet DecompositionsSignal-Adaptive, Nonuniform Filter Bank (NUFB) DecompositionsIIR Filter BanksSinusoidal CodersAnalysis/Synthesis Audio CodecHarmonic and Individual Lines Plus Noise CoderFM SynthesisHybrid Sinusoidal CodersLinear-Prediction-Based CodersMultipulse ExcitationDiscrete Wavelet Excitation CodingSinusoidal Excitation CodingFrequency Warped LPAudio Coding StandardsISO/IEC 11172-3 (MPEG-1) and ISO/IEC IS13818-3 (MPEG-2 BC)ISO/IEC IS13818-7 (MPEG-2 NBC/AAC)ISO/IEC 14 496-3 (MPEG-4)Precision Adaptive Subband CodingAdaptive Transform Acoustic CodingSony Dynamic Digital Sound (SDDS)Lucent Technologies Perceptual Audio Coder (PAC), Enhanced PAC (EPAC), and Multichannel PAC (MPAC)DOLBY AC-2, AC-2AQuality Measures for Perceptual Audio CodingSubjective Quality MeasuresConfounding Factors in Subjective EvaluationsSubjective Evaluations of Two-Channel Standardized CodecsSubjective Evaluations of 5.1-Channel Standardized CodecsConclusionSummary of Applications for Commercial and International StandardsSummary of Recent Research and Future Research Directions