1 Audio quality determination based on perceptual measurement techniques 1 John G. Beerends

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1 Contents List of Figures List of Tables Contributing Authors xiii xxi xxiii Introduction Karlheinz Brandenburg and Mark Kahrs xxix 1 Audio quality determination based on perceptual measurement techniques 1 John G. Beerends 1.1 Introduction Basic measuring philosophy Subjective versus objective perceptual testing Psychoacoustic fundamentals of calculating the internal sound representation Computation of the internal sound representation The perceptual audio quality measure (PAQM) Validation of the PAQM on speech and music codec databases Cognitive effects in judging audio quality ITU Standardization ITU-T, speech quality ITU-R, audio quality Conclusions 37 2 Perceptual Coding of High Quality Digital Audio 39 Karlheinz Brandenburg 2.1 Introduction 39

2 vi APPLICATIONS OF DSP TO AUDIO AND ACOUSTICS 2.2 Some Facts about Psychoacoustics Masking in the Frequency Domain Masking in the Time Domain Variability between listeners 2.3 Basic ideas of perceptual coding Basic block diagram Additional coding tools Perceptual Entropy 2.4 Description of coding tools Filter banks Perceptual models Quantization and coding Joint stereo coding Prediction Multi-channel: to matrix or not to matrix 2.5 Applying the basic techniques: real coding systems Pointers to early systems (no detailed description) MPEG Audio MPEG-2 Advanced Audio Coding (MPEG-2 AAC) MPEG-4 Audio 2.6 Current Research Topics 2.7 Conclusions 3 Reverberation Algorithms William G. Gardner 3.1 Introduction Reverberation as a linear filter Approaches to reverberation algorithms 3.2 Physical and Perceptual Background Measurement of reverberation Early reverberation Perceptual effects of early echoes Reverberation time Modal description of reverberation Statistical model for reverberation Subjective and objective measures of late reverberation Summary of framework 3.3 Modeling Early Reverberation 3.4 Comb and Allpass Reverberators Schroeder s reverberator The parallel comb filter Modal density and echo density Producing uncorrelated outputs Moorer s reverberator Allpass reverberators 3.5 Feedback Delay Networks

3 Contents vii Jot s reverberator Unitary feedback loops Absorptive delays Waveguide reverberators Lossless prototype structures Implementation of absorptive and correction filters Multirate algorithms Time-varying algorithms Conclusions Digital Audio Restoration Simon Godsill, Peter Rayner and Olivier Cappé 4.1 Introduction 4.2 Modelling of audio signals 4.3 Click Removal Modelling of clicks Detection Replacement of corrupted samples Statistical methods for the treatment of clicks 4.4 Correlated Noise Pulse Removal 4.5 Background noise reduction Background noise reduction by short-time spectral attenuation Discussion Pitch variation defects Frequency domain estimation Reduction of Non-linear Amplitude Distortion Distortion Modelling Non-linear Signal Models Application of Non-linear models to Distortion Reduction Parameter Estimation Examples Discussion Other areas Conclusion and Future Trends Digital Audio System Architecture Mark Kahrs 5.1 Introduction 5.2 Input/Output Analog/Digital Conversion Sampling clocks 5.3 Processing Requirements Processing Synthesis

4 viii APPLICATIONS OF DSP TO AUDIO AND ACOUSTICS Processors 5.4 Conclusion 6 Signal Processing for Hearing Aids James M. Kates 6.1 Introduction 6.2 Hearing and Hearing Loss Outer and Middle Ear 6.3 Inner Ear Retrocochlear and Central Losses Summary 6.4 Linear Amplification System Description Dynamic Range Distortion Bandwidth 6.5 Feedback Cancellation 6.6 Compression Amplification Single-Channel Compression Two-Channel Compression Multi-Channel Compression 6.7 Single-Microphone Noise Suppression 6.7.Adaptive Analog Filters Spectral Subtraction Spectral Enhancement 6.8 Multi-Microphone Noise Suppression Directional Microphone Elements Two-Microphone Adaptive Noise Cancellation Arrays with Time-Invariant Weights Two-Microphone Adaptive Arrays Multi-Microphone Adaptive Arrays Performance Comparison in a Real Room 6.9 Cochlear Implants 6.10 Conclusions 7 Time and Pitch scale modification of audio signals Jean Laroche 7.1 Introduction 7.2 Notations and definitions An underlying sinusoidal model for signals A definition of time-scale and pitch-scale modification 7.3 Frequency-domain techniques Methods based on the short-time Fourier transform Methods based on a signal model 7.4 Time-domain techniques

5 7.4.1 Principle Pitch independent methods Periodicity-driven methods 7.5 Formant modification Time-domain techniques Frequency-domain techniques 7.6 Discussion Generic problems associated with time or pitch scaling Time-domain vs frequency-domain techniques 8 Wavetable Sampling Synthesis Dana C. Massie 8.1 Background and introduction Transition to Digital Flourishing of Digital Synthesis Methods Metrics: The Sampling - Synthesis Continuum Sampling vs. Synthesis 8.2 Wavetable Sampling Synthesis Playback of digitized musical instrument events Entire note - not single period Pitch Shifting Technologies Looping of sustain Multi-sampling Enveloping Filtering Amplitude variations as a function of velocity Mixing or summation of channels Multiplexed wavetables 8.3 Conclusion 9 Audio Signal Processing Based on Sinusoidal Analysis/Synthesis T.F. Quatieri and R. J. McAulay 9.1 Introduction 9.2 Filter Bank Analysis/Synthesis Additive Synthesis Phase Vocoder Motivation for a Sine-Wave Analysis/Synthesis 9.3 Sinusoidal-Based Analysis/Synthesis Model Estimation of Model Parameters Frame-to-Frame Peak Matching Synthesis Experimental Results Applications of the Baseline System Time-Frequency Resolution 9.4 Source/Filter Phase Model Contents ix

6 x APPLICATIONS OF DSP TO AUDIO AND ACOUSTICS Model Phase Coherence in Signal Modification Revisiting the Filter Bank-Based Approach Additive Deterministic/Stochastic Model Model Analysis/Synthesis Applications Signal Separation Using a Two-Voice Model Formulation of the Separation Problem Analysis and Separation The Ambiguity Problem Pitch and Voicing Estimation FM Synthesis Principles Representation of Musical Sound Parameter Estimation Extensions Conclusions Principles of Digital Waveguide Models of Musical Instruments 417 Julius O. Smith III 10.1 Introduction Antecedents in Speech Modeling Physical Models in Music Synthesis Summary The Ideal Vibrating String The Finite Difference Approximation Traveling-Wave Solution Sampling the Traveling Waves Relation to Finite Difference Recursion Alternative Wave Variables Spatial Derivatives Force Waves Power Waves Energy Density Waves Root-Power Waves Scattering at an Impedance Discontinuity The Kelly-Lochbaum and One-Multiply Scattering Junctions Normalized Scattering Junctions Junction Passivity Scattering at a Loaded Junction of N Waveguides The Lossy One-Dimensional Wave Equation Loss Consolidation Frequency-Dependent Losses The Dispersive One-Dimensional Wave Equation Single-Reed Instruments 455

7 Contents xi Clarinet Overview Single-Reed Theory Bowed Strings Violin Overview The Bow-String Scattering Junction Conclusions 466 References 467 Index 535