Audio Signal Processing and Coding

pklite

语音信号处理及压缩编码算法介绍

1 INTRODUCTION 1
1.1 Historical Perspective 1
1.2 A General Perceptual Audio Coding Architecture 4
1.3 Audio Coder Attributes 5
1.3.1 Audio Quality 6
1.3.2 Bit Rates 6
1.3.3 Complexity 6
1.3.4 Codec Delay 7
1.3.5 Error Robustness 7
1.4 Types of Audio Coders – An Overview 7
1.5 Organization of the Book 8
1.6 Notational Conventions 9

2 SIGNAL PROCESSING ESSENTIALS 13
2.1 Introduction 13
2.2 Spectra of Analog Signals 13
2.3 Review of Convolution and Filtering 16
2.4 Uniform Sampling 17
2.5 Discrete-Time Signal Processing 20
2.5.1 Transforms for Discrete-Time Signals 20
2.5.2 The Discrete and the Fast Fourier Transform 22
2.5.3 The Discrete Cosine Transform 23
2.5.4 The Short-Time Fourier Transform 23
2.6 Difference Equations and Digital Filters 25
2.7 The Transfer and the Frequency Response Functions 27
2.7.1 Poles, Zeros, and Frequency Response 29
2.7.2 Examples of Digital Filters for Audio Applications 30
2.8 Review of Multirate Signal Processing 33
2.8.1 Down-sampling by an Integer 33
2.8.2 Up-sampling by an Integer 35
2.8.3 Sampling Rate Changes by Noninteger Factors 36
2.8.4 Quadrature Mirror Filter Banks 36
2.9 Discrete-Time Random Signals 39
2.9.1 Random Signals Processed by LTI Digital Filters 42
2.9.2 Autocorrelation Estimation from Finite-Length Data 44
2.10 Summary 44

3 QUANTIZATION AND ENTROPY CODING 51
3.1 Introduction 51
3.1.1 The Quantization–Bit Allocation–Entropy Coding Module 52
3.2 Density Functions and Quantization 53
3.3 Scalar Quantization 54
3.3.1 Uniform Quantization 54
3.3.2 Nonuniform Quantization 57
3.3.3 Differential PCM 59
3.4 Vector Quantization 62
3.4.1 Structured VQ 64
3.4.2 Split-VQ 67
3.4.3 Conjugate-Structure VQ 69
3.5 Bit-Allocation Algorithms 70
3.6 Entropy Coding 74
3.6.1 Huffman Coding 77
3.6.2 Rice Coding 81
3.6.3 Golomb Coding 82
3.6.4 Arithmetic Coding 83
3.7 Summary 85

4 LINEAR PREDICTION IN NARROWBAND AND WIDEBAND
CODING 91
4.1 Introduction 91
4.2 LP-Based Source-System Modeling for Speech 92
4.3 Short-Term Linear Prediction 94
4.3.1 Long-Term Prediction 95
4.3.2 ADPCM Using Linear Prediction 96
4.4 Open-Loop Analysis-Synthesis Linear Prediction 96
4.5 Analysis-by-Synthesis Linear Prediction 97
4.5.1 Code-Excited Linear Prediction Algorithms 100
4.6 Linear Prediction in Wideband Coding 102
4.6.1 Wideband Speech Coding 102
4.6.2 Wideband Audio Coding 104
4.7 Summary 106

5 PSYCHOACOUSTIC PRINCIPLES 113
5.1 Introduction 113
5.2 Absolute Threshold of Hearing 114
5.3 Critical Bands 115
5.4 Simultaneous Masking, Masking Asymmetry, and the Spread of Masking 120
5.4.1 Noise-Masking-Tone 123
5.4.2 Tone-Masking-Noise 124
5.4.3 Noise-Masking-Noise 124
5.4.4 Asymmetry of Masking 124
5.4.5 The Spread of Masking 125
5.5 Nonsimultaneous Masking 127
5.6 Perceptual Entropy 128
5.7 Example Codec Perceptual Model: ISO/IEC 11172-3(MPEG - 1) Psychoacoustic Model 1 130
5.7.1 Step 1: Spectral Analysis and SPL Normalization 131
5.7.2 Step 2: Identification of Tonal and Noise Maskers 131
5.7.3 Step 3: Decimation and Reorganization of Maskers 135
5.7.4 Step 4: Calculation of Individual Masking Thresholds 136
5.7.5 Step 5: Calculation of Global Masking Thresholds 138
5.8 Perceptual Bit Allocation 138
5.9 Summary 140

6 TIME-FREQUENCY ANALYSIS: FILTER BANKS AND
TRANSFORMS 145
6.1 Introduction 145
6.2 Analysis-Synthesis Framework for M-band Filter Banks 146
6.3 Filter Banks for Audio Coding: Design Considerations 148
6.3.1 The Role of Time-Frequency Resolution in Masking
Power Estimation 149
6.3.2 The Role of Frequency Resolution in Perceptual Bit
Allocation 149
6.3.3 The Role of Time Resolution in Perceptual Bit
Allocation 150
6.4 Quadrature Mirror and Conjugate Quadrature Filters 155
6.5 Tree-Structured QMF and CQF M-band Banks 156
6.6 Cosine Modulated “Pseudo QMF” M-band Banks 160
6.7 Cosine Modulated Perfect Reconstruction (PR) M-band Banks
and the Modified Discrete Cosine Transform (MDCT) 163
6.7.1 Forward and Inverse MDCT 165
6.7.2 MDCT Window Design 165
6.7.3 Example MDCT Windows (Prototype FIR Filters) 167
6.8 Discrete Fourier and Discrete Cosine Transform 178
6.9 Pre-echo Distortion 180
6.10 Pre-echo Control Strategies 182
6.10.1 Bit Reservoir 182
6.10.2 Window Switching 182
6.10.3 Hybrid, Switched Filter Banks 184
6.10.4 Gain Modification 185
6.10.5 Temporal Noise Shaping 185
6.11 Summary 186

7 TRANSFORM CODERS 195
7.1 Introduction 195
7.2 Optimum Coding in the Frequency Domain 196
7.3 Perceptual Transform Coder 197
7.3.1 PXFM 198
7.3.2 SEPXFM 199
7.4 Brandenburg-Johnston Hybrid Coder 200
7.5 CNET Coders 201
7.5.1 CNET DFT Coder 201
7.5.2 CNET MDCT Coder 1 201
7.5.3 CNET MDCT Coder 2 202
7.6 Adaptive Spectral Entropy Coding 203
7.7 Differential Perceptual Audio Coder 204
7.8 DFT Noise Substitution 205
7.9 DCT with Vector Quantization 206
7.10 MDCT with Vector Quantization 207
7.11 Summary 208

8 SUBBAND CODERS 211
8.1 Introduction 211
8.1.1 Subband Algorithms 212
8.2 DWT and Discrete Wavelet Packet Transform (DWPT) 214
8.3 Adapted WP Algorithms 218
8.3.1 DWPT Coder with Globally Adapted Daubechies
Analysis Wavelet 218
8.3.2 Scalable DWPT Coder with Adaptive Tree Structure 220
8.3.3 DWPT Coder with Globally Adapted General
Analysis Wavelet 223
8.3.4 DWPT Coder with Adaptive Tree Structure and
Locally Adapted Analysis Wavelet 223
8.3.5 DWPT Coder with Perceptually Optimized Synthesis
Wavelets 224
8.4 Adapted Nonuniform Filter Banks 226
8.4.1 Switched Nonuniform Filter Bank Cascade 226
8.4.2 Frequency-Varying Modulated Lapped Transforms 227
8.5 Hybrid WP and Adapted WP/Sinusoidal Algorithms 227
8.5.1 Hybrid Sinusoidal/Classical DWPT Coder 228
8.5.2 Hybrid Sinusoidal/M-band DWPT Coder 229
8.5.3 Hybrid Sinusoidal/DWPT Coder with WP Tree
Structure Adaptation (ARCO) 230
8.6 Subband Coding with Hybrid Filter Bank/CELP Algorithms 233
8.6.1 Hybrid Subband/CELP Algorithm for Low-Delay
Applications 234
8.6.2 Hybrid Subband/CELP Algorithm for
Low-Complexity Applications 235
8.7 Subband Coding with IIR Filter Banks 237

9 SINUSOIDAL CODERS 241
9.1 Introduction 241
9.2 The Sinusoidal Model 242
9.2.1 Sinusoidal Analysis and Parameter Tracking 242
9.2.2 Sinusoidal Synthesis and Parameter Interpolation 245
9.3 Analysis/Synthesis Audio Codec (ASAC) 247
9.3.1 ASAC Segmentation 248
9.3.2 ASAC Sinusoidal Analysis-by-Synthesis 248
9.3.3 ASAC Bit Allocation, Quantization, Encoding, and
Scalability 248
9.4 Harmonic and Individual Lines Plus Noise Coder (HILN) 249
9.4.1 HILN Sinusoidal Analysis-by-Synthesis 250
9.4.2 HILN Bit Allocation, Quantization, Encoding, and
Decoding 251
9.5 FM Synthesis 251
9.5.1 Principles of FM Synthesis 252
9.5.2 Perceptual Audio Coding Using an FM Synthesis
Model 252
9.6 The Sines + Transients + Noise (STN) Model 254
9.7 Hybrid Sinusoidal Coders 255
9.7.1 Hybrid Sinusoidal-MDCT Algorithm 256
9.7.2 Hybrid Sinusoidal-Vocoder Algorithm 257
9.8 Summary 258

10 AUDIO CODING STANDARDS AND ALGORITHMS 263
10.1 Introduction 263
10.2 MIDI Versus Digital Audio 264
10.2.1 MIDI Synthesizer 264
10.2.2 General MIDI (GM) 266
10.2.3 MIDI Applications 266
10.3 Multichannel Surround Sound 267
10.3.1 The Evolution of Surround Sound 267
10.3.2 The Mono, the Stereo, and the Surround Sound
Formats 268
10.3.3 The ITU-R BS.775 5.1-Channel Configuration 268
10.4 MPEG Audio Standards 270
10.4.1 MPEG-1 Audio (ISO/IEC 11172-3) 275
10.4.2 MPEG-2 BC/LSF (ISO/IEC-13818-3) 279
10.4.3 MPEG-2 NBC/AAC (ISO/IEC-13818-7) 283
10.4.4 MPEG-4 Audio (ISO/IEC 14496-3) 289
10.4.5 MPEG-7 Audio (ISO/IEC 15938-4) 309
10.4.6 MPEG-21 Framework (ISO/IEC-21000) 317
10.4.7 MPEG Surround and Spatial Audio Coding 319
10.5 Adaptive Transform Acoustic Coding (ATRAC) 319
10.6 Lucent Technologies PAC, EPAC, and MPAC 321
10.6.1 Perceptual Audio Coder (PAC) 321
10.6.2 Enhanced PAC (EPAC) 323
10.6.3 Multichannel PAC (MPAC) 323
10.7 Dolby Audio Coding Standards 325
10.7.1 Dolby AC-2, AC-2A 325
10.7.2 Dolby AC-3/Dolby Digital/Dolby SR · D 327
10.8 Audio Processing Technology APT-x100 335
10.9 DTS – Coherent Acoustics 338
10.9.1 Framing and Subband Analysis 338
10.9.2 Psychoacoustic Analysis 339
10.9.3 ADPCM – Differential Subband Coding 339
10.9.4 Bit Allocation, Quantization, and Multiplexing 341
10.9.5 DTS-CA Versus Dolby Digital 342

11 LOSSLESS AUDIO CODING AND DIGITAL WATERMARKING 343
11.1 Introduction 343
11.2 Lossless Audio Coding (L2AC) 344
11.2.1 L2AC Principles 345
11.2.2 L2AC Algorithms 346
11.3 DVD-Audio 356
11.3.1 Meridian Lossless Packing (MLP) 358
11.4 Super-Audio CD (SACD) 358
11.4.1 SACD Storage Format 362
11.4.2 Sigma-Delta Modulators (SDM) 362
11.4.3 Direct Stream Digital (DSD) Encoding 364
11.5 Digital Audio Watermarking 368
11.5.1 Background 370
11.5.2 A Generic Architecture for DAW 374
11.5.3 DAW Schemes – Attributes 377
11.6 Summary of Commercial Applications 378

12 QUALITY MEASURES FOR PERCEPTUAL AUDIO CODING 383
12.1 Introduction 383
12.2 Subjective Quality Measures 384
12.3 Confounding Factors in Subjective Evaluations 386
12.4 Subjective Evaluations of Two-Channel Standardized Codecs 387
12.5 Subjective Evaluations of 5.1-Channel Standardized Codecs 388
12.6 Subjective Evaluations Using Perceptual Measurement Systems 389
12.6.1 CIR Perceptual Measurement Schemes 390
12.6.2 NSE Perceptual Measurement Schemes 390
12.7 Algorithms for Perceptual Measurement 391
12.7.1 Example: Perceptual Audio Quality Measure (PAQM) 392
12.7.2 Example: Noise-to-Mask Ratio (NMR) 396
12.7.3 Example: Objective Audio Signal Evaluation (OASE) 399
12.8 ITU-R BS.1387 and ITU-T P.861: Standards for Perceptual
Quality Measurement 401
12.9 Research Directions for Perceptual Codec Quality Measures 402

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