Preface xiii
Acronyms xix
Notation xxiii
1 Introduction 1
1.1 Overview of Speech Coding 2
1.2 Classification of Speech Coders 8
1.3 Speech Production and Modeling 11
1.4 Some Properties of the Human Auditory System 18
1.5 Speech Coding Standards 22
1.6 About Algorithms 26
1.7 Summary and References 31
2 Signal Processing Techniques 33
2.1 Pitch Period Estimation 33
2.2 All-Pole and All-Zero Filters 45
2.3 Convolution 52
2.4 Summary and References 57
Exercises 57
3 Stochastic Processes and Models 61
3.1 Power Spectral Density 62
3.2 Periodogram 67
3.3 Autoregressive Model 69
3.4 Autocorrelation Estimation 73
3.5 Other Signal Models 85
3.6 Summary and References 86
Exercises 87
4 Linear Prediction 91
4.1 The Problem of Linear Prediction 92
4.2 Linear Prediction Analysis of Nonstationary Signals 96
4.3 Examples of Linear Prediction Analysis of Speech 101
4.4 The Levinson-Durbin Algorithm 107
4.5 The Leroux-Gueguen Algorithm 114
4.6 Long-Term Linear Prediction 120
4.7 Synthesis Filters 127
4.8 Practical Implementation 131
4.9 Moving Average Prediction 137
4.10 Summary and References 138
Exercises 139
5 Scalar Quantization 143
5.1 Introduction 143
5.2 Uniform Quantizer 147
5.3 Optimal Quantizer 149
5.4 Quantizer Design Algorithms 151
5.5 Algorithmic Implementation 155
5.6 Summary and References 158
Exercises 158
6 Pulse Code Modulation and Its Variants 161
6.1 Uniform Quantization 161
6.2 Nonuniform Quantization 166
6.3 Differential Pulse Code Modulation 172
6.4 Adaptive Schemes 175
6.5 Summary and References 180
Exercises 181
7 Vector Quantization 184
7.1 Introduction 185
7.2 Optimal Quantizer 188
7.3 Quantizer Design Algorithms 189
7.4 Multistage VQ 194
7.5 Predictive VQ 216
7.6 Other Structured Schemes 219
7.7 Summary and References 221
Exercises 222
8 Scalar Quantization of Linear Prediction Coefficient 227
8.1 Spectral Distortion 227
8.2 Quantization Based on Reflection Coefficient and Log Area Ratio 232
8.3 Line Spectral Frequency 239
8.4 Quantization Based on Line Spectral Frequency 252
8.5 Interpolation of LPC 256
8.6 Summary and References 258
Exercises 260
9 Linear Prediction Coding 263
9.1 Speech Production Model 264
9.2 Structure of the Algorithm 268
9.3 Voicing Detector 271
9.4 The FS1015 LPC Coder 275
9.5 Limitations of the LPC Model 277
9.6 Summary and References 280
Exercises 281
10 Regular-pulse Excitation Coders 285
10.1 Multipulse Excitation Model 286
10.2 Regular-Pulse-Excited-Long-Term Prediction 289
10.3 Summary and References 295
Exercises 296
11 Code-excited Linear Prediction 299
11.1 The CELP Speech Production Model 300
11.2 The Principle of Analysis-by-Synthesis 301
11.3 Encoding and Decoding 302
11.4 Excitation Codebook Search 308
11.5 Postfilter 317
11.6 Summary and References 325
Exercises 326
12 The Federal Standard Version of CELP 330
12.1 Improving the Long-Term Predictor 331
12.2 The Concept of the Adaptive Codebook 333
12.3 Incorporation of the Adaptive Codebook to the CELP Framework 336
12.4 Stochastic Codebook Structure 338
12.5 Adaptive Codebook Search 341
12.6 Stochastic Codebook Search 344
12.7 Encoder and Decoder 346
12.8 Summary and References 349
Exercises 350
13 Vector Sum Excited Linear Prediction 353
13.1 The Core Encoding Structure 354
13.2 Search Strategies for Excitation Codebooks 356
13.3 Excitation Codebook Searches 357
13.4 Gain Related Procedures 362
13.5 Encoder and Decoder 366
13.6 Summary and References 368
Exercises 369
14 Low-delay CELP 372
14.1 Strategies to Achieve Low Delay 373
14.2 Basic Operational Principles 375
14.3 Linear Prediction Analysis 377
14.4 Excitation Codebook Search 380
14.5 Backward Gain Adaptation 385
14.6 Encoder and Decoder 389
14.7 Codebook Training 391
14.8 Summary and References 393
Exercises 394
15 Vector Quantization of Linear Prediction Coefficient 396
15.1 Correlation Among the LSFs 396
15.2 Split VQ 399
15.3 Multistage VQ 403
15.4 Predictive VQ 407
15.5 Summary and References 418
Exercises 419
16 Algebraic CELP 423
16.1 Algebraic Codebook Structure 424
16.2 Adaptive Codebook 425
16.3 Encoding and Decoding 433
16.4 Algebraic Codebook Search 437
16.5 Gain Quantization Using Conjugate VQ 443
16.6 Other ACELP Standards 446
16.7 Summary and References 451
Exercises 451
17 Mixed Excitation Linear Prediction 454
17.1 The MELP Speech Production Model 455
17.2 Fourier Magnitudes 456
17.3 Shaping Filters 464
17.4 Pitch Period and Voicing Strength Estimation 466
17.5 Encoder Operations 474
17.6 Decoder Operations 477
17.7 Summary and References 481
Exercises 482
18 Source-controlled Variable Bit-rate CELP 486
18.1 Adaptive Rate Decision 487
18.2 LP Analysis and LSF-Related Operations 494
18.3 Decoding and Encoding 496
18.4 Summary and References 498
Exercises 499
19 Speech Quality Assessment 501
19.1 The Scope of Quality and Measuring Conditions 501
19.2 Objective Quality Measurements for Waveform Coders 502
19.3 Subjective Quality Measures 504
19.4 Improvements on Objective Quality Measures 505
Appendix A Minimum-phase Property of the Forward Prediction-error Filter 507
Appendix B Some Properties of Line Spectral Frequency 514
Appendix C Research Directions in Speech Coding 518
Appendix D Linear Combiner for Pattern Classification 522
Appendix E CELP: Optimal Long-term Predictor to Minimize the Weighted Difference 531
Appendix F Review of Linear Algebra: Orthogonality, Basis, Linear Independence, and the Gram-schmidt Algorithm 537
Bibliography 542
Index 553
