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