Speech coding algorithms

SPEECH CODING

ALGORITHMS

Foundation and Evolution

of Standardized Coders

WAI C. CHU

Mobile Media Laboratory

DoCoMo USA Labs

San Jose, California

A JOHN WILEY & SONS, INC., PUBLICATION

SPEECH CODING

ALGORITHMS

SPEECH CODING

ALGORITHMS

Foundation and Evolution

of Standardized Coders

WAI C. CHU

Mobile Media Laboratory

DoCoMo USA Labs

San Jose, California

A JOHN WILEY & SONS, INC., PUBLICATION

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Library of Congress Cataloging-in-Publication Data:

Chu, Wai C. —

Speech coding algorithms: Foundation and evolution of standardized coders

ISBN 0-471-37312-5

Printed in the United States of America

10 9 8 7 6 5 4 3 2 1

Intelligence is the fruit of industriousness

Accretion of knowledge creates genii

A Chinese proverb

CONTENTS

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

vii

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

viii CONTENTS

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

CONTENTS ix

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

x CONTENTS

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

CONTENTS xi

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

xii CONTENTS