Speech Enhancement: Theory and Practice, Second Edition, 2nd Edition (Hardback) book cover

Speech Enhancement

Theory and Practice, Second Edition, 2nd Edition

By Philipos C. Loizou

CRC Press

711 pages | 207 B/W Illus.

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With the proliferation of mobile devices and hearing devices, including hearing aids and cochlear implants, there is a growing and pressing need to design algorithms that can improve speech intelligibility without sacrificing quality. Responding to this need, Speech Enhancement: Theory and Practice, Second Edition introduces readers to the basic problems of speech enhancement and the various algorithms proposed to solve these problems. Updated and expanded, this second edition of the bestselling textbook broadens its scope to include evaluation measures and enhancement algorithms aimed at improving speech intelligibility.

Fundamentals, Algorithms, Evaluation, and Future Steps

Organized into four parts, the book begins with a review of the fundamentals needed to understand and design better speech enhancement algorithms. The second part describes all the major enhancement algorithms and, because these require an estimate of the noise spectrum, also covers noise estimation algorithms. The third part of the book looks at the measures used to assess the performance, in terms of speech quality and intelligibility, of speech enhancement methods. It also evaluates and compares several of the algorithms. The fourth part presents binary mask algorithms for improving speech intelligibility under ideal conditions. In addition, it suggests steps that can be taken to realize the full potential of these algorithms under realistic conditions.

What’s New in This Edition

  • Updates in every chapter
  • A new chapter on objective speech intelligibility measures
  • A new chapter on algorithms for improving speech intelligibility
  • Real-world noise recordings (on accompanying CD)
  • MATLAB® code for the implementation of intelligibility measures (on accompanying CD)
  • MATLAB and C/C++ code for the implementation of algorithms to improve speech intelligibility (on accompanying CD)

Valuable Insights from a Pioneer in Speech Enhancement

Clear and concise, this book explores how human listeners compensate for acoustic noise in noisy environments. Written by a pioneer in speech enhancement and noise reduction in cochlear implants, it is an essential resource for anyone who wants to implement or incorporate the latest speech enhancement algorithms to improve the quality and intelligibility of speech degraded by noise.

Includes a CD with Code and Recordings

The accompanying CD provides MATLAB implementations of representative speech enhancement algorithms as well as speech and noise databases for the evaluation of enhancement algorithms.


"… indispensable for anyone trying to further his or her understanding in the field of digital speech processing. This book is critical in helping the professional address the growing demand to design algorithms that can improve speech intelligibility, in the presence of noise, without sacrificing quality for hearing aids and cochlear implants and address the equally important growing need to design rooms in which we can hear better naturally. Loizou's clarity of presentation of the mathematical foundation of different algorithms for speech enhancement has a comprehensibility that can only come with the level of expertise possessed by Loizou and serves well for all professionals from acoustical engineers to audiologists. This book provides an exceptional foundation and insight into past, present and future innovative processing techniques. This book is valuable for students and professionals of all experience levels."

—Bonnie Schnitta, SoundSense, LLC, Wainscott, New York, USA, from Noise Control Engineering Journal, January-February 2015

"… by far the most comprehensive treatment of speech enhancement available. All the most important techniques in the broad field of speech enhancement are covered, yet the author at the same time manages to treat each topic in great detail. … The algorithms are complex, but Loizou's exposition is outstanding. The second edition brings the material right up to date, covering recent significant breakthroughs in binary masking algorithms … . One of the great strengths of this text is the availability of code, allowing readers to better understand, deploy, and extend existing algorithms for speech enhancement. … This volume is in reality far more than a textbook on speech enhancement. It is also one of the most important works on the effect of noise on speech perception, and as such will make a huge contribution to the education of the next generation of auditory scientists, and feed technological developments in all aspects of speech communication, particularly for individuals with hearing impairment."

—Prof. Martin Cooke, Ikerbasque and University of the Basque Country, Vitoria, Spain

"This textbook offers outstanding reference material for teaching the clinical application of spectral enhancement to the audiology community. Dr. Loizou offers the reader tremendous insight into the fundamentals of digital signal processing, speech production and perception, and the characteristics of various noise sources. … The textbook is essential for engineers, audiologists, and other professionals who seek to improve the listener’s ability to hear a target signal against a background filled with competing noise using the spectral enhancement technique."

—Amyn M. Amlani, Ph.D., University of North Texas, Denton, USA

"… a highly informative presentation of the fundamentals, seminal and current algorithms, evaluation metrics, and future work that is desirable for any new or experienced students and researchers in the exciting area of speech enhancement. … I greatly appreciate the excellent organization of dividing the book into Fundamentals, Algorithms, Evaluation, and Future Steps, which can allow instructors and researchers to quickly decide on the material they want to teach their students, or learn or review themselves … Dr. Loizou takes students and researchers with a range of experiences on an amazing journey through the exciting field of speech enhancement."

—Marek Trawicki, Marquette University, Wauwatosa, Wisconsin, USA

"The first edition of this book established itself as the best reference for single-channel speech enhancement. Amazingly, this new edition is even better, and could be the most authoritative work in the area of modern single-channel techniques for speech enhancement to date. … This is a unique book, combining both thorough theoretical developments and practical implementations. I highly recommend it to those interested in speech enhancement, as well as applied signal processing."

Association of Computing Machinery (ACM) Computing Reviews, July 2013

Reviewer: Vladimir Botchev, Analog Devices, Wilmington, Massachusetts, USA

Table of Contents


Understanding the Enemy: Noise

Classes of Speech Enhancement Algorithms

Book Organization


Part I Fundamentals

Discrete-Time Signal Processing and Short-Time Fourier Analysis

Discrete-Time Signals

Linear Time-Invariant Discrete-Time Systems


Discrete-Time Fourier Transform

Short-Time Fourier Transform

Spectrographic Analysis of Speech Signals



Speech Production and Perception

Speech Signal

Speech Production Process

Engineering Model of Speech Production

Classes of Speech Sounds

Acoustic Cues in Speech Perception



Noise Compensation by Human Listeners

Intelligibility of Speech in Multiple-Talker Conditions

Acoustic Properties of Speech Contributing to Robustness

Perceptual Strategies for Listening in Noise



Part II Algorithms

Spectral-Subtractive Algorithms

Basic Principles of Spectral Subtraction

Geometric View of Spectral Subtraction

Shortcomings of the Spectral Subtraction Method

Spectral Subtraction Using Oversubtraction

Nonlinear Spectral Subtraction

Multiband Spectral Subtraction

MMSE Spectral Subtraction Algorithm

Extended Spectral Subtraction

Spectral Subtraction Using Adaptive Gain Averaging

Selective Spectral Subtraction

Spectral Subtraction Based on Perceptual Properties

Performance of Spectral Subtraction Algorithms



Wiener Filtering

Introduction to Wiener Filter Theory

Wiener Filters in the Time Domain

Wiener Filters in the Frequency Domain

Wiener Filters and Linear Prediction

Wiener Filters for Noise Reduction

Iterative Wiener Filtering

Imposing Constraints on Iterative Wiener Filtering

Constrained Iterative Wiener Filtering

Constrained Wiener Filtering

Estimating the Wiener Gain Function

Incorporating Psychoacoustic Constraints in Wiener Filtering

Codebook-Driven Wiener Filtering

Audible Noise Suppression Algorithm



Statistical-Model-Based Methods

Maximum-Likelihood Estimators

Bayesian Estimators

MMSE Estimator

Improvements to the Decision-Directed Approach

Implementation and Evaluation of the MMSE Estimator

Elimination of Musical Noise

Log-MMSE Estimator

MMSE Estimation of the pth-Power Spectrum

MMSE Estimators Based on Non-Gaussian Distributions

Maximum A Posteriori (Map) Estimators

General Bayesian Estimators

Perceptually Motivated Bayesian Estimators

Incorporating Speech Absence Probability in Speech Enhancement

Methods for Estimating the A Priori Probability of Speech Absence



Subspace Algorithms


Using SVD for Noise Reduction: Theory

SVD-Based Algorithms: White Noise

SVD-Based Algorithms: Colored Noise

SVD-Based Methods: A Unified View

EVD-Based Methods: White Noise

EVD-Based Methods: Colored Noise

EVD-Based Methods: A Unified View

Perceptually Motivated Subspace Algorithms

Subspace-Tracking Algorithms



Noise-Estimation Algorithms

Voice Activity Detection vs. Noise Estimation

Introduction to Noise-Estimation Algorithms

Minimal-Tracking Algorithms

Time-Recursive Averaging Algorithms for Noise Estimation

Histogram-Based Techniques

Other Noise-Estimation Algorithms

Objective Comparison of Noise-Estimation Algorithms



Part III Evaluation

Evaluating Performance of Speech Enhancement Algorithms

Quality vs. Intelligibility

Evaluating Intelligibility of Processed Speech

Evaluating Quality of Processed Speech

Evaluating Reliability of Quality Judgments: Recommended Practice



Objective Quality and Intelligibility Measures

Objective Quality Measures

Evaluation of Objective Quality Measures

Quality Measures: Summary of Findings and Future Directions

Speech Intelligibility Measures

Evaluation of Intelligibility Measures

Intelligibility Measures: Summary of Findings and Future Directions



Comparison of Speech Enhancement Algorithms

NOIZEUS: A Noisy Speech Corpus for Quality Evaluation of Speech Enhancement Algorithms

Comparison of Enhancement Algorithms: Speech Quality

Comparison of Enhancement Algorithms: Speech Intelligibility



Part IV Future Steps

Algorithms That Can Improve Speech Intelligibility

Reasons for the Absence of Intelligibility Improvement with Existing Noise-Reduction Algorithms

Algorithms Based on Channel Selection: A Different Paradigm for Noise Reduction

Channel-Selection Criteria

Intelligibility Evaluation of Channel-Selection-Based Algorithms: Ideal Conditions

Implementation of Channel-Selection-Based Algorithms in Realistic Conditions

Evaluating Binary Mask Estimation Algorithms

Channel Selection and Auditory Scene Analysis




Appendix A: Special Functions and Integrals

Appendix B: Derivation of the MMSE Estimator

Appendix C: MATLAB® Code and Speech/Noise Databases


About the Author

Philipos C. Loizou earned his bachelor’s, master’s, and doctorate degrees in electrical engineering from Arizona State University in Tempe. A pioneer in the field of speech enhancement and noise reduction in cochlear implants, Dr. Loizou was one of the first to develop specific enhancement algorithms that directly improve intelligibility. He was a postdoctoral fellow in the Department of Speech and Hearing Science at Arizona State University, an assistant professor at the University of Arkansas in Little Rock, and Cecil and Ida Green Professor in the Department of Electrical Engineering at the University of Texas at Dallas. Dr. Loizou was a fellow of the Acoustical Society of America. He was an associate editor of the International Journal of Audiology (2010–2012), IEEE Transactions on Biomedical Engineering (2009–2011), IEEE Transactions on Speech and Audio Processing (1999–2002), and IEEE Signal Processing Letters (2006–2009) and a member of the Speech Technical Committee (2008–2010) of the IEEE Signal Processing Society. He authored or coauthored numerous publications, including three textbooks.

For more information, see Dr. Loizou’s profile at the University of Texas at Dallas.

Watch a video of Dr. Loizou talking about technology that would allow cochlear implant users to easily adjust settings on their hearing devices through a smartphone.

Subject Categories

BISAC Subject Codes/Headings:
TECHNOLOGY & ENGINEERING / Mobile & Wireless Communications