Preface
Noise is everywhere and in most applications that are related to audio and
speech, such as human-machine interfaces, hands-free communications, voice
over IP (VoIP), hearing aids, teleconferencing/telepresence/telecollaboration
systems, and so many others, the signal of interest (usually speech) that is
picked up by a microphone is generally contaminated by noise. As a result,
the microphone signal has to be cleaned up with digital signal processing tools
before it is stored, analyzed, transmitted, or played out. This cleaning pro-
cess is often called noise reduction and this topic has attracted a considerable
amount of research and engineering attention for several decades. One of the
objectives of this book is to present in a common framework an overview
of the state of the art of noise reduction algorithms in the single-channel
(one microphone) case. The focus is on the most useful approaches, i.e., fil-
tering techniques (in different domains) and spectral enhancement methods.
Readers who are interested in algorithms based on multiple microphones (or
microphone arrays) are invited to consult the recent book by J. Benesty, J.
Chen, and Y. Huang, Microphone Array Signal Processing, Berlin, Germany:
Springer-Verlag, 2008, and the references therein.
Several books on speech enhancement can be found in the literature. But
they either do not cover state-of-the-art noise reduction techniques or are not
rigorous in the explanations on how and why the noise reduction algorithms
really work. This is how the idea of writing a book on Noise Reduction in
Speech Processing came up. Therefore, the other objective of this text is to
derive the most important and well-known techniques in this area of research
and engineering in a rigorous way yet clear way, and prove many fundamental
and intuitive results often taken for granted.
This book is especially written for graduate students and research engi-
neers who work on noise reduction for speech and audio applications and
want to understand the subtle mechanisms behind each approach. We hope
the readers will find many new and interesting concepts that are presented in
this book useful and inspiring.
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