Preface
The study and implementation of microphone arrays originated over
20
years
ago. Thanks
to
the research
and
experimental developments pursued
to
the
present day, the field has
matured
to
the point
that
array-based technology
now has immediate applicability
to
a number of current systems
and
a vast
potential for the improvement of existing products and
the
creation of future
devices.
In
putting
this book together, our goal was to provide, for
the
first time,
a single complete reference on microphone arrays.
We
invited
the
top
re-
searchers in the field to contribute articles addressing their specific topic(s)
of study.
The
reception
we
received from our colleagues was quite enthusi-
astic and very encouraging. There was the general consensus
that
a work
of this kind was well overdue.
The
results provided in this collection cover
the
current
state
of
the
art
in microphone array research, development, and
technological application.
This
text
is organized into four sections which roughly follow
the
major
areas of microphone array research today.
Parts
I and
II
are primarily the-
oretical in
nature
and emphasize
the
use of microphone arrays for speech
enhancement and source localization, respectively.
Part
III
presents a num-
ber of specific applications of array-based technology.
Part
IV addresses some
open questions
and
explores the future of the field.
Part
I concerns
the
problem of enhancing the speech signal acquired by
an array of microphones. For a variety of applications, including human-
computer interaction and hands-free telephony,
the
goal is
to
allow users
to
roam unfettered in diverse environments while still providing a high quality
speech signal
and
robustness against background noise, interfering sources,
and reverberation effects. The use of microphone arrays gives one the oppor-
tunity
to
exploit
the
fact
that
the source of the desired speech signal and
the
noise sources are physically separated in space. Conventional array process-
ing techniques, typically developed for applications such as
radar
and sonar,
were initially applied
to
the hands-free speech acquisition problem. However,
the environment in which microphone arrays
is
used
is
significantly different
from
that
of conventional array applications. Firstly, the desired speech signal
has
an
extremely wide bandwidth relative to its center frequency, meaning
that
conventional narrowband techniques are not suitable. Secondly, there
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