From Wikipedia, the free encyclopedia
The Soundfield microphone is an audio
microphone comprised of four closely spaced subcardioid
(unidirectional) microphone capsules positioned in a
tetrahedron. It was invented by
Michael Gerzon and Peter Craven, and is a part of, but not
exclusive to,
Ambisonics, a
surround sound technology.
A Soundfield microphone kit, consisting of the microphone and
a signal processor, produces two distinct sets of audio signals.
The first set, the A-format, is produced by the Soundfield
microphone itself and consists of the four signals from the
microphone capsules. These four signals are not intended to be
used without further processing. The A-Format is then normally
transformed into the second set of audio signals, the B-format.
This process is described in references 1 and 2. Depending on
the mic, this transformation is performed in either hardware or
software.
The B-format is the standard audio format produced by a
Soundfield kit. It consists of the following four signals:
- W - a pressure signal (mono) corresponding to the output
from an omni-directional microphone
- X - the front-to-back directional information, a
forward-pointing velocity or "figure-of-eight" microphone
- Y - the side-to-side directional information, a
leftward-pointing figure-of-eight microphone
- Z - the up-to-down directional information, an
upward-pointing figure-of-eight microphone
By combining these signals in various proportions, it is
possible to derive any number of first-order microphones,
pointing in any direction. For example, a forward-facing
cardioid is produced by
.
Examples of software that perform these calculations are the
Visual Virtual Microphone and Soundfield Research
Surround Zone plugin.
References
- Michael A. Gerzon
(1975). "The
Design of Precisely Coincident Microphone Arrays for Stereo
and Surround Sound". 50th Convention of the Audio
Engineering Society: Preprint L-20.
- Peter G. Craven and Michael A. Gerzon. "Coincident
Microphone Simulation Covering Three Dimensional Space and
Yielding Various Directional Outputs".
US patent 4042779.
External links
-
SoundField Limited, a soundfield mic manufacturer
-
AGM Digital Arts GmbH, a soundfield mic manufacturer
-
Core Sound, a soundfield mic manufacturer