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| The '''Soundfield microphone''' is an audio [[microphone]] composed of four closely spaced [[Microphone#Microphone polar patterns|subcardioid]] or [[Microphone#Microphone polar patterns|cardioid]] (unidirectional) microphone capsules arranged 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. It can function as a mono, stereo or surround sound microphone, optionally including height information. | | The author's title is Christy. My spouse doesn't like it the way I do but what I free psychic reading ([http://www.onbizin.co.kr/xe/?document_srl=320614 www.onbizin.co.kr]) really like doing is caving but I don't have the time lately. Alaska is the only place I've been psychic readers ([http://isaworld.pe.kr/?document_srl=392088 isaworld.pe.kr]) residing in but now I'm contemplating other options. Office supervising is where my primary earnings arrives from but I've usually needed my own business.<br><br>my web-site :: psychic love readings, [http://www.chk.woobi.co.kr/xe/?document_srl=346069 visit this website link], |
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| == History ==
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| The soundfield mic was invented by [[Michael Gerzon]] and Peter Craven. Their theoretical design was developed into a practical microphone system by Calrec Audio Limited, who launched the first soundfield mic in 1978.<ref>{{cite web
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| |url = http://www.calrec.com/uk/Company/Pages/History.aspx
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| |title = The changing face of broadcast
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| |publisher = Calrec Audio Limited
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| |location = Hebden Bridge, West Yorkshire
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| |accessdate = 9 January 2012
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| |quote = 1978: Calrec launches the Soundfield microphone, the world’s first single point-source microphone capable of recording sound in three-dimensions for surround-compatible playback.
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| }}</ref>
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| In 1993, the soundfield mic part of Calrec was separated out as the company SoundField Limited, who further developed the range of products.<ref>{{cite web
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| |url = http://www.soundfield.com/company/company.php
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| |title = The Company - background and history
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| |publisher = SoundField Limited
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| |location = Wakefield, West Yorkshire
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| |accessdate = 9 January 2012
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| |quote = In 1993, the company SoundField Ltd. was formed specifically to manufacture and further develop the range of products and their application in both stereo and multi-channel audio environments.
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| }}</ref> Since the original patents relating to the soundfield mic expired, other companies have started to manufacture soundfield mics.
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| == Signals ==
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| A Soundfield microphone kit, consisting of the microphone and a signal processor, produces two distinct sets of audio signals called ''A-Format'' and ''B-Format''.
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| === A-Format ===
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| [[File:Tetrahedron.png|thumb|The A-Format is the signals from four microphones on the faces of a [[tetrahedron]].]]
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| 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 normally transformed into the second set of audio signals, the B-Format. This process is described in the two sources listed under [[#Further reading|Further reading]]. Depending on the microphone model, this transformation can be performed in either hardware or software.
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| === B-Format ===
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| The B-Format is the standard audio format produced by a soundfield kit. It consists of the following four signals:
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| * W - a pressure signal corresponding to the output from an omnidirectional microphone
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| * X - the front-to-back directional information, a forward-pointing velocity or "figure-of-eight" microphone
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| * Y - the side-to-side directional information, a leftward-pointing "figure-of-eight" microphone
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| * Z - the up-to-down directional information, an upward-pointing "figure-of-eight" microphone
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| These are the constant (W) and linear (X, Y, Z) terms in the [[multipole expansion]] of a function on the sphere – in effect, it approximates the [[wave field synthesis|wave field]] on a sphere around the microphone.
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| It is possible to recreate the three dimensional soundfield, however the soundfield microphone particularly shows its versatility in a stereo or mono application. For example, a forward-facing cardioid is produced by<math>\sqrt2 W + X</math>. By combining the signals in various proportions, it is possible to derive any number of first-order microphones, pointing in any direction, before and after recording. For instance, provided the W, X, Y and Z signals are recorded separately, it is possible to pinpoint the microphone to a certain response from the audience even after recording. Examples of software that perform these calculations are
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| [http://vvaudio.com/vvmic/ Visual Virtual Microphone], SoundField's [http://www.soundfield.com/products/s_zone.php Surround Zone] and Ambisonic Studio's [http://www.radio.uqam.ca/ambisonic/b2x.html B2X decoders] plug-ins. | |
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| In other words, the B-format recording can be decoded to model any number of microphones pointing in arbitrary directions: each microphone's pattern can be selected to be omnidirectional, cardioid, hypercardioid, figure-of-eight, or anything in between. This can be done live or in post-production (after the recording is made).
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| The playback configuration is equally flexible. Again in post-production, the B-format recording can be decoded to any number of speakers arranged in both the horizontal and vertical planes.
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| Note however that this information only allows the direction of sound at the microphone to be reproduced – microphone responses pointing in any ''direction'' can be synthesized, but it does not allow the reconstruction of what a microphone at a different ''point in space'' would record. To do that requires reconstructing the wave field in more detail (as in [[wave field synthesis]]).
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| == References ==
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| {{Reflist}}
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| == Further reading ==
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| {{Refbegin}}
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| * {{cite conference
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| |author=Michael A. Gerzon
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| |title=The Design of Precisely Coincident Microphone Arrays for Stereo and Surround Sound
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| |booktitle=50th Convention of the Audio Engineering Society
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| |year=1975
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| |pages=Preprint L-20
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| |url=http://www.aes.org/e-lib/browse.cfm?elib=2466
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| }}
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| * {{cite paper
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| |author=Peter G. Craven and Michael A. Gerzon
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| |title= Coincident Microphone Simulation Covering Three Dimensional Space and Yielding Various Directional Outputs
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| |publisher={{Cite patent|US|4042779}}
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| |year=1975
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| }}
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| {{Refend}}
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| == External links ==
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| * [http://www.soundfield.com/ SoundField Limited], a soundfield mic manufacturer
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| * [http://www.core-sound.com/ Core Sound LLC], a soundfield mic manufacturer
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| * [http://www.oktavausa.com/ProductsPages/Ambient4DMic.html Oktava], a Russian mic manufacturer whose range includes a soundfield mic
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| {{Use dmy dates|date = September 2010}}
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| [[Category:Microphones]]
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| [[Category:Ambisonics]]
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