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| | The name of the writer is Jayson. To perform lacross is some thing I truly appreciate performing. Distributing manufacturing is how he makes a living. North Carolina is the place he enjoys most but now he is considering other choices.<br><br>Also visit my website; best psychic ([http://www.youronlinepublishers.com/authWiki/AdolphvhBladenqq http://www.youronlinepublishers.com/]) |
| {{Refimprove|date=January 2009}}
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| <!-- Commented out: [[Image:AmbisonicLogo.svg|200px|right]] -->
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| {{Main|Ambisonics}}
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| This page focusses on decoding of classic first-order [[Ambisonics]]. Other relevant information is available on the [[Ambisonic reproduction systems]] page.
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| The Ambisonic B-format WXYZ signals define what the listener should hear. How these signals are presented to the listener by the speakers for best results, depends on the number of speakers and their location. Ambisonics treats directions where no speakers are placed with as much importance as speaker positions. It is undesirable for the listener to be conscious that the sound is coming from a discrete number of speakers. Some simple decoding equations are known to give good results for common speaker arrangements. | |
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| But Ambisonic Speaker Decoders can use much more information about the position of speakers, including their exact position and distance from the listener. Because human beings use different mechanisms to locate sound, '''Classic Ambisonic Decoders''' it is desirable to modify the speaker feeds at each frequency to present the best information using Shelf Filters.
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| Some views on the complexities of '''Shelf Filters''' and '''Distance Compensation''' are explained in "Ambisonic Surround Decoders"<ref>{{cite web
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| | first = Richard
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| | last = Lee
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| | title = Ambisonic Surround Decoder
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| | url = http://www.ambisonia.com/Members/ricardo/ASD.htm
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| | publisher = Ambisonia.com
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| | date = 18 February 2007
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| | accessdate = 4 April 2009
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| | archiveurl= http://web.archive.org/web/20090319141348/http://ambisonia.com/Members/ricardo/ASD.htm| archivedate= 19 March 2009 <!--DASHBot-->| deadurl= no}}</ref> and "SHELF FILTERS for Ambisonic Decoders"<ref>{{cite web
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| | first = Richard
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| | last = Lee
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| | title = SHELF FILTERS for Ambisonic Decoders
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| | url = http://www.ambisonia.com/Members/ricardo/shelfs.zip/view
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| | publisher = Ambisonia.com
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| | format = Zipped Microsoft Word document
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| | date = 14 April 2007
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| | accessdate = 4 April 2009
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| | archiveurl= http://web.archive.org/web/20090415152926/http://www.ambisonia.com/Members/ricardo/shelfs.zip/view| archivedate= 15 April 2009 <!--DASHBot-->| deadurl= no}}</ref> in the [[#External links|External links]].
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| There are specialised decoders for large audiences in large spaces.
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| Hardware decoders have been commercially available since the late 1970s; currently, Ambisonics is standard in surround products offered by [[Meridian Audio, Ltd.]]. Ad hoc software decoders are also available (see [[#External links|External links]]).
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| There are five main types of decoder:
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| == Diametric decoders ==
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| This design is intended for a domestic, small room setting, and allows
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| speakers to be arranged in diametrically opposed pairs.
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| == Regular Polygon decoders ==
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| This design is intended for a domestic, small room setting. The speakers are equidistant from the listener and lie equally spaced on the circumference of a circle. The simplest [[Regular polygon|Regular Polygon]] decoder is a Square with the listener in the centre. At least four speakers are required. Triangles do not work, exhibiting large "holes" between the speakers. Regular Hexagons perform better than Squares especially to the sides.
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| For the simplest (two dimensional) case (no height information), and spacing the loudspeakers equally in a circle, we derive the loudspeaker signals from the B-format W, X and Y channels:
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| :<math>P_n = W + X \cos\theta_n + Y \sin\theta_n</math>
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| where <math>\theta_n</math> is the direction of the speaker under consideration.
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| The most useful of these is the Square 4.0 decoder.
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| The [[coordinate system]] used in Ambisonics follows the [[right hand rule]] convention with positive X pointing forwards, positive Y pointing to the left and positive Z pointing upwards. Horizontal angles run [[anticlockwise]] from due front and vertical angles are positive above the horizontal, negative below.
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| == Auditorium decoders ==
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| This design is intended for a large, [[public space]] setting.
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| == "Vienna" decoders ==
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| These are so named because the paper introducing them was presented at the 1992 [[Audio Engineering Society|AES]] conference held in Vienna. This design was covered by {{Cite patent|US|5757927}}<ref>{{ cite patent
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| | country = US
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| | number = 5757927
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| | status = patent
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| | title = Surround sound apparatus
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| | gdate = 1998-05-26
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| | invent1 = [[Michael Gerzon|Gerzon, Michael Anthony]]
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| | invent2 = Barton, Geoffrey James
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| | class = H04S3/02
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| }}</ref> from Trifield Productions (see [[#External links|External links]]). The technology provides one approach to the decoding of Ambisonic signals to irregular loudspeaker arrays (such as [[International Telecommunication Union|ITU]]) commonly used for 5.1 [[surround sound]] replay.
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| == Parametric decoders ==
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| The idea behind parametric decoding is to treat the sound's direction of incidence as a parameter that can be estimated through [[time–frequency analysis]]. A large body of research into human spatial hearing<ref>{{cite book
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| | last = Blauert
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| | first = Jens
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| | authorlink = Jens Blauert
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| | title = Spatial Hearing: The Psychophysics of Human Sound Localization
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| | url = http://books.google.com/books?id=wBiEKPhw7r0C
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| | accessdate = 6 January 2011
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| | edition = Revised
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| | year = 1997
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| | publisher = MIT Press
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| | location = Cambridge, MA
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| | isbn = 978-0-262-02413-6
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| }}</ref><ref>{{cite book
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| | last = Bregman
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| | first = Albert S.
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| | authorlink = Albert Bregman
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| | title = Auditory Scene Analysis: The Perceptual Organization of Sound
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| | url = http://books.google.ca/books?id=jI8muSpAC5AC&dq=%22Auditory+scene+analysis%22+Bregman&source=gbs_navlinks_s
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| | accessdate = 12 May 2012
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| | series = Bradford Books
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| | date = 29 September 1994
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| | publisher = MIT Press
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| | location = Cambridge, MA
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| | isbn = 978-0-262-52195-6
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| }}</ref> suggests that our auditory cortex applies similar techniques in its [[auditory scene analysis]], which explains why these methods work.
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| The major benefits of parametric decoding is a greatly increased angular resolution and the separation of analysis and synthesis into separate processing steps. This separation allows B-format recordings to be rendered using any [[Panning (audio)|panning]] technique, including delay panning, VBAP<ref>{{cite web
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| | url = http://www.acoustics.hut.fi/research/cat/vbap/
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| | title = Vector base amplitude panning
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| | date = 18 January 2006
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| | work = Research / Spatial sound
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| | publisher = TKK Acoustics
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| | location = Otakaari, Finland
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| | accessdate = 12 may 2012
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| }}</ref> and [[HRTF]]-based synthesis.
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| Parametric decoding was pioneered by Lake DSP<ref>{{cite patent
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| | country = US
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| | number = 6628787
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| | status = patent
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| | title = Wavelet conversion of 3-D audio signals
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| | gdate = 2003-09-30
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| | invent1 = McGrath, David Stanley
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| | invent2 = McKeag, Adam Richard
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| | class = H04S3/02
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| }}</ref> in the late 1990s and independently suggested by Farina and Ugolotti in 1999.<ref>{{cite conference
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| | url =http://pcfarina.eng.unipr.it/Public/Papers/126-AESC99.PDF
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| | title =Subjective Comparison Between Stereo Dipole and 3D Ambisonic Surround Systems for Automotive Applications
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| | first1 =Angelo
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| | last1 =Farina
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| | first2 =Emanuele
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| | last2 =Ugolotti
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| |date=April 1999
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| | conference =AES 16th International conference on Spatial Sound Reproduction
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| | conferenceurl =http://www.acoustics.hut.fi/aes16/main.htm
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| | booktitle =Proceedings of the AES 16th International Conference
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| | publisher =[[Audio Engineering Society|AES]]
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| | location =Rovaniemi, Finland
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| | format =PDF
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| | id =s78357
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| | accessdate =12 May 2012
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| }}</ref> Later work in this domain includes the DirAC method<ref name="DirAC">{{cite web
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| | url = http://www.acoustics.hut.fi/research/cat/DirAC/
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| | title = Directional Audio Coding
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| | date = 23 May 2011
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| | work = Research / Spatial sound
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| | publisher = TKK Acoustics
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| | location = Otakaari, Finland
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| | accessdate = 12 may 2012
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| }}</ref> and the Harpex method.<ref>{{cite web
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| | url = http://harpex.net/
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| | title = Harpex
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| | year = 2011
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| | publisher = Harpex Limited
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| | location = Oslo, Norway
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| | accessdate = 12 May 2012
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| }}</ref>
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| == Irregular Layout Decoders ==
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| Decoding for arbitrary irregular speaker layouts is a subject of ongoing research. The [[Rapture3D]] decoder from [[Blue Ripple Sound]] supports this and is already used in a number of computer games using [[OpenAL]].
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| == See also ==
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| * [[Ambisonics]]
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| * [[Ambisonic UHJ format#Decoding UHJ|Ambisonic UHJ format: Decoding UHJ]]
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| * [[Meridian Audio, Ltd.]], manufacturer of hardware decoders
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| == References ==
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| {{Reflist}}
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| == External links ==
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| * [http://members.tripod.com/martin_leese/Ambisonic/faq_latest.html Ambisonic Surround Sound FAQ] (Sections 17 and 18 for hardware decoders)
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| * [http://www.ambisonia.com/wiki/index.php/Playback_Software Ambisonia website] Bruce Wiggins's WAD decoders for 4.0, 6.0 and 8.0 are nearly Classic Ambisonic Decoders and easy to use plugins for [[Windows Media Player]].
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| * [http://www.radio.uqam.ca/ambisonic/b2x.html B2X Plug-Ins] B2D, B2G and B2Stereo software decoders, in VST and Audio Unit formats, for Mac OS X
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| * [http://www.ambisonia.com/Members/ricardo/ Shelf Filters and Distance Compensation] "Ambisonic Surround Decoder" and "SHELF FILTERS for Ambisonic Decoders" explain these important features of Classic Ambisonic Decoders for those designing software decoders
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| * [http://harpex.net Harpex Ltd] (for stand-alone and plug-in versions of the Harpex method)
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| * [http://www.blueripplesound.com Blue Ripple Sound Limited] Rapture3D and TOA regular and irregular speaker decoders, binaural stereo and more.
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| [[Category:Sound production technology]]
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| [[Category:Ambisonics]]
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