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Ambisonics defined

October 18, 2006

How exactly is ambisonics defined? This question came up the other day at the sursound list. Richard Lee provided the following answer and I’m quoting/storing for future reference:

Gerzon defines Ambisonic in the Vienna paper and we have repeated &amp explained it in ours.

Ambisonic Decoders for HDTV – M Gerzon &amp Geoffrey Barton preprint 3345 AES Vienna mar92

“Localization in Horizontal-Only Ambisonic Systems” – Benjamin Lee &amp Heller AES oct06 San Francisco

A decoder or reproduction system for 360° surround
sound is defined to be Ambisonic if for
a central listening position it is designed such
i) velocity and energy vector directions are
the same at least up to around 4 kHz such
that the reproduced azimuth qV = qE is
substantially unchanged with frequency
ii) at low frequencies say below around 400
Hz the magnitude of the velocity vector
is near unity for all reproduced azimuths
iii) at mid/high frequencies say between
around 700 Hz and 4 kHz the energy
vector magnitude rE is substantially
maximised across as large a part of the
360° sound stage as possible.

Further elaboration on these concepts is in "General Metatheory .. ". So its defined by what is achieved rather than how this is achieved.

A while back Eric Benjamin provided a more verbatim explanation of the principles of ambisonics blogged here.