On 05/26/2012 04:51 PM, Augustine Leudar wrote:
Hi Michael,
thanks for the reply - there is no doubt Ive missed something !
I am aware of the need for W coordinate and have included it in my encoder
as instructed although I have to admit I am still not clear on its
function - but my question specifically relates to the information gained
from the 3 fig of eight patterns gained form a mic design such as this one :
http://www.shapeways.com/model/143678/velan-140-internals.html
Am I right in thinking the W component gives you enhanced distance
information for a given sound source ?
we cannot hear absolute phase, so if you are listening to a figure of
eight microphone, there is no way to tell whether the sound you're
hearing was coming into the (positive) frontal lobe or the (inverted)
rear lobe. hence, the only information we can get from a lonely fig8 is
"it's obviously not coming from the side".
now if you add an omni to the equation, all of a sudden you have the
possibilty to discern between the two lobes of the fig8: one is in-phase
with the omni, the other isn't.
thus, the 0th order component helps you resolve the ambiguities of all
the 1st order signals.
btw, if you move to second order, the situation is the same: with a
cloverleaf directivity, you only know "it's either coming from
front-or-back, or from left-or-right". only with the first-order
information, the ambiguity can be resolved.
W also has a subtle role in distance coding, but its main job is really
to help us make sense of the fig8s.
to wrap up, three real fig8s won't ever give you ambisonics. but if you
obtain the fig8s by subtracting two back-to-back cardioids, you can also
add them, which then gives you a nice omnidirectional component. note
that you will have to attenuate the resulting omni signal according to
the number of capsules you used.
best,
jörn
--
Jörn Nettingsmeier
Lortzingstr. 11, 45128 Essen, Tel. +49 177 7937487
Meister für Veranstaltungstechnik (Bühne/Studio)
Tonmeister VDT
http://stackingdwarves.net
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