On 01/26/2011 06:33 AM, Augustine Leudar wrote:
out of curiosity Why the need
for the w coordinate - cant the sound pressure level be gleaned from the x,y
and z ?
you can't deduce w from figures-of-eight, because they simply don't move
when the pressure rises uniformly (and if they do, that's an artefact of
capsule diameter vs. wavelength and not something we could use).
if the fig8s you've worked with are the double-diaphragm, switchable
pattern type: of course you could take both diaphragms and add them
in-phase, and that would work, because you fake a velocity transducer
with two at least partly pressure-sensitive ones. but that's cheating
and doesn't change the fact that xyz and w are totally independent.
w is important as a phase reference: without w, you couldn't say from
where the signal in x, y, or z was coming, because your ears can't
detect absolute polarity...
try taking away the centre mic from an m/s pair, and just listen to L=s
and R=-s. no localisation at all.
This type of localisation
has proved extremely effective and don't think that any system no matter how
clever at fooling the human ear can improve upon a sound actually coming
from the direction its meant to
absolutely. this approach is perfect if your sound event is a point
source, and all you want is the direct sound. if you have wider sources,
or you need to convey ambience, reverb, reflections, it doesn't work so
well, but that's not an objective here iiuc.
Where ambisonics could help in the installation is the insect
noises - at the moment there are large 4 speaker areas with 4mic recorded
insect noises . Gaps in the image are plugged with other speakers with say
cicadas on them - despite the doubts expressed here it also has been
effective perhaps because insect noises are high frequency and the leaves
on the bushes and trees disperse the sound filling out the sound field.
Generally the effect is pretty similar to being in the rain forest- except
you don't get bitten.
recording insects with a soundfield will probably yield even better results.
you could also use "cheat wave field synthesis" if you can place
speakers every meter or so. i heard iosono present such a system at
TMT2010, and they did focused sources (!) :-o
at this speaker distance, spatial aliasing will be terrible, but their
sound example was, brace yourselves: rain. presto. virtual sources all
over the place. should work with insects beautifully, although calling
it wfs might be slightly questionable.
for fairness, i should say that ambi is just as bad in reproducing
insect or rain noises, but the artefacts (ambiguity, jumpy localisation,
coloration, phasiness) are generally beneficial, as they increase the
"density" and "buzz" of the rain, insect swarm, whatever.
so unless you want your listeners to be able to track the queen bee in
the swarm, you should be fine.
There
is no way a physical decoder could be in the biome - we generally have to
throw speakers away or sell them on ebay after a few uses because of the
ants and humidity (wav players are in sealed plastic boxes).
i don't understand this. are you perhaps using paper membranes? it
should be possible to obtain outdoor speakers that withstand these
conditions for years. of course they will cost a lot more, but that
should be negligible if you have to replace your current speakers that
often...
what do the ants do to the speakers, btw?
for purely technical reasons you should probably go for 70 or 100v
versions, as i expect your speaker lines to be loooong. the problem is
that 70/100 amplifiers are meant to drive many speakers in parallel,
not many channels discretely, so the price per amp channel might be
prohibitive. but it does give you the option to run the amps and players
outside of the habitat, in conditions appropriate to semiconductors.
--
Jörn Nettingsmeier
Lortzingstr. 11, 45128 Essen, Tel. +49 177 7937487
Meister für Veranstaltungstechnik (Bühne/Studio), Elektrofachkraft
Audio and event engineer - Ambisonic surround recordings
http://stackingdwarves.net
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