At 07:39 PM 2008-12-18, Marc Myers wrote:
>I'm thinking a little lower tech: Two listening stations with very
>directional microphones and head phones or maybe just a passive
>listening tube on a tripod, an attached GPS with electronic compass,
>some field notebooks and walkie-talkies. Gibbons start calling: Two
>observers locate the calls, coordinating with walkie-talkies. Using
>the compass and GPS location a bearing is taken on the call. The
>results can be analyzed with a map or GIS software. Thoughts?
A few thoughts from someone who has only been partially following
this fascinating thread.
(1) Directionality is a challenge with reflections from whatever and
diffusion from the ground. Also, foliage may distort the directionality.
(2) How do you know if both listeners are really listening to the
same call? You might consider a link between the two locations so
that one observer (or a third "conductor") is listening to both to
make sure you're recording the same one from both locations. If the
baseline is reasonably short and the target gibbons are between the
two stations, that should be reasonably easy, I would think, for
someone to ascertain, but I don't think two people can discern that
they're on the same animal just via walkie-talkie cues.
I would look at a high-quality radio mic link from one mic to the
recorder and then have the recorder by the second mic. For initial
feasibility testing, balanced lines run on cheap unshielded cable
should work -- especially if you've got good audio transformers at both end=
s.
(3) I've used a "Big Ears" Parabolic reflector for sports TV and it
seems the most directional reasonably wideband receiver with
reasonable gain. I wonder if a parabolic mic might be a better
solution than a listening tube. These lose directionality once the
wavelength is as large as the dish diameter. So you won't have much
below about 400 Hz, but, then again, stuff that low isn't very directional.
(4) recording the two mics coincidentally on the same recorder (I
think the SD702T can also record timecode and is much cheeeper than
the Zakscom, but you'd still need some external reference locking the
two together) would allow you to post-process delay information when
combined with azimuth information that you record in the field could
conceivably provide confirmation of distance information and perhaps
refine the rougher triangulation values.
(5) I still see isolating a single gibbon among many as the biggest
challenge and this must be confirmed.
This was a fun thought exercise after spending a day attempting to
figure out what to do about a physically crashed hard drive with 3000
records of an historic collection in my community. Thanks for the
opportunity to vent -- and no, I don't want to talk about the hard
drive on this list, I've done it on several others with great results.
One other thought exercise. When thinking of the sounds that bacteria
and virii make, would these be of much higher frequency than human
hearing due to the small size? I'm imagining this cacophony well
above bat-frequencies <smile>.
Cheers,
Richard
Richard L. Hess
Aurora, Ontario, Canada http://www.richardhess.com/
Detailed contact information: http://www.richardhess.com/tape/contact.htm =
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