At 09:33 AM 4/12/2004 +0200, you wrote:
>Lang,
>
>Yes, the overall self-noise floor of the microphones itself will also drop
>by 3dB if the two channels are mixed together. So, you could even use more
>microphones to increase that effect. Though, the effect would be relativel=
y
>small (each doubling of the microphone count would provide a 3 dB noise dr=
op
>only). Unfortunately, mixing several microphone signals together might
>also lead
>to unwanted phase cancelations in the sounds you want to record.
>
>Raimund
A very interesting analysis, thanks to Lang, Martyn and Raimund.
In most *practical* situations 3 dB, as we all know, is barely perceptible=
to most listeners, and of course doubles you mic cost. Still, I have
recorded in stereo for years for many other reasons. During lab play-back,=
I have always found a stereo sound keeps my attention and alerts me to
faint sounds much better, as they are likely to stand out spatially from
other sounds. My ears need all the help I can give them. ;^0
A more important matter is: if the bird moves or you slightly miss-aim
somewhere in the leaves then one of the mics usually gets the better signal=
and you then later simply use it. This is a VERY common situation in
getting the best species-specific sounds, happening on every trip to
everywhere, whereas actually encountering a Sennheiser mic noise floor is
out there somewhere with finding the last Ivory-bill - very nice but I'm
not expecting it anytime soon.
But this phase cancellation Raimund mentions would only occur if the two
wave travel paths were in any way different. As we frequently have
mentioned, this can occur through improper mic placement or from
atmospheric effects from mixing air paths of different velocity,
(temperature or humidity), from gentle convection or breezes. Under
morning, still conditions these effects are usually minimal, especially for=
mics this close together. In any event, the highest frequencies would be
affected the most, because the shorter wavelengths get phase shifted by the=
smallest path length differences. This is one reason high frequencies are=
attenuated naturally with increasing distance (try recording jingling keys=
with any mic at more than 20 to 30 meters) - you lose it anyway, parabola
or no. Any flexible parabolic shape will suffer such multiple-path losses=
above 12 to 16 kHz. Not that I would care - haven't heard such sounds in
years. ;^)
Carry on; my best regards to all,
Marty Michener, MIST Software Assoc. Inc., P. O. Box 269, Hollis, NH 03049
830 plus species of bird sounds on a disc:
http://www.enjoybirds.com/
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