> Or perhaps it was comb-filtering from the ground bounce. As the
> plane nears, the difference in path lengths between the direct
> arrival from the plane and the bounce becomes progressively shorter.
Eric,
It's an interesting effect and I've eliminated ground bounce. The
ground is steep and very irregular and covered in thick grass or thick
shrubbery. I mount my mics almost on the ground to reduce the ground
effect. On other aircraft I can sometimes hear the finely tuned 108Hz
ringing at the one frequency but the original plane hit it spot on.
I've got an audiogram:
http://www.stowford.org/images\dr1000_2080plane.gif
Note the "waveform" is log scale. The peaks at about 00:15 secs and
01:45 are a close bird.
I've since checked with a slow sweep tone from a portable loudspeaker
and there is no hint of a resonance either close or distant so the
effect seems to come from above and at a distance, so the house at the
top of a slope is still the chief suspect.
What is different between left and right mics is that on the left side
are big trees and my oddly shaped house walls, and only the walls
could produce this sharp resonance, perhaps with some help from the
rear lobes of the MKH416.
I wrote about it as I was surprised at the effect and I will look out
for reflection effects in the future. Our ears "tune out" many of
these effects but of course mics don't.
David
David Brinicombe
North Devon, UK
Cogito cogito ergo cogito sum - Ambrose Bierce
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