7. Re: Advice please on what mics for recording in quiet outdoor enviro

["Avocet" madl74]

> Just take a listen what I recorded this spring out on remote public
> lands in Central Oregon the middle of the night. I believe this is
> anthronoise from an aerial drone - not natural sound.
> http://snd.sc/U9BV3X

John,

An interesting recording. On a power spectrum there is clear banding
which lowers in frequency and then rises again as it passes,
suggesting a comb filtering between direct sound and a reflection. At
the low point, the bands are 120Hz apart giving an effective path
length difference of about 2.8metres from a reflector about 1.4met
away at the highest passing angle.

The engine/prop noise drops from 1514 to 1321 giving an airspeed (not
allowing for angles) of roughly 50m/s or 110mph, or in practice,
greater than that. On the spectrum, as the engine/prop whine passes
through the comb filter bands, it cancels and reinforces as would be 
expected.

These are rough figures but probably consistent with a prop powered
aircraft passing not directly overhead.

David

David Brinicombe
North Devon, UK
Cogito cogito ergo cogito sum - Ambrose Bierce