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

Subject: 1. Re: Advice please on what mics for recording in quiet outdoor enviro
From: "rock_scallop" rock_scallop
Date: Sat Sep 15, 2012 10:40 am ((PDT))
Interesting analysis David. What affect would diffraction through trees in a 
forest have on frequency of an object passing overhead?

John Hartog

--- In  "Avocet" <> wrote:
> > 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.
> >
> 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

"While a picture is worth a thousand words, a 
sound is worth a thousand pictures." R. Murray Schafer via Bernie Krause.

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