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Re: Peculiarities of sound propagation

Subject: Re: Peculiarities of sound propagation
From: Walter Knapp <>
Date: Mon, 17 Mar 2003 01:38:35 -0500
Syd Curtis wrote:
> We have in the past considered at length, the problems peculiar to nature
> sound recording arising from the fact that the real world does not provid=
e
> the controlled conditions of a recording studio.  That no matter how good
> our equipment and techniques, we are faced with the situation that the so=
und
> reaching our microphone(s) is likely to be different from that which left
> the source.
>
> I don't wish re-open that discussion, but simply report a situation right
> here in front of my computer - at 8:00 AM, March 17.
>
> My head is one metre from an open window - albeit screened with wire gauz=
e
> to frustrate our Brisbane mosquitoes.  Somewhere between 5 and 10 metres
> from the window, and approx. on the same level (c. 4 m above ground), as =
far
> as I can tell, a cicada is singing - a continuous buzz that goes on for
> minutes at a time.
>
> I hear it plainly though not loud.  However, if I move my head half a met=
re
> further away from the window, the sound cuts out completely, at least to =
my
> ears.  Somehow interference (out of phase?) is cancelling the sound.  Thi=
s
> confirms that the position of a mic can have a considerable effect on a
> nature recording, quite apart from the obvious effect of attenuation of a
> signal with distance from the sound source, and consequential deteriorati=
on
> of signal/noise ratio.

This is why it pays to walk around a little before starting to record,
just listening.

Interesting that it should cancel that much. But nothing surprises me in
this regard.

> BTW, I wonder if in other languages there are interesting common names fo=
r
> cicadas.  Because of their songs, cicadas attract the attention of childr=
en.
> And children come up with some delightful names - Black Friday, Floury
> Baker, Razor Grinder, White Drummer, are some of our local ones here.  I'=
ve
> not managed to find the cicada singing outside my window, but choosing fr=
om
> among the song descriptions in our State Museum's book "Wildlife of
> Brisbane", my guess is that I have a "Brown Bunyip", Tamasa tristigma.

They sometimes get called locusts here. Though most call them cicadas.

And I sometimes call them much less flattering names when trying to
record frogs in their din. My pickup range shrinks quite a bit once they
start calling.

> For non-Australians, a Bunyip is a mythological creature, a sort of swamp
> version of the Loch Ness monster, given to appearing above the surface of
> the water at night and making very strange noises.  (I don't suppose you
> found any bunyips in the outback, Walter?)

Nope, just easily identified stuff.

Though you never know, I might be one. Except my appearances above water
at night tend to be quiet.

Walt




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