On Sun, 21 Aug 2005 19:22:47 -0700, Chad Irby wrote
(in article ):

Kinda makes you wonder if they used a particular kind of "noisy" sound
wave, or simple shapes like sine waves.

It'd be really funny if it turned out to work with random or
less-patterned noise, and they missed it because they were too
organized...

One would be tempted to think this, but all noise (including triangle and
square waves) can be constructed from a sum of sines and cosines. It is
called Fourier's Theorem, and it works so well nearly all digital signal
processing is based on it to some extent. Note that the researcher's 400 Hz
signal (close to the A flat above middle C) could form some pretty irritating
beats with the engine/propeller. Concert A is 440 and I suspect anybody who
has worked with military aviation is familiar with the sound of the 400 Hz
power systems.

-- Charlie Springer