Olin is mostly right, but I think he means to say "delta function".
Gamma function is an extension of factorial to non-integers.

It should be sufficient, if you need to perform system identification
on the room, to use a swept-frequency sinusoid and look at the
received vs transmitted amplitude and phase to give you a Bode plot of
the room's characteristics, with the appropriate transducer/mic type
and placement.

Sean


On Tue, May 17, 2011 at 11:37 AM, Olin Lathrop
<olin_piclist@embedinc.com> wrote:
> Look up impulse or "gamma function", and you'll see it's a function defin=
ed
> to have zero duration but a area of 1. =A0That's rather hard to do in
> practise. =A0Usually you make due with short enough for the highest frequ=
ency
> of interest and adjust the amplitude or compensate for it in the math as
> appropriate. =A0Another trick is to use a step function, which is general=
ly a
> little easier to realize well enough. =A0Since a step is the integral of =
a
> impulse, the system response you get is the integral of the impulse
> response. =A0Math can convert that to the impulse response, but since it'=
s
> taking the derivative is susceptible to noise.
>

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