| Paul Winkler wrote:
[...]
> Oh, no, now we're back to blowing up houses!
>
> PW
>
Although there are some common caveats, I object to a direct comparison
of the two techniques. You're probably referring to a past discussion
which centered on how to best capture the essence of massive explosions.
The purpose there, was, well, to capture the essence of massive
explosions. The purpose here is how best to create an approximation of
the unit impulse.
It is true, as you imply, that the technique of shorting together mains
lines, could sometimes have the side-effect of destroying the house.
Well, ok, presumably if you are using this approach it isn't in your own
house, but rather in some spacious church or concert hall. I mean, why
would you be interested in the impluse-response of your boring, carpet
and curtain laden house. You wouldn't of course. Details. So, ok, one
side-effect of this technique is that you run the risk of destroying
some spacious antique church or famous concert hall.
The best way to think of this, is to make an analogy to the C funtion
"printf()". Yes, this function does indeed return some value. I think it
is the number of characters printed, or something like that. The point
is, that nobody cares. While the function does indeed return a value, we
in most cases are only interested in its side-effects, which is that of
producing output. Ooops. Wait a miniute. This is kind of the opposite of
the power-cord-short example, where we *don't* care about the
side-effects (the building gets destroyed), and only care about the
return value (recording the impulse response). Oh well, I picked the
wrong example, but I hope the point is made, if only in reverse.
In summary, I think, over all, that the person who suggested the idea of
recording a venue's impulse response by supplying the sound created by
the equivalent of sticking a paper clip into an electrical outlet, is on
sound theoretical ground. As a practical matter, you would want to be
sure that:
a) The reverberation that you are recording decays to a negligable
amplitude before being adulterated by the sounds of crackling building.
b) You do not plug your recording equipment into the same electrical
system as the one you are shorting out to generate the unit-impulse
(duh!)
I hope this helps.
Larry
-- Larry Troxler -- lt@westnet.com -- Patterson, NY USA --
|