convolution

[Sean Costello]

Martin Czech wrote:

> But how can I obtain a impulse response if I don't have anything that
> makes such a impulse. I could clap in my hands (not very reproduceable)
> or use two pieces of wood etc...

A starting pistol is often used for this purpose - this would probably provide
the best impulse. I have heard of people popping balloons, but it seems like
this would add some coloration to the sound (a balloon popping doesn't sound
like white noise to me).

Be sure to try all sorts of sounds as impulse responses. Hit a frying pan and
record the results, then use it as an impulse response for a very metallic
coloration. Any percussive sound can be used as a "resonator." For the "ideal"
reverb, use exponentially decaying white noise (synthesized with something like
Csound). Run a one-shot pulse (that is as close to infinitely thin as you can
get) through your favorite analog setup, and use the result to get an "analog"
sound.

There is an excellent essay by Curtis Roads, called "Sound transformation by
convolution" in the book "Musical Signal Processing" (Curtis Roads, Stephen
Travis Pope, Aldo Piccialli, Giovanni De Poli, eds., Swets & Zeitlinger, 1997).
I would HIGHLY recommend this book to anyone working with computer music. Curtis
Roads is currently working on a new book, "Microsound," that will cover in
greater detail his work with combining convolution with granular techniques.

Sean Costello