While hunting round on the Gearslutz forums, I found a very cool impulse response AU plugin (thanks to "imagineaudio" for his post)....
LAConvolver from Learnvall Audio convolves your input signal with your impulse response:
VERY TECHNICAL BIT
An impulse, or "spike" is a short transient, that contains all frequencies (similar to a short burst of while noise). The Impulse Response is a recording of the behavior of the room/device when an impulse is played through it (in practice, a true impulse is impossible to create, so a starter pistol shot is used, or a tone sweep, which is then "deconvolved" to calculate the effect an impulse would have had).
The Impulse response and the plugin input signals are passed through FFT (Fast Fourier Transform) algorithms. The resultant spectra are multiplied with each other, and the product run through an IFFT (Inverse Fast Fourier Transform) algorithm, which makes the signal sound as if it had run through the same room/device the impulse response was recorded through.
What does that mean? Well, if you can get hold of impulse response recordings of, for example, a mic'ed up guitar cab, you can make your signal sound as if it also ran through the same setup - in fact, why not click here for some very cool guitar cab impulses! (GuitarHack IRs).
"LAConvolver Impulse Response plugin (free!)" > read the full post