Scott Gravenhorst wrote:
music-dsp@music.columbia.edu wrote:
>On 2015-08-30, Scott Gravenhorst wrote:
>
>> This amounted to using a microphone to sample the effects of an
>> impulse (starter's pistol or some such) on some audio environment like
>> a church or concert hall,....
-- ScottG
I haven't browsed over all the answers yet, but yeah that's fun, making and playing with
sampled impulses. Of course, for the proper linear system theory to work as in to give you
all correct reverb responses to all possible excitations, with long delays being part of
the system to be modeled, essentially proper theory says you get problems because of the
alarm-shot sound having made a single snapshot, which you can only apply once, because for
the second sample of your own input to the linear system represented by the convolution of
the measured input with your own input signal, the air mass isn't anymore "at rest", or in
other words there are different initial conditions, so linear system theory is broken, and
also, linear systems with delays have infinite poles/zeros, so there's that.
It's still fun, but it sounds decidedly flat and boring on musical input signals is my
experience, and yes most likely there's a difference between the Free and Open Source
implementations of a "brute force" and FFT based long convolutor programs. Probably the
FFT ones will show a certain dimensionality in their computations, as a consequence of the
length of the chosen FFT. Might not be important for some applications, but when I make
audio productions that must work professionally, it could well be a first grade issue. I
didn't decode the whole source code (I think Fons, who offered the FOS "jconvolve" I've
tried was actually a graduate from the same university as I), nor run any direct
comparisons between the two convolution variations, which could be an interesting thing to
do, but I'm too busy programming some actual current digital synthesizers I work on. Also,
it's important to include shift invariance in the considerations about computations with
impulses.
Regards
T.
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