[pd] FFT sine to saw oscilator (was:[pd] hanning window + fft)

Chuckk Hubbard badmuthahubbard at gmail.com
Fri Sep 8 02:31:13 CEST 2006


On 9/7/06, Charles Henry <czhenry at gmail.com> wrote:
> On 9/5/06, Chuckk Hubbard <badmuthahubbard at gmail.com> wrote:
> > Just a thought... the output of a recursive filter from an input of an
> > impulse would be several impulses of linearly changing amplitude at
> > equally spaced intervals, and it would seem like that ought to give
> > some sort of sawtooth if you put it through IFFT.
>
> I tried to do this, like you said, but couldn't figure it out.
> I tried to use z~ with a throw~ and catch~ on very small blocksizes,
> but I couldn't get the throw/catch to work.  same with send~/recieve~
>
> then, I ran the output to ifft~ on overlapping blocks and windowed
> with the hanning window
>
> Let me know if you get it working
>
> Chuck

I was thinking something like this.  I was wrong, it's exponential
decay, not linear, so it wouldn't create a sawtooth exactly.  I also
can't for the life of me figure out why the impulse response moves
every time I hit bang on here.  It seems like it should always start
right at the left side of the graph, but sometimes it doesn't show up,
and other times it skips around in the graph.
But if you set coefficients for the filter, bang until something shows
in the response, and set the volume, it does make a harmonic sound.

-Chuckk
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