[PD] butterworth filter

[Stephen Sinclair]

> I'm attempting to emulate something in PD that calls for a 4 pole
> Butterworth low pass filter with a cutoff frequency of 10 Hz. I have
> very little idea what that is. But I'm wondering if it's possible to
> construct something that would do the same thing in PD. If so, anyone
> have any ideas on how to make something like that with PD's existing
> objects?

Try this filter designer to get coefficients to use in biquad~ objects:
http://www-users.cs.york.ac.uk/~fisher/mkfilter/trad.html

Here's some code too, which might be more clear:
http://www.musicdsp.org/showone.php?id=227

For 4-pole you'll need to use more than one biquad, I think.
I'm not sure how, but you can split it over multiple biquads.

Start with 2-pole for a single biquad, to make things easy.


Steve