[PD] butterworth filter

[Mathieu Bouchard]

On Thu, 26 Oct 2006, Pall Thayer wrote:

> Yeah, I thought about that but does one then set each of the lop~'s for 
> 10Hz or try to spread the 10 between them like:
> [lop~ 2.5]*4 or [lop~ 10]*4

You want to cut at 10 Hz so you put four of them at 10 Hz.

Each linear filter has a fixed gain for each frequency. The log-log 
spectrum of one filter drops suddenly around 10 Hz with a straight slope. 
With several filters in series, the log-log spectra add up, so the slope 
becomes steeper.

I suppose that you've seen log-log graphs before? for a function y=f(x), 
they have log(y) and log(x) axes, instead of y and x axes.

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| Mathieu Bouchard - tél:+1.514.383.3801 - http://artengine.ca/matju
| Freelance Digital Arts Engineer, Montréal QC Canada