Drawing Filter Display

Does anyone have any idea how people draw those filter displays you see in some plugins? You know, like something in the picture below. I've been wondering this for the longest time, but I can't find any kind of explanation on it. Is the filters actual frequency response used to draw it, or how is it being drawn? If anyone knows, I'd be really grateful if you'd share. I love those displays and would love to make one myself. Even a simple one like Ableton's. 

The easiest way to do it is to use a filter library that can calculate the frequency response directly for you. Otherwise you will need to do some reverse engineering math on the filter algorithm used. (Which is not easy if you don't already know how to do it.) 

Vinnie Falco's filter library provides the frequency responses of the filters :


The library is unfortunately slightly difficult to use for basic filtering tasks, but not exceedingly so. (And it's a pretty good bonus it does provide the frequency response of the filter too.)

Another option might be to do some kind of an analysis of the filter's response each time the parameters are changed, for example with FFT. (I recall this has been suggested somewhere but I haven't tried that approach myself.)

Hey Jordan,

I’d love to implement something like this myself, and using Vinnie’s filters is not an option. Did you ever come up with anything?


Hey pizzafilms,

I can PM you a link to a basic filter GUI I started a while ago as an example for people but still haven’t gotten round to finishing. The parameters setup isn’t quite finished etc.

The display works just fine though. It currently just uses a one pole virtual analogue filter but the display should work for any kind of transfer function.