# [chuck-users] filter

Kassen signal.automatique at gmail.com
Sat Jul 1 06:51:26 EDT 2006

```> Could someone explain that the coefficients mean? (or link to some
> material that explains it)...
>

Well...... A digital filter is one big mathematical function, right?
The coeficients are the numbers in the equation. Everything the filter
does follows from those, the cutoff and the resonance follow from them
but also wether or not the filter is stable (which kinda means "wether
or not it works at all").

As I understand the theory what you have is very short delays and
amplification factors and the coeficients are simply numbers like how
much to amplify by at various stages before summing. The problem is
that fimding what numbers represent the exact filter you need is quite
hard and not so much fun to go do manually.

If you want to go there I sugest a serious book on DSP. Beware that
this stuff gets very serious very quickly.

I wanted to have a good look at how ChucK implements this and actually
started reading on DSP but then I saw that there is a plan to clean up
how these work in a future version. This made me wait for this
cleaning, I'd sugest you do the same.

> Yeah, that looks like a nice book, might pick it up. I imagine a lot of
> future users being just as ignorant as me about filer coefficients and
> the like. So may I propose that a couple of simple to use analog style
> filters is added to chuck + a bit of explanation about using the current
>   filters + links (if possible) to background material.
>

Yeah, I'd like to have that book too.

I realise this post isn't much help but at least it should be somewhat
clear *why* it's not so helpfull. What would be nice would be
something like "how to deal with filters in ChucK without going insane
over 1000 page tomes that asume you want to design a mobile phone".

Maybe if the filters do get cleaned up Perry might write something on
them, I can't imagine he designs a IIR filter for every musical piece
he does.

Kas.
```