[PD] Equalizer

[pix]

On Tue, 28 Aug 2001 02:42:12 +0200 (CEST)
Álvaro Castro <alvcastro at yahoo.es> wrote:

> Hi all!!
> 
> Some days ago I posted an e-mail asking for help for
> building an equalizer. I didn't get many help, that's
> the reason I write again. If I'm writing to the wrong
> list, please tell me.
> I just want to know the basics of an equalizer so I
> can start working. As you see, I'm a beginner, but I
> don't know how to start.

the main reason you probably haven't received much help is because this is
not really a pd question but a general dsp question. so ideally you would
look into some dsp resources, where you will find that you need to know a
fair amount about digital filtering to make an equalizer, then maybe you
would get some help on building filters in pd.
 
> I choosed to learn PD instead of other sound programs
> or programming languages because I thought it was very
> powerful and not very difficult to learn.
> But when I started working with PD I discovered that
> one of the most important things for me (the low and
> high pass filters) don't work very powerfully. I tried
> filtering a sample and I realized that the filters
> didn't cut TOTALLY the frequencies they just decreased
> the amplitude a little bit.

this is common with digital filters... to get a really sharp roll off you
normally need a more complicated filter... you can also try recursively
applying the same filter...

> Finally, I would like to know what's the best way to
> work with pure (or almost pure) frecuencies. That's
> the reason I want to build an equalizer. I would like
> to add, increase, delete or decrease specific
> frecuencies. Is that posible with Pure-data??

well, adding frequencies is easy... [osc~] and [+~] :)

> Thank you very much for your time!
> I will appreciate any answer, because I don't know
> what to do now!!

there is a dsp book available for download at www.dspguide.com, it's
reasonably accessible as an introductory text.

pix.