Another paper by Nika was done some time ago, but I just finished to read it.

It's a pdf about digital filters : it deals with equalizers, lowpass, highpass, sample rate converion, and digital reverb.
It explains the IIR and FIR filters.

For all who still believe that equalizers use Fourier Transform calculation...

http://www.prosoundweb.com/recpit/viewtopic.php?t=2164

This will come in use as a good reference. I think i'll start looking through it. It's all of the worthwhile. Thanks for the link and for sharing it with us.