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Re: digital filter design

 > From: Farsheed <hamidito@xxxxxxxx>
 For my senior design project we are working on making a
 touchpad filter equalizer, so that you can boost or attenuate
 frequencies on the fly using your finger.  My question for you
 is, would you recommend any texts to read regarding choosing a
 good DSP filter for such a design?  We would like to be able
 to control Q, boost/attenuation, and frequency for a
> bandstop/bandpass filter directly, using one algorithm only.

I'm not sure it goes as far as what you're looking for, but I've worked on ways to easily make variable-Q (or damping) and variable-Frequency pole pairs or zero pairs (e.g. for resonators) with separate frequency and damping parameters and simple math (just multiplication and addition, no trig, log, exp, sqrt, etc.). With one pole pair and one zero pair you could make a simple equalizer capable of band boost or band cut with variable frequency, Q, and amount, but the parameterization of your equalizer may not map directly to what I've done here.

The only writeup is in a patent (US 5,355,329):

The first technique described (simplest, but only a usable
approximation for pole frequency way below sample rate) is in the
public domain because we published it before doing the better
versions that are patented; the better versions work to somewhat
higher frequency and damping, but generally not for pole frequencies
and above about half the Nyquist frequency, and best for low damping
(high Q).  I can't say whether the assignee would ever care about
this patent.

I can provide a PDF of the patent on request.