Subject: Re: digital filter design From: Ramdas Kumaresan <kumar(at)ELE.URI.EDU> Date: Sun, 30 Jan 2005 07:26:19 -0500Farsheed, Also take a look at L.B.Jackson's text book "Digital filters and Signal processing" Kluwer publishing, Ch.4. It has a unity gain resonator which can be tuned by varying just one coefficient. Incidentally that was the first digital filter ever built (with J.F.kaiser, and J.McDonald) some time in 1964?? RK Quoting "Richard F. Lyon" <DickLyon(at)ACM.ORG>: > > > From: Farsheed <hamidito(at)uiuc.edu> > > > > >> 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): > http://patft.uspto.gov/netacgi/nph-Parser?Sect1=PTO1&Sect2=HITOFF&d=PALL&p=1&u=/netahtml/srchnum.htm&r=1&f=G&l=50&s1=5,355,329.WKU.&OS=PN/5,355,329&RS=PN/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. > > Dick >