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*To*: AUDITORY@xxxxxxxxxxxxxxx*Subject*: Re: digital filter design*From*: "Richard F. Lyon" <DickLyon@xxxxxxx>*Date*: Sat, 29 Jan 2005 22:56:05 -0800*Comments*: cc: Farsheed <hamidito@uiuc.edu>*Delivery-date*: Sun Jan 30 02:02:43 2005*In-reply-to*: <200501292339.j0TNdShL020769@manfred.music.uiuc.edu>*References*: <200501292339.j0TNdShL020769@manfred.music.uiuc.edu>*Reply-to*: "Richard F. Lyon" <DickLyon@xxxxxxx>*Sender*: AUDITORY Research in Auditory Perception <AUDITORY@xxxxxxxxxxxxxxx>

> 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): 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

**Follow-Ups**:**Re: digital filter design***From:*Ramdas Kumaresan

**References**:**digital filter design***From:*beaucham

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