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From: jbuck@galileo.berkeley.edu (Joe Buck)
Newsgroups: comp.dsp
Subject: Re: Digital Filters
Message-ID: <39600@ucbvax.BERKELEY.EDU>
Date: 15 Nov 90 20:33:13 GMT
References: <1990Nov15.121559.11290@watserv1.waterloo.edu>
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Reply-To: jbuck@galileo.berkeley.edu (Joe Buck)
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In article <1990Nov15.121559.11290@watserv1.waterloo.edu>, optadm7@watserv1.waterloo.edu (J.Cassidy - Optometry) writes:
> I have a really interesting application for digital filtering
> using a DSP chip, but I am having some difficulty understanding
> the derrivations for a filter's tap coefficients.

> I understand that the expression of a FIR filter is:

> b0*a[n] + b1*a[n-1] + b2*a[n-2] + etc...

> where b[0] to b[n] are the tap coefficients and assume they
> are what determine the performance of the filter.  But how
> to I generate b[n], given that I have the filter parameters
> such as filter type (butterworth/bandpass), lowpass cutoff
> frequency, highpass cutoff frequency, etc.

A Butterworth filter is an IIR filter, so you can't represent it
using an IIR filter.  There are several design techniques for FIR
filters given a specification of cutoff frequencies and other
parameters; the best (in most cases) is the Parks-McClellan
algorithm for designing optimal FIR filters.

Find the book "Programs for digital signal processing" (I think
that's the title) published by IEEE Press (I think you can also
get a tape) for many DSP programs written in spaghetti Fortran.

--
Joe Buck
jbuck@galileo.berkeley.edu	 {uunet,ucbvax}!galileo.berkeley.edu!jbuck