Newsgroups: comp.dsp
Path: utzoo!utgpu!watserv1!optadm7
From: optadm7@watserv1.waterloo.edu (J.Cassidy - Optometry)
Subject: Digital Filters
Message-ID: <1990Nov15.121559.11290@watserv1.waterloo.edu>
Organization: University of Waterloo
Distribution: na
Date: Thu, 15 Nov 90 12:15:59 GMT
Lines: 31


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.

I have been searching for this algorithm/program for a while
now.  Most application notes that I see show the filter 
algorithm and the values of b[n], but never show how they
derrived the values of b[n], given the filter's parameters.

Any help would be greatly appreciated!

Jim C.

=========================================================================
Jim Cassidy                           optadm7@watserv1.waterloo.{edu,cdn}
University of Waterloo                optadm7@watserv1.uwaterloo.ca
200 University Ave.                   VE3RTS
Waterloo, Ontario, Canada N2L 3G1     (519) 885-1211 ext. 6240