Nikolai,

Thanks for that information, it was the best short-and-sweet
explanation of IIR anf FIR filters I ever heard.

I think too many people get lost in the theoretical mathematics which
derive the IIR and FIR behaviors from the similar continuous time
filters.  Many university courses approach this from continuous time
circuits, then Fourier series, then Fourier transforms, then sampling,
then Z transforms, then digital filters.  By that time many are
confused!

But you can also explain "backwards" by learning about sampling,
then talk of averaging samples, (FIR, equal co-efficients, right?!)
Then talk of weighted averages (FIR, unequal coefficients), and so
on.  Then go on to feedback and IIR techniques.  This makes the
practical digital techniques clear.  Of course, understanding the
design of a complex (or excellent) digital filter makes us get back to
Z transforms some day.  But it makes more sense to me when I
remember to start at sampled data and averaging!

------------
Barry King, Engineering Manager
NRG Systems "Measuring the Wind's Energy"
www.nrgsystems.com
Phone: 802-482-2255
FAX:   802-482-2272