Message for Sergey: Bessel filters

[Alex Matulich <alex@xxxxxxxxxxxxxx>]

Sergey Efremov:  I don't have your address.  You posted to the omega
list a few times about Bessel filters:

http://www.purebytes.com/archives/omega/2004/msg02619.html
http://www.purebytes.com/archives/omega/2004/msg02625.html
http://www.purebytes.com/archives/omega/2004/msg02626.html
http://www.purebytes.com/archives/omega/2004/msg02629.html

I had responded at one time:
> Bessel filters also have the gentlest roll-off in the frequency
> spectrum, losing more low-frequency information than you might
> want to lose, while not attenuating all the high frequency noise

This turns out to be incorrect.  A Bessel seems is actually about the
same as a critically-damped filter, better in some ways.

I have compiled the recipes for constructing 2-pole Butterworth, Bessel,
and Critically-Damped filters.

     http://unicorn.us.com/trading/2polefilters.html

This was a lot of work.  Ironically, I wanted filter recipes like
this so that I wouldn't have to learn how to derive filters, but I
had to learn about deriving filters to get the Bessel.

These recipes are, to my mind, more useful than the filter design
tools available in MatLab and such, because the recipes show you
generalized formulas for any cutoff frequency, rather than specific
numeric values for the coefficients of a particular filter.

-- 
  ,|___    Alex Matulich -- alex@xxxxxxxxxxxxxx
 // +__>   Director of Research and Development
 //  \ 
 // __)    Unicorn Research Corporation -- http://unicorn.us.com