>> I COULD make an active filter (Butterworth or something), but I dislike =
the
>> phase characteristics.

A digital filter and an Analog filter are only as good at best as the
algorithm they implement.

If you don't like a Butterworth in analog you won't like it in digital.

If you want maximally constant phases delay you need to implement a
Bessel filter (which is maximally constant phase by definition, with
less performance in other areas such as passband edge cutoff rate).
("At a distance" they all look the same).

An advantage and a  "danger" with digital filters is that you can hack
around with parameters to try and make it do what you want. You can -
but what you ware usually doing is wandering to & fro across
'solution-space" already well described by classical solutions.
Knowing that there are formal solution that meet certain needs (choose
any one) is a good first start.





                Russell
--=20
http://www.piclist.com PIC/SX FAQ & list archive
View/change your membership options at
http://mailman.mit.edu/mailman/listinfo/piclist
.