[sdiy] standard filters from ladder topology?

[JH.]

> For that application I think you will enjoy using either a Butterworth or
> Bessel filter. The Butterworths maximum flatness keeps the passband free,
but
> the group delay is not really optimum. The Bessel/Thompson is much better
in
> this respect with a fairly quite passband, but benefits in maximum
flatness of
> group delay, which would show up as a slightly added delay to that of the
BBD,
> so that is certainly usefull. If you care about phases, Chebyshev variants
is
> not for you.

I read about some intermediate filter types in that AD book on opamps from
last year.
Something that has better phase response than Bessel in the pass band, and
a slope almost as good as Butterworth in the stop band. I don't remember the
name, but the idea was not to design for the same goal over the whole range.
Instead, optimise for phase up to some frequency, then allow for some
gradual
attenuation till the -3db point is reached, and finally make a steeper slope
your main goal.

I have no idea if this is really useful either, but probably worth
experimenting.

JH.