[sdiy] more-pole filter

[Antti Huovilainen]

On Mon, 11 Aug 2008, Richard Wentk wrote:

> Higher orders are more susceptible to variations from component tolerances 
> and thermal issues.
>
> So if you duplicate a four pole, you'll get an eight-ish pole filter, because 
> the poles will start to smear out from their ideal positions. This is most 
> obvious with higher Q.

Moog filter should be relatively good for this as the transconductance is 
inherently similar for all stages. The main source of mismatch is then 
from the capacitors. Any volunteers to test this? :)

Some mismatch wouldn't necessarily be a bad thing for high pole filter, at 
least if the mismatch tracked the cutoff (so relative mismatch would be 
same for low and high cutoffs). The resonance peak would be slightly wider 
and required feedback gain would be slightly increased.

Antti

"No boom today. Boom tomorrow. There's always a boom tomorrow"
   -- Lt. Cmdr. Ivanova