[sdiy] more-pole filter

[Antti Huovilainen]

On Sun, 10 Aug 2008, Richard Wentk wrote:

> Surprisingly, also not a huge difference in sound between a 4 pole and 8 
> pole. Obviously there's *some* difference, but it's not as musically 
> distinctive as you might expect.
>
> Considering the huge extra complexity involved in making an accurate 8 pole 
> design, it's never been worth the time, money or effort.

What would be the problem with the accuracy for higher filter orders?
I don't see how a Moog filter (for example) would be complicated by adding 
more stages.

As for 2 vs 3 poles, the choice changes the allowed filter topologies 
completely in most cases. 3 poles allows cascaded RC filter to be used 
while 2 poles requires SVF, Sallen-Key or similar design.

Ps. 3 pole filters were used - in Oberheim Expander. Half of the modes 
disable one pole and increase feedback gain 2x.

Antti

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