[sdiy] FatMan Hacking ( and I dont mean hitting me with anAxe!)

[harry]

I've played a little with the Moog Ladder... and trying the feedback from
other than the last stage is not too useful (IMHO).  If you tap the second
stage and put the
feedback there... the last two stages still LPF the signal.

I guess a way of looking at it is that the filter section of the SVF can
have
gain, where as the Ladder is loss only (gain is added back in the post
amplifier).

I have to play more....

H^) harry

Don Tillman wrote:

>    Date: Sun, 28 Oct 2001 01:19:19 -0500
>    From: harry <harrybissell at prodigy.net>
>
>    BTW a SVF can be configured to have constant peak response by
>    putting the input into the Q feedback, rather than the normal
>    point.
>
>    So why can't you do the same with the Moog Ladder ???
>
>    Can any "mathy" types put this in "non-guru" form for us ?????
>
> Oh Harry, you know the answer to this one...
>
> The SVF (that's a State Variable Filter, for anybody who's asking) is
> a topology that requires more attenuation in a local negative feedback
> path to increase the Q, while the ladder filter adds negative feedback
> (which happens to be postive at the resonant frequency) to increase
> the Q.  So the basic workings are different.
>
> The SVF normally has constant passband gain.  To get constant resonant
> frequency gain you just insert the signal before the attenuator
> instead of after it.  Cool, easy.
>
> The ladder filter normally has unity resonant frequency gain.  To get
> unity passband gain out of a ladder filter you need to do something
> like summing the normal output with the signal after the Q attenuator.
>
> Hmmm, I've never heard of anybody do this.
>
>   -- Don
>
> --
> Don Tillman
> Palo Alto, California, USA
> don at till.com
> http://www.till.com

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