[sdiy] What's going on in the M12 filter circuit?

[Happy Harry]

There is some high powered math that says you can get almost any
filter response from summing these sections in the correct phase
and amplitude. The one tricky part is one filter section
is bypassed by making the capacitor way too small for it to be a
filter stage anymore...

You could use the 2040 as well... or probably the 2044. I have simulated 
these but not built.

H^) harry


>From: "DJ Marmalade" <djmarmalade at planetp.org>
>To: "Synth-DIY" <synth-diy at dropmix.xs4all.nl>
>Subject: [sdiy] What's going on in the M12 filter circuit?
>Date: Fri, 29 Mar 2002 07:06:47 -0500
>
>Hi All,
>
>Well, I tried to have this discussion on AH but it seems AH is more
>interested in arguing with one another than discussing technical issues.
>
>Playing the devils advocate, perhaps it's not worthy of discussion,
>nevertheless, if you know what's going on, I'd appreciate some input, reply
>privately if you don't think it should be on list.
>
>In the M12 voice schematic, seen here :
>
>http://www.planetp.org/xpvoice.jpg
>
>The 3372 LPF is used as a multimode filter.  The circuit on the right
>apparantly sums at different levels, the signals available from the filter
>caps.
>
>I'm interested to know what is going on here, why does this work?  I also
>want to know if there is something unique about the 3372 or could this idea
>be applied to any number of filter chips, say for example, the 2044?
>
>Thanks
>Daryl
>
>




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