[sdiy] moog high pass flter

[benno]

i am enjoying the response to my questions very much. once again this list
is cheerfully insightful. but i'm still learning so i'm gonna pester
everyone a bit more yet ;)

on 9/12/02 3:20 AM, harrybissell at harrybissell at prodigy.net wrote:

> There is/was a copy of a Japanese version of the Moog Ladder that included
> LPF, HPF, and BPF responses, by injecting the signal to the bottom, top, or
> both ends of the ladder, respectively.  I'd experiment with that one first,
> for sure.
> At least you can get around the really hard matching process, and you'd have
> resonance in all modes.  Osamu Hoshuyama had this on his site.  TomG also
> did a variation on this technique @ the EFM-Synth list.

the highpass version i saw on osamu hoshuyama's site obtained the highpass
by mixing the output with the inverted input (well thats how i think he did
it if i'm looking at the right one).

i have seen tom g's version. this looks like a much easier solution, but
makes me wonder how driving/loading the top pole of the filter affects the
response of the top pole of the filter.

has anyone tried this? does injecting a signal from a low impedance source
into the top of the filter distort or effectively remove the top pole from
the filter?

or am i not learning yet?

cheers.
b