[sdiy] Anyone do a voltage controlled "Tilt" Filter?

Neil Harper metadata at gmx.com
Sun May 30 19:21:13 CEST 2021

I recently breadboarded this tilt equalizer filter as found on EDN:


A similar (the same?) circuit is shown here:

It's pretty cool, low parts count and can sound interesting - i'm kinda
digging it to eq an fx for sample.

of course my next question was "how can I get this under voltage control"?

here's what I plan to try, maybe you can steer me in the right direction.

my first guess was to replace the potentiometer (P1) with two
vactrols/LDRs, but I'm not sure how to basically 'crossfade' the two
vactrols in opposite directions and I think the response curves of the
vactrols with regard to voltage input (light) and resistance are far
from linear.

i've read that OTA's like the LM13700 (the monty python chip) can be
used as voltage controlled resistors, but I've never seen them
implemented as a pair replacing a potentiometer - so I don't know if
that route is possible either.

my last guess was wondering if an equivalent circuit could be made by
combining a lowpassed and hipassed audio signal and then crossfading
them. I can imagine it would somewhat similar, but I'm not sure if you
would get the same totally flat frequency response in the middle setting.

/// Neil Harper
/// Every Wave is New Until it Breaks

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