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

Mike Bryant mbryant at futurehorizons.com
Sun May 30 20:49:26 CEST 2021

I think your final suggestion is the most likely to succeed well.

-----Original Message-----
From: Synth-diy [mailto:synth-diy-bounces at synth-diy.org] On Behalf Of Neil Harper via Synth-diy
Sent: 30 May 2021 18:21
To: synth-diy at synth-diy.org
Subject: [sdiy] Anyone do a voltage controlled "Tilt" Filter?

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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