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

cheater cheater cheater00social at gmail.com
Sun May 30 22:47:22 CEST 2021

I might be missing something - what's the functional difference
between this and a pair of shelving equalizers with opposite control
from a single potentiometer?

(parts count is not a functional difference)

On Sun, May 30, 2021 at 7:25 PM Neil Harper via Synth-diy
<synth-diy at synth-diy.org> wrote:
> I recently breadboarded this tilt equalizer filter as found on EDN:
> https://www.edn.com/implement-an-audio-frequency-tilt-equalizer-filter/
> A similar (the same?) circuit is shown here:
> https://sound-au.com/articles/eq.htm#s10
> 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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