[sdiy] Vactrols subbed for dual-gang pot

[cheater cheater]

Yeah, I know all about non-linearities - but you can usually get some
sort of general idea anyways. I guessed low-pass-ish, but I wonder if
it's more 12dB/Oct or 24dB/Oct or ... :)

Cheers,
D.

On Sun, Jul 11, 2010 at 05:57,  <lanterma at ece.gatech.edu> wrote:
>
> On Jul 10, 2010, at 12:39 PM, cheater cheater wrote:
>
>> Gotcha. So the LDR works as an LPF. I wonder what the transfer
>> function of that is?
>
> Hmmm... "transfer function" analysis, as you are using the words, presumes linearity, and I think it would be pretty tricky to try to characterize the LED/LDR drive combination that way. It's probably better thought of a "slew," as in op amp slew (which can lead to frequency response sort of calculations), but even then there's probably all sorts of weird nonlinear and asymmetric behaviors going on.
>
> I did have a student try to build a weird nonlinear filtery kind of waveshaper by exploiting the limited vactrol slew:
>
> http://users.ece.gatech.edu/~lanterma/studentprojects/andrew_SSM01_manual.pdf
>
> From the student's writeup:
>
> "I don’t blame you if you still don’t exactly understand what the circuit is supposed to do. I think it best described as a low pass-ish, waveshapey thinga-mabob..."
>
> Come to think of it, this is probably a similar notion to the Polyvox filter:
>
> http://m.bareille.free.fr/modular1/vcf_polivoks/vcf_polivoks.htm
>
> - Aaron
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