Envelope / Filter Thoughts and Questions...

[liquids]

I've been tinkering and looking into envelope controlled filters a lot lately, learning a lot by studying and experimenting with them.  I've read R.G.'s and Mark Hammers articles amongst others, searched here quite a bit, and gathered lots of information, yet a lot of it is still mystery to me.  I have lots of questions I'm a bit sheepish to ask....but here goes...

While I'm messing with the typical filter schematics, many of which I like, the idea of controling your classic 'true' inductor-based wah/filter, being controlled by an envelope detector has provoked a lot of thought.  Maybe I wouldn't like it in reality, but imagining it is fun....   

Ignoring the wah part, I'm pondering how I could even manage to make such an envelope voltage control a 3 terminal voltage divider pot, rather than wired as the typical a variable resistor. 

All I can think of is that I would need something like two identical envelope detectors seeing the same signal, feeding two photocouplers or the like....One envelope detector would be biased 'up' -- to start dark to go bright feeding LED A, while the other biased 'down' starting bright and go dark with LED B.  One leg of the 'resistor' side of variable resistor A would be tied to one leg of variable resistor B to act as a 'wiper' of the pot.   I  hope that description is clear enough....

I always assume this has been thought of before, but I don't yet see a photocoupler designed like this.  Is there one? If not, is there an easier way to do this than the above?

[Mark Hammer]

Actually the first TW-1 from Boss, while not exactly the same circuit as a Cry Baby, was an inductor-based wah, controlled by the input envelope.

http://www.experimentalistsanonymous.com/diy/Schematics/Filters%20Wahs%20and%20VCFs/BOSS%20TW-1.jpg

[daverdave]

I used a ldr as a variable voltage divider, it worked ok, if you search ldr voltage divider on google you'll come up with some stuff. There's also aan article on tonegods site showing how to use 2 ldrs as a linear pot.