Has this been done before?

[micromegas]

Here it is what came to my mind, but I don't know if there's a diy project for this:

A pedal in you chain that would act as an envelope detector (with sensitivity/threshold controls) with an expression/cv output to control any expression parameter in another pedal.
This way you could have envelope controlled rate or mix in any pedal with a jack for an expression pedal.

Thanks to Cortexturizer btw, whose latest project gave me the idea.

I think it can be done digitally with Rob's CV-controlled pot (or with a less complicated setup), but there has to be an easier (purely analog) way to do it.

[culturejam]

It's a really good idea, I think. The cheap/easy way to do it is to just use a LM386 to light up some diodes to ground and use a LDR as the variable resistance element. Or an op amp, but it requires a few more components.

But the cheap/easy way also doesn't offer a lot of flexibility.

[micromegas]

It's a really good idea, I think. The cheap/easy way to do it is to just use a LM386 to light up some diodes to ground and use a LDR as the variable resistance element. Or an op amp, but it requires a few more components.

But the cheap/easy way also doesn't offer a lot of flexibility.

Maybe something like Anderton's envelope follower?
http://img166.imageshack.us/img166/9351/andertonenvelopefolloweql2.gif

There's a 8-pages thread at DIYSB started in 2005 with the name "Making a generic envelope follower", maybe I could find some info there.

[micromegas]

other options (more complicated but with good tracking):

http://www.musicfromouterspace.com/index.php?MAINTAB=SYNTHDIY&PROJARG=ENVELOPE_FOLLOWER/efpg2.html&VPW=1270&VPH=809

Harry Bissell's envelop detector:
https://www.muffwiggler.com/forum/userpix/6768_bissell_ef_schematics_1.png

[stecykmi]

One challenge you'll have is selecting the type of output you want to design. A CV output, for example, will not be compatible with resistive output like an LDR, so you're going to have to choose between guitar-oriented (resistive output) vs synth-oriented (CV output).

Not all of those followers have the same type of output, the anderton one is a resistive output, meaning it will replace a pot or other resistance. The MFOS follower has a current output because it's driving a OTA (the lm3700), but it can be modified to output a voltage fairly easily by removing Q1 & Q2 and adjusting the gain. I feel like that one could also be simplified, 6 op-amp stages is kind of a lot to generate an envelope. I can't get the muffwiggler image to load.

[micromegas]

One challenge you'll have is selecting the type of output you want to design. A CV output, for example, will not be compatible with resistive output like an LDR, so you're going to have to choose between guitar-oriented (resistive output) vs synth-oriented (CV output).

Not all of those followers have the same type of output, the anderton one is a resistive output, meaning it will replace a pot or other resistance. The MFOS follower has a current output because it's driving a OTA (the lm3700), but it can be modified to output a voltage fairly easily by removing Q1 & Q2 and adjusting the gain. I feel like that one could also be simplified, 6 op-amp stages is kind of a lot to generate an envelope. I can't get the muffwiggler image to load.

yep, I know. I think passive could be the way to go as this is meant to be used with guitar pedals.
However, some CV-output envelope detectors could be morphed into resistive-output with the addition of some simple circuitery.

both MFOS and Harry Bissel's are complicated, but people like how good those track the envelope.

Here's an image of Bissel's envelope detector for reference: