question about a custom expression pedal

[opiateofthemasses]

Hey everyone, I just found this site so I figured I'd ask a question that I've had for a long while now.

There is a particular effect in a song called Wings for Marie by Tool that I need help with. The effect sounds like a uni-vibe tremolo/pan/chorus-y type effect. The effect is run through a custom expression pedal that was built for this specific purpose. Based on interviews it seems that the expression pedal is changing the values of a stomp box, adding depth and speed as its rocked forward.

Basically I'm wondering if it would be possible to make an expression pedal that could do that with a pedal like this:

The song: http://www.youtube.com/watch?v=rl4Jav58n48

[Hides-His-Eyes]

Changing the speed with an expression pedal is trivial.

Changing both speed and depth simultaneously is slightly less trivial, but still very possible.

You could probably do it most easily with one of those £15 volume pedals (made under many names, e.g. Bespeco) by running TWO stereo cables to the volume pedal (which will be your exp) and attaching each to one half of a dual gang pot.

You can then put two switching sockets in your pedal so that it still works as normal without the expression, or so you can control one or the other if you wish.

HOWEVER, I would recommend instead a from-scratch build like the ROG "tri-vibe" for this purpose, since that specific pedal may not be perfectly suited to modding.