I don't know the difference and it's been bugging me for a while now. I think the term "expression pedal" is thrown around loosely and that's what's confusing me. Can I get a technical description of what an expression pedal is supposed to do? Does a pedal like the DL4 send a voltage and get a different voltage back? I'm extra confused because my Memory Lane can take an expression pedal, but it's just sending an FX loop so what really needs is a volume pedal to lower the gain of the return, causing the feedback to be lowered. Rocktron makes an expression AND volume pedal http://www.musiciansfriend.com/product/Rocktron-Hex-Expression-Volume-Pedal-?sku=150144 that can take either an in and out TS or one TRS for MIDI stuff. Is that TRS just getting a lowered gain signal back like a volume pedal would do? Or is it a separate pot that give back a voltage or somethign? Can I send a TRS cable from the Memory Lane to the Rocktron? Am I making any sense?!?!?