Well Paul, back in the prehysteric(!) sixties/seventies, Mr. Emerson went on the road with an analog (!), monophonic(!!) MOOG modular synthesizer that was truly the most unplayable, unreliable, and truly aggravating piece of crap that was dazzlingly cutting-edge high tech in its time. Remember this is FIFTEEN years before DX7s. (By the way, DXs pioneered BREATH CONTROLLERS, but that's a bedtime story for another day)
The ribbon controller operated as indicated above by Mr. MoonLiner. As I remember, he had to wipe his pants with it quite a bit !
J o e y
PS Someday we'll talk about arpeggiators and ADSRs !