I think it's easier to turn the speed knob until it exactly follows the song, than trying to calculate the exact voltage value that should correspond with the midi value of the signal.
There's no such thing as a digital clock or pulse generator going on in that thing, just an analog oscillator that shifts the time intervals between two audio signals. That goes in millivolts and milliseconds.
Good luck, I hope you're familiar with analog and digital electronica, and became good friends with your calculator.
Well I'm not that much into it, but I found a voltage that slowly raises og falls in "sync" with the speed, putting an Oscillocope on it, makes it easier to find the right point.
In the youtube video I posted, I'd like to have the high part of the sound just the right place when changing chords, so I started the strings when the oscilloscope was in the right place.
No I don't think Jarre's Small Stone is in sync, that is ok when he was the first to play the song, no mater what it is always right
) ...But when we try to replicate, it is more difficould.
BTW. Try to listen at the Small Stone in Oxygene 9, it is cutted several places, and not in sync. In Oxygene and Equinoxe, it is played in one piece.