"D4: (+ 1 parameter) Sets the "multiple voice" effect of a track, for lack of a better term. The higher the
value, the more it will seem like each note is being played on several keys (or instruments) simultaneously.
The effect is most significant with the organ, creating a difference between what sounds like an electric organ
(think "Come On, Baby Light My Fire" by The Doors), and a pipe organ (think church)."
Hm, this must be the same as the F4 XX command in FFVI...? I've always wondered what it does exactly. I'm not entirely sure I grasp you definition of it though, are you saying it allows a track to play over other channels and/or instruments?
All I know is that most songs that include it seem to have it in just one track usually, and when I use it in my custom songs it seems to make the song as a whole quieter usually, especially if I use it more than once, which leads me to think I'm using it incorrectly. I've been throwing it around on things like string sections, and as you mentioned here, organs - basically instruments that have drawn-out lengths.
Might you happen to know anything further about this command, like when and how it should be used for the best effect/result? And when to not bother using it at all. Also, does channel pan have any influence over it?