Since 1994, I've used MIDI to arrange certain rolls, using a Roland
SoundCanvas for playback.  (The SoundCanvas is a synthesizer that can
play back several different-sounding instruments at the same time.
It doesn't duplicate the sound of a real orchestrion or band organ,
but it sort of simulates the sound of the pipes and drums.)

When playing back a complex arrangement with three or more instruments
on different channels (piano, extra tuned instrument, and untuned
percussions), the synthesizer frequently plays an occasional note on
one instrument a little later than other "simultaneous" notes.  Drum
beats and percussive notes (piano, xylophone, etc.) are the most
obvious.

I have no way of measuring the discrepancy, but it's enough to make me
think the note is in the wrong place.  I frequently hear a misplaced
drum beat or note, go into "event view" to find it, only to verify that
it is indeed in the right place in the program.  When I back up (or
"rewind") just a short distance before the event and play it back again
with no "bottleneck of events," it plays right on the beat.

I can only attribute this to the serial MIDI data stream getting
constipated.  In my system, this effect can't be caused by solenoids or
pneumatics -- there aren't any!

I've discussed this with certain pipe organ builders who have
encountered the same problem with MIDI playback computers connected to
pipe organs.  However, I've never heard timing problems in theatre
organs equipped with Trousdale playback computers, even when playing
the most complex arrangements.  These instruments, including the
8,000-pipe Victorian Palace theatre organ with its vast array of
effects, ranging from the subtle to the hair-raising, prove to me that
it is possible for electronic systems to work right.

Nor have I noticed the problem in music that has been arranged in
recent years for the Mills Violano-Virtuoso electronic playback system.
I attribute this to the relatively fewer "simultaneous" events, which
fall within the capability of MIDI and don't cause noticeable timing
problems.

When one arranges a paper music roll in MIDI, the computer file only
"plays" the roll perforator in slow motion, not real instruments in
real time.  As a result, there is no constipation of data, and the
perforations don't have timing problems.

Art Reblitz