Something I've wondered about for years, and was reminded to ask about
by the Welte posting:  Has there ever been a mechanical instrument that
varied the speed of the music medium (cylinder, disk, roll, book, ...)
in response to signals (pins, holes, ...) in the medium?  Reproducing
and expression pianos use roll codings to change the loudness, and some
organs change registrations (stops).  But how about tempo?

I can think of two purposes:

One, to provide expressive tempo variations to a rigidly notated
medium.  The note spacings never change, but a ritard or rubato would
be achieved with coding that slows down the drive.  Standard MIDI files
work this way, but I said "mechanical" :-)

Two, to use the medium more efficiently.  If a musical piece consists
mostly of half-note chords, but with a couple measures of rippling
16ths, then on most instruments the medium must travel fast enough to
play those worst-case 16ths, with wide open spaces in the slow
measures.

For this, I can imagine that some maker of extreme music boxes
(pleriodienique, helicoid, longue marche, etc.) might have added a pin
or two that would double or halve the speed of the cylinder as needed
to fit a long overture or set of variations on the cylinder.

A fairly simple planetary gearbox would do the trick.

I'd also expect that some large orchestrions would use this scheme to
fit the maximum amount of music on a roll and give the patrons more
time before the program repeated.  (Or maybe the salon proprietor
wanted the customers to pay up and leave when they started hearing the
same songs over again :-)

Of course, I have piano rolls where the "player" is told to make
radical changes in tempo during a light-classical piece (goal #2)
and with Temponamic plot-lines for goal #1.

But did anyone ever mechanize the process?

Thanks for listening,
Mike Knudsen

 [ The Duo-Art Concertola was able to adjust the starting tempo of the
 [ music roll while the leader was advancing.  Perhaps someone could
 [ describe the details of this system.  -- Robbie