Hello Craig,  Congratulations, you have the right ideas about the
difficulties you will encounter constructing a roll reader.  Here
are some tips to circumvent most of them.

The named sensors can act with a speed of 8 MHz, so there is no slow
down.  The bottleneck is the surplus stepper motor, if you make
stepping too fine.  With a stepping of 0.8 mm you can test the rolls
with a speed of Tempo 120 or more.  Don't punch a test roll, just read
the same rolls a few times. They should count the same amount of holes
each time.

Mark a distance of one, two and three feet on the roll.  The computer
will tell you the amount of steps it needed.  Use a friction wheel at
the rubber roll transporting the paper, like a printer, and different
friction rods at the stepper motor, and fine tune them.

You need three DC motors also: One to reroll or tighten the paper, one
for a light tension to roll up, and a third one for tracking, just the
way the Ampico and other pianos do.

The computer does the stepping and that is the syncing.  It makes the
motor do one step.  Then the row of holes is read as if it was done by
the tracker bar.  The result is written to a file if you want a geo-
metrical image of the roll.  (In this case take a step width of 0.1 mm
or less.)

Don't make the speed too slow, because then the stepper motor will
toggle.  With the right speed it doesn't.  The known step width that
was used for punching the roll is another point for synchronization.

Or, if you want to let that device play as if the roll were a MIDI-
file, take a step width of 0.8 mm.  Then after reading the holes the
computing of intensity tracks to MIDI-velocity is done.  (The data is
then output quickly to a buffering computer which will output the MIDI
data as slow as three per millisecond).  Then the timer is interrogated
until the chosen milliseconds are past and the next step is commanded.
Computers are fast nowadays ;-).

To over-read the bridges, prolong the "ON" some steps and delay the
"OFF" the same amount.  That is easier and faster than computing a
window.  As it is a digital device dust or wear won't affect it.
Be assured it will work for many a year :).

Hoping you and the MMD roll scanners will like these tricks.  Happy
constructing and best regards,

Horst Mohr