Yesterday, John Grant pointed out that optical systems do
not inherently reproduce tracker bar behavior.  I wrote the
following reply before I read the other postings from yesterday,
and this may be redundant now...

John,
   You are quite correct that in an optical system
compensation must be made for the tracker bar & pneumatic behavior
and for the expression mechanism's behavior too if you intend to take
it to a MIDI format suitable for synthesizers.  Mark Fontana discusses
one way of dealing with chain perforations earlier in this digest.  The
inverse of is also true -- if you have a "correct" MIDI score, you must
massage it to make it suitable for perforating.  One of the arguments
for doing reading optically is that you _CAN_ accommodate different
roll formats with minimum machining, since you need only re-tool if
you need to accommodate a different spool type. Its clear that there
is some "retooling" that has to be done in software to "emulate" the
correct behavior of the new tracker bar.  I personally like adjusting
programs more than adjusting contacts, and you can re-adjust the program
later and reprocess the saved image data.  The pneumatic method completely
avoids problems with paper-coloration artifacts.  Neither method is
perfect.

Jody