I need to get my two cents worth in here.  Roll (and organ book)
editing is an art, at least in part to the fact that the instrument
has inherent time delays in its mechanical components.  MIDI encodes
the time the sound _STARTS_ (and ends).  I'm not real familiar with
pneumatic pianos, but I can attest to the fact that playing MIDI on a
solenoid piano requires some "smarts" on the part of the driving
circuitry so that the soft notes hit when they are supposed to!  This
is done by having the computer delay the time power is applied
to the solenoids for the loud notes.  The percussoin pneumatics on
a band organ have the same problem.  You have to apply the signal
"early" to get the sound to happen at the right time.

Pneumatic devices have time delay characteristcs as well, and the
expression coding must preceed the notes to be played.  I'm uncertain
if the editors "adjusted" the positions of the holes for the "soft"
notes, but I wouldn't be surprised.

As for converting the holes of pneumatic expression rolls to MIDI, its
very tempting to put a MIDI "record" device on a pneumatic piano and
just play the rolls in the piano.  This method is hardly scientific.
Its prone to all kinds of errors from the condition of the instrument,
the presence of dirt in the bleeds, etc, etc, etc.

To get a good MIDI file, its first necessary to have an "archival
quality" image of the holes in a disk file.  No expression
interpretation, just the EXACT positions of the holes.  Then you can
message the data, mathmatically, to do what the piano was supposed to
do to it.

What ?  We don't know exactly, mathmatically, what the piano was
going to do to it ?  Probably true.  But we now have the "exact" data
from the roll, so when we get a better mathmatical model of the
piano, we do the conversion again.  The rolls may have turned to dust
by now, but we still have the EXACT data that was on them.

Its worth noting that having the EXACT image of the roll on disk
would make it possible to re-cut exact roll copies later.  You could
also install solenoid valves on a real expression piano (that used
the same expression encoding) and play the roll image.

Having only an MIDI file of a tune does not imply you can re-cut the
roll.  The hardest part of the editor's task when making an
expression roll is putting the expression encoding in correctly.

I pose three "problems" to the readers of the digest:

  1)  Come up with better mathmatical models of the expression pianos
      that we all love so much.

  2)  Come up with a program to use the model to convert roll data to
      MIDI accurately.  Some of our readers have written such programs,
      but I don't think this is a problem that can't be improved upon,
      especially as computers get faster and the models get better (and
      more complicated).

  3)  Come up with a program to use the model to convert _FROM_ MIDI to
      a given EXPRESSION piano system.  This is not likely to be a
      trival task, but it would be really nice to be able to do
      conversions in this direction.  There are a growing number of
      expression pianos which have had solenoid valves put on them so
      that roll images can be played back through them from a computer.
      There so muchgood MIDI material now, it would be nice to make it
      possible for that material to be enjoyed on thes "hybrid" expression
      pianos.  Such "hybrid" pianos still need the same data that would
      have been on the roll.

  Jody