[ Permission has been arranged with MBSI to republish Mike's
 [ article, "MIDI: Musical Instrument Digital Interface", that
 [ was first published in Mechanical Music, Vol. 47, No 1,
 [ Spring 2001.  An excerpt follows. -- Robbie

In our hobby we have all heard the old saying, "A poor piano
restoration will not be improved by the addition of a well-restored
player mechanism."  It is also true that a MIDI player system will
not make a badly restored or tired musical instrument play better.
It is absurd to assume that anyone who cares about the integrity and
originality of an antique musical instrument would purposely harm it in
any way.  If anything, the MIDI installer is apt to be more sensitive
to these subtleties.

It is possible, and a good idea, to install a MIDI player system
without injuring or changing the instrument in any way.  With
appropriate design, the MIDI system can be removed without evidence
that it was ever there.  The anti-MIDI purists have also suggested
that, in addition to ruining instruments, MIDIization will cause people
to throw away or abuse their music rolls.  This is not the case.  If
anything, MIDI will preserve the rolls by reducing handling.

The creation of MIDI tune files by the recording of music rolls may
be most easily accomplished by the use of a standard roll frame and
a pouch chest.   The weighted or spring-loaded pouches can have small
magnets attached to each pouch that move toward a switch (Hall effect
device).  As the pouches are actuated by the piano roll holes passing
across the tracker bar, the pouches move closer to, or further away
from, the Hall switch.  The Hall switch is connected to a MIDI encoder.

The MIDI signals from the encoder can be recorded in a computer or onto
a floppy disk player/recorder.  Other techniques can be used, such as
modified optical page scanners or IR photo sensors.  These systems will
make MIDI recordings that are adequate to listen to, and adequate to
operate automatic musical instruments.  Most of these recordings are
not accurate enough to be used to make master roll (perforator) quality
recordings.

Mike Ames
Solana Beach, CA

 [ The complete text with illustrations appears in the section
 [ about "Valves & Pneumatic Controls" at the MMD Tech site,
 [ http://mmd.foxtail.com/Tech/  -- Robbie