Although I am no great whiz at MIDI, I've done quite a bit of study
trying to learn enough to be dangerous.

Some good information is at the MIDIbox site at http://www.ucapps.de/ 
See the MIDIO128 project in particular.  It references Willy van der
Reijden's article at

  http://www.mmdigest.com/Gallery/Tech/mvdReijden.html 

The original MIDIO128 has been upgraded to Version 3; take a look at
both the old Version 2 and the new Version 3 for details.

  http://midibox.org/    the blog
  http://www.ucapps.de/  "Non-commercial DIY Projects ..."
  http://www.ucapps.de/midio128_v2.html  MIDIO128 V2, September 2001
  http://www.ucapps.de/midio128.html     MIDIO128 V3, July 2011

Hardware schematics and printed circuit board layouts and software
are free for non-commercial use, and kits are available at

  http://www.midibox-shop.com/ and http://www.mikes-elektronikseite.de/ 

Also take a look at abc notation at http://abcnotation.com/  It is
a text based music notation system with many programs, freeware,
shareware and commercial, that will allow you to transfer abc into
scores or MIDI sound files.

Then there is http://huizen.daxis.nl/~Ppaardekam/index.htm  home of
Midiboek and Noteur programs for arranging and printing templates for
street organs and other mechanical musical instruments.

Mickey Sadler
Dublin, Ohio