There has recently been discussion in the MMD of MIDI-operated
mechanical organs. Thinking through the way MIDI changes sound patches,
how would one correlate MIDI program change messages to organ stop
settings ?

It would seem that the MIDI system is more appropriate to synthesisers
with a number of preset sounds rather than an organ which can have any
number of ranks of pipes selected or not from what could be a large
array.

With the MIDI program change message being 7 bits, allowing full on/off
control of pipe ranks individually restricts you to just 7 registers,
which seems rather limited. An alternative system could be envisgaed
where the program change message selects one of 128 'patches' which
have been pre- defined as mixtures of different organ registers.

Could anyone please comment on which system, if either, is used in MIDI
pipe organ applications ?

Thanks,

John Wale,¶
Coventry, England.

 [ Editor's Note:
 [
 [ I've studied several organ relay systems which used MIDI as
 [ the transport medium between the console and the relay system
 [ which was near the pipework.  None used MIDI program changes to
 [ represent register changes.  Each used its own proprietary
 [ method of encoding stop changes.  For organs of any size,
 [ representing the playing notes of each manual (or division)
 [ as notes on a seperate MIDI channel works well.  For small
 [ organs, representing the positions of the stop tabs as note
 [ on and note off events works well, and is handy for editing.
 [ You can treat them as "non-playing notes" on the same MIDI
 [ channel or you can segregate them into a seperate channel.
 [
 [ For large organs, particularly ones with combination actions
 [ (organist defined presets), the number of note on/note off
 [ events which may happen at one time can be a problem.  For
 [ editing purposes, note on/note off is still a good representation.
 [ However, for the MIDI wireline, it can be a problem because
 [ it takes about a millisecond per event.  If you change 50
 [ stop tabs at the same time, it would take 50ms to send that
 [ over the MIDI wire line.  At least one theatre organ relay
 [ system vendor I know of uses a proprietary encoding which
 [ transmits the tab positions on the MIDI wire line as a bit
 [ stream, 7 stop-tabs per MIDI byte.  Its a quite efficient
 [ encoding method. Unfortunately this vendor uses this same
 [ encoding in the MIDI file, which makes the MIDI file
 [ impossible to edit with standard MIDI editing tools...
 [
 [ Jody