Leighton,
I happen to be a musician and of course I am a fan of the now very rare
calliope (=steam organ) best known from circus parades and the Mississippi
show boats from the early 1900s. As far as I know calliopes have been both
played mechanically (similar to the piano rolls) and/or by hand.
Of course compressed air would yield a different, more harsh sound than
steam - we know that from steam whistles in museums that are demonstrated
sometimes with compressed air - and I almost bet that one needs to re-tune
an organ when changing from steam to air or vice versa, if that is at all
possible. So one must take into account that higher steam (or air) pressure
will affect the musical pitch. It must be the exact steam (air) flow, the
same applies to air driven pipe organs as found in churches or as part of
the Wurlitzer cinema organs.
Here are some URL to web sites dedicated to the rare calliopes:
http://www.wdm.ca/nov29cal.htmhttp://www.neworleansonline.com/neworleans/music/calliope.htmlI sincerely hope this helps, even if I didn't answer your question directly.
If I remember correctly, Mr. Scott Andrews from the TMRA (Titanicmodel.com)
restores and maintains pipe organs. He might be able to help further.
Regards
Christian (passionate Great Eastern amateur modeler and researcher)