I am presently constructing an orchestrion that uses Hupfeld "Helios"
rolls.  It isn't intended to be an exact reproduction, but I would like
for it to use the full capabilities of the roll, multiplexing and all.

What is still presently a mystery is how the soft swell mechanism
works.  The tracker bar I have has an elongated hole with 2 (bleed)
holes underneath.  I do understand that the playing level of the
instrument is determined by the spacing of the chain perforation on
the roll.

How does the instrument accomplish this pneumatically/mechanically.
Can anyone shed some light on this or point me the right direction?

Thank you

Brian Thornton, Short Mtn. Music Works
109 N. Cannon St., Woodbury,  TN 37190
615-563-5814
http://www.mindspring.com/~goatboy/smmw.htm

 [ Sounds to me as though it's "pulse duty-cycle modulation", with a
 [ slow time-constant due to the swell pneumatic exhausing through the
 [ tiny bleeds at the tracker bar.  The swell shades would move
 [ according to the average amount of the "on" time compared to the
 [ total cycle time.  Anyone know for sure?
 [ -- Robbie