Greetings,  Julian Dyer's letter [031206 MMDigest] reminded me about
the leak in the theme regulator in UK-made Duo-Arts.

Recently I performed some tests of vacuum levels while the Duo-Art was
playing.  MIDI files were designed to test specific theories as to how
the Duo-Art regulator worked.  Information from these tests was used by
Warren Trachtman in developing his Duo-Art emulation model.  Some very
interesting effects were discovered.

It was found that the theme regulator pressure decayed very slowly if
the theme valves remained closed.  Examination of coding on certain
rolls suggests that the editors were well aware of this and exploited
it for subtle effects.

There are examples of using theme (snakebite) codes after the theme
accordions have returned to rest to produce a very smooth diminuendo.
Theme codes of varying duration are used to release the captive vacuum
of the regulator faster than the decay rate.  This release is into the
stack so the vacuum is also boosted if the theme regulator level is
greater than the stack.  It is not clear why the roll editors chose to
do it this way, and it is possibly a coding style of one particular
person, but the resulting effect can be excellent.

The question is what happens when this roll is played on a UK machine.
I believe there are also some late model US machines that also have the
vent hole.

Best regards,
Spencer Chase
Laytonville, CA 95454
http://www.spencerserolls.com/