I have written a full article on Angelus 65 note rolls, which incident-
ally Julian Dyer gets tomorrow for next month's PPG journal.  Whilst
I'll post the full article here next month after the journal is
published I feel safe in saying that yes, Melodant and Themodist do
operate from the roll in the same manner.  Both use the same "snake-
bite" type marginal punchings (as both were originally conceived for
the 65-note format) and both punchings are placed marginally ahead of
the note to be accented.

Only 88-note Melodant rolls will play on Themodist players -- simply
the 65-note rolls are upside down and back to front on slightly
different width spools, the drive pins are the opposite way about and
one roll will not fit into the spoolbox of the other instrument without
tinkering about with tools on the spool.  All the Angelus 88-note rolls
are the same as normal 88-note rolls, however, so no problem.

The Themodist system operates by causing the supply of suction to
increase momentarily from a reserve when the snakebite hole operates
this function.  You have to set the player to "solo" mode which reduces
the overall suction so a contrast between both levels can be heard when
the roll operates this mechanism.

The Angelus however, in it's original early form, played the note by
allowing atmospheric pressure to inflate large pouch pneumatics which
were completely enclosed in a cabinet to which suction was applied.
The difference between the two played the note.  Essentially it works
the opposite way around pressure-wise to a normal rubber-cloth
pneumatic stack.

The theme buttons on an original Angelus player when operated admit
suction to the corresponding 1/2 of the stack thus reducing the
atmospheric pressure admitted to the pouch pneumatics and hence
reducing the pressure difference between inside the pouch pneumatic
and the outside with the result that the note plays softer.

The Melodant, once engaged, admits suction reducing the overall level
and when the perforation opens it close up the suction allowing full
atmospheric pressure to give the note the maximum play.  It is not the
case that the stack is divided outside the pouches so that suction
outside the pouches is varied with atmosphere inside remaining
constant.

The response would have been too slow had they adopted this method as
the whole half of all the space round the entire encased stack would
have to have had it's pressure alternated which would have taken longer
for the pump and would have been simply a phenomenal waste of suction.
In practice Melodant works very well.

Regards

Adam Ramet