Vincent Thébault asked about Duo-Art coding techniques.  Some
thoughts...

Aeolian recorded expression coding for classical Duo-Art rolls as the
artist played, using a console with two dials so the recording editor
could encode the Theme and Accompaniment dynamic levels in real time.

There are strong suggestions that the original intention was to add the
accenting "snakebite" codes at the same time by the editor's use of
foot pedals, but this was presumably beyond the editors' dexterity and
surviving original recording-piano rolls show these accents were added
afterwards.

The initial idea was clearly to produce fully-finished rolls in real
time, ready for playing as soon as the pianist had played.  Aeolian was
the only reproducing piano company that ever even attempted this!

This technique resulted in a continuous series of somewhat jagged
expression codes.  Earlier rolls, and all of those produced in London,
therefore have Theme dynamics coded even when there are no accents.
Later rolls in the US replaced the recorded dynamics with averaged-out
coding, and the Theme levels are only set when there is an accent --
a technique which makes the piano's performance less sensitive to the
speed with which the expression levels change.  Sometimes a few accents
are added when no notes are starting, always after a major crescendo,
to drop suction levels in the Theme regulator (which in earlier pianos
lacked a bleed, although this was added later).

Other things that Vincent notes arise similarly from expression box
design, particularly the way that expression levels drop as more air
passes, its "droop" characteristic.  Accenting perforations occurring at
zero Theme level give a slight accent; thanks to having two regulators
removing air from the system overall regulator droop is reduced so that
playing levels rise.

Theme and Accompaniment dynamic coding affect each other by means of
the spill valve, which affects the suction supply level within the
expression box -- the higher the suction the less the droop, so playing
levels rise slightly.

Julian Dyer