The Duo-Art test roll's 'Play / Don't Play' section is explicit that
a 3-note chord won't play at level zero: that chord is the very one
used for the test, with and without pedal on.  Any piano that will
play such a chord is set too high, as discussed earlier.

However, the debate's about "Clair de lune," which doesn't actually
play three notes at the same time, so we're not discussing the right
issue!  Instead, "Clair de lune" plays two notes with the third played
a short while later.  This somewhat alters the situation as seen by
the Duo-Art regulator.

The Duo-Art regulator's 'droop' characteristic is its response to
incoming air.  There are three sources for this air: (1) a note
starting to play so a burst of air comes out of the pneumatic (2) air
coming through the bleed from any note that's playing and (3) static
leakage into the stack.  The significance of these is in decreasing
order, so the very start of a note has more effect than when its
pneumatic has been evacuated.

Excessive static leakage will swamp the regulator and upset the
'Play / Don't Play' balance: my "ideal" static leakage would be enough
to counter any seepage through the knife valve and drop higher stack
tensions, but not be enough to push the droop out of the range the
rolls expect.

A two-note chord being quite different to a three-note chord at zero
level, there's going to be more chance of the first two notes playing
in the problematic chord, and I rather suspect that's what my Duo-Art
achieves.  The "Clair de lune" roll is a fairly early one, number 5611
(of a catalogue that started at 5500), which is before the editing
process had been refined and standardised -- although you need to check
the age of the actual roll you have, because some early coding was
revised later.

My QRS (hence un-dateable original) copy has a few places where 2-note
bass chords are played at zero level, so I suspect this is always going
to be a marginal roll for those wanting to achieve the best low-level
playing from their Duo-Art.  Personally, I'd sacrifice this chord for
the sake of the many other later rolls that will sound more musical for
the lower setting.

Julian Dyer