While converting Duo-Art Organ and 116-note rolls into MIDI format,
I have developed a deeper understanding of the scheme used by Aeolian.
Most of what I have learned has only limited use to the general
community of collectors.  Even so, it is important to publish my
findings.

One confusing aspect of the 116-note roll player is the switch that
controls "Unison, Normal, Reverse" function.  We generally think of
these functions as controlling the top and lower row hole assignments
in the twin row, organ tracker bar.  "Normal" causes the top row of
holes to play the "Manual II" (upper) keyboard, and the lower row of
holes to play "Manual I" (lower) keyboard.  The "Reverse" function just
reverses these assignments.  "Unison" will cause both top and bottom
holes to play both keyboards.  Aeolian calls the console selector
switch that controls these functions, the "coupler".  Instructions on
the use of the "coupler" are printed on most 116-note roll leaders.

Early in my involvement with organ rolls, I wondered why Aeolian
bothered with all this switching mechanism when the rolls could have
just been punched to provide the necessary changes.  Now, I think
I know why.

In real life, an organist often plays the same pipe stops on the pedal
as is played on the Manual I, or lower keyboard.  This is done by using
the consoles "Manual I to Pedal" coupler.  This means the pedal klavier
is now playing on the pipes assigned to Manual I.  In the Aeolian 116-note
roll scheme, this combining of pedal and keyboard in the lower holes
conserved tracker space and also simplified imitating the "Manual I
to Pedal" function.

Most published tracker scales that help us understand how instruments
work don't explain the logic behind the scheme.  For the 116-note tracker
scale, we find that the lower row of holes contains the pedal notes,
also.  The lowest 13 notes of the lower row controls both the selected
keyboard and the bottom octave of the pedal klavier.

As the complexities of the music dictate, the organist may find that
the bass notes need to be on the stops assigned to the upper keyboard.
In this case, the organist turns off the "Manual I to Pedal" and turns
on the "Manual II to Pedal".  It is this configuration that requires the
"Reverse" function in the 116-note roll player.  The pedal notes are hard
wired to the bottom row, lowest 13 notes.  This is why Aeolian couldn't
just change the hole punchings to achieve the "Reverse" function.  So
in truth, the Aeolian coupler for "Unison, Normal, Reverse" is really
present to make the pedal work correctly.  Of course the Unison position
is primarily to eliminate the duplicate holes, top and bottom, in roll
production.

Like the 116-note rolls that preceded them, some early Duo-Art rolls
depend on "Unison, Normal, Reverse" functions to play correctly.  That
scheme was soon abandoned.  I have examples of the same roll in both
formats.  That is, the early version of the roll requires the Duo-Art
to switch the coupler from Normal to Reverse.  But the same roll is
later issued with the holes in the roll being punched to achieve the
same result.

The Duo-Art, unlike the earlier 116-note player, has the capability of
switching the pedal assignment from the lower holes to the upper holes.
The pedal notes are not hard wired.  Known as hole 176, Ped to Upper,
this function in essence could be called "Manual II to Pedal".

Some collectors have found Duo-Art organs with some of the complex
pedal octave switching mechanism removed or missing, and have
suggested that the use of the feature is really not important.
It is my opinion that all coded functions in the rolls are quite
important.  The scope of discovery is broadest when we use the rolls,
not a few individual instruments, to investigate.  Granted that some
very interesting variants are discovered by instrument study.

The most complex aspect of Duo-Art roll is the pedal.  Through
multiplexing, the roll can play all 32 notes of the pedal klavier.
And as just stated, the pedal can be coupled to either row of holes.
There are many rolls that make extensive use of the full pedal
mechanism.  Pedal notes in the second octave are sometimes the heart
and soul of the music.  If those notes are played one octave lower,
the rumbling bass totally overrides the delicate nature of the music.

My finished data files of rolls scans have four tracks.  Two tracks
are for the notes, upper and lower.  Another track is for the Duo-Art
codes.  And the fourth track is for the pedal notes.  This fourth track
requires no switching during play as I have incorporated that into the
track.  In other words, this track contains all the notes that result
from the Duo-Art switching.  If used on any MIDI organ, my scans will
operate the pedal correctly.

It is this deep involvement in Duo-Art organ rolls that has broadened
my understanding of the Aeolian rolls.  While the general audience here
may not be able to use this information, there is still some chance it
might come in handy.  So the next time someone asks, "Why did Aeolian
put the Reverse switch on the 116-note console?", you can smugly
answer, "It's obvious, they did it to couple Manual II to the pedal".

There will be more obscure findings posted later.

Happy New Year to all!

Bob Taylor
http://members.socket.net/~rtaylor/aeolian_pipe_organ.html