Confirming Mr. Taylor's measurements of the perforations of the Aeolian
Pipe Organ 116-note rolls, 0.043" hole diameter is a good average.

Measuring several rolls, I get a variation from 0.039" to 0.045".
There is apparently a slight difference between samples; on the rolls
with smaller holes, the scalloping between appears more pronounced,
due to the slightly smaller hole diameter.  But this small variance is
probably due to the condition of the punch and die, and the position of
the particular roll in the 'stack' being punched, rather than any
deliberate change in the standard.  This should not be significant.

However, all the rolls I examined have a punch advance rate of 28 steps
per inch.  This is an important constant.  The 116-note tracker bar is
laid out in two rows of alternating holes, 0.25" inch apart.  (The
lower row replicates the layout of the earlier 58-note tracker bar and
plays the lower manual; the added upper row plays the upper manual.)
When any notes are expected to play on both manuals simultaneously, the
array of perforations for the upper manual is set back seven steps
behind the lower manual punchings.  If the step rate were not
accurately held to 28 ppi., the music would not come out right.

There is another parameter which is important.  The ports in the
tracker bar are 0.0625" top-to bottom; much larger than the holes in
the paper.  Therefore, a note is actuated for about two 'step times'
for each perforation, assuming that the contact closes when about half
of the perforation comes across the top edge of the port.  In other
words, the note plays for a slightly longer period than the length of
its slot would indicate.

This required the use of an unusual convention in the roll arrangements.
When a passage of music is meant to play legato, one punch is omitted
between the end of one note's slot, and the beginning punch of the
following note.  If the more usual music roll practice were used, where
the beginning and ending perforations of sequential notes overlapped,
there would be a short period when both notes were 'on'.  This would
produce a muddy, overly legato effect.  This convention would have to
be allowed for in any method of copying the 116-note (or the similarly
made 176-note) rolls electronically.

Incidentally, this produces a problem when playing 58-note rolls on a
116-note player.  For back-compatibility, 116-note players have a
'58 note music' switch which turns off the upper row of holes in the
tracker bar.  (They had to, so the owner could get a decent selection
of popular music; only a few 116-note pops were issued.)  58-note rolls
are physically identical to 116-note rolls, and the lower holes in the
116-note tracker bar match the 58-note layout, so they work on 116-note
players.  But 58-note rolls have huge perforations, and the end punching
of one note overlaps the beginning punching of the following note.
These rolls are designed to play on 58-note organs, whose tracker ports
are much narrower top-to-bottom, and have large bleeds.

When a 58-note roll perforation barely crosses the top edge of the wide
116-note port, with its tiny bleed, the note is triggered.  But the
preceding, overlapping note keeps on playing for a bit, until its
trailing edge almost covers the lower edge of its port.  Thus, such
rolls do sound sloppy when played on a 116-note instrument.

This defect can be largely cured by having a second set of very large
bleeds in the channels to the lower pouches, which are uncovered only
during the 58-note mode.  According to Ord-Hume, this feature was
included in some 116-note reed organs, although it is not present in
the 116-note pipe organ consoles that I have seen.  Since most 116-note
players use a pressurized spoolbox rather than vacuum to read the roll,
the bleeds are on the outside of the pouch boards, venting to
atmosphere.  Therefore, such an arrangement is comparatively easy to
add.  In my experience, it makes a real difference, making 58-note rolls
sound much crisper when played on the 116-note organ.

Richard Vance