My interest in scanning music rolls goes back to 1973, when I built a
"reader" for transferring music rolls to tape.  The resulting tapes were
used with a device called the IMI CC-3 Cassette Converter, which played
Ampico instruments from cassettes.  At that time, I did a number of
experiments to determine the precision required to ensure that the
performances would not suffer.

What I learned is pretty much what you would expect.  The manufacturers
of music rolls pushed their technology to its limits in an attempt to
create the best possible musical result.  On all three of the major
reproducing systems (Ampico, Duo-Art, Welte) there are many examples of
"close" coding, in which one or more notes are played with a given
dynamic, and notes in the following row (punch step) are played at a
different, usually softer, level.

Of course, the position of the expression coding with respect to these
notes is critical.  An error of even a small fraction of a row (punch
step) disturbs the effect, resulting in a smaller dynamic difference
between the accented and unaccented notes.  (Listeners describe the
subjective result as a "mushy" or "less crisp" sound.)  Large errors
destroy the effect completely.

None of this is news to readers of the Digest.  Neither is the solution,
which is now being called "hole-for-hole" copying.  However, contrary to
what some contributors seem to believe, hole-for-hole copying is neither
expensive nor exotic.

Making hole-for-hole copies involves two steps.  First, an original roll
(not a recut) must be scanned and the hole-for-hole punch pattern
recovered from the scan.  This can be done by using phase-lock-loop
techniques to find the center of each row.  Each hole in the roll is then
assigned to its correct row.  Second, a new roll must be made (using this
pattern) with a row advance equal to the advance of the original roll.
This involves changing the gear ratio in the perforator to match the
advance.

It may come as a surprise to learn how many different row advances were
used during the period.  Early Duo-Art rolls used a row advance of
(nominally) 256 rows per foot; in the mid-1920s this was upgraded to 384.
Early Ampico rolls advance at 240 rows per foot; around 1921 this changed
to 360.

Some very late Ampico rolls dating from after the merger with Aeolian
were perforated on Duo-Art equipment, and therefore use one of the two
Duo-Art advances; there are therefore four different advances for Ampico,
not counting the Stoddard-Ampico rolls (which used 400 rows per foot).
Early Welte-Mignon Licensee rolls were perforated at 360 rows per foot
using the Republic perforators; in 1921 this too was changed, to 405.

Accommodating this large number of row advances is a nuisance.  It calls
for removing gears or sprockets and mounting different ones in their
places.  However, it is the only thing that needs to be changed to make
hole-for-hole copies.

Wayne Stahnke