For many years I have wondered about the intended note duration that
a single punch on a piano roll creates.  As the hole slides across
the tracker bar opening, at some point the bleed is overcome and the
note sounds.  But what is the ideal?

As the hole in the paper passes the tracker bar, at what point does
The note sound?  Is the hole 50%, 40% or 30% open when that occurs?
(I know that all players are not the same).

If someone has the specific criteria for this, I would like to know.

Bob Taylor

 [ The measured and/or theoretical output versus input behavior of an
 [ amplifying device such as a valve is called the transfer function,
 [ typically presented as a chart or a graph plus equations that
 [ approximate the observed data.  The input data may be measured as
 [ the area of the exposed hole or (better) as the airflow into the
 [ pouch chamber.
 [
 [ Dr. Hickman gathered data of this sort on the ball-check unit valve
 [ for the Ampico B.  He wrote in the "Service Manual 1929" for the
 [ Ampico B action: "The proper sizes for the valve, valve seats, pouch
 [ and bleeds have been determined by most careful measurements with
 [ specially designed scientific instruments.  The amount of valve
 [ travel between its seats is very accurately adjusted so that all
 [ valves pass the same amount of air."
 [
 [ I use this 'rule of thumb' for static or slow-speed conditions such
 [ as when transcribing music rolls using a pneumatic reader: the valve
 [ turns 'on' when one-half the hole area is over the tracker bar slot.
 [
 [ Richard Tonnesen determined long ago that a single hole passing over
 [ the tracker bar of his transcriber system would be truncated by
 [ roughly 0.08 inch to yield a single-punch 'impulse' in the perforator
 [ control file.  At that time he was using a tracker bar from a Welte
 [ Licensee piano.
 [
 [ -- Robbie