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MMD > Archives > September 1997 > 1997.09.14 > 04Prev  Next

Truncating a MIDI-file for Perforating
By Craig Brougher

I have a question about the explanation Robbie gave in regard to how
long a player or a perforator responds to the hole passing over the
trackerbar.  Robbie explained it this way:

> Now imagine a single hole in the paper passing over the hole in the
> tracker bar.  The pneumatic valve will be 'on' while the paper moves
> the distance of the sum of the height of the tracker-bar hole plus
> about one-half of the diameter of the hole in the paper, or 0.045
> + 0.068 / 2 = 0.079 .  This distance (0.079) is roughly 3.5 times the
> advance distance, or 3.5 x .0222 .

I don't doubt the figures at all.  But just for drill, it seems to be
that as soon as 1/2 the hole has uncovered the trackerbar hole, the valve
should operate.  So that makes the effective length of the "actuation
area" 1 trackerbar hole length plus 1/2 of a perforation diameter.

Now the paper travels the hole across the trackerbar hole to the bottom
edge of the trackerbar hole.  The valve is still "on," actuated.  The
valve stays on until 1/2 of that hole has passed the bottom edge of the
trackerbar hole.  Then (ideally) it switches off.  That makes the total
length equal to a trackerbar hole plus a diameter.

Actually, The actuation of most valves occurs when the hole has just
passed 1/2 its diameter, and doesn't turn off again until the hole has
_passed_ or is greater than 3/4ths of its diameter, so really, the
effective actuation length is greater than a trackerbar hole plus a
diameter, by probably 1/4th of a single perforation (as a rough guess).

Maybe Robbie could tell me if this is right, or where I am missing
something, here.

Craig Brougher

 [ You're probably closer than my explanation was, Craig.  I wrote my
 [ quick reply to Tim Baxter without proper preparation (such as finding
 [ my notes from many years ago), and as I read it now I'm still confused.
 [ The one thing I'm sure of, though, is that Richard Tonnesen uses a
 [ 100-hole Welte tracker bar to read the roll, and he truncates each
 [ note-length by 3 steps for the 45-rows-per-inch perforator.  Long ago
 [ I made careful experiments with his system at resolutions up to 270
 [ rows-per-inch, and determined that the optimal figure should be about
 [ 3-1/2 steps truncation.  But now I can't explain it. :-(   -- Robbie

(Message sent Sun 14 Sep 1997, 12:43:57 GMT, from time zone GMT.)

Key Words in Subject:  MIDI-file, Perforating, Truncating

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