Re: Roll Speed
By Bill Jelen
Mark Fontana wrote:
> Are the rolls generally encoded such that when played on a standard-sized
> takeup spool, the tempo will remain as intended despite the effect of
> othe increasing layers of paper accelerating the transport speed?
I believe the answer is no. I encounted this question while working on a project to convert live MIDI files to piano roll. I asked QRS and they do not currently compensate for tempo variation when encoding a single roll. They may sometimes use a different rate for the second song in a medley roll.
> It occurred to me that I could include a function in my scanning software
> to adjust for the speed-up effect mathematically... Perhaps I could
> measure the diameter of the takeup spool (with music) at the end of a roll,
> then have the software correct the timing in the scanned data based on
> that measurement, the duration of the piece, and the original circumference
> of the takeup spool.
I have performed this experiment with the intention of calculating "on-the-fly" a variable tempo adjustment when converting live-played MIDI files to piano rolls. I couldn't belive the results. They indicated a 25 foot roll that started at a tempo of 70 was actually travelling at a tempo of 85 at the end of the roll. This is what the math said, but it did not intuitively seem correct. I was perplexed until I read Zoltan Janosy's thesis. He noted that this increase of tempo is countered somewhat, "since the increasing mass (of paper on the take-up spool) slows down the low torque pneumatic winding motor." Although he noted that these forces won't exactly cancel each other out.
--Bill Jelen
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(Message sent Sun 11 Jun 1995, 18:18:00 GMT, from time zone GMT-0500.) |
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