Re: Duo-Art Expression Coding
By Jody Kravitz
I need to get my two cents worth in here. Roll (and organ book) editing is an art, at least in part to the fact that the instrument has inherent time delays in its mechanical components. MIDI encodes the time the sound _STARTS_ (and ends). I'm not real familiar with pneumatic pianos, but I can attest to the fact that playing MIDI on a solenoid piano requires some "smarts" on the part of the driving circuitry so that the soft notes hit when they are supposed to! This is done by having the computer delay the time power is applied to the solenoids for the loud notes. The percussoin pneumatics on a band organ have the same problem. You have to apply the signal "early" to get the sound to happen at the right time.
Pneumatic devices have time delay characteristcs as well, and the expression coding must preceed the notes to be played. I'm uncertain if the editors "adjusted" the positions of the holes for the "soft" notes, but I wouldn't be surprised.
As for converting the holes of pneumatic expression rolls to MIDI, its very tempting to put a MIDI "record" device on a pneumatic piano and just play the rolls in the piano. This method is hardly scientific. Its prone to all kinds of errors from the condition of the instrument, the presence of dirt in the bleeds, etc, etc, etc.
To get a good MIDI file, its first necessary to have an "archival quality" image of the holes in a disk file. No expression interpretation, just the EXACT positions of the holes. Then you can message the data, mathmatically, to do what the piano was supposed to do to it.
What ? We don't know exactly, mathmatically, what the piano was going to do to it ? Probably true. But we now have the "exact" data from the roll, so when we get a better mathmatical model of the piano, we do the conversion again. The rolls may have turned to dust by now, but we still have the EXACT data that was on them.
Its worth noting that having the EXACT image of the roll on disk would make it possible to re-cut exact roll copies later. You could also install solenoid valves on a real expression piano (that used the same expression encoding) and play the roll image.
Having only an MIDI file of a tune does not imply you can re-cut the roll. The hardest part of the editor's task when making an expression roll is putting the expression encoding in correctly.
I pose three "problems" to the readers of the digest:
1) Come up with better mathmatical models of the expression pianos
that we all love so much.
2) Come up with a program to use the model to convert roll data to
MIDI accurately. Some of our readers have written such programs,
but I don't think this is a problem that can't be improved upon,
especially as computers get faster and the models get better (and
more complicated).
3) Come up with a program to use the model to convert _FROM_ MIDI to
a given EXPRESSION piano system. This is not likely to be a
trival task, but it would be really nice to be able to do
conversions in this direction. There are a growing number of
expression pianos which have had solenoid valves put on them so
that roll images can be played back through them from a computer.
There so muchgood MIDI material now, it would be nice to make it
possible for that material to be enjoyed on thes "hybrid" expression
pianos. Such "hybrid" pianos still need the same data that would
have been on the roll.
Jody
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(Message sent Thu 31 Oct 1996, 05:47:02 GMT, from time zone GMT-0800.) |
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