Roll Transcribing Methodologies
By John Grant
In digest 95.11.24 Walter Tenten hits upon one of the least-talked about but, IMHO, most critical aspects of transcribing roll data into faithful electronic copies: The effective pneumatic "length" (both in their time and displacement senses) of the holes as influenced by the non-uniform size and placement of tracker bar holes, as they differ among formats. (WHEW!) I will assume (always dangerous!) until someone tells me differently that most if not all of the optical roll scanning techniques tried so far "look" at the roll along a straight, essentially zero width line which is perpendicular to the line of travel of the paper. Reading even a simple non-expression roll in such a manner cannot, absent careful data manipulation, produce a sufficiently faithful electronic copy, either for electronic playback or for producing new copies of the roll. Typically, the optical sensor will trigger "on" as soon as the leading edge of the hole passes the sensing line and will not go "off" until the trailing edge has passed the same line. Pneumatic sensing requires that the hole be a bit more open (or closed) before a transition is sensed and so will produce a shorter duration for the hole than will optical sensing. Consequently, the electronic image will sound "smeared" as notes ending will overlap following notes sounding by "half-a-hole" or so.
Now, complicate this by such considerations as this: On a Duo-Art tracker bar, the holes for the eight intensity tracks are approximately 0.26" in advance of the note holes and are approximately three times as "long" as the note holes. The resulting pneumatic performance of this tracker bar MUST be duplicated. On the Ampico "B" tracker bar, some holes are effectively elongated by being routed out and the intensity holes (2B, 4B, 6B, 6T, 4T, and 2T) are "delayed" by several thousandths of an inch beyond the note holes (bet you never noticed!) This is presumedly what allows "B" coded rolls to reproduce relatively accurately on "A" mechanisms. When played on "B" mechanisms, the faster actuating "B" expression mechanisms are delayed by this distance so that the effective expression between the "A" and the "B" is equalized. (Anybody want to discourse on this as a separate topic?)
Now I'm quite sure that a data manipulation algorithm could be produced that could compensate for these problems. Remember though, you'll need a different algorithm for EVERY different roll format and EVERY specified tempo value! But why bother with all this when a *properly designed and used* pneumatic reader cleverly ignores (or automatically compensates) for these considerations. After all, the goal should be to reproduce the (digital) pneumatic performance of the tracker bar as it responds to a roll.
And of what use is the finished electronic image? In my estimation, there are three: 1)To produce an image that can be used, with properly designed equipment, to produce new copies of the roll. Richard Tonnesen is probably the leader in this process. 2) To allow existing *properly restored* pneumatic instruments to be operated *faithfully* by means of a sensitively designed (and reversibly installed) apparatus which would be, in effect, an electronic replacement for the paper. (Remember the CC-3 Cassette Converter of the '70's?!) 3) The third use would be to allow existing roll performances to be recreated, with proper expression, on modern day synthesizers. This, while technically interesting, does not seem to me to be as much of a necessity as the others. However, I loudly applaud the efforts of Richard Brandle (and others) who are engaged in efforts to this end. The dual of this, i.e., manipulating modern (MIDI) performances so that they can by used, perhaps with the help of the equipment in 2) above, on vintage instruments, can also be debated.
I will have more to say on 2) above in a future post.
-John Grant
|
(Message sent Mon 27 Nov 1995, 05:14:46 GMT, from time zone GMT-0500.) |
|
|
Mechanical
Music Digest™ Archives
