[MEI-L] @trans.diat and @trans.semi

[Roland, Perry (pdr4h)]

Looking at the documentation for these 2 attributes, it isn't exactly clear what values are expected.  The documentation for trans.diat says, 

   "records the amount of diatonic pitch shift, e.g. C to C♯ = 0, C to D♭ = 1.
   Transposition requires both trans.diat and trans.semi attributes in order to distinguish
   the difference, for example, between a transposition from C to C♯ and one from C to D♭."

while for trans.semi, it says, 

  "contains the amount of pitch shift in semitones, C to C♯ = 1, C to D♭ = 1.
  Transposition requires both trans.diat and trans.semi attributes in order to distinguish
  the difference, for example, between a transposition from C to C♯ and one from C to D♭."

So, for the clarinet in B♭should the values be trans.diat="1" and trans.semi="2", or should they read trans.diat="-1" and trans.semi="-2" ?

It seems to me that the first set of values is somewhat redundant since the written pitches for the clarinet are already recorded as one step "too high" with respect to concert pitch. This redundancy, however, could be used to mean that the written pitches are not errors; that is, that an F# on the clarinet staff is correct in the concert key of C.

Another way to approach these attributes (which is, by the way, used in the musicxml2mei XSL transform) is to use them to indicate the amount of "correction" necessary to achieve the concert pitch from the written one.  In this case, the second set of values would be more helpful; that is, given a pitch of D4, to get a performable concert pitch, subtract the value of trans.semi. (Or perhaps more technically correct, add -2 semitones.)

So, having made the decision once before (when writing the XSL transform), it would be convenient to make the documentation agree with the already-made decision.  However, if anyone has a good argument, other than tradition, why this decision (and the documentation) should be reversed, please speak up.

--
p.

__________________________
Perry Roland
Music Library
University of Virginia
P. O. Box 400175
Charlottesville, VA 22904
434-982-2702 (w)
pdr4h (at) virginia (dot) edu