[MEI-L] Fwd: MEI Customisation
j.ingram at netcologne.de
Wed May 25 13:14:12 CEST 2016
Hi Andrew, Zoltan,
Zoltan: thanks for your answers to this thread on the W3C CG list. This
reply to Andrew (below) continues the thread here, so its also a reply
to what you said.
> AH: For rhythm and duration we differentiate between "@dur" (written
> duration) and "@dur.ges" (performed duration). Both of these are
> available on note and rest objects.
Yes, that's one of the problems -- see below. :-)
>> JI: I want to make an MEI customisation that uses most of the symbols
>> that are used by CWMN, but without assuming tempo. If there is no
>> tempo, then neither tuplets nor grace-notes make sense. It should
>> also be possible for the description of /more than one/ temporal
>> instantiation to be stored inside the XML elements that represent the
>> score's graphics.
> AH: I'm not sure I understand this. Tempo is generally expressed by a
> playback mechanism. It can be hinted at in the encoding, but most
> systems have controls for overriding it.
The @dur attribute describes both the shape of the symbol and its
meaning (the number of beats it represents in a <measure>). Beats mean
tempo, and that's a problem if I'm trying to create a customisation that
does without it.
I want to separate the meaning of each duration symbol from its visual
appearance by putting the temporal information in an enclosed element.
Lets call the enclosed element <time>. Actually, I want (potentially)
to have a /list/ of <time> elements inside each duration symbol, each
position in such lists containing the temporal information for a
different performance of the piece.
The first <time> element would describe the symbol's default duration,
which in MusicXML and MEI Go can be calculated from the tempo, ppq,
logical value of @dur. etc.
If used in CWMN, the <time> element would make all that tempo, ppq,
logical value @dur.ges stuff redundant. Simplification is always a good
idea! :-) Note that this strategy means that @dur's logical value and
@dur.ges are both being treated as being in the same dimension (time).
Pretending that att.duration.musical and att.duration.performed need to
be treated differently is, I think, a mistake.
Note also that the latest MIDI standard (the Web MIDI API) no longer
supports tempo. Including tempo in the 1981 MIDI standard was a mistake,
which has now been rectified. The Web MIDI API just uses milliseconds.
Even CWMN scores should be allowed to contain descriptions of additional
temporal renderings, apart from the default, metronomic one... This
strategy makes metronomes redundant, since scores can contain accurate
temporal renderings of what the composer really meant, not just an
implied mechanical realisation.
The simplest case would be if the <time> element simply had an @ms
attribute which would be its duration in milliseconds. But this element
should also be able to contain more complex temporal information. A
<note> or <chord> symbol can contain ornaments that can be described
using MIDI information. All MIDI info is purely temporal. So the
duration of the <time> elements embedded in <note>s and <chord>s should
really be calculated from the durations in the contained MIDI sequence.
A <time> element in a <rest> might just have a simple @ms attribute.
But lets forget about such refinements for the moment and just note that
the <time> element has a (or defines) a duration.
I want to use <measure>, but here again, I want to separate its
graphical aspects from its meaning.
*Question:* Does setting measure at metcon to false do that? If @metcon is
false, can I then use arbitrary symbols in the various contained
<level>s, and ignore the logical values of all the @dur attributes?
Graphically, a measure is just two vertical lines enclosing <staff>
elements that enclose <layer> elements that enclose duration symbols
(<note>s, <chord>s and <rest>s) and other "events" in a left-right sequence.
The duration symbols' left-right sequence in the measure corresponds to
their earlier-later sequence in time, so there has to be a mechanism for
describing the left-right sequence of all the symbols in a <measure>.
My current solution for this, is to use the default millisecond duration
of the symbol's <time> element (an integer) as a dimensionless number.
The algorithm that creates an (SVG) instantiation of the abstract XML
info first uses this number as a spatial unit (a number of pixels) in a
space wide enough to position the symbols so that they don't overlap,
then compresses the width of the system into the actually available
space. My algorithm is recursive, and results in spacing that
corresponds to what I think is the best, (most legible) way to space
music symbols. If the width is too small for the symbols to be spaced
proportionally to their durations (the usual case), then less space is
given to the longer durations.
While the logical durations of the @dur attributes may not have to add
up in a tempoless <measure>, the <measure> still imposes a restriction
on the durations of the <time> elements. The durations of the <time>
elements in each <layer> have to add up to the same value in any
particular performance. They don't, of course, have to add up to the
same value across different performances. How can I express that in a
schema? Maybe I don't /need/ to express that explicitly, but its still
something that can be validated automatically by software.
> AH: I'm really not sure where you're going with the duration symbols
> and fixed meanings, though. Why would you be adding gracenotes and
In a tempoless notation, there is no need to litter the score with
little numbers and brackets (tuplets) or to make some symbols smaller in
order to make it clear that some notes are outside the counting scheme
(grace-notes) or to add little dots to the symbols to mean that they are
longer than they would be otherwise (augmentation dots). I think of all
these as /annotations/ that can be added ad lib to a score, without
affecting the playback of the contained temporal information.
Tuplets and grace-notes only make sense in music that has tempo (CWMN).
I'm not so sure about augmentation dots -- which could be used as
annotations in tempoless music to imply that the note should be
performed longishly... But a tenuto articulation could do that just as
well. Its probably something that should be left to the composer to
decide. Maybe the composer wants to use tenuto to imply something else
(emphasis of some kind).
Apropos verification: Maybe there's some way in CWMN to ensure that the
default <time> durations inside a tuplet are as equal as possible. But
those durations *must be **integers* in order to prevent the endless
hassle with rounding floating point numbers. None of the durations in
the default (metronomic) performance should be allowed to be more than
one millisecond longer than any of the others. Grace notes inside
tuplets complicate things of course, but the problem should not be
>> JI: Can you imagine such a hierarchy of customisations? I'm also
>> thinking of the container hierarchy that could become part of the W3C
>> standard for describing /any /polyphonic music notation.
> AH: A customization is not arranged in a hierarchy. The primary reason
> for a customization is to produce a schema that will validate an
That's not a problem.
I was thinking more of another level: I think that all polyphonic music
notations could share the same container hierarchy. The
page->system->staff->layer hierarchy is actually independent of the
graphics. Notations can use the same terms, even if they are read left
to right, top to bottom or round in circles. The graphic representation
is really just up to the software that instantiates the score. I just
didn't want to miss the chance of some more modularity.
Its probably not very important in polyphonic music, but it might help
the evolution of software for homophonic music, if the developers always
used the same names for their simplified container hierarchy. For
Hope that helps,
-------------- next part --------------
An HTML attachment was scrubbed...
More information about the mei-l