Between-note tremolo gains a spurious visible tuplet bracket on MusicXML round-trip

[leahchilders]

music21 version

9.9.2 and 10.3.0

Operating System(s) checked
This was checked on Linux but is not OS-specific because it's pure Python logic

Problem summary

When using tremolos between notes, roundtrips add a spurious visible tuplet bracket with the number visible. Two notes in the time of one note give a 2/1 time-modification which is not a printed tuplet, but tuplet notation is not properly suppressed after a parse --> write reconstruction back into musicxml roundtrip.

Steps to reproduce

import music21
from music21 import converter

# Minimal between-note tremolo: two whole notes (E3, G3) in the time of one.
# NOTE: there is no <tuplet> element anywhere -- only <time-modification>.
src = '''<?xml version="1.0" encoding="UTF-8"?>
<score-partwise version="4.0">
  <part-list><score-part id="P1"><part-name>Piano</part-name></score-part></part-list>
  <part id="P1">
    <measure number="1">
      <attributes>
        <divisions>256</divisions>
        <key><fifths>0</fifths></key>
        <time><beats>2</beats><beat-type>2</beat-type></time>
        <clef><sign>F</sign><line>4</line></clef>
      </attributes>
      <note>
        <pitch><step>E</step><octave>3</octave></pitch>
        <duration>512</duration><voice>1</voice><type>whole</type>
        <time-modification><actual-notes>2</actual-notes><normal-notes>1</normal-notes></time-modification>
        <notations><ornaments><tremolo type="start">4</tremolo></ornaments></notations>
      </note>
      <note>
        <pitch><step>G</step><octave>3</octave></pitch>
        <duration>512</duration><voice>1</voice><type>whole</type>
        <time-modification><actual-notes>2</actual-notes><normal-notes>1</normal-notes></time-modification>
        <notations><ornaments><tremolo type="stop">4</tremolo></ornaments></notations>
      </note>
    </measure>
  </part>
</score-partwise>'''

s = converter.parse(src, format='musicxml')

# The importer left the auto-created tuplet visible, even though the source
# had no <tuplet> element:
for n in s.recurse().notes:
    t = n.duration.tuplets[0]
    print(n.nameWithOctave, 'bracket=', t.bracket, 'actualShow=', t.tupletActualShow)
# E3 bracket= True actualShow= number
# G3 bracket= True actualShow= number

out = s.write('musicxml')
xml = open(out, encoding='utf-8').read()
print('bracket="yes" in output:', 'bracket="yes"' in xml)   # -> True

Expected vs. actual behavior

Expected: Round trip should keep the tremolo and time-modification but NOT emit a visible tuplet bracket (either no <tuplet> element, or <tuplet bracket="no" show-number="none">), since the source drew no bracket.)

Actual: output contains <tuplet bracket="yes" number="1" placement="above" type="start"> … <tuplet type="stop"/>
More information

Issue appears to be a fallback tuplet from when there are no tuplet definitions in the tuplet tag. (MeasureParser.xmlToTuplets() in music21/musicxml/xmlToM21.py)

Possible fix: when the fallback 2:1 tuplet is created from <time-modification> alone (no matching <tuplet>), set tup.bracket = False, tup.tupletActualShow = None, and tup.tupletNormalShow = None. Clearest when note has a <tremolo type="start|stop"> ornament, where the 2:1 time-modification is directly from the tremolo and not a tuplet.

[mscuthbert]

Thanks for taking the time to write, but a Time Modification w/o <tuplet> does not mean show no brackets. It means it is up to the interpreter to decide how to display, and the most logical default display is to put numbers on tuplets.

To create a tuplet w/o number or bracket, a tuplet with bracket="no" and show-number="none" must be used, like Finale does:

        <notations>
          <tuplet bracket="no" number="1" show-number="none" type="start"/>
        </notations>

Music21 respects this and exports w/ more verbosity:

        <notations>
          <tuplet bracket="no" number="1" show-number="none" type="start">
            <tuplet-actual>
              <tuplet-number>3</tuplet-number>
              <tuplet-type>eighth</tuplet-type>
            </tuplet-actual>
            <tuplet-normal>
              <tuplet-number>2</tuplet-number>
              <tuplet-type>eighth</tuplet-type>
            </tuplet-normal>
          </tuplet>
        </notations>

MuseScore 4 (4.7.2) and Dorico and Finale import this properly and respects the number. (MuseScore 3 does not)

[leahchilders]

This is my very first open source contribution attempt, so forgive me if I'm out of line, but I am curious and I wanted to ask so that I can learn for next time - you specifically said it doesn't work for Musescore 3. I have also tested in Sibelius (doesn't work) and Noteflight (doesn't work). If it doesn't break it for the other platforms, why wouldn't you want to expand coverage?

[mscuthbert]

Hi Leah -- I appreciate that you've taken the time to make a contribution!

MuseScore 3 doesn't support any import of tuplets w/o numbers etc. so it doesn't matter what (whether you remove the <tuplet> completely or put show number = none) so there's no way to import it properly there. Can you show me a musicxml file not made from music21 that Sibelius or Noteflight accurately import that omits the tuplet marks? I haven't used Sibelius in a long time, but Noteflight didn't allow this last time I checked. Those are limitations of those software, not music21.

We're not going to change the interpretation of music21's import system because it currently matches the musicxml standard. The change that you suggested would bring music21 out of line from the standard. (I know the 2:1 tremolo trick, which makes the best-looking tremolos, but does not export the semantics properly into MusicXML)

[mscuthbert]

What software are you using that you can't export w/ hidden numbers and brackets?

[leahchilders]

Ah okay, thank you so much for explaining! I appreciate the time.