[Lilypond-auto] Issue 3838 in lilypond: midiInstrument sometimes appear twice in the MIDI output

[lilypond]

Status: Accepted
Owner: ----
Labels: Type-Enhancement

New issue 3838 by address@hidden: midiInstrument sometimes appear twice  
in the MIDI output
http://code.google.com/p/lilypond/issues/detail?id=3838

NB: Issue 3823 has an added @KNOWNISSUE in the NR for this.


> address@hidden wrote:
> > \score {
> >    \new Staff {
> >      \set Staff.midiInstrument = #"electric bass (finger)" % 34
> >      \set Staff.midiPanPosition = #0
> >      a'1
> >    }
> >    \midi { }
> > }

> >          ['patch_change', 0, 0, 33],
> >          ['control_change', 0, 0, 10, 64],
> >          ['control_change', 0, 0, 42, 0],
> >          ['patch_change', 0, 0, 33],
> >          ['instrument_name', 0, 'electric bass (finger)'],
> >          ['control_change', 0, 0, 10, 64],
> >          ['control_change', 0, 0, 42, 0],
> >          ['control_change', 0, 0, 7, 100],

> >   As seen by the output, patch_change and control messages for panning
> > (10 is pan MSB, 42 is LSB pan) are done twice.

On 19/01/14 00:45, Devon Schudy wrote:

> This is because a quirk of ordering makes Staff_performer treat these
> properties as both changes and preexisting settings.
> Staff_performer::acknowledge_audio_element creates the Audio_staff as
> needed to perform Audio_items, and in this case the first Audio_item
> is the patch change. This happens during do_announces, after the
> context properties have already changed, so the Audio_staff starts
> with extra control messages to set its initial state to match the
> properties. Immediately afterwards, the control changes are performed.
> The first copy of each change is the initial setting; the second is
> the explicit change.

> This happens only when properties change at the beginning of an
> Audio_staff (which is not rare). I don't see a simple way to fix it,
> but fortunately it's harmless.


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