Re: chord.ly to extract notes from chords breaks with new Guile

[mskala]

On Wed, 31 May 2023, Gilles Thibault wrote:

> Not hardly tested but this should work :

Thanks for looking at it further.  I hate to impose on you because I've
already decided to solve this problem in external postprocessing of the
MIDI files, so I hope you won't put a lot of effort into trying to satisfy
my use case with modifications to your script.  I don't think doing it in
Lilypond is really the right solution for me because to really solve it I
need to automatically handle *all* cases of simultaneous notes.  I need,
at each point in time, to have at most one note per track, exactly one
track per note, and silence in any leftover tracks, regardless of the
voice/chord structure of the music.

The code you provide works for the specific example I gave, where the
desired silence comes from a note written as a single note instead of a
chord, but there are many other cases (illustrating the problem with
minimal examples).  In particular:

* change b2 to <b>2 and the b2 comes out in two tracks.  Maybe it would
  never occur to me to write a one-note chord, but a similar issue can
  happen between two- and three-note chords, or anywhere the number of
  notes per chord in a voice is not always the same.

* a one-voice passage added outside the << >> construct comes out in two
  tracks

* if each of two voices sometimes contains two simultaneous notes, but
  only at most three notes are simultaneous overall, then I need to either
  use four output tracks, or carefully split and then merge to bring it
  down to three, and handling this kind of thing becomes steadily more
  complicated as the number of voices and simultaneous notes grows.

Resolving these points and any other similar ones that may come up, seems
like a lot of work.  If an in-Lilypond solution means I need to do things
like maintain the same number of Voice contexts throughout the entire
piece of music, or think hard about which note/voice index needs to merge
with which other one to minimize the overall number of tracks without ever
having more than one note simultaneous in a track, then we quickly
approach a point where it would be less work for me to just write out the
intended output by hand and not have Lilypond calculate it at all.

In external MIDI processing it's relatively easy:  at every "Note on"
message in chronological order, I can route the note to an unused track or
else know unambiguously that I need more tracks.  At every "Note off," the
track in question becomes available again.  The external code basically
does the same thing that a polyphonic synthesizer would do, just with
output to new MIDI tracks instead of directly to hardware voices.  No need
for separate handling of Lilypond's "single note," "chord," and "voice"
concepts.

-- 
Matthew Skala
mskala@ansuz.sooke.bc.ca                 People before tribes.
https://ansuz.sooke.bc.ca/