Lilypond changing staves with tremolo on single notes

Question

I'm on Lilypond 2.20 and trying to write a passage where I have several 8th notes tremolo'd to 16ths, and I'm trying to get them to change staves—but whenever I do, the beams glitch out and can't be placed correctly.

As an example, try running the following code: \autochange { c8:16 c'':16 c:16 c'':16 }

Any idea what I can do about this? Thank you!

Answer 1

Best I can come up with is creating two voices in top staff. First voice has 8th notes, second voice has 1/4 notes in space of 8th notes and they "hold the tremolo sign" Created variables for up and down staff. Two functions for: beam adjustment, and tremolo height. Might need. Very hacky but works.

\version "2.20.0"
beamPos =
#(define-music-function
     (parser location beg-end)
     (pair?)
   #{
     \once \override Beam.positions = #beg-end
   #})

tremPosition =
#(define-music-function
     (parser location y-offset)
     (number?)
   #{
     \once \override StemTremolo.Y-offset = #y-offset
   #})

csu = { \change Staff = "up" \stemDown }
csd = { \change Staff = "down" \stemUp }

up = \relative c {
  %\csd c8 \csu c'' \csd c \csu c''
  << 
    \relative c {
      \csd \beamPos #'(4 . 4) c8 \csu c'' \csd c,, \csu c''
      \csd \beamPos #'(4 . 4) c,,8 \csu c'' \csd c,, \csu c''
    }
    \\
     \relative c {
       \csd  c4 * 1/2:8 \csu c'':8 \csd c,,:8 \csu c'':8
       \csd \tremPosition #3 c,,4 * 1/2:8 \csu \tremPosition #-2 c'':8 \csd \tremPosition #1 c,,:8 \csu \tremPosition #-1 c'':8
     }
  >>
}

down = \relative c' {
  s1 | s1 |
}

\score {
   <<
    \new Staff = "up" \with {
      midiInstrument = "acoustic grand"
    } \up
    \new Staff = "down" \with {
      midiInstrument = "acoustic grand"
    } { \clef bass \down }
  >>
  \layout { }
  \midi { }
}

First shows default output. Second shows altering tremolo signs. Both have beam adjusted. Don't forget spacer rests in down staff to:

keep the staff alive!