alto stems up, tenor stems down

[Luc Saffre]

Hello,

in a songbook for SATB choir, I'd like to save paper by turning the alto
stems up and the tenor stems down whenever this is possible. For many
songs, this would make the result more dense without being less readable.

If you look at the attached satb2.pdf:
- the first line is the default output with the alto stems down.
- the second line is how I would like the result to look.

But I had to cheat in order to get the second line. I had to move the
alto voice partly to the soprano (and tenor to bass). This is more
difficult to write and has other disadvantages (e.g. I won't get
separate midi channels for each voice).

Is there a way to keep each voice definition separated and to insert
commands like "please merge the stems of alto and soprano" and "please
stop merging"? Something like:

  \context Voice = "soprano" \relative g' {
     \key c \major
     \voiceOne g4 e e2 | f4 d d2 | }
  \context Voice = "alto" \relative c' {
     \voiceTwo \mergeStemsTo "soprano" e4 c c2 |
        \stopMerging b8( c) d( c) b2 | }

Thanks in advance for any hints.
Luc

satb2.pdf
Description: Adobe PDF document

\version "2.10.25"

\score{ 
\context StaffGroup<<

  \context Staff = "upper" <<
  \clef treble
  \context Voice = "soprano" \relative g' {
     \key c \major
     \voiceOne g4 e e2 | f4 d d2 | }
  \context Voice = "alto" \relative c' {
     \voiceTwo e4 c c2 | b8( c) d( c) b2 | }
  >>
            
  \lyricsto "soprano" \new Lyrics { 
    \lyricmode { Häns- chen klein ging al- lein } } 
            
  \context Staff = "lower" <<
  \clef bass 
  \context Voice = "tenor" \relative c' {
    \key c \major
    \voiceThree c4 c c2 | g4 g g2 | }
  \context Voice = "bass" \relative c {
    \voiceFour c4 c c2 | g4 g g2 | }
  >>
>>
}

\score{ 

\context StaffGroup<<
  \context Staff = "upper" <<
  \clef treble
  \context Voice = "soprano" \relative g' {
     \key c \major
     \voiceOne <g e>4 <e c> <e c>2 | f4 d <d b>2 | }
  \context Voice = "alto" \relative c' {
     \voiceTwo s4 s s2 | b8( c) d( c) s2 | }
  >>
            
  \lyricsto "soprano" \new Lyrics { 
    \lyricmode { Häns- chen klein ging al- lein } } 
            
  \context Staff = "lower" <<
  \clef bass 
  \context Voice = "tenor" \relative c' {
    \key c \major
    \voiceThree s4 s s2 | s4 s s2 | }
  \context Voice = "bass" \relative c {
    \voiceFour <c c'>4 <c c'> <c c'>2 | <g g'>4 <g g'> <g g'>2 | }
  >>
>>
}