Re: Temporarily combine two Voices on the same Staff

[H. S. Teoh]

On Tue, Dec 20, 2016 at 11:30:51PM +0100, Simon Albrecht wrote:
> On 20.12.2016 22:54, H. S. Teoh wrote:
> > I'm typesetting some complex polyphonic music, and have 3 Voices
> > sharing the same Staff. In the middle of the bar, the top two Voices
> > share the same rhythm, so I'd like to combine stems beams on them
> > just for 2 beats, and have them be treated independently again
> > afterwards. There is a 3rd Voice on the same Staff with downward
> > Beams, so without combining, the top two Voices would have
> > hard-to-read clashing beams.
> 
> Please give an example, else it’s hard to judge. But it would be very
> unusual in an otherwise strictly polyphonic work to use chords for
> just two beats.
[...]

Sorry, I didn't make it clear.  I was actually transcribing a Bach
piece, BWV 850 (fugue in D major in 4 voices, WTC book 1). I chose to
transcribe it using 4 Voices (there are several Staff crossings
throughout the piece, so this way I can use \change Staff="...", but
that's not pertinent here.) In measure 7, for example, I have:

        \include "english.ly"
        voiceA = \relative c'' {
                % m.7
                \voiceOne
                | g'=''4  fs8. e16  d8. e16  c8. c16
        }

        voiceB = \relative c'' {
                % m.7
                \voiceThree
                | cs=''8~ cs32 e d cs  d8. cs16  b4  e,4
        }

        voiceC = \relative c'' {
                % m.7
                \voiceFour
                | a='4  a8. g16  fs8. g16  a4
        }

        voiceD = \relative c, {
                % m.7
                \oneVoice
                | r4  d32 e fs g fs e fs d  b'8. b16  a8. g16
        }

        \new PianoStaff <<
                \new Staff {
                        \clef treble
                        <<
                                \new Voice \voiceA
                                \new Voice \voiceB
                                \new Voice \voiceC
                        >>
                }
                \new Staff {
                        \clef bass
                        \new Voice \voiceD
                }
        >>

The edition I'm using as reference has, in this bar, the first 3 voices
on the upper staff, and the bass on the lower staff.  In beat 2 in the
Lilypond output, voiceA and voiceB have stems and beams that clash with
each other, because there simply isn't enough space to fit everything in
otherwise.  Whereas in the edition, in this beat voiceA and voiceB are
collapsed into 2-note chords so that they can share the same beam, thus
making it easier to read, even though they are still logically two
separate voices. In beats 3 and 4, because voiceA and voiceB are no
longer co-rhythmic, they are typeset the same way Lilypond does it.

So my question was, is it possible to tell Lilypond to merge the two
voices into chords just for beat 2? Or do I just have to "hack" it by
using spacers in voiceB and spelling out the chords in voiceA?


T

-- 
Mediocrity has been pushed to extremes.