Lilypond: merging notes from two voices to one beam OR faking note length

Question

Chopin's Raindrop prelude, first measure.

The notes marked in red technically do not fit into their group (connected by the beam). If I define two voices however, they will be no longer connected to the beam. There are official editions out there that do separate those two note from the group, but I really prefer the way shown in the picture.

But how would I do this? How do I connect both "wrong" notes to this beam? Can I just fake and override the duration of these notes? I did not find a way to do this. And merging notes – as far as I found – only deals with same notes but different types of heads at the same time.

Edit: As I continued to look for solutions I found a way to fake the duration:

\override NoteHead.duration-log = #1 <des' f'> \revert NoteHead.duration-log

But still: Is there an elegant or correct way to deal with this via voicings?

Answer 1

Lilypond does have this wonderful little macro \mergeDifferentlyHeadedOn. Using this we can easily achieve this:

\new PianoStaff <<
  \new Staff {
    \key des\major
    f''8. des''16 as'2 bes'4
  }
  \new Staff {
    \clef bass
    \key des\major
    \mergeDifferentlyHeadedOn
    <<
      {
        s4 <des' f'>2 4
      }
      \\
      {
        des8 as des' as as as des' as
      }
    >>
  }
>>

Note that this is technically slightly different from the engraving here, as this would gives us the (eighth) Db with a stem down and the (half) Db and F with a stem up. The engraving here does this reversely, so only the F has a stem up while both notes are on the stem down.

So the way Lilypond does this does make more sense musically. By the way in the autograph Chopin notated this without a stem up.