Automatic part combining

Automatic part combining is used to merge two separate parts of music onto a single staff. This can be especially helpful when typesetting orchestral scores. A single Voice is printed while the two parts of music are the same, but in places where they differ, a second Voice is printed. Stem directions are set up & down accordingly while Solo and a due parts are also identified and marked appropriately.

The syntax for automatic part combining is:

\partCombine musicexpr1 musicexpr2

The following example demonstrates the basic functionality, putting parts on a single staff as polyphony and setting stem directions accordingly. The same variables are used for the independent parts and the combined staff.

instrumentOne = \relative {
  c'4 d e f |
  R1 |
  d'4 c b a |
  b4 g2 f4 |
  e1 |
}

instrumentTwo = \relative {
  R1 |
  g'4 a b c |
  d4 c b a |
  g4 f( e) d |
  e1 |
}

<<
  \new Staff \instrumentOne
  \new Staff \instrumentTwo
  \new Staff \partCombine \instrumentOne \instrumentTwo
>>

Both parts have identical notes in the third measure, so only one instance of the notes is printed. Stem, slur, and tie directions are set automatically, depending on whether the parts are playing solo or in unison. When needed in polyphony situations, the first part (with context called one) gets “up” stems, while the second (called two) always gets “down” stems. In solo situations, the first and second parts get marked with “Solo” and “Solo II”, respectively. The unison (a due) parts are marked with the text “a2”.

By default, the part combiner merges two notes of the same pitch as an a due note, combines notes with the same rhythm less than a ninth apart as chords and separates notes more than a ninth apart (or when the voices cross) into separate voices. This can be overridden with an optional argument of a pair of numbers after the \partCombine command: the first specifies the interval where notes start to be combined (the default is zero) and the second where the notes are split into separate voices. Setting the second argument to zero means that the part combiner splits notes with an interval of a second or more, setting it to one splits notes of a third or more, and so on.

instrumentOne = \relative {
  a4 b c d |
  e f g a |
  b c d e |
}

instrumentTwo = \relative {
  c'4 c c c |
  c c c c |
  c c c c |
}

<<
  \new Staff \partCombine \instrumentOne \instrumentTwo
  \new Staff \partCombine #'(2 . 3) \instrumentOne \instrumentTwo
>>

Both arguments to \partCombine will be interpreted as separate Voice contexts, so if the music is being specified in relative mode then both parts must contain a \relative function, i.e.,

\partCombine
  \relative … musicexpr1
  \relative … musicexpr2

A \relative section that encloses a \partCombine has no effect on the pitches of musicexpr1 or musicexpr2.

In professional scores, voices are often kept apart from each other for long passages of music even if some of the notes are the same in both voices, and could just as easily be printed as unison. Combining notes into a chord, or showing one voice as solo is, therefore, not ideal as the \partCombine function considers each note separately. In this case the \partCombine function can be overridden with one of the following commands. All of the commands may be preceded with \once in order to have them only apply to the next note in the music expression.

• \partCombineApart keeps the notes as two separate voices, even if they can be combined into a chord or unison.
• \partCombineChords combines the notes into a chord.
• \partCombineUnisono combines both voices as “unison”.
• \partCombineSoloI prints only voice one, and marks it as a “Solo”.
• \partCombineSoloII prints only voice two and marks it as a “Solo”.
• \partCombineAutomatic ends the functions of the commands above, and reverts back to the standard \partCombine functionality.

instrumentOne = \relative c' {
  \partCombineApart c2^"apart" e |
  \partCombineAutomatic e2^"auto" e |
  \partCombineChords e'2^"chord" e |
  \partCombineAutomatic c2^"auto" c |
  \partCombineApart c2^"apart"
    \once \partCombineChords e^"chord once" |
  c2 c |
}
instrumentTwo = \relative {
  c'2 c |
  e2 e |
  a,2 c |
  c2 c' |
  c2 c |
  c2 c |
}

<<
  \new Staff { \instrumentOne }
  \new Staff { \instrumentTwo }
  \new Staff { \partCombine \instrumentOne \instrumentTwo }
>>

Using \partCombine with lyrics

The \partCombine command is not designed to work with lyrics; if one of the voices is explicitly named in order to attach lyrics to it, the part combiner will stop working. However, this effect can be achieved using a NullVoice context. See Polyphony with shared lyrics.

Selected Snippets

Combining two parts on the same staff

The part combiner tool (i.e., the \partCombine command) allows the combination of several different parts on the same staff. Text directions such as “solo” or “a2” are added by default; to remove them, simply set the property printPartCombineTexts to #f.

For vocal scores (hymns), there is no need to add “solo/a2” texts, so they should be switched off. However, it might be better not to use them if there are any solos, as they won’t be indicated. In such cases, standard polyphonic notation may be preferable.

This snippet presents the three ways two parts can be printed on a same staff: standard polyphony, \partCombine without texts, and \partCombine with texts.

musicUp = \relative c'' {
  \time 4/4
  a4 c4.( g8) a4 |
  g4 e' g,( a8 b) |
  c b a2.
}

musicDown = \relative c'' {
  g4 e4.( d8) c4 |
  r2 g'4( f8 e) |
  d2 \stemDown a
}

\score {
  <<
    \new Staff \with {
      instrumentName = "standard polyphony"
    } << \musicUp \\ \musicDown >>

    \new Staff \with {
      instrumentName =
        \markup { \typewriter "\\partCombine" without text}
      printPartCombineTexts = ##f
    } \partCombine \musicUp \musicDown

    \new Staff \with {
      instrumentName =
        \markup { \typewriter "\\partCombine" with text}
    } \partCombine \musicUp \musicDown
  >>

  \layout {
    indent = 6.0\cm
    \context {
      \Score
      % Setting this to a large value avoids a bar line at the
      % beginning that would connect the three staves otherwise.
      \override SystemStartBar.collapse-height = 30
    }
  }
}

Changing \partCombine texts

When using the automatic part combining feature, the printed text for the solo and unison sections may be changed.

\new Staff <<
  \set Staff.soloText = "girl"
  \set Staff.soloIIText = "boy"
  \set Staff.aDueText = "together"
  \partCombine
    \relative c'' {
      g4 g r r
      a2 g
    }
    \relative c'' {
      r4 r a( b)
      a2 g
    }
>>

See also

Music Glossary: a due, part.

Notation Reference: Writing parts.

Snippets: Simultaneous notes.

Internals Reference: PartCombineMusic, Voice.

Known issues and warnings

All \partCombine… functions can only accept two voices.

\partCombine… functions cannot be placed inside a \tuplet or \relative block.

If printPartCombineTexts is set and the two voices play the same notes “on and off”, in the same measure, the part combiner may typeset a2 more than once in that measure.

\partCombine only knows when a note starts in a Voice; it cannot, for example, remember if a note in one Voice has already started when combining notes that have just started in the other Voice. This can lead to a number of unexpected issues including “Solo” or “Unison” marks being printed incorrectly.

\partCombine keeps all spanners (slurs, ties, hairpins, etc.) in the same Voice so that if any such spanners start or end in a different Voice, they may not be printed properly or at all.

If the \partCombine function cannot combine both music expressions (i.e., when both voices have different durations), it will give the voices, internally, its own custom names: one and two respectively. This means if there is any “switch” to a differently named Voice context, the events in that differently named Voice will be ignored.

Refer also to Known issues and warnings when using \partCombine with tablature in Default tablatures and the Note in Automatic beams when using automatic beaming.

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LilyPond Notation Reference v2.25.15 (development-branch).