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@node Simultaneous notes
@section Simultaneous notes

@lilypondfile[quote,ragged-right,line-width=16\cm,staffsize=16]
{simultaneous-headword.ly}

Polyphony in music refers to having more than one voice occurring
in a piece of music.  Polyphony in LilyPond refers to having more
than one voice on the same staff.

@menu
* Single voice::                
* Multiple voices::             
@end menu


@node Single voice
@subsection Single voice

@menu
* Chorded notes::                      
* Clusters::                    
@end menu

@node Chorded notes
@subsubsection Chorded notes

@cindex Chords

A chord is formed by a enclosing a set of pitches between @code{<}
and @code{>}.  A chord may be followed by a duration, and a set of
articulations, just like simple notes:

@lilypond[verbatim,ragged-right,fragment,quote,relative=1]
<c e g>4 <c>8
@end lilypond

For more information about chords, see @ref{Introducing chord
names}.

@seealso

Music Glossary: @rglos{chord}.

Notation Reference: @ref{Introducing chord names}.

Snippets: @lsrdir{Simultaneous,Simultaneous-notes}.

@refbugs

Music expressions like @code{<< @{ g8 e8 @} a4 >>} are not printed
accurately.  Use @code{<g a>8 <e a>8} instead.



@node Clusters
@subsubsection Clusters

@cindex cluster

A cluster indicates a continuous range of pitches to be played.
They can be denoted as the envelope of a set of notes.  They are
entered by applying the function @code{makeClusters} to a sequence
of chords, e.g.,

@lilypond[quote,ragged-right,relative=2,fragment,verbatim]
\makeClusters { <c e > <b f'> }
@end lilypond

Ordinary notes and clusters can be put together in the same staff,
even simultaneously.  In such a case no attempt is made to
automatically avoid collisions between ordinary notes and
clusters.

@seealso

Snippets: @lsrdir{Simultaneous,Simultaneous-notes}.

Internals Reference: @internalsref{ClusterSpanner},
@internalsref{ClusterSpannerBeacon},
@internalsref{Cluster_spanner_engraver}.

Examples: @c @lsr{contemporary,cluster@/.ly}.



@node Multiple voices
@subsection Multiple voices

@menu
* Collision resolution::        
* Automatic part combining::    
* Writing music in parallel::   
@end menu

@node Collision resolution
@subsubsection Collision resolution

@cindex merging notes
@cindex note collisions

Normally, note heads with a different number of dots are not
merged, but when the object property
@code{merge-differently-dotted} is set in the
@internalsref{NoteCollision} object, they are merged:

@lilypond[quote,verbatim,fragment,ragged-right,relative=2]
\new Voice << {
  g8 g8
  \override Staff.NoteCollision
    #'merge-differently-dotted = ##t
  g8 g8
} \\ { g8.[ f16] g8.[ f16] } >>
@end lilypond

Similarly, you can merge half note heads with eighth notes, by
setting @code{merge-differently-headed}:

@lilypond[quote,ragged-right,fragment,relative=2,verbatim]
\new Voice << {
  c8 c4.
  \override Staff.NoteCollision
    #'merge-differently-headed = ##t
c8 c4. } \\ { c2 c2 } >>
@end lilypond

@noindent
@code{merge-differently-headed} and
@code{merge-differently-dotted} only apply to opposing stem
directions (i.e. Voice 1 & 2).

LilyPond also vertically shifts rests that are opposite of a stem,
for example

@lilypond[quote,ragged-right,fragment,verbatim]
\new Voice << c''4 \\ r4 >>
@end lilypond

@cindex shift note

If three or more notes line up in the same column,
@code{merge-differently-headed} cannot successfully complete the
merge of the two notes that should be merged.  To allow the merge
to work properly, apply a @code{\shift} to the note that should
not be merged.  In the first measure of following example,
@code{merge-differently-headed} does not work (the half-note head
is solid).  In the second measure, @code{\shiftOn} is applied to
move the top @code{g} out of the column, and
@code{merge-differently-headed} works properly.

@lilypond[quote,ragged-right,fragment,verbatim,relative=2]
\override Staff.NoteCollision #'merge-differently-headed = ##t
<<
  { d=''2 g2 } \\
  { \oneVoice d=''8 c8 r4 e,8 c'8 r4 } \\
  { \voiceFour e,,2 e'2}
>>
<<
  { d'=''2 \shiftOn g2 } \\ 
  { \oneVoice d=''8 c8 r4 e,8 c'8 r4 } \\
  { \voiceFour e,,2 e'2}
>>
@end lilypond

@cindex multiple voices
@cindex polyphonic music
@cindex shifting voices

In some instances of complex polyphonic music, you may need
additional voices to avoid collisions between notes.  Additional
voices are added by defining an variable, as shown below:

@lilypond[quote,verbatim,ragged-right,relative=2]
voiceFive = #(context-spec-music (make-voice-props-set 4) 'Voice)

\relative c''' <<
  { \voiceOne g4 ~  \stemDown g32[ f( es d c b a b64 )g] } \\
  { \voiceThree  b4} \\
  { \voiceFive d,} \\
  { \voiceTwo g,}
>>
@end lilypond



@refcommands

@funindex \oneVoice
@code{\oneVoice},
@funindex \voiceOne
@code{\voiceOne},
@funindex \voiceTwo
@code{\voiceTwo},
@funindex \voiceThree
@code{\voiceThree},
@funindex \voiceFour
@code{\voiceFour}.

@funindex \voiceNeutralStyle
@funindex \voiceOneStyle
@funindex \voiceTwoStyle
@funindex \voiceThreeStyle
@funindex \voiceFourStyle
@example
\voiceNeutralStyle
\voiceOneStyle
\voiceTwoStyle
\voiceThreeStyle
\voiceFourStyle
@end example

@funindex \shiftOn
@code{\shiftOn},
@funindex \shiftOnn
@code{\shiftOnn},
@funindex \shiftOnnn
@code{\shiftOnnn},
@funindex \shiftOff
@code{\shiftOff}: these commands specify the degree to which
chords of the current voice should be shifted.  The outer voices
(normally: voice one and two) have @code{\shiftOff}, while the
inner voices (three and four) have @code{\shiftOn}.
@code{\shiftOnn} and @code{\shiftOnnn} define further shift
levels.

When LilyPond cannot cope, the @code{force-hshift} property of the
@internalsref{NoteColumn} object and pitched rests can be used to
override typesetting decisions.

@lilypond[quote,verbatim,ragged-right]
\relative <<
{
  <d g>
  <d g>
} \\ {
  <b f'>
  \once \override NoteColumn #'force-hshift = #1.7
  <b f'>
} >>
@end lilypond


@seealso

Snippets: @lsrdir{Simultaneous,Simultaneous-notes}.

Internals Reference: the objects responsible for resolving
collisions are @internalsref{NoteCollision} and
@internalsref{RestCollision}.


@refbugs

When using @code{merge-differently-headed} with an upstem eighth
or a shorter note, and a downstem half note, the eighth note gets
the wrong offset.

There is no support for clusters where the same note occurs with
different accidentals in the same chord.  In this case, it is
recommended to use enharmonic transcription, or to use special
cluster notation (see @ref{Clusters}).


@node Automatic part combining
@subsubsection Automatic part combining
@cindex automatic part combining
@cindex part combiner
@cindex combining parts

Automatic part combining is used to merge two parts of music onto
a staff.  It is aimed at typesetting orchestral scores.  When the
two parts are identical for a period of time, only one is shown.
In places where the two parts differ, they are typeset as separate
voices, and stem directions are set automatically.  Also, solo and
@emph{a due} parts are identified and can be marked.

The syntax for part combining is

@example
\partcombine @var{musicexpr1} @var{musicexpr2}
@end example


The following example demonstrates the basic functionality of the
part combiner: putting parts on one staff, and setting stem
directions and polyphony.

@lilypond[quote,verbatim,ragged-right,fragment]
\new Staff \partcombine
  \relative g' { g g a( b) c c r r }
  \relative g' { g g r4 r e e g g }
@end lilypond

The first @code{g} appears only once, although it was specified
twice (once in each part).  Stem, slur, and tie directions are set
automatically, depending whether there is a solo or unisono.  The
first part (with context called @code{one}) always gets up stems,
and @q{Solo}, while the second (called @code{two}) always gets
down stems and @q{Solo II}.

If you just want the merging parts, and not the textual markings,
you may set the property @code{printPartCombineTexts} to false.

@lilypond[quote,verbatim,ragged-right,fragment,relative=2]
\new Staff <<
  \set Staff.printPartCombineTexts = ##f
  \partcombine
    \relative g' { g a( b) r }
    \relative g' { g r4 r f }
>>
@end lilypond

To change the text that is printed for solos or merging, you may
set the @code{soloText}, @code{soloIIText}, and @code{aDueText}
properties.

@lilypond[quote,verbatim,ragged-right,fragment,relative=2]
\new Staff <<
  \set Score.soloText = #"ichi"
  \set Score.soloIIText = #"ni"
  \set Score.aDueText = #"tachi"
  \partcombine
    \relative g' { g4 g a( b) r }
    \relative g' { g4 g r r f }
>>
@end lilypond

Both arguments to @code{\partcombine} will be interpreted as
@internalsref{Voice} contexts.  If using relative octaves,
@code{\relative} should be specified for both music expressions,
i.e.,

@example
\partcombine
  \relative @dots{} @var{musicexpr1}
  \relative @dots{} @var{musicexpr2}
@end example

@noindent
A @code{\relative} section that is outside of @code{\partcombine}
has no effect on the pitches of @var{musicexpr1} and
@var{musicexpr2}.

@seealso

Music Glossary: @rglos{a due}.

Snippets: @lsrdir{Simultaneous,Simultaneous-notes}.

Internals Reference: @internalsref{PartCombineMusic}, @internalsref{Voice}.

@refbugs

When @code{printPartCombineTexts} is set, if the two voices play
the same notes on and off, the part combiner may typeset @code{a2}
more than once in a measure.

@code{\partcombine} cannot be inside @code{\times}.

@code{\partcombine} cannot be inside @code{\relative}.

Internally, the @code{\partcombine} interprets both arguments as
@code{Voice}s named @code{one} and @code{two}, and then decides
when the parts can be combined.  Consequently, if the arguments
switch to differently named @internalsref{Voice} contexts, the
events in those will be ignored.


@node Writing music in parallel
@subsubsection Writing music in parallel

@cindex Writing music in parallel
@cindex Interleaved music

Music for multiple parts can be interleaved:

@lilypond[quote,fragment,verbatim]
\parallelMusic #'(voiceA voiceB) {
  r8 g'16[ c''] e''[ g' c'' e''] r8 g'16[ c''] e''[ g' c'' e''] |
  c'2                               c'2                         |
  r8 a'16[ d''] f''[ a' d'' f''] r8 a'16[ d''] f''[ a' d'' f''] |
  c'2                               c'2                         |
}
\new StaffGroup <<
  \new Staff \new Voice \voiceA
  \new Staff \new Voice \voiceB
>>
@end lilypond

This works quite well for piano music.

@c  It would be nice if the first bar fit onto one 66-char line.
@c  Maybe simplify the example?  -gp
@lilypond[quote,verbatim]
music = {
  \key c \major
  \time 4/4
  \parallelMusic #'(voiceA voiceB voiceC voiceD) {
    % Bar 1
    r8  g'16[ c''] e''[ g' c'' e'']
      r8 g'16[ c''] e''[ g' c'' e''] |
    c'2
      c'2 |
    r8  a16[ d'] f'[ a d' f']
      r8  a16[ d'] f'[ a d' f'] |
    c2
      c2 |

    % Bar 2
    a'8 b'      c'' d''    e'' f''    g'' a'' |
    d'4         d'         d'         d' |
    c16 d e f   d e f g    e f g a    f g a b |
    a,4         a,4        a,4        a,4 |

    % Bar 3 ...
  }
}

\score {
  \new PianoStaff <<
    \music
    \new Staff <<
      \voiceA \\
      \voiceB
    >>
    \new Staff {
      \clef bass
      <<
        \voiceC \\
        \voiceD
      >>
    }
  >>
}
@end lilypond

@seealso

Snippets: @lsrdir{Simultaneous,Simultaneous-notes}