@c -*- coding: utf-8; mode: texinfo; -*-

@node Simultaneous notes
@section Simultaneous notes

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

@anchor{Chords}
@unnumberedsubsubsec Chords

@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}.


@anchor{Clusters}
@unnumberedsubsubsec 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

Program reference: @internalsref{ClusterSpanner},
@internalsref{ClusterSpannerBeacon},
@internalsref{Cluster_spanner_engraver}.

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

@refbugs

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



@node Multiple voices
@subsection Multiple voices

@anchor{Basic polyphony}
@unnumberedsubsubsec Basic polyphony

@cindex polyphony

The easiest way to enter fragments with more than one voice on a staff
is to enter each voice as a sequence (with @code{@{...@}}), and combine
them simultaneously, separating the voices with @code{\\}

@funindex \\

@lilypond[quote,verbatim,fragment]
\new Staff \relative c' {
  c16 d e f
  <<
    { g4 f e | d2 e2 } \\
    { r8 e4 d c8 ~ | c b16 a b8 g ~ g2 } \\
    { s2. | s4 b4 c2 }
  >>
}
@end lilypond

The separator causes @internalsref{Voice} contexts@footnote{Polyphonic
voices are sometimes called @q{layers} in other notation packages}
@cindex layers
to be instantiated.  They bear the names @code{"1"}, @code{"2"}, etc.  In
each of these contexts, vertical direction of slurs, stems, etc., is set
appropriately.

These voices are all separate from the voice that contains the notes just
outside the @code{<< \\ >>} construct.  This should be noted when making
changes at the voice level.  This also means that slurs and ties cannot go
into or out of a @code{<< \\ >>} construct.  Conversely, parallel voices
from separate @code{<< \\ >>} constructs on the same staff are the
same voice.  Here is the same example, with different noteheads and
colors for each
voice.  Note that the change to the note-head style in the main voice does
not affect
the inside of the @code{<< \\ >>} constructs.  Also, the change to the
second
voice in the first @code{<< \\ >>} construct is effective in the second
@code{<< \\ >>}, and the voice is tied across the two constructs.

@cindex note heads, styles

@lilypond[quote,verbatim,fragment]
\new Staff \relative c' {
  \override NoteHead #'style = #'cross
  \override NoteHead #'color = #red
  c16 d e f
  <<
    { g4 f e } \\
    { \override NoteHead #'style = #'triangle
      \override NoteHead #'color = #blue
    r8 e4 d c8 ~ }
  >> |
  <<
    { d2 e2 } \\
    { c8 b16 a b8 g ~ g2 } \\
    { \override NoteHead #'style = #'slash 
      \override NoteHead #'color = #green
      s4 b4 c2 }
  >>
}
@end lilypond

Polyphony does not change the relationship of notes within a
@code{\relative @{ @}} block.  Each note is calculated relative
to the note immediately preceding it.

@example
\relative @{ noteA << noteB \\ noteC >> noteD @}
@end example

@code{noteC} is relative to @code{noteB}, not @code{noteA};
@code{noteD} is relative to @code{noteC}, not @code{noteB} or
@code{noteA}.


@anchor{Explicitly instantiating voices}
@unnumberedsubsubsec Explicitly instantiating voices

@internalsref{Voice} contexts can also be instantiated manually
inside a @code{<< >>} block to create polyphonic music, using
@code{\voiceOne}, up to @code{\voiceFour} to assign stem directions
and a horizontal shift for each part.

Specifically,
@example
<< \upper \\ \lower >>
@end example

@noindent
is equivalent to

@example
<<
  \new Voice = "1" @{ \voiceOne \upper @}
  \new Voice = "2" @{ \voiceTwo \lower @}
>>
@end example

The @code{\voiceXXX} commands set the direction of stems, slurs, ties,
articulations, text annotations, augmentation dots of dotted
notes, and fingerings.  @code{\voiceOne} and @code{\voiceThree} make
these objects point upwards, while @code{\voiceTwo} and @code{\voiceFour}
make them point downwards.
The command @code{\oneVoice} will revert back to the normal setting.

An expression that appears directly inside a @code{<< >>} belongs to
the main voice.  This is useful when extra voices appear while the main
voice is playing.  Here is a more correct rendition of the example from
the previous section.  The crossed colored noteheads demonstrate that the main
melody is now in a single voice context.

@lilypond[quote,ragged-right,verbatim]
\new Staff \relative c' {
  \override NoteHead #'style = #'cross
  \override NoteHead #'color = #red
  c16 d e f
  \voiceOne
  <<
    { g4 f e | d2 e2 }
    \new Voice="1" { \voiceTwo
      r8 e4 d c8 ~ | c8 b16 a b8 g ~ g2
      \oneVoice
    }
    \new Voice { \voiceThree
      s2. | s4 b4 c2
      \oneVoice
    }
  >>
  \oneVoice
}
@end lilypond

The correct definition of the voices allows the melody to be slurred.
@lilypond[quote,ragged-right,verbatim]
\new Staff \relative c' {
  c16^( d e f
  \voiceOne
  <<
    { g4 f e | d2 e2) }
    \context Voice="1" { \voiceTwo
      r8 e4 d c8 ~ | c8 b16 a b8 g ~ g2
      \oneVoice
    }
    \new Voice { \voiceThree
      s2. s4 b4 c2
      \oneVoice
    }
  >>
  \oneVoice
}
@end lilypond

Avoiding the @code{\\} separator also allows nesting polyphony
constructs, which in some case might be a more natural way to typeset
the music.

@lilypond[quote,ragged-right,verbatim]
\new Staff \relative c' {
  c16^( d e f
  \voiceOne
  <<
    { g4 f e | d2 e2) }
    \context Voice="1" { \voiceTwo
      r8 e4 d c8 ~ |
      <<
        {c8 b16 a b8 g ~ g2}
        \new Voice { \voiceThree
          s4 b4 c2
          \oneVoice
        }
      >>
    \oneVoice
    }
  >>
  \oneVoice
}
@end lilypond

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


@anchor{Collision Resolution}
@unnumberedsubsubsec Collision Resolution

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 (ie. 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

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


@refcommands

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

@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

Program 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}).


@anchor{Automatic part combining}
@unnumberedsubsubsec Automatic part combining
@cindex automatic part combining
@cindex part combiner

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

Program reference: @internalsref{PartCombineMusic}.

@refbugs

When @code{printPartCombineTexts} is set, when 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.


@anchor{Writing music in parallel}
@unnumberedsubsubsec 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

@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