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@c -*- coding: utf-8; mode: texinfo; -*-
@ignore
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@c \version "2.11.51"


@node Simultaneous notes
@section Simultaneous notes

@lilypondfile[quote]{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

This section discusses simultaneous notes inside the same voice.

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


@node Chorded notes
@unnumberedsubsubsec Chorded notes

@cindex chords
@cindex brackets, angle
@funindex <
@funindex >
@funindex <...>

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

@lilypond[verbatim,quote,relative=1]
<c e g>2 <c f a>4-> <e g c>-.
@end lilypond

Relative mode can be used for pitches in chords; the preceding pitch
into the same chord is still used as a reference for relative pitches,
but when a chord is completed, the reference pitch for relative mode
is the first note of this chord --not the last note of the chord.

For more information about chords, see @ref{Chord notation}.

@seealso

Music Glossary:
@rglos{chord}.

Learning Manual:
@rlearning{Combining notes into chords}.

Notation Reference:
@ref{Chord notation}.

Snippets:
@rlsr{Simultaneous notes}.

@ignore
@knownissues

For some reason, music expressions like @code{<< @{ g8 e8 @} a4 >>}
that should automatically turn into chords, appear split in two
staves.  To avoid this, use explicit chords instead as in
@code{<g a>8 <e a>8}.
@end ignore


@node Clusters
@unnumberedsubsubsec Clusters

@cindex cluster
@funindex \makeClusters

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,relative=2,verbatim]
\makeClusters { <g b>2 <c g'> }
@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

Music Glossary:
@rglos{cluster}.

Snippets:
@rlsr{Simultaneous notes}.

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

@knownissues

Clusters look good only if they span at least two chords; otherwise
they appear too narrow.

Clusters do not have a stem and cannot indicate durations by
themselves.  Separate clusters would need a separating rest between
them.


@node Multiple voices
@subsection Multiple voices

This section discusses simultaneous notes in multiple voices or
multiple staves.

@menu
* Single-staff polyphony::
* Voice styles::
* Collision resolution::
* Automatic part combining::
* Writing music in parallel::
@end menu


@node Single-staff polyphony
@unnumberedsubsubsec Single-staff polyphony

The basic structure of code needed to achieve multiple, independent
voices in a single staff is illustrated in the following example:

@lilypond[quote,relative=3,verbatim]
\new Staff <<
  \new Voice = "first"
    { \voiceOne r8 r16 g e8. f16 g8[ c,] f e16 d }
  \new Voice= "second"
    { \voiceTwo d16 c d8~ d16 b c8~ c16 b c8~ c16 b8. }
>>
@end lilypond

Here, voices are instantiated explicitly and are given a name. The
@code{\voiceOne} ... @code{\voiceFour} commands set up the voices so
that first and third voices get stems up, second and fourth voices get
stems down, third and fourth voice note heads are horizontally
shifted, and rests in the respective voices are automatically moved to
avoid collisions.  Using the @code{\oneVoice} command, all the voice
settings are put back to the neutral directions typical of a
single-voice passage.

We can make a voice to be into the same @code{Voice} context before
and after a temporary polyphonic passage.  For example, the following
construct keeps a voice alive throughout the polyphonic section.  Said
voice is the first one inside of the two-voice section, and the extra
voice is the second one.

@example
<< @{ \voiceOne ... @} \new Voice @{ \voiceTwo ... @} >> \oneVoice
@end example

Using the name given when created, this allows lyrics to be assigned
to one consistent voice.

@lilypond[quote, verbatim, relative=2]
<<
  \new Voice = "melody" {
    a4
    <<
      {
        \voiceOne
        g f
      }
      \new Voice {
        \voiceTwo
        e d
      }
    >>
    \oneVoice
    e
  }
  \new Lyrics \lyricsto "melody" {
  This is my song.
  }
>>
@end lilypond

Here, the \voiceOne and \voiceTwo commands help to make clear what
settings does each voice receive.

The @code{<<@{...@} \\ @{...@}>>} construction, where the two (or
more) voices are separated by double backslashes, can be used as a
simplified method to print multiple voices in a single staff.  Our
first example could be typeset as follows:

@lilypond[quote,relative=3,verbatim]
<<
  { r8 r16 g e8. f16 g8[ c,] f e16 d }
  \\
  { d16 c d8~ d16 b c8~ c16 b c8~ c16 b8. }
>>
@end lilypond

This syntax is simpler and can be used where it does not matter that
temporary voices are created and then discarded.  These implicitly
created voices are given the settings equivalent to the effect of the
@code{\voiceOne} ... @code{\voiceFour} commands, in the order in which
they appear in the code.  In the following example, the intermediate
voice has stems up, therefore we enter it in the third place, so it
becomes voice three which has the stems up as desired.

@lilypond[quote,relative=3,verbatim]
<<
  { r8 g g  g g f16 es f8 d }
  \\
  { es,8 r es r d r d r }
  \\
  { d'8 s c s bes s a s }
>>
@end lilypond

Spacing rests are often used to avoid too many rests, as seen in the
example above.

In all but simplest works it is advisable to create explicit
@code{Voice} contexts using the @code{\new} and @code{\context}
commands as it is explained in @rlearning{Contexts and engravers} and
@rlearning{Explicitly instantiating voices}.

In the special case that we want to typeset parallel pieces of music
that have the same rhythm, we can combine them into a single
@code{Voice} context, thus forming chords.  To achieve this, enclose
them in a simple simultaneous music construction and make it to be an
explicit voice:

@lilypond[quote,relative=2,verbatim]
\new Voice <<
  { e4 f8 d e16 f g8 d4 }
  { c4 d8 b c16 d e8 b4 }
>>
@end lilypond

This method leads to strange beamings and warnings if the pieces of
music do not have the same rhythm.

@predefined

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

@seealso

Learning Manual:
@rlearning{Voices contain music},
@rlearning{Explicitly instantiating voices}.

Notation Reference:
@ref{Percussion staves}.

Snippets:
@rlsr{Simultaneous notes}.


@node Voice styles
@unnumberedsubsubsec Voice styles

@cindex voice styles
@cindex styles, voice
@cindex coloring voices

Voices may be given distinct colors and shapes, allowing them to be
easily identified:

@lilypond[quote,relative=2,verbatim]
<<
  { \voiceOneStyle d4 c2 b4 }
  \\
  { \voiceTwoStyle e,2 e }
  \\
  { \voiceThreeStyle b2. c4 }
  \\
  { \voiceFourStyle g'2 g }
>>
@end lilypond

To revert the standard presentation, the @code{\voiceNeutralstyle}
command is used.

@predefined

@funindex \voiceOneStyle
@code{\voiceOneStyle},
@funindex \voiceTwoStyle
@code{\voiceTwoStyle},
@funindex \voiceThreeStyle
@code{\voiceThreeStyle},
@funindex \voiceFourStyle
@code{\voiceFourStyle},
@funindex \voiceNeutralStyle
@code{\voiceNeutralStyle}.

@seealso

Learning Manual:
@rlearning{I'm hearing Voices},
@rlearning{Other sources of information}.

Snippets:
@rlsr{Simultaneous notes}.


@node Collision resolution
@unnumberedsubsubsec Collision resolution

@cindex merging notes
@cindex note collisions
@cindex collisions
@funindex \shiftOn
@funindex \shiftOnn
@funindex \shiftOnnn
@funindex \shiftOff
@cindex shift rest, automatic

Note heads with equal durations are automatically merged, while
note heads with unequal durations are not merged.  Rests opposite
a stem are shifted vertically.

@lilypond[quote,verbatim,relative=2]
<<
  {
    c8 d e d c d c4
    g'2 fis
  } \\ {
    c2 c8. b16 c4
    e,2 r
  } \\ {
    \oneVoice
    s1
    e8 a b c d2
  }
>>
@end lilypond

Note heads with different note heads may be merged, with the
exception of half-note heads and quarter-note heads:

@lilypond[quote,verbatim,relative=2]
<<
  {
    \mergeDifferentlyHeadedOn
    c8 d e d c d c4
    g'2 fis
  } \\ {
    c2 c8. b16 c4
    e,2 r
  } \\ {
    \oneVoice
    s1
    e8 a b c d2
  }
>>
@end lilypond

Note heads with different dots may be merged:

@lilypond[quote,relative=2,verbatim]
<<
  {
    \mergeDifferentlyHeadedOn
    \mergeDifferentlyDottedOn
    c8 d e d c d c4
    g'2 fis
  } \\ {
    c2 c8. b16 c4
    e,2 r
  } \\ {
    \oneVoice
    s1
    e8 a b c d2
  }
>>
@end lilypond

@cindex shift note

The collision on the second measure happens because
@code{merge-differently-headed} cannot successfully complete the
merge when three or more notes line up in the same column -- in
fact, you will obtain a warning for this reason.  To allow the
merge to work properly, apply a @code{\shift} to the note that
should not be merged.  Here, @code{\shiftOn} is applied to move
the top @code{g} out of the column, and
@code{merge-differently-headed} works properly.

@lilypond[quote,relative=2,verbatim]
<<
  {
    \mergeDifferentlyHeadedOn
    \mergeDifferentlyDottedOn
    c8 d e d c d c4
    \shiftOn
    g'2 fis
  } \\ {
    c2 c8. b16 c4
    e,2 r
  } \\ {
    \oneVoice
    s1
    e8 a b c d2
  }

>>
@end lilypond

The @code{\shiftOn}, @code{\shiftOnn}, and @code{\shiftOnnn}
commands specify the degree to which chords of the current voice
should be shifted.  The outer voices (normally: voices 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.

Notes are only merged if they have opposing stem directions (i.e., in
@code{Voice} 1 and 2).

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

@predefined

@funindex \mergeDifferentlyDottedOn
@code{\mergeDifferentlyDottedOn},
@funindex \mergeDifferentlyDottedOff
@code{\mergeDifferentlyDottedOff},
@funindex \mergeDifferentlyHeadedOn
@code{\mergeDifferentlyHeadedOn},
@funindex \mergeDifferentlyHeadedOff
@code{\mergeDifferentlyHeadedOff}.

@funindex \shiftOn
@code{\shiftOn},
@funindex \shiftOnn
@code{\shiftOnn},
@funindex \shiftOnnn
@code{\shiftOnnn},
@funindex \shiftOff
@code{\shiftOff}.

@snippets

@lilypondfile[verbatim,lilyquote,texidoc,doctitle]
{additional-voices-to-avoid-collisions.ly}

@lilypondfile[verbatim,lilyquote,texidoc,doctitle]
{forcing-horizontal-shift-of-notes.ly}

@seealso

Music Glossary:
@rglos{polyphony}.

Learning Manual:
@rlearning{Multiple notes at once},
@rlearning{Voices contain music},
@rlearning{Collisions of objects}.

Snippets:
@rlsr{Simultaneous notes}.

Internals Reference:
@rinternals{NoteColumn},
@rinternals{NoteCollision},
@rinternals{RestCollision}.

@knownissues

When using @code{merge-differently-headed} with an upstem eighth
or a shorter note, and a downstem half note, the eighth note stem
gets a slightly wrong offset because of the different width of the
half note head symbol.

@c investigate! Sometimes it works, sometimes not. --FV
The requirements for successfully merging different note heads that
are at the same time differently dotted are not clear.

There is no support for chords 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
@unnumberedsubsubsec Automatic part combining

@cindex automatic part combining
@cindex part combiner
@cindex combining parts
@funindex \partcombine

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
@notation{a due} parts are identified and marked by default.

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.  The same variables are used for the
independent parts and the combined staff.

@lilypond[quote,verbatim]
instrumentOne = \relative c' {
  c4 d e f
  R1
  d'4 c b a
  b4 g2 f4
  e1
}

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

<<
  \new Staff \instrumentOne
  \new Staff \instrumentTwo
  \new Staff \partcombine \instrumentOne \instrumentTwo
>>
@end lilypond

The notes in the third measure appear only once, although they
were specified in both parts.  Stem, slur, and tie directions are
set automatically, depending whether there is a solo or unison.
When needed in polyphony situations, the first part (with context
called @code{one}) always gets up stems, while the second (called
@code{two}) always gets down stems.  In solo situations, the parts
get marked with @q{Solo} and @q{Solo II}, respectively.  The
unisono (@notation{a due}) parts are marked by default with the
text @qq{a2}.

Both arguments to @code{\partcombine} will be interpreted as
@code{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}.

@snippets

@lilypondfile[verbatim,lilyquote,texidoc,doctitle]
{combining-two-parts-on-the-same-staff.ly}

@lilypondfile[verbatim,lilyquote,texidoc,doctitle]
{changing-partcombine-texts.ly}

@seealso

Music Glossary:
@rglos{a due},
@rglos{part}.

Notation Reference:
@ref{Writing parts}.

Snippets:
@rlsr{Simultaneous notes}.

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

@knownissues

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 @rinternals{Voice} contexts, the
events in those will be ignored.

@c IIRC in users list someone pointed out more issues. TODO: lookup FV


@node Writing music in parallel
@unnumberedsubsubsec Writing music in parallel

@cindex Writing music in parallel
@cindex Interleaved music
@funindex parallelMusic

Music for multiple parts can be interleaved in input code.  The
function @code{\parallelMusic} accepts a list with the names of a
number of variables to be created, and a musical expression.  The
content of alternate measures from the expression become the value
of the respective variables, so you can use them afterwards to
print the music.

@warning{Bar checks @code{|} must be used, and the measures must
be of the same length.}

@lilypond[quote,verbatim]
\parallelMusic #'(voiceA voiceB voiceC) {
  % Bar 1
  r8 g'16 c'' e'' g' c'' e'' r8 g'16 c'' e'' g' c'' e'' |
  r16 e'8.~   e'4            r16 e'8.~   e'4            |
  c'2                        c'2                        |

  % Bar 2
  r8 a'16 d'' f'' a' d'' f'' r8 a'16 d'' f'' a' d'' f'' |
  r16 d'8.~   d'4            r16 d'8.~   d'4            |
  c'2                        c'2                        |

}
\new StaffGroup <<
  \new Staff << \voiceA \\ \voiceB >>
  \new Staff { \clef bass \voiceC }
>>
@end lilypond

Relative mode may be used.  Note that the @code{\relative} command
is not used inside @code{\parallelMusic} itself.  The notes are
relative to the preceding note in the voice, not to the previous
note in the input -- in other words, relative notes for
@code{voiceA} ignore the notes in @code{voiceB}.

@lilypond[quote,verbatim]
\parallelMusic #'(voiceA voiceB voiceC) {
  % Bar 1
  r8 g16 c e g, c e r8 g,16 c e g, c e  |
  r16 e8.~ e4       r16 e8.~  e4        |
  c2                c                   |

  % Bar 2
  r8 a,16 d f a, d f r8 a,16 d f a, d f |
  r16 d8.~  d4       r16 d8.~  d4       |
  c2                 c                  |

 }
\new StaffGroup <<
  \new Staff << \relative c'' \voiceA \\ \relative c' \voiceB >>
  \new Staff \relative c' { \clef bass \voiceC }
>>
@end lilypond

This works quite well for piano music.  This example maps four
consecutive measures to four variables:

@lilypond[quote,verbatim]
global = {
  \key g \major
  \time 2/4
}

\parallelMusic #'(voiceA voiceB voiceC voiceD) {
  % Bar 1
  a8    b     c   d     |
  d4          e         |
  c16 d e fis d e fis g |
  a4          a         |

  % Bar 2
  e8      fis  g     a   |
  fis4         g         |
  e16 fis g  a fis g a b |
  a4           a         |

  % Bar 3 ...
}

\score {
  \new PianoStaff <<
     \new Staff {
       \global
       <<
         \relative c'' \voiceA
         \\
         \relative c'  \voiceB
       >>
     }
     \new Staff {
       \global \clef bass
       <<
         \relative c \voiceC
         \\
         \relative c \voiceD
       >>
     }
  >>
}
@end lilypond

@seealso

Learning Manual:
@rlearning{Organizing pieces with variables}.

Snippets:
@rlsr{Simultaneous notes}.