[lilypond.git] / Documentation / user / rhythms.itely

@c -*- coding: utf-8; mode: texinfo; -*-
@ignore
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    When revising a translation, copy the HEAD committish of the
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@node Rhythms
@section Rhythms

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

This section discusses rhythms, durations, and bars.

@menu
* Writing rhythms::             
* Writing rests::               
* Displaying rhythms::          
* Beams::                       
* Bars::                        
* Special rhythmic concerns::   
@end menu


@node Writing rhythms
@subsection Writing rhythms

@menu
* Durations::                   
* Tuplets::                     
* Scaling durations::           
@end menu

@node Durations
@unnumberedsubsubsec Durations

@cindex duration
@funindex \longa
@funindex \breve
@funindex \maxima

When entering notes, durations are designated by numbers and dots:
durations are entered as their reciprocal values.  For example, a
quarter note is entered using a @code{4} (since it is a 1/4 note),
while a half note is entered using a @code{2} (since it is a 1/2
note).  For notes longer than a whole you must use the
@code{\longa} (a double breve) and @code{\breve} commands.  Note
durations as short as 64th notes may be specified.

@c Two 64th notes are needed to obtain beams
@lilypond[quote,ragged-right,verbatim,fragment,relative=2]
\time 8/1
c\longa c\breve c1 c2
c4 c8 c16 c32 c64 c64
@end lilypond

@noindent
and the same durations with automatic beaming turned off 
see @ref{Automatic beams}:

@lilypond[quote,ragged-right,verbatim,fragment,relative=2]
\time 8/1
\autoBeamOff
c\longa c\breve c1 c2
c4 c8 c16 c32 c64 c64
@end lilypond

If the duration is omitted then it is set to the previously
entered duration.  The default for the first note is a quarter
note.

@lilypond[quote,ragged-right,verbatim,fragment,relative=2]
a a a2 a a4 a a1 a
@end lilypond


@funindex .

To obtain dotted note lengths, simply add a dot (@samp{.}) to the
number.  Double-dotted notes are produced in a similar way.

@lilypond[quote,ragged-right,fragment,verbatim,relative=2]
a4 b c4. b8 a4. b4.. c8.
@end lilypond

Some durations cannot be entered using only binary durations
and dots, and can only be represented by tying two or more 
notes together.  Tied notes are covered in @ref{Ties}.

@refcommands

Dots are normally moved up to avoid staff lines, except in
polyphonic situations.  The following commands may be used to
force a particular direction manually

@funindex \dotsUp
@code{\dotsUp},
@funindex \dotsDown
@code{\dotsDown},
@funindex \dotsNeutral
@code{\dotsNeutral}.

@c TODO: after deciding the link question, fix these.  -gp
Durations are entered in the same way in @code{drummode},
@code{chordmode}, @code{figuremode} and (optionally) 
in @code{lyricmode}.

@seealso

For ways of specifying durations for the syllables of lyrics
and ways of aligning lyrics to notes see
This manual: @ref{Vocal music}

For a description of how to enter rests see
This manual: @ref{Writing rests}

A note with the duration of a quadruple breve may be
entered with \maxima, but this is supported only within
ancient music notation.  
See this manual: @ref{Ancient notation}

Optionally, notes can be spaced proportionately to their duration.
For details of this and other settings which control
proportional notation see @ref{Proportional notation}.

Program reference: @internalsref{Dots}, and
@internalsref{DotColumn}.


@node Tuplets
@unnumberedsubsubsec Tuplets

@cindex tuplets
@cindex triplets
@funindex \times

@c TODO Add Tuplet to glossary

Tuplets are made out of a music expression by multiplying all
durations with a fraction

@example
\times @var{fraction} @var{musicexpr}
@end example

@noindent
The duration of @var{musicexpr} will be multiplied by the 
fraction.  The fraction's denominator will be printed over or 
under the notes, optionally with a bracket.  The most common 
tuplet is the triplet in which 3 notes have the length of 2, so 
the notes are 2/3 of their written length.

@lilypond[quote,ragged-right,fragment,verbatim,relative=2]
g4 \times 2/3 {c4 c c} d4 d4
@end lilypond

Tuplets may be nested, for example,

@lilypond[fragment,ragged-right,verbatim,relative=2]
\override TupletNumber #'text = #tuplet-number::calc-fraction-text
\times 4/6 {
  a4 a
  \times 3/5 { a a a a a }
}
@end lilypond

@refcommands

@funindex \tupletUp
@code{\tupletUp},
@funindex \tupletDown
@code{\tupletDown},
@funindex \tupletNeutral
@code{\tupletNeutral}.


@commonprop

@funindex tupletNumberFormatFunction
@cindex tuplet formatting

The property @code{tupletSpannerDuration} specifies how long each
bracket should last.  With this, you can make lots of tuplets
while typing @code{\times} only once, thus saving lots of typing.
In the next example, there are two triplets shown, while
@code{\times} was only used once

@lilypond[quote,fragment,relative=2,ragged-right,verbatim]
\set tupletSpannerDuration = #(ly:make-moment 1 4)
\times 2/3 { c8 c c c c c }
@end lilypond

@noindent
For more information about @code{make-moment}, see
@ref{Time administration}.

The format of the number is determined by the property @code{text}
in @code{TupletNumber}.  The default prints only the denominator,
but if it is set to the function
@code{tuplet-number::calc-fraction-text}, @var{num}:@var{den} will
be printed instead.

To avoid printing tuplet numbers, use

@lilypond[quote,fragment,relative=2,ragged-right,verbatim]
\times 2/3 { c8 c c } \times 2/3 { c8 c c }
\override TupletNumber #'transparent = ##t
\times 2/3 { c8 c c } \times 2/3 { c8 c c }
@end lilypond

Use the @code{\tweak} function to override nested tuplets
beginning at the same music moment.  In this example,
@code{\tweak} specifies fraction text for the outer
@code{TupletNumber} and denominator text for the
@code{TupletNumber} of the first of the three inner tuplets.

@lilypond[quote,ragged-right,verbatim,relative=2]
\new Staff {
  \tweak #'text #tuplet-number::calc-fraction-text
  \times 4/3 {
     \tweak #'text #tuplet-number::calc-denominator-text
     \times 2/3 { c8[ c8 c8] }
     \times 2/3 { c8[ c8 c8] }
     \times 2/3 { c8[ c8 c8] }
  }
}
@end lilypond

Here @code{\tweak} and @code{\override} work together to specify
@code{TupletBracket} direction.  The first @code{\tweak} positions
the @code{TupletBracket} of the outer tuplet above the staff.  The
second @code{\tweak} positions the @code{TupletBracket} of the
first of the three inner tuplets below the staff.  Note that this
pair of @code{\tweak} functions affects only the outer tuplet and
the first of the three inner tuplets because only those two
tuplets begin at the same music moment.  We use @code{\override}
in the usual way to position the @code{TupletBrackets} of the
second and third of the inner tuplets below the staff.

@lilypond[quote,ragged-right,verbatim,relative=2]
\new Staff {
  \tweak #'text #tuplet-number::calc-fraction-text
  \tweak #'direction #up
  \times 4/3 {
     \tweak #'direction #down
     \times 2/3 { c8[ c8 c8] }
     \override TupletBracket #'direction = #down
     \times 2/3 { c8[ c8 c8] }
     \times 2/3 { c8[ c8 c8] }
  }
}
@end lilypond

Tuplet brackets can be made to run to prefatory matter or the next
note

@lilypond[ragged-right]
\new RhythmicStaff {
  \set tupletFullLength = ##t
  \time 4/4
  \times 4/5 {
    c4 c1
  }
  \set tupletFullLengthNote = ##t
  \time 2/4
  \times 2/3 {
    c4 c c 
  }
  \time 3/4
  c4 
}
@end lilypond

Tuplets which cross barlines will prevent a line break at that
point.

@seealso

Program reference: @internalsref{TupletBracket},
@internalsref{TupletNumber}, and @internalsref{TimeScaledMusic}.



@node Scaling durations
@unnumberedsubsubsec Scaling durations

You can alter the length of duration by a fraction @var{N/M}
appending @samp{*@var{N/M}} (or @samp{*@var{N}} if @var{M=1}).
This will not affect the appearance of the notes or rests
produced.  These may be combined such as @samp{*M*N}.

In the following example, the first three notes take up exactly
two beats, but no triplet bracket is printed.

@lilypond[quote,ragged-right,fragment,relative=2,verbatim]
\time 2/4
a4*2/3 gis4*2/3 a4*2/3
a4 a4 a4*2
b16*4 c4
@end lilypond


@seealso

This manual: @ref{Tuplets}.




@node Writing rests
@subsection Writing rests

@menu
* Rests::                       
* Skips::                       
* Multi measure rests::         
@end menu

@node Rests
@unnumberedsubsubsec Rests
@cindex Rests

@funindex \rest
@funindex r
@funindex \maxima

Rests are entered like notes with the note name @code{r}

@c \time 16/1 is used to avoid spurious barlines
@c and long tracts of empty bars
@lilypond[fragment,quote,ragged-right,verbatim]
\new Staff {
  \time 16/1
  \override Staff.TimeSignature #'stencil = ##f
  r\maxima
  r\longa r\breve r1 r2
  r4 r8 r16 r32 r64
}
@end lilypond

Whole bar rests, centered in middle of the bar, must be entered as
multi-measure rests.  They can be used for a single bar as well as
many bars, and are discussed in @ref{Multi measure rests}.

To explicitly specify a rest's vertical position, write a note
followed by @code{\rest}.  A rest will be placed in the position
where the note would appear,

@lilypond[fragment,quote,ragged-right,verbatim,relative=2]
a4\rest d4\rest
@end lilypond

@noindent
This makes manual formatting of polyphonic music much easier,
since the automatic rest collision formatter will leave these
rests alone.

@seealso

Program reference: @internalsref{Rest}.


@node Skips
@unnumberedsubsubsec Skips

@cindex Skip
@cindex Invisible rest
@cindex Space note
@funindex \skip
@funindex s

An invisible rest (also called a @q{skip}) can be entered like a
note with note name @samp{s} or with @code{\skip @var{duration}}

@lilypond[fragment,quote,ragged-right,verbatim,relative=2]
a4 a4 s4 a4 \skip 1 a4
@end lilypond

The @code{s} syntax is only available in note mode and chord mode.
In other situations, for example, when entering lyrics, you should
use the @code{\skip} command

@lilypond[quote,ragged-right,verbatim,relative=2]
<<
  { a2 a2 }
  \new Lyrics \lyricmode { \skip 2 bla2 }
>>
@end lilypond

The skip command is merely an empty musical placeholder.  It does
not produce any output, not even transparent output.

The @code{s} skip command does create @internalsref{Staff} and
@internalsref{Voice} when necessary, similar to note and rest
commands.  For example, the following results in an empty staff.

@lilypond[quote,ragged-right,verbatim]
{ s4 }
@end lilypond

The fragment @code{@{ \skip 4 @} } would produce an empty page.

@seealso

Program reference: @internalsref{SkipMusic}.


@node Multi measure rests
@unnumberedsubsubsec Multi measure rests

@cindex multi measure rests
@cindex full measure rests
@cindex Rests, multi measure
@cindex Rests, full measure
@cindex whole rests for a full measure
@funindex R

Rests for one or more full measures are entered using
@code{R} followed by a duration (see @ref{Durations}).
The duration should correspond to an integral number 
of bars, otherwise a barcheck warning is printed.  
Multi-measure rests are principally used to indicate
that a part in a multi-part score should be silent:

@c Ragged-right is omitted here as otherwise
@c the annotation collides.  When a better
@c way of avoiding collisions is discovered this
@c example should be changed
@c TODO But leaving it out seems to have no effect!!
@lilypond[quote,fragment,verbatim]
{
  \set Score.skipBars = ##t
  R1*4^"Instrumental"
  R1*24^"Solo"
  R1*4^"Instrumental"
  b'2^"Tutti" b'4 a'4
}
@end lilypond

A multi-measure rest can be expanded in the printed score
to show all the rest bars explicitly, or, as above, it can be 
condensed to a single bar
containing a multi-measure rest symbol, with the number of
bars of rest printed above the bar.  This expansion
is controlled by the property @code{Score.skipBars}.  If this is
set to true, empty measures will condensed to a single bar.

@lilypond[quote,ragged-right,fragment,verbatim]
\time 4/4 r1 | R1 | R1*2 | 
\time 2/4 R2 | 
\time 4/4
\set Score.skipBars = ##t 
R1*17 | R1*4 |
@end lilypond

The @code{1} in @code{R1} is similar to the duration notation 
used for notes and is the length of a bar in 2/2 or 4/4 time.
The duration in a multi-measure rest must always be an integral
number of bar-lengths, so in other time signatures augmentation
dots or fractions must be used:

@lilypond[quote,ragged-right,fragment,verbatim]
\set Score.skipBars = ##t
\time 3/4
R2. | R2.*2
\time 13/8
R1*13/8 | R1*13/8*12 |
\time 10/8 
R4*5*4 |
@end lilypond

An @code{R} spanning a single measure is printed as either a whole
or breve rest, centered in the measure, regardless of the time
signature.

@c TODO: add link to @rglos{church rests}

If there are 10 or fewer measures of rest, LilyPond prints
@notation{church rests} (a series of longa and breve rests)
in the staff and
prints a simple line otherwise.  This default number of 10
may be changed by overriding 
@code{MultiMeasureRest.expand-limit}.

@lilypond[quote,ragged-right,fragment,verbatim]
\set Score.skipBars = ##t
R1*2 | R1*5 | R1*9
\override MultiMeasureRest #'expand-limit = 3
R1*2 | R1*5 | R1*9
@end lilypond

Note that the vertical position on the staff of the multi-measure
rest symbol of either form cannot be changed.

@cindex text on multi-measure rest
@cindex script on multi-measure rest
@cindex fermata on multi-measure rest

Text can be added to multi-measure rests by using the
@var{note}-@code{markup} syntax @ref{Text markup}.  A variable
(@code{\fermataMarkup}) is provided for adding fermatas

@lilypond[quote,ragged-right,verbatim,fragment]
\set Score.skipBars = ##t
\time 3/4
R2.*10^\markup { \italic "ad lib." }
R2.^\fermataMarkup
@end lilypond

Warning!  This text is created by @code{MultiMeasureRestText}, not
@code{TextScript}.

@lilypond[quote,ragged-right,verbatim,fragment]
\override TextScript #'padding = #5
R1^"low"
\override MultiMeasureRestText #'padding = #5
R1^"high"
@end lilypond

Text attached to a multi-measure rest will be centered above
(or below) it.  Long text attached in this way will not cause
the bar to expand, and may collide with text in adjacent bars.
Long text is better attached to a zero-length skip note preceding
the rest, preceded by @code{\fatText}, since this will 
cause the bar to expand to accommodate
the length of the text:

@lilypond[quote,ragged-right,verbatim,fragment]
\set Score.skipBars = ##t
\fatText
s1*0^\markup {[MAJOR GENERAL]}
R1*19
s1*0^\markup {[MABEL] }
s1*0_\markup {\italic {Cue: ... it is yours}}
R1*30
s1^\markup {CHORUS} % Chorus notes would go here
@end lilypond


@seealso

This manual: @ref{Text}

Program reference: 

@internalsref{MultiMeasureRest}.

The layout object @internalsref{MultiMeasureRestNumber} is for the
default number, and @internalsref{MultiMeasureRestText} for user
specified texts.


@refbugs

If an attempt is made to use fingerings (e.g., 
@code{R1*10-4}) to put numbers over multi-measure rests, the
fingering numeral (4) may collide with the bar counter 
numeral (10).  

@cindex condensing rests

There is no way to automatically condense multiple rests into a
single multi-measure rest.  Multi-measure rests do not take part
in rest collisions.

Be careful when entering multi-measure rests followed by whole
notes.  The following will enter two notes lasting four measures
each

@example
R1*4 cis cis
@end example


@node Displaying rhythms
@subsection Displaying rhythms

@menu
* Time signature::              
* Upbeats::                     
* Unmetered music::             
* Polymetric notation::         
* Automatic note splitting::    
@end menu

@node Time signature
@unnumberedsubsubsec Time signature

@cindex Time signature
@cindex meter
@funindex \time

Time signature indicates the meter of a piece: a regular pattern
of strong and weak beats.  It is denoted by a fraction at the
start of the staff.

The time signature is set with the @code{\time} command

@lilypond[quote,ragged-right,fragment,verbatim,relative=2]
\time 2/4 c2 \time 3/4 c2.
@end lilypond

@commonprop

The symbol that is printed can be customized with the @code{style}
property.  Setting it to @code{#'()} uses fraction style for 4/4
and 2/2 time,

@lilypond[fragment,quote,ragged-right,verbatim,relative=2]
\time 4/4 c1
\time 2/2 c1
\override Staff.TimeSignature #'style = #'()
\time 4/4 c1
\time 2/2 c1
@end lilypond

There are many more options for its layout.  See @ref{Ancient time
signatures}, for more examples.

@code{\time} sets the property @code{timeSignatureFraction},
@code{beatLength} and @code{measureLength} in the @code{Timing}
context, which is normally aliased to @internalsref{Score}.  The
property @code{measureLength} determines where barlines should be
inserted, and how automatic beams should be generated.  Changing
the value of @code{timeSignatureFraction} also causes the symbol
to be printed.

@cindex Measure groupings
 
More options are available through the Scheme function
@code{set-time-signature}.  In combination with the
@internalsref{Measure_grouping_engraver}, it will create
@internalsref{MeasureGrouping} signs.  Such signs ease reading
rhythmically complex modern music.  In the following example, the
9/8 measure is subdivided in 2, 2, 2 and 3.  This is passed to
@code{set-time-signature} as the third argument @code{(2 2 2 3)}

@lilypond[quote,ragged-right,verbatim]
\score {
  \relative c'' {
    #(set-time-signature 9 8 '(2 2 2 3))
    g8[ g] d[ d] g[ g] a8[( bes g]) |
    #(set-time-signature 5 8 '(3 2))
    a4. g4
  }
  \layout {
    \context {
      \Staff
      \consists "Measure_grouping_engraver"
    }
  }
}
@end lilypond


@seealso

Program reference: @internalsref{TimeSignature}, and
@internalsref{Timing_translator}.

Examples: @lsr{contemporary,compound-time-signature.ly}.


@refbugs

Automatic beaming does not use the measure grouping specified with
@code{set-time-signature}.


@node Upbeats
@unnumberedsubsubsec Upbeats

@cindex anacrusis
@cindex upbeat
@cindex partial measure
@cindex measure, partial
@cindex shorten measures
@funindex \partial

Partial measures, such as an anacrusis or upbeat, are entered
using the

@lilypond[quote,ragged-right,fragment,verbatim,relative=2]
\partial 16*5 c16 cis d dis e | a2. c,4 | b2
@end lilypond

The syntax for this command is

@example
\partial @var{duration}
@end example

where @code{duration} is the rhythmic length to be added before
the next bar.

This is internally translated into

@example
\set Timing.measurePosition = -@var{length of duration}
@end example

The property @code{measurePosition} contains a rational number
indicating how much of the measure has passed at this point.  Note
that this is a negative number; @code{\partial 4} is internally
translated to mean @qq{there is a quarter note left in the bar.}


@refbugs

This command does not take into account grace notes at the start
of the music.  When a piece starts with graces notes in the
pickup, then the @code{\partial} should follow the grace notes

@lilypond[verbatim,quote,ragged-right,relative,fragment]
\grace f16
\partial 4
g4
a2 g2
@end lilypond

@code{\partial} is only intended to be used at the beginning of a
piece.  If you use it after the beginning, some odd warnings may
occur.


@node Unmetered music
@unnumberedsubsubsec Unmetered music

@cindex cadenza
@funindex \cadenzaOn
@funindex \cadenzaOff

Barlines and bar numbers are calculated automatically.  For
unmetered music (cadenzas, for example), this is not desirable.
To turn off automatic barlines and bar numbers, use the commands
@code{\cadenzaOn} and @code{\cadenzaOff}.

@lilypond[verbatim,quote,ragged-right,relative=2,fragment]
c4 d e d
\cadenzaOn
c4 c d8 d d f4 g4.
\cadenzaOff
\bar "|"
d4 e d c
@end lilypond


@refbugs

LilyPond will only insert line breaks and page breaks at a
barline.  Unless the unmetered music ends before the end of the
staff line, you will need to insert invisible barlines

@example
\bar ""
@end example

@noindent
to indicate where breaks can occur.


@node Polymetric notation
@unnumberedsubsubsec Polymetric notation

@cindex double time signatures
@cindex signatures, polymetric
@cindex polymetric signatures
@cindex meter, polymetric

Double time signatures are not supported explicitly, but they can
be faked.  In the next example, the markup for the time signature
is created with a markup text.  This markup text is inserted in
the @internalsref{TimeSignature} grob.  See also
@lsr{contemporary,compound-time-signature}.

@lilypond[verbatim,ragged-right]
% create 2/4 + 5/8
tsMarkup =\markup {
  \override #'(baseline-skip . 2) \number {
    \column { "2" "4" }
    \vcenter "+"
    \bracket \column { "5" "8" }
  }
}

{
  \override Staff.TimeSignature #'stencil =
    #ly:text-interface::print
  \override Staff.TimeSignature #'text = #tsMarkup
  \time 3/2
  c'2 \bar ":" c'4 c'4.
}
@end lilypond

Each staff can also have its own time signature.  This is done by
moving the @internalsref{Timing_translator} to the
@internalsref{Staff} context.

@example
\layout @{
  \context @{ \Score
     \remove "Timing_translator"
     \remove "Default_bar_line_engraver"
  @}
  \context @{
    \Staff
    \consists "Timing_translator"
    \consists "Default_bar_line_engraver"
  @}

@}
@end example


Now, each staff has its own time signature.

@example
<<
  \new Staff @{
    \time 3/4
    c4 c c | c c c |
  @}
  \new Staff @{
    \time 2/4
    c4 c | c c | c c
  @}
  \new Staff @{
    \time 3/8
    c4. c8 c c c4. c8 c c
  @}
>>
@end example

@lilypond[quote,ragged-right]
\layout{
  \context{
     \Score
     \remove "Timing_translator"
     \remove "Default_bar_line_engraver"
    }
  \context{ \Staff
    \consists "Timing_translator"
    \consists "Default_bar_line_engraver"
  }
}

\relative c' <<
  \new Staff {
    \time 3/4
    c4 c c | c c c |
  }
  \new Staff {
    \time 2/4
    c4 c | c c | c c
  }
  \new Staff {
    \time 3/8
    c4. c8 c c c4. c8 c c
  }
>>
@end lilypond


A different form of polymetric notation is where note lengths have
different values across staves, but the bars are all the same 
length.

This notation can be created by setting a common time signature
for each staff but replacing it manually using
@code{timeSignatureFraction} to the desired fraction.  Then the
printed durations in each staff are scaled to the common time
signature.  The latter is done with @code{\compressMusic}, which
is used in a similar way to @code{\times}, but does not create 
a tuplet bracket.  The syntax is 

@example 
\compressMusic 
#'(@var{numerator} . @var{denominator}) @var{musicexpr} 
@end example



In this example, music with the time signatures of 3/4, 9/8, and
10/8 are used in parallel.  In the second staff, shown durations
are multiplied by 2/3, so that 2/3 * 9/8 = 3/4, and in the third
staff, shown durations are multiplied by 3/5, so that 3/5 * 10/8 =
3/4.

@lilypond[quote,ragged-right,verbatim,fragment]
\relative c' { <<
  \new Staff {
    \time 3/4
    c4 c c | c c c |
  }
  \new Staff {
    \time 3/4
    \set Staff.timeSignatureFraction = #'(9 . 8)
    \compressMusic #'(2 . 3)
      \repeat unfold 6 { c8[ c c] }
  }
  \new Staff {
    \time 3/4
    \set Staff.timeSignatureFraction = #'(10 . 8)
    \compressMusic #'(3 . 5) {
      \repeat unfold 2 { c8[ c c] }
      \repeat unfold 2 { c8[ c] }
      | c4. c4. \times 2/3 { c8 c c } c4
    }
  }
>> }
@end lilypond


@refbugs

When using different time signatures in parallel, the spacing is
aligned vertically, but barlines distort the regular spacing.


@node Automatic note splitting
@unnumberedsubsubsec Automatic note splitting

Long notes which overrun barlines can be converted 
automatically to tied notes.  This is
done by replacing the @internalsref{Note_heads_engraver} by the
@internalsref{Completion_heads_engraver}.  In the following
examples, notes crossing the barline are split and tied.

@lilypond[quote,fragment,verbatim,relative=1,line-width=12\cm]
\new Voice \with {
  \remove "Note_heads_engraver"
  \consists "Completion_heads_engraver"
} {
  c2. c8 d4 e f g a b c8 c2 b4 a g16 f4 e d c8. c2
}
@end lilypond

This engraver splits all running notes at the barline, and
inserts ties.  One of its uses is to debug complex scores: if the
measures are not entirely filled, then the ties exactly show how
much each measure is off.

If you want to allow line breaking on the barlines where
@internalsref{Completion_heads_engraver} splits notes, you must
also remove @internalsref{Forbid_line_break_engraver}.


@refbugs

Not all durations (especially those containing tuplets) can be
represented exactly with normal notes and dots, but the engraver
will not insert tuplets.

@code{Completion_heads_engraver} only affects notes; it does not
split rests.


@seealso

Program reference: @internalsref{Completion_heads_engraver}.




@node Beams
@subsection Beams

@menu
* Automatic beams::             
* Manual beams::                
@end menu

@node Automatic beams
@unnumberedsubsubsec Automatic beams

By default beams are inserted automatically

@lilypond[quote,ragged-right,fragment,verbatim,relative=2]
\time 2/4 c8 c c c
\time 6/8 c c c c8. c16 c8
@end lilypond

When these automatic decisions are not good enough, beaming 
can be entered explicitly.  It is also possible to define beaming
patterns that differ from the defaults.  See @ref{Manual beams}
and @ref{Setting automatic beam behavior}.

@cindex autoBeamOn
@cindex autoBeamOff

@noindent
Automatic beaming may be turned off and on with
@code{\autoBeamOff} and @code{\autoBeamOn} commands:

@lilypond[quote,ragged-right,fragment,relative=1,verbatim]
c4 c8 c8. c16 c8. c16 c8
\autoBeamOff
c4 c8 c8. c16 c8.
\autoBeamOn
c16 c8
@end lilypond


@commonprop

@funindex stemLeftBeamCount
@funindex stemRightBeamCount

LilyPond can automatically determine beaming patterns within a
beam, but this automatic behavior can sometimes produce odd
results; therefore the @code{stemLeftBeamCount} and
@code{stemRightBeamCount} properties can be used to override the
defaults.  If either property is set, its value will be used only
once, and then it is erased.

@lilypond[quote,ragged-right,fragment,relative=1,verbatim]
{
   f8[ r16
      f g a]
   f8[ r16
   \set stemLeftBeamCount = #1
      f g a]
}
@end lilypond

The property @code{subdivideBeams} can be set in order to
subdivide all 16th or shorter beams.
When set, multiple beams will be sub-divided at beat 
positions, defined by the current value of @code{beatLength},
by drawing only one beam over the beat.

@lilypond[fragment,ragged-right,quote,relative=2,verbatim]
c16[ c c c c c c c]
\set subdivideBeams = ##t
c16[ c c c c c c c]
\set Score.beatLength = #(ly:make-moment 1 8)
c16[ c c c c c c c]
@end lilypond
@funindex subdivideBeams

@noindent
For more information about @code{make-moment}, see
@ref{Time administration}.

@c TODO Consider whether the section Setting automatic
@c beam behavior should all be moved here.  For now
@c here's a link to it.

For details about modifying the automatic beam behaviour
see @ref{Setting automatic beam behavior}

@funindex breakable

Line breaks are normally forbidden when beams cross barlines.
This behavior can be changed by setting the @code{breakable} 
property: @code{\override Beam #'breakable = ##t}.

@cindex beams and line breaks
@cindex beams, kneed
@cindex kneed beams
@cindex auto-knee-gap

Kneed beams are inserted automatically when a large gap is
detected between the note heads.  This behavior can be tuned
through the @code{auto-knee-gap} property.  A kneed beam is
drawn if the gap is larger than the value of 
@code{auto-knee-gap} plus the width of the beam object (which
depends on the duration of the notes and the slope of the beam).
By default @code{auto-knee-gap} is set to 5.5 staff spaces.

@lilypond[fragment,ragged-right,quote,verbatim]
f8 f''8 f8 f''8
\override Beam #'auto-knee-gap = #6
f8 f''8 f8 f''8
@end lilypond


@seealso

Program reference: @internalsref{Beam}.


@refbugs

Automatically kneed cross-staff beams cannot be used together with
hidden staves.  See @ref{Hiding staves}.

Beams can collide with noteheads and accidentals in other voices

@node Manual beams
@unnumberedsubsubsec Manual beams

@cindex beams, manual

Individual notes may be marked with @code{\noBeam} to prevent them
from being beamed:

@lilypond[quote,ragged-right,fragment,verbatim,relative=2]
\time 2/4 c8 c\noBeam c c
@end lilypond

@funindex ]
@funindex [

In some cases it may be necessary to override the automatic
beaming algorithm.  For example, the autobeamer will not put beams
over rests or barlines, and in choral scores the beaming is
often set to follow the meter of the lyrics rather than the
notes. Such beams can be specified manually by
marking the begin and end point with @code{[} and @code{]}

@lilypond[quote,ragged-right,fragment,relative=1,verbatim]
{
  r4 r8[ g' a r8] r8 g[ | a] r8
}
@end lilypond

@cindex beams, feathered
@funindex \featherDurations 

Feathered beams are used to indicate that a small group of notes
should be played at an increasing (or decreasing) tempo, without
changing the overall tempo of the piece.  The extent of the 
feathered beam must be indicated manually using @code{[} and
@code{]}, and the beam feathering is turned on by specifying a 
direction to the Beam property @code{grow-direction}.

If the placement of the notes and the sound in the MIDI output
is to reflect the ritardando or accelerando indicated by the
feathered beam the notes must be grouped as a
music expression delimited by braces and preceded by a
@code{featheredDurations} command which specifies the ratio
between the durations of the first and last notes in the group.

The square brackets
show the extent of the beam and the braces show
which notes are to have their durations modified.  Normally 
these would delimit the same group of notes, but this is not
required: the two commands are independent. 

In the following example the eight 16th notes occupy exactly
the same time as a half note, but the first note is twice
as short as the last one, with the intermediate notes gradually
lengthening.  The first four 32nd notes gradually speed up,
while the last four 32nd notes are at a constant tempo.

@lilypond[ragged-right,relative=1,fragment,verbatim,quote]
\override Beam #'grow-direction = #LEFT
\featherDurations #(ly:make-moment 2 1)
{ c16[ c c c c c c c] }
\override Beam #'grow-direction = #RIGHT
\featherDurations #(ly:make-moment 2 3)
{ c32[ d e f] }
% revert to non-feathered beams
\override Beam #'grow-direction = #'()
{ g32[ a b c] }
@end lilypond

@noindent
The spacing in the printed output represents the 
note durations only approximately, but the midi output is exact.


@commonprop

Line breaking is prevented by beams which straddle barlines. The
@samp{breakable} property of @code{Beam} allows this behaviour
to be overridden:

@lilypond[ragged-right,relative=2,fragment,verbatim,quote]
\override Beam #'breakable = ##t
c8 \repeat unfold 15 {c[ c] } c
@end lilypond


@refbugs

The @code{\featherDurations} command only works with very short
music snippets, and when numbers in the fraction are small.


@node Bars
@subsection Bars


@menu
* Bar lines::                   
* Bar numbers::                 
* Bar and bar number checks::   
* Rehearsal marks::             
@end menu

@node Bar lines
@unnumberedsubsubsec Bar lines

@cindex Bar lines
@cindex Barlines
@funindex \bar
@cindex measure lines
@cindex repeat bars

Barlines delimit measures, and are also used to indicate
repeats.  Normally, simple barlines are automatically inserted
into the printed output at places
based on the current time signature.  It is not invalid if the
final note in a bar does not end on the automatically entered 
barline: the note is assumed to carry over into the next bar.  

The simple barlines inserted automatically can be changed to 
other types with the @code{\bar} command.  For example, a closing
double barline is usually placed at the end of a piece:

@lilypond[quote,ragged-right,relative=1,fragment,verbatim]
e4 d c2 \bar "||"
@end lilypond

This and other special barlines may be inserted manually at any
point.  When they coincide with the end of a bar they replace
the simple barline which would have been inserted there 
automatically.  When they do not coincide
with the end of a bar the specified barline is inserted at that
point in the printed output.  Such insertions do not affect
the calculation and placement of subsequent automatic barlines.  

The simple barline and four types of double barline are available
for manual insertion:

@lilypond[quote,ragged-right,fragment,relative=1,verbatim]
f1 \bar "|" g \bar "||" a \bar ".|" b \bar ".|." c \bar "|." d
@end lilypond

@noindent
together with dotted and dashed barlines:

@lilypond[quote,ragged-right,fragment,relative=1,verbatim]
f1 \bar ":" g \bar "dashed" a
@end lilypond

@noindent
and three types of repeat barline:

@lilypond[quote,ragged-right,fragment,relative=1,verbatim]
f1 \bar "|:" g \bar ":|:" a \bar ":|" b
@end lilypond

Although the barline types signifying repeats may be inserted
manually they do not in themselves cause LilyPond to recognise
a repeated section.  Such repeated sections are better entered
using the various repeat commands (see @ref{Repeats}), which
automatically print the appropriate barlines.

In addition, you can specify @code{"||:"}, which is equivalent to
@code{"|:"} except at line breaks, where it gives a double bar
line at the end of the line and a start repeat at the beginning of
the next line. 

@lilypond[quote,ragged-right,relative=2,fragment,verbatim]
\override Score.RehearsalMark #'padding = #3
c c c c
\bar "||:" 
c c c c \break
\bar "||:" 
c c c c
@end lilypond

Entered music is
automatically broken into lines, but this happens only at
manually inserted barlines or at automatically inserted barlines
where these occur at the     
end of complete bars, i.e. where the end of a note coincides
with the end of a bar.  If this never happens, perhaps due to
an error in entering durations, the outputted music can appear
very compressed as no place can be found to make a line break.

To allow a line break without printing a barline, use

@example
\bar ""
@end example

@noindent
This will insert an invisible barline and allow (but not
force) a line break to occur at this point.  The bar number 
counter is not increased.  To force a line break see 
@ref{Line breaking}.

In scores with many staves, a @code{\bar} command in one staff is
automatically applied to all staves.  The resulting barlines are
connected between different staves of a @code{StaffGroup},
@code{PianoStaff}, or @code{GrandStaff}.

@lilypond[quote,ragged-right,fragment,verbatim]
<<
  \new StaffGroup <<
    \new Staff {
      e'4 d'
      \bar "||"
      f' e'
    }
    \new Staff { \clef bass c4 g e g }
  >>
  \new Staff { \clef bass c2 c2 }
>>
@end lilypond


@commonprop

@funindex whichBar
@funindex defaultBarType

The command @code{\bar }@var{bartype} is a short cut for
@code{\set Timing.whichBar = }@var{bartype}.  A barline is 
created whenever the @code{whichBar} property is
set.  

The default bar type used for automatically inserted barlines is
@code{"|"}.  This may be changed at any time
with @code{\set Timing.defaultBarType = }@var{bartype}.  

@seealso

In this manual: @ref{Repeats}, @ref{System start delimiters}.

Program reference: @internalsref{BarLine} (created at
@internalsref{Staff} level), @internalsref{SpanBar} (across
staves), @internalsref{Timing_translator} (for Timing 
properties).


@node Bar numbers
@unnumberedsubsubsec Bar numbers

@cindex Bar numbers
@cindex measure numbers
@funindex currentBarNumber

Bar numbers are typeset by default at the start of every line
except the first line.  The
number itself is stored in the @code{currentBarNumber} property,
which is normally updated automatically for every measure.  It
may also be set manually:

@lilypond[verbatim,ragged-right,quote,fragment,relative]
\repeat unfold 4 {c4 c c c} \break
\set Score.currentBarNumber = #50
\repeat unfold 4 {c4 c c c}
@end lilypond

Bar numbers may only be printed at barlines; to print a bar
number at the beginning of a piece, an empty barline must be
inserted there:

@lilypond[verbatim,ragged-right,quote,fragment,relative]
\set Score.currentBarNumber = #50
\bar ""
\repeat unfold 4 {c4 c c c} \break
\repeat unfold 4 {c4 c c c}
@end lilypond

Bar numbers can be typeset at regular intervals instead of at the
beginning of every line.  This is illustrated in the following
example, which also shows how to enclose bar numbers in boxes and
circles.

@lilypond[verbatim,ragged-right,quote,fragment,relative]
% Avoid printing a bar number at the end of a line
\override Score.BarNumber  #'break-visibility = #end-of-line-invisible

% Print a bar number every 3th bar
\set Score.barNumberVisibility = #(every-nth-bar-number-visible 3)

% Increase the size of the bar number by 2 
\override Score.BarNumber #'font-size = #2

% Draw a box round the following bar number(s)
\override Score.BarNumber  #'stencil
   = #(make-stencil-boxer 0.1 0.25 ly:text-interface::print)
\repeat unfold 5 { c1 } \bar "|"

% Draw a circle round the following bar number(s)
\override Score.BarNumber  #'stencil
  = #(make-stencil-circler 0.1 0.25 ly:text-interface::print)
\repeat unfold 4 { c1 } \bar "|."
@end lilypond

Bar numbers can be removed entirely by removing the Bar number
engraver from the score context.

@lilypond[verbatim,ragged-right,quote]
\layout {
  \context {
    \Score
    \remove "Bar_number_engraver"
  }
}
\relative c''{
  c4 c c c \break
  c4 c c c
}
@end lilypond


@seealso

Program reference: @internalsref{BarNumber}.

Examples: @lsrdir{staff}


@refbugs

Bar numbers can collide with the top of the 
@internalsref{StaffGroup} bracket, if there is one.
To solve this, the @code{padding} property of 
@internalsref{BarNumber} can be used to
position the number correctly.


@node Bar and bar number checks
@unnumberedsubsubsec Bar and bar number checks

@cindex Bar check
@funindex barCheckSynchronize
@funindex |

Bar checks help detect errors in the entered durations.
A bar check may be entered using the bar symbol, @samp{|}, 
at any place where a barline is expected to fall.  
If bar check lines are encountered at other places, 
a list of warnings is printed in the log file,
showing the line numbers and lines  
in which the bar checks failed.  In the next
example, the second bar check will signal an error

@example
\time 3/4 c2 e4 | g2 |
@end example

Bar checks can also be used in lyrics, for example

@example
\lyricmode @{
  \time 2/4
  Twin -- kle | Twin -- kle |
@}
@end example

An incorrect duration can result in a completely garbled score,
especially if the score is polyphonic, so a good place to start
correcting input is by scanning for failed bar checks and
incorrect durations.

@funindex |
@funindex pipeSymbol

It is also possible to redefine the action taken when a bar check 
or pipe symbol, @samp{|}, is encountered in the input, so that 
it does something other than a bar check.  This is done by 
assigning a music expression to @code{pipeSymbol}.  
In the following example @samp{|} is set to insert a double bar 
line wherever it appears in the input, rather than checking 
for end of bar.

@lilypond[quote,ragged-right,verbatim]
pipeSymbol = \bar "||"
{ 
  c'2 c'2 |
  c'2 c'2
  c'2 | c'2
  c'2 c'2
}
@end lilypond

When copying large pieces of music, it can be helpful to check
that the LilyPond bar number corresponds to the original that you
are entering from.  This can be checked with
@code{\barNumberCheck}, for example,

@verbatim
\barNumberCheck #123
@end verbatim

@noindent
will print a warning if the @code{currentBarNumber} is not 123
when it is processed.


@node Rehearsal marks
@unnumberedsubsubsec Rehearsal marks

@cindex Rehearsal marks
@funindex \mark

To print a rehearsal mark, use the @code{\mark} command

@lilypond[quote,ragged-right,fragment,verbatim,relative=2]
c1 \mark \default
c1 \mark \default
c1 \mark #8
c1 \mark \default
c1 \mark \default
@end lilypond

@noindent
The letter@tie{}@q{I} is skipped in accordance with engraving
traditions.  If you wish to include the letter @q{I}, then use

@example
\set Score.markFormatter = #format-mark-alphabet
@end example

The mark is incremented automatically if you use @code{\mark
\default}, but you can also use an integer argument to set the
mark manually.  The value to use is stored in the property
@code{rehearsalMark}.

The style is defined by the property @code{markFormatter}.  It is
a function taking the current mark (an integer) and the current
context as argument.  It should return a markup object.  In the
following example, @code{markFormatter} is set to a pre-defined
procedure.  After a few measures, it is set to a procedure that
produces a boxed number.

@lilypond[fragment,quote,ragged-right,verbatim,relative=2]
\set Score.markFormatter = #format-mark-numbers
c1 \mark \default
c1 \mark \default
\set Score.markFormatter = #format-mark-box-numbers
c1 \mark \default
c1 \mark \default
c1
@end lilypond

The file @file{scm/@/translation@/-functions@/.scm} contains the
definitions of @code{format-mark-numbers} (the default format),
@code{format-mark-box-numbers}, @code{format-mark-letters} and
@code{format-mark-box-letters}.  These can be used as inspiration
for other formatting functions.

You may use @code{format-mark-barnumbers},
@code{format-mark-box-barnumbers}, and
@code{format-mark-circle-barnumbers} to get bar numbers instead of
incremented numbers or letters.

Other styles of rehearsal mark can be specified manually

@example
\mark "A1"
@end example

@noindent
@code{Score.markFormatter} does not affect marks specified in this
manner.  However, it is possible to apply a @code{\markup} to the
string.

@example
\mark \markup@{ \box A1 @}
@end example

@cindex segno
@cindex coda
@cindex D.S al Fine

Music glyphs (such as the segno sign) may be printed inside a
@code{\mark}

@lilypond[fragment,quote,ragged-right,verbatim,relative]
c1 \mark \markup { \musicglyph #"scripts.segno" }
c1 \mark \markup { \musicglyph #"scripts.coda" }
c1 \mark \markup { \musicglyph #"scripts.ufermata" }
c1
@end lilypond

@noindent
See @ref{The Feta font}, for a list of symbols which may be
printed with @code{\musicglyph}.

For common tweaks to the positioning of rehearsal marks, see
@ref{Text marks}.

@seealso

This manual: @ref{Text marks}.

Program reference: @internalsref{RehearsalMark}.

Init files: @file{scm/@/translation@/-functions@/.scm} contains
the definition of @code{format-mark-numbers} and
@code{format-mark-letters}.  They can be used as inspiration for
other formatting functions.

Examples: @lsr{parts,rehearsal-mark-numbers.ly}


@node Special rhythmic concerns
@subsection Special rhythmic concerns


@menu
* Grace notes::                 
* Aligning to cadenzas::        
* Time administration::         
@end menu

@node Grace notes
@unnumberedsubsubsec Grace notes

@funindex \grace
@cindex ornaments
@cindex grace notes
@cindex appoggiatura
@cindex acciaccatura

Grace notes are ornaments that are written out.  The most common
ones are acciaccatura, which should be played as very short.  It
is denoted by a slurred small note with a slashed stem.  The
appoggiatura is a grace note that takes a fixed fraction of the
main note, and is denoted as a slurred note in small print without
a slash.  They are entered with the commands @code{\acciaccatura}
and @code{\appoggiatura}, as demonstrated in the following example

@lilypond[quote,ragged-right,relative=2,verbatim,fragment]
b4 \acciaccatura d8 c4 \appoggiatura e8 d4
\acciaccatura { g16[ f] } e4
@end lilypond

Both are special forms of the @code{\grace} command.  By prefixing
this keyword to a music expression, a new one is formed, which
will be printed in a smaller font and takes up no logical time in
a measure.

@lilypond[quote,ragged-right,relative=2,verbatim,fragment]
c4 \grace c16 c4
\grace { c16[ d16] } c2 c4
@end lilypond

@noindent
Unlike @code{\acciaccatura} and @code{\appoggiatura}, the
@code{\grace} command does not start a slur.

The placement of grace notes is synchronized between different
staves.  In the following example, there are two sixteenth grace
notes for every eighth grace note

@lilypond[quote,ragged-right,relative=2,verbatim,fragment]
<< \new Staff { e4 \grace { c16[ d e f] } e4 }
   \new Staff { c4 \grace { g8[ b] } c4 } >>
@end lilypond

@funindex \afterGrace

If you want to end a note with a grace, use the @code{\afterGrace}
command.  It takes two arguments: the main note, and the grace
notes following the main note.

@lilypond[ragged-right, verbatim,relative=2,fragment]
c1 \afterGrace d1 { c16[ d] } c4
@end lilypond

This will put the grace notes after a @q{space} lasting 3/4 of the
length of the main note.  The fraction 3/4 can be changed by
setting @code{afterGraceFraction}, ie.

@example
#(define afterGraceFraction (cons 7 8))
@end example

@noindent
will put the grace note at 7/8 of the main note.

The same effect can be achieved manually by doing

@lilypond[quote,ragged-right,fragment,verbatim,relative=2]
\new Voice {
  << { d1^\trill_( }
     { s2 \grace { c16[ d] } } >>
  c4)
}
@end lilypond

@noindent
By adjusting the duration of the skip note (here it is a
half-note), the space between the main-note and the grace
may be adjusted.

A @code{\grace} music expression will introduce special
typesetting settings, for example, to produce smaller type, and
set directions.  Hence, when introducing layout tweaks, they
should be inside the grace expression, for example,

@lilypond[quote,ragged-right,fragment,verbatim,relative=2]
\new Voice {
  \acciaccatura {
    \stemDown
    f16->
    \stemNeutral
  }
  g4
}
@end lilypond

@noindent
The overrides should also be reverted inside the grace expression.

The layout of grace expressions can be changed throughout the
music using the function @code{add-grace-property}.  The following
example undefines the @code{Stem} direction for this grace, so
that stems do not always point up.

@example
\new Staff @{
  #(add-grace-property 'Voice 'Stem 'direction '())
  @dots{}
@}
@end example

@noindent
Another option is to change the variables @code{startGraceMusic},
@code{stopGraceMusic}, @code{startAcciaccaturaMusic},
@code{stopAcciaccaturaMusic}, @code{startAppoggiaturaMusic},
@code{stopAppoggiaturaMusic}.  The default values of these can be
seen in the file @file{ly/@/grace@/-init@/.ly}.  By redefining
them other effects may be obtained.

@noindent
The slash through the stem in acciaccaturas can be obtained in
other situations by @code{\override Stem  #'stroke-style =
#"grace"}.


@commonprop

Grace notes may be forced to use align with regular notes
in other staves by setting @code{strict-grace-spacing} to
##t:

@lilypond[relative=2,ragged-right]
<<
  \override Score.SpacingSpanner #'strict-grace-spacing = ##t
  \new Staff {
     c'4
     \afterGrace
     c'4
     { c'16[ c'8 c'16] }
     c'4
  }  
  \new Staff {
     c'16[ c'16 c'16 c'16]
     c'16[ c'16 c'16 c'16]
     c'4
  }
>>
@end lilypond


@seealso

Program reference: @internalsref{GraceMusic}.


@refbugs

Grace note synchronization can also lead to surprises.  Staff
notation, such as key signatures, barlines, etc., are also
synchronized.  Take care when you mix staves with grace notes and
staves without, for example,

@lilypond[quote,ragged-right,relative=2,verbatim,fragment]
<< \new Staff { e4 \bar "|:" \grace c16 d4 }
   \new Staff { c4 \bar "|:" d4 } >>
@end lilypond

@noindent
This can be remedied by inserting grace skips of the corresponding
durations in the other staves.  For the above example

@lilypond[quote,ragged-right,relative=2,verbatim,fragment]
<< \new Staff { e4 \bar "|:" \grace c16 d4 }
   \new Staff { c4 \bar "|:" \grace s16 d4 } >>
@end lilypond

Grace sections should only be used within sequential music
expressions.  Nesting or juxtaposing grace sections is not
supported, and might produce crashes or other errors.

@node Aligning to cadenzas
@unnumberedsubsubsec Aligning to cadenzas

In an orchestral context, cadenzas present a special problem: when
constructing a score that includes a cadenza, all other
instruments should skip just as many notes as the length of the
cadenza, otherwise they will start too soon or too late.

A solution to this problem are the functions
@code{mmrest-of-length} and @code{skip-of-length}.  These Scheme
functions take a piece of music as argument, and generate a
multi-rest or @code{\skip}, exactly as long as the piece.  The use
of @code{mmrest-of-length} is demonstrated in the following
example.

@lilypond[verbatim,ragged-right,quote]
cadenza = \relative c' {
  c4 d8 << { e f g } \\ { d4. } >>
  g4 f2 g4 g
}

\new GrandStaff <<
  \new Staff { \cadenza c'4 }
  \new Staff {
    #(ly:export (mmrest-of-length cadenza))
    c'4
  }
>>
@end lilypond


@node Time administration
@unnumberedsubsubsec Time administration

@cindex Time administration

@funindex currentBarNumber
@funindex measurePosition
@funindex measureLength

Time is administered by the
@code{Timing_translator}, which by default is
to be found in the @code{Score} context.  An
alias, @code{Timing}, is added to the context in which
the @code{Timing_translator} is placed.

The following properties of @code{Timing} are used
to keep track of timing within the score.
 
@table @code
@item currentBarNumber
The current measure number.  For an example showing the
use of this property see @ref{Bar numbers}.

@item measureLength
The length of the measures in the current time signature.  For a
4/4 time this is@tie{}1, and for 6/8 it is 3/4.  Its value
determines when barlines are inserted and how automatic beams
should be generated.

@item measurePosition
The point within the measure where we currently are.  This
quantity is reset by subtracting @code{measureLength} whenever
@code{measureLength} is reached or exceeded.  When that happens, 
@code{currentBarNumber} is incremented.

@item timing
If set to true, the above variables are updated for every time
step.  When set to false, the engraver stays in the current
measure indefinitely.

@end table

Timing can be changed by setting any of these variables
explicitly.  In the next example, the default 4/4 time 
signature is printed, but @code{measureLength} is set to 5/4.
At 4/8 though the third bar, the @code{measurePosition} is
advanced by 1/8 to 5/8, shortening that bar by 1/8.
The next barline then falls at 9/8 rather than 5/4.

@lilypond[quote,ragged-right,verbatim,relative,fragment]
\set Score.measureLength = #(ly:make-moment 5 4)
c1 c4
c1 c4
c4 c4
\set Score.measurePosition = #(ly:make-moment 5 8)
b4 b4 b8
c4 c1
@end lilypond

@noindent
As the example illustrates, @code{ly:make-moment n m} constructs a
duration of n/m of a whole note.  For example,
@code{ly:make-moment 1 8} is an eighth note duration and
@code{ly:make-moment 7 16} is the duration of seven sixteenths
notes.

@seealso

This manual: @ref{Bar numbers}, @ref{Unmetered music}

Program Reference: @internalsref{Timing_translator},
@internalsref{Score}