Setting automatic beam behavior

When automatic beaming is enabled, the placement of automatic beams is determined by three context properties: baseMoment, beatStructure, and beamExceptions. The default values of these variables may be overridden as described below, or alternatively the default values themselves may be changed as explained in Time signature.

If a beamExceptions rule is defined for the time signature in force, that rule alone is used to determine the beam placement; the values of baseMoment and beatStructure are ignored.

If no beamExceptions rule is defined for the time signature in force, the beam placement is determined by the values of baseMoment and beatStructure.

Beaming based on baseMoment and beatStructure

By default, beamExceptions rules are defined for most common time signatures, so the beamExceptions rules must be disabled if automatic beaming is to be based on baseMoment and beatStructure. The beamExceptions rules are disabled by

\set Timing.beamExceptions = #'()

When beamExceptions is set to #'(), either due to an explicit setting or because no beamExceptions rules are defined internally for the time signature in force, the ending points for beams are on beats as specified by the context properties baseMoment and beatStructure. beatStructure is a Scheme list that defines the length of each beat in the measure in units of baseMoment. By default, baseMoment is one over the denominator of the time signature. By default, each unit of length baseMoment is a single beat.

Note that there are separate beatStructure and baseMoment values for each time signature. Changes to these variables apply only to the time signature that is currently in force, hence those changes must be placed after the \time command which starts a new time signature section, not before it. New values given to a particular time signature are retained and reinstated whenever that time signature is reestablished.

\relative c'' {
  \time 5/16
  c16^"default" c c c c |
  % beamExceptions are unlikely to be defined for 5/16 time,
  % but let's disable them anyway to be sure
  \set Timing.beamExceptions = #'()
  \set Timing.beatStructure = 2,3
  c16^"(2+3)" c c c c |
  \set Timing.beatStructure = 3,2
  c16^"(3+2)" c c c c |
}

\relative {
  \time 4/4
  a'8^"default" a a a a a a a
  % Disable beamExceptions because they are definitely
  % defined for 4/4 time
  \set Timing.beamExceptions = #'()
  \set Timing.baseMoment = \musicLength 4
  \set Timing.beatStructure = 1,1,1,1
  a8^"changed" a a a a a a a
}

Beam setting changes can be limited to specific contexts. If no setting is included in a lower-level context, the setting of the enclosing context will apply.

\new Staff {
  \time 7/8
  % No need to disable beamExceptions
  % as they are not defined for 7/8 time
  \set Staff.beatStructure = 2,3,2
  <<
    \new Voice = one {
      \relative {
        a'8 a a a a a a
      }
    }
    \new Voice = two {
      \relative {
        \voiceTwo
        \set Voice.beatStructure = 1,3,3
        f'8 f f f f f f
      }
    }
  >>
}

When multiple voices are used the Staff context must be specified if the beaming is to be applied to all voices in the staff:

\time 7/8
% rhythm 3-1-1-2
% Change applied to Voice by default --  does not work correctly
% Because of auto-generated voices, all beating will
% be at baseMoment (1 . 8)
\set beatStructure = 3,1,1,2
<< \relative {a'8 a a a16 a a a a8 a} \\ \relative {f'4. f8 f f f} >>

% Works correctly with context Staff specified
\set Staff.beatStructure = 3,1,1,2
<< \relative {a'8 a a a16 a a a a8 a} \\ \relative {f'4. f8 f f f} >>

The value of baseMoment can be adjusted to change the beaming behavior, if desired. When this is done, the value of beatStructure must be set to be compatible with the new value of baseMoment.

\time 5/8
% No need to disable beamExceptions
% as they are not defined for 5/8 time
\set Timing.baseMoment = \musicLength 16
\set Timing.beatStructure = 7,3
\repeat unfold 10 { a'16 }

baseMoment is a moment; a unit of musical duration. For more information about this type, see Time administration.

By default baseMoment is set to one over the denominator of the time signature. Any exceptions to this default can be found in scm/time-signature-settings.scm.

Beaming based on beamExceptions

Special auto-beaming rules (other than ending a beam on a beat) are defined in the beamExceptions property.

The value for beamExceptions, a somewhat complex Scheme data structure, is easiest generated with the \beamExceptions function. This function is given one or more manually beamed measure-long rhythmic patterns (measures have to be separated by a bar check | since the function has no other way to discern the measure length). Here is a simple example:

\relative c'' {
  \time 3/16
  \set Timing.beatStructure = 2,1
  \set Timing.beamExceptions =
    \beamExceptions { 32[ 32] 32[ 32] 32[ 32] }
  c16 c c |
  \repeat unfold 6 { c32 } |
}

When the time signature is changed, default values of Timing.baseMoment, Timing.beatStructure, and Timing.beamExceptions are set. Setting the time signature will reset the automatic beaming settings for the Timing context to the default behavior.

\relative a' {
  \time 6/8
  \repeat unfold 6 { a8 }
  % group (4 + 2)
  \set Timing.beatStructure = 4,2
  \repeat unfold 6 { a8 }
  % go back to default behavior
  \time 6/8
  \repeat unfold 6 { a8 }
}

The default automatic beaming settings for a time signature are determined in scm/time-signature-settings.scm. Changing the default automatic beaming settings for a time signature is described in Time signature.

Many automatic beaming settings for a time signature contain an entry for beamExceptions. For example, 4/4 time tries to beam the measure in two if there are only eighth notes. The beamExceptions rule can override the beatStructure setting if beamExceptions is not reset.

\time 4/4
\set Timing.baseMoment = \musicLength 8
\set Timing.beatStructure = 3,3,2
% This won't beam (3 3 2) because of beamExceptions
\repeat unfold 8 {c''8} |
% This will beam (3 3 2) because we clear beamExceptions
\set Timing.beamExceptions = #'()
\repeat unfold 8 {c''8}

In a similar fashion, eighth notes in 3/4 time are beamed as a full measure by default. To beam eighth notes in 3/4 time on the beat, reset beamExceptions.

\time 3/4
% by default we beam in (6) due to beamExceptions
\repeat unfold 6 {a'8} |
% This will beam (1 1 1) due to default baseMoment and beatStructure
\set Timing.beamExceptions = #'()
\repeat unfold 6 {a'8}

In engraving from the Romantic and Classical periods, beams often begin midway through the measure in 3/4 time, but modern practice is to avoid the false impression of 6/8 time (see Gould, p. 153). Similar situations arise in 3/8 time. This behavior is controlled by the context property beamHalfMeasure, which has effect only in time signatures with 3 in the numerator:

\relative a' {
  \time 3/4
  r4. a8 a a |
  \set Timing.beamHalfMeasure = ##f
  r4. a8 a a |
}

How automatic beaming works

When automatic beaming is enabled, the placement of automatic beams is determined by the context properties baseMoment, beatStructure, and beamExceptions.

The following rules, in order of priority, apply when determining the appearance of beams:

• If a manual beam is specified with […] set the beam as specified, otherwise
• if a beam ending rule is defined in beamExceptions for the beam type, use it to determine the valid places where beams may end, otherwise
• if a beam ending rule is defined in beamExceptions for a longer beam type, use it to determine the valid places where beams may end, otherwise
• use the values of baseMoment and beatStructure to determine the ends of the beats in the measure, and end beams at the end of beats.

In the rules above, the beam type is the duration of the shortest note in the beamed group.

The default beaming rules can be found in scm/time-signature-settings.scm.

Selected Snippets

Subdividing beams

The beams of consecutive 16th (or shorter) notes are, by default, not subdivided. That is, the beams of more than two stems stretch unbroken over entire groups of notes. This behavior can be modified to subdivide the beams into sub-groups by setting the property subdivideBeams to true (#t). When set, a number of beamlets between two consecutive stems are removed at intervals multiple beams will be subdivided at intervals to match the metric value of the subdivision. Properties minimumBeamSubdivisionInterval and maximumBeamSubdivisionInterval allow configuring limits of automatic beam subdivision: the minimum rhythmic interval at which to subdivide beams and the number of beamlets removed depending on the interval respectively. If the numerator of maximumBeamSubdivisionInterval is not a power of 2, the smaller rhythmic intervals considered for subdivision are maximumBeamSubdivisionInterval divided by powers of 2 and stay greater than or equal to minimumBeamSubdivisionInterval. If maximumBeamSubdivisionInterval < minimumBeamSubdivisionInterval, then the depths of beam subdivision are limited to maximumBeamSubdivisionInterval, but not the frequency/intervals, therefore possibly deviating from the correct expected metric value. If respectIncompleteBeams is set to true (##t), the depth of the subdivision (number of beams) reflects the longest possible subdivision interval within the remaining length of the beam from the current stem. However, the last two stems of the beam are exempt from this rule.

\relative c'' {
  c32[ c c c c c c c]

  \set subdivideBeams = ##t
  c32[ c c c c c c c]

  % Set minimum beam subdivision interval to 1/8 just for this beam
  \once \set minimumBeamSubdivisionInterval = \musicLength 8
  c32[ c c c c c c c]

  % Set maximum beam subdivision interval to 1/16 just for this beam
  \once \set maximumBeamSubdivisionInterval = \musicLength 16
  c32[ c c c c c c c]

  % Set maximum beam subdivision interval to 3/8 just for this beam
  \once \set maximumBeamSubdivisionInterval = \musicLength 8*3
  [ \repeat unfold 16 c64 ] r2.

  % Set maximum beam subdivision interval to 1/64 to limit subdivision depth,
  % despite not being metrically correct
  \once \set minimumBeamSubdivisionInterval = \musicLength 32
  \once \set maximumBeamSubdivisionInterval = \musicLength 64
  [ \repeat unfold 32 c128 ] r2.

  % Shorten beam by 1/32
  c32[ c c c c c c] r32

  % Shorten beam by 3/32
  c32[ c c c c] r16.

  % Respect the incomplete beams of the previous two examples
  \set respectIncompleteBeams = ##t
  c32[ c c c c c c] r32
  % no visual change here as last two stems are exempt from this
  % special rule
  c32[ c c c c] r16.
}

Strict beat beaming

Beamlets can be set to point in the direction of the beat to which they belong. The first beam avoids sticking out flags (the default); the second beam strictly follows the beat.

\relative c'' {
  \time 6/8
  a8. a16 a a
  \set strictBeatBeaming = ##t
  a8. a16 a a
}

Conducting signs, measure grouping signs

Beat grouping within a measure is controlled by the beatStructure context property. Values of beatStructure are established for many time signatures in file scm/time-signature-settings.scm. Values of beatStructure can be changed or set with \set. Alternatively, \time can be used to both set the time signature and establish the beat structure. For this, you specify the internal grouping of beats in a measure as a list of numbers (in Scheme syntax) before the time signature.

\time applies to the Timing context, so it will not reset values of beatStructure or baseMoment that are set in other lower-level contexts, such as Voice.

If the Measure_grouping_engraver is included in one of the display contexts, measure grouping signs will be created. Such signs ease reading rhythmically complex modern music. In the example, the 9/8 measure is grouped in two different patterns using the two different methods, while the 5/8 measure is grouped according to the default setting in scm/time-signature-settings.scm:

\score {
  \new Voice \relative c'' {
    \time 9/8
    g8 g d d g g a( bes g) |
    \set Timing.beatStructure = 2,2,2,3
    g8 g d d g g a( bes g) |
    \time 4,5 9/8
    g8 g d d g g a( bes g) |
    \time 5/8
    a4. g4 |
  }
  \layout {
    \context {
      \Staff
      \consists "Measure_grouping_engraver"
    }
  }
}

Beam endings in Score context

Beam-ending rules specified in the Score context apply to all staves, but can be modified at both Staff and Voice levels:

\relative c'' {
  \time 5/4
  % Set default beaming for all staves
  \set Score.baseMoment = \musicLength 8
  \set Score.beatStructure = 3,4,3
  <<
    \new Staff {
      c8 c c c c c c c c c
    }
    \new Staff {
      % Modify beaming for just this staff
      \set Staff.beatStructure = 6,4
      c8 c c c c c c c c c
    }
    \new Staff {
      % Inherit beaming from Score context
      <<
        {
          \voiceOne
          c8 c c c c c c c c c
        }
        % Modify beaming for this voice only
        \new Voice {
          \voiceTwo
          \set Voice.beatStructure = 6,4
          a8 a a a a a a a a a
        }
      >>
    }
  >>
}

See also

Notation Reference: Time signature.

Installed Files: scm/time-signature-settings.scm.

Snippets: Rhythms.

Internals Reference: Auto_beam_engraver, Beam, BeamForbidEvent, beam-interface.

Known issues and warnings

If a score ends while an automatic beam has not been ended and is still accepting notes, this last beam will not be typeset at all. The same holds for polyphonic voices, entered with << … \\ … >>. If a polyphonic voice ends while an automatic beam is still accepting notes, it is not typeset. The workaround for these problems is to manually beam the last beam in the voice or score.

By default, the Timing translator is aliased to the Score context. This means that setting the time signature in one staff will affect the beaming of the other staves as well. Thus, a time signature setting in a later staff will reset custom beaming that was set in an earlier staff. One way to avoid this problem is to set the time signature in only one staff.

<<
  \new Staff {
    \time 3/4
    \set Timing.baseMoment = \musicLength 8
    \set Timing.beatStructure = 1,5
    \set Timing.beamExceptions = #'()
    \repeat unfold 6 { a'8 }
  }
  \new Staff {
    \repeat unfold 6 { a'8 }
  }
>>

The default beam settings for the time signature can also be changed, so that the desired beaming will always be used. Changes in automatic beaming settings for a time signature are described in Time signature.

<<
  \new Staff {
    \overrideTimeSignatureSettings
      3/4               % timeSignatureFraction
      1/8               % baseMoment
      1,5               % beatStructure
      #'()		% beamExceptions
    \time 3/4
    \repeat unfold 6 { a'8 }
  }
  \new Staff {
    \time 3/4
    \repeat unfold 6 { a'8 }
  }
>>