2.4.1 Automatic beams

By default, beams are inserted automatically:

\relative c'' {
  \time 2/4 c8 c c c
  \time 6/8 c8 c c c8. c16 c8
}

If these automatic decisions are not satisfactory, beaming can be entered explicitly; see Manual beams. Beams must be entered manually if beams are to be extended over rests.

If automatic beaming is not required, it may be turned off with \autoBeamOff and on with \autoBeamOn:

\relative c' {
  c4 c8 c8. c16 c8. c16 c8
  \autoBeamOff
  c4 c8 c8. c16 c8.
  \autoBeamOn
  c16 c8
}

Beaming patterns that differ from the automatic defaults can be created; see Setting automatic beam behavior.

Predefined commands

\autoBeamOff, \autoBeamOn.

Selected Snippets

Beams across line breaks

Normally, LilyPond refuses to automatically break a line at places where a beam crosses a bar line. This behavior can be changed by setting the Beam.breakable property to #t.

This property does not affect manual breaks inserted with commands like \break.

music = {
  \repeat unfold 8 c8
  c8 \repeat unfold 7 { c[ c] }  c
  \repeat unfold 8 c8
}

\relative c'' {
  <>^\markup { \typewriter Beam.breakable set to \typewriter "#t" }
  \override Beam.breakable = ##t
  \music
}

\relative c'' {
  <>^\markup { \typewriter Beam.breakable not set }
  \music
}

\paper {
  line-width = 100\mm
  tagline = ##f
}

Changing beam knee gap

Kneed beams are inserted automatically when a large gap is detected between the note heads. This behavior can be tuned through the auto-knee-gap property. A kneed beam is drawn if the gap is larger than the value of 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 auto-knee-gap is set to 5.5 staff spaces.

{
  f8 f''8 f8 f''8
  \override Beam.auto-knee-gap = 6
  f8 f''8 f8 f''8
}

Partcombine and \autoBeamOff

The function of \autoBeamOff when used with \partCombine can be difficult to understand. It may be preferable to use

\set Staff.autoBeaming = ##f

instead to ensure that auto-beaming is turned off for the entire staff. Use this at a spot in your score where no beam generated by the auto-beamer is still active.

Internally, \partCombine works with four voices – stem up single, stem down single, combined, and solo. In order to use \autoBeamOff to stop all auto-beaming when used with \partCombine, it is necessary to use four calls to \autoBeamOff.

{
  % \set Staff.autoBeaming = ##f % turns off all auto-beaming

  \partCombine {
    \autoBeamOff   % applies to split up-stems
    \repeat unfold 4 a'16
    % \autoBeamOff % applies to combined stems
    \repeat unfold 4 a'8
    \repeat unfold 4 a'16
    % \autoBeamOff % applies to solo
    \repeat unfold 4 a'16
    r4
  } {
    % \autoBeamOff % applies to split down-stems
    \repeat unfold 4 f'8
    \repeat unfold 8 f'16 |
    r4
    \repeat unfold 4 a'16
  }
}

See also

Notation Reference: Manual beams, Setting automatic beam behavior.

Installed Files: scm/auto-beam.scm.

Snippets: Rhythms.

Internals Reference: Auto_beam_engraver, Beam_engraver, Beam, BeamEvent, BeamForbidEvent, beam-interface, unbreakable-spanner-interface.

Known issues and warnings

The properties of a beam are determined at the start of its construction and any additional beam property changes that occur before the beam has been completed will not take effect until the next, new beam starts.

2.4.2 Setting automatic beam behavior

When automatic beaming is enabled, the placement of automatic beams is determined by three context properties: beatBase, 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 beatBase 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 beatBase and beatStructure.

Beaming based on beatBase 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 beatBase 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 beatBase and beatStructure. beatStructure is a Scheme list that defines the length of each beat in the measure in units of beatBase. By default, beatBase is one over the denominator of the time signature. By default, each unit of length beatBase is a single beat.

Note that there are separate beatStructure and beatBase 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.beatBase = #1/4
  \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 beatBase #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 beatBase 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 beatBase.

\time 5/8
% No need to disable beamExceptions
% as they are not defined for 5/8 time
\set Timing.beatBase = #1/16
\set Timing.beatStructure = 7,3
\repeat unfold 10 { a'16 }

By default beatBase 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.beatBase, 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.beatBase = #1/8
\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 beatBase 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 beatBase, 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 beatBase 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 beamMinimumSubdivision and beamMaximumSubdivision 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 beamMaximumSubdivision is not a power of 2, the smaller rhythmic intervals considered for subdivision are beamMaximumSubdivision divided by powers of 2 and stay greater than or equal to beamMinimumSubdivision. If beamMaximumSubdivision < beamMinimumSubdivision, then the depths of beam subdivision are limited to beamMaximumSubdivision, 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 beamMinimumSubdivision = #1/8
  c32[ c c c c c c c]

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

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

  % Set maximum beam subdivision interval to 1/64 to limit subdivision depth,
  % despite not being metrically correct
  \once \set beamMinimumSubdivision = #1/32
  \once \set beamMaximumSubdivision = #1/64
  [ \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

Context properties control the grouping of beats within a measure: beatStructure lists the length of each beat in units of beatBase. Default values are established in scm/time-signature-settings.scm. These properties may be changed particularly with \set.

Alternatively, \time optionally accepts a beat structure to use instead of the default. \time applies to the Timing context, so it does not reset values of properties that are set in 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. For the 4/4 measure you have to explicitly set beatBase to eighths so that the bar’s irregular pattern gets displayed.

\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 |
    \time 3,3,2 4/4
    \set Timing.beatBase = #1/8
    f4 d8 f4 d8 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.beatBase = #1/8
  \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.beatBase = #1/8
    \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              % beatBase
      1,5               % beatStructure
      #'()              % beamExceptions
    \time 3/4
    \repeat unfold 6 { a'8 }
  }
  \new Staff {
    \time 3/4
    \repeat unfold 6 { a'8 }
  }
>>

2.4.3 Manual beams

In some cases it may be necessary to override the automatic beaming algorithm. For example, the auto-beamer will not put beams over rests or bar lines, 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 [ and ].

\relative { r4 r8[ g' a r] r g[ | a] r }

Beaming direction can be set manually using direction indicators:

\relative { c''8^[ d e] c,_[ d e f g] }

Individual notes may be marked with \noBeam to prevent them from being beamed:

\relative {
  \time 2/4
  c''8 c\noBeam c c
}

Grace note beams and normal note beams can occur simultaneously. Unbeamed grace notes are not put into normal note beams.

\relative {
  c''4 d8[
  \grace { e32 d c d }
  e8] e[ e
  \grace { f16 }
  e8 e]
}

Even more strict manual control with the beams can be achieved by setting the properties stemLeftBeamCount and stemRightBeamCount. They specify the number of beams to draw on the left and right side, respectively, of the next note. If either property is set, its value will be used only once, and then it is erased. In this example, the last f is printed with only one beam on the left side, i.e., the eighth-note beam of the group as a whole.

\relative a' {
  a8[ r16 f g a]
  a8[ r16
  \set stemLeftBeamCount = 2
  \set stemRightBeamCount = 1
  f16
  \set stemLeftBeamCount = 1
  g16 a]
}

Predefined commands

\noBeam.

Selected Snippets

Beam nibs

Beam nibs at the start and end of beams together with beams attached to solitary notes that look like flat flags are possible with a combination of stemLeftBeamCount, stemRightBeamCount, and paired [] beam indicators.

For imitating right-pointing flat flags on lone notes, use paired [] beam indicators and set stemLeftBeamCount to zero. For imitating left-pointing flat flags on lone notes, set stemRightBeamCount to zero instead (line one).

For right-pointing nibs at the end of a run of beamed notes, set stemRightBeamCount to a positive value. For left-pointing nibs at the start of a run of beamed notes, set stemLeftBeamCount instead (line two).

Sometimes it may make sense for a lone note surrounded by rests to carry both a left- and right-pointing nib. Do this with paired [] beam indicators alone (line three).

Note that \set stemLeftBeamCount is always equivalent to \once \set. In other words, the beam count settings are not “sticky”, so the pair of nibs attached to the lone 16th note in the last example has nothing to do with the \set command for the beam before.

\score {
  <<
    \new RhythmicStaff {
      \set stemLeftBeamCount = 0
      c16[] r8.
      r8.
      \set stemRightBeamCount = 0
      16[]
    }
    \new RhythmicStaff {
      16 16
      \set stemRightBeamCount = 2
      16 r r
      \set stemLeftBeamCount = 2
      16 16 16
    }
    \new RhythmicStaff {
      16 16
      \set stemRightBeamCount = 2
      16 r16
      16[] r16
      \set stemLeftBeamCount = 2
      16 16
    }
  >>
}

Using alternative flag styles

Alternative shapes for flags on eighth and shorter notes can be displayed by overriding the stencil property of Flag. LilyPond provides the following functions: modern-straight-flag, old-straight-flag, and flat-flag. Use \revert to restore the default shape.

To get stacked (i.e., vertically more compact) flags, call the command \flagStyleStacked, which can be reset with \flagStyleDefault.

Overriding the Flag stencil does not change how flag elements are positioned vertically. This is especially noticeable for flat flags: LilyPond doesn’t dynamically adjust the vertical gaps between flag elements in the same way as it does for beams. A possible solution to harmonize the appearance is to replace flat flags with half beams, as shown in the second staff; however, this can’t be done automatically. In the code of this snippet, such half beams are entered with @ as a prefix, for example @c8.

Be aware that half beams are not Flag grobs. This means in particular that modifying Flag properties won’t have any effect on them (you have to use Beam properties instead), and properties for their associated Stem grob will also behave beam-like.

"@" =
#(define-music-function (music) (ly:music?)
  #{ \set stemLeftBeamCount = 0 $music [] #})

testnotes = {
  \autoBeamOff
  c8 d16 e''32 f64 \acciaccatura { g,,,8 } a128 b
}

\relative c' {
  \override TextScript.staff-padding = 6
  \time 1/4
    <>^"default" \testnotes
  \override Flag.stencil = #modern-straight-flag
    <>_"modern straight" \testnotes
  \override Flag.stencil = #old-straight-flag
    <>^"old straight" \testnotes
  \override Flag.stencil = #flat-flag
    <>_"flat" \testnotes
  \revert Flag.stencil

  \flagStyleStacked
    <>^"stacked" \testnotes
  \flagStyleDefault
    <>_"default" \testnotes
}

\relative c' {
  \time 3/4
  \override Flag.stencil = #flat-flag

  <>^"flat" c8 c[ c] d16 d[ d] e''32 e[ e] f64 f[ f]
    \acciaccatura { g,,,8 } a128 a[ a a a a]
  <>^"beam-like" @c8 c[ c] @d16 d[ d] @e''32 e[ e] @f64 f[ f]
    \acciaccatura { g,,,8 } @a128 a[ a a a a]
}

\layout {
  indent = 0
  \context {
    \Score
    \override NonMusicalPaperColumn.line-break-permission = ##f
  }
}

See also

Notation Reference: Direction and placement, Grace notes.

Snippets: Rhythms.

Internals Reference: Beam, BeamEvent, Beam_engraver, beam-interface, Stem_engraver.

2.4.4 Feathered beams

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 [ and ], and the beam feathering is turned on by specifying a direction to the Beam property 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 \featherDurations 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 one half as long 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.

\relative c' {
  \override Beam.grow-direction = #LEFT
  \featherDurations 2/1
  { c16[ c c c c c c c] }
  \override Beam.grow-direction = #RIGHT
  \featherDurations 2/3
  { c32[ d e f] }
  % revert to non-feathered beams
  \override Beam.grow-direction = #'()
  { g32[ a b c] }
}

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

Predefined commands

\featherDurations.

See also

Snippets: Rhythms.

Known issues and warnings

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

2.4.5 Slashed beams

Slashed beams are printed by using the special stencil procedure beam::slashed-stencil. The slash may be printed at the left or right side of the beam and is further customizable by overrides of the details subproperties over-beam-height, slash-slope, slash-side, slash-stem-fraction, slash-thickness, and slash-X-positions. Note that those subproperties negotiate with each other to get a pleasing output, i.e., changing one of them may have impact on others.

mus = \repeat unfold 4 a16

{
  \override TextScript.rotation = #'(15 1 0)
  \override Beam.stencil = #beam::slashed-stencil
  \mus
  <>^"slash-side" %% default: LEFT
  \once \override Beam.details.slash-side = #RIGHT
  \mus
  <>^"over-beam-height" %% default: 0.75
  \once \override Beam.details.over-beam-height = #1.5
  \mus
  <>^"slash-slope" %% default: 2
  \once \override Beam.details.slash-slope = #1.0
  \mus
  <>^"slash-stem-fraction" %% default: 0.3
  \once \override Beam.details.slash-stem-fraction = #0.6
  \mus
  <>^"slash-thickness" %% default: 0.1
  \once \override Beam.details.slash-thickness = #0.2
  \mus
  <>^"slash-X-positions" %% default: (-0.5 . 1)
  \once \override Beam.details.slash-X-positions = #'(-1 . 2)
  \mus
}