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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 } | }
Note: A beamExceptions
value must be complete
exceptions list. That is, every exception that should be applied
must be included in the setting. It is not possible to add, remove,
or change only one of the exceptions. While this may seem cumbersome,
it means that the current beaming settings need not be known in order
to specify a new beaming pattern.
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
andbeatStructure
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
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 } } >>
[ << Musical notation ] | [Top][Contents][Index] | [ Specialist notation >> ] |
[ < Automatic beams ] | [ Up : Beams ] | [ Manual beams > ] |