I'm attempting to improve the very brief description
of feathered beams in the GDP Notation Reference.
Could those of you more knowledgeable than I am please
check the following draft and either correct or confirm
it. Thanks.
Trevor D
"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. Within the group
the
tempo accelerates (or decelerates) then returns to the
original
tempo. Such figures may be printed by setting the
'grow-direction' property of a beam and specifying
a fraction which indicates the ratio of the duration of the
first note of the group to the last. This fraction is
supplied
to the \featherDurations music function which operates on
the
following short music expression to adjust the durations of
the
notes. The beam extent must be indicated manually using [
and ].
The spacing in the printed output represents the note
lengths
only approximately, but the midi output is exact.
"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."
\paper {
ragged-right = ##t
}
\relative c' {
\override Beam #'grow-direction = #LEFT
\featherDurations #(ly:make-moment 2 1)
{ c16[ c c c c c c c] }
}
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