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<a name="Feathered-beams"></a>
Previous: <a rel="previous" accesskey="p" href="Manual-beams.html#Manual-beams">Manual beams</a>,
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<h5 class="subsubsection">1.2.4.4 Feathered beams</h5>
<p><a name="index-beams_002c-feathered-635"></a><a name="index-g_t_005cfeatherDurations-636"></a><a name="index-g_t_005cfeatherDurations-637"></a>
<p>TODO – this section relies on overrides. We need to either add
a predefined, move this to snippets (whole section), or violate
policy for this section.
<p>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>[</code> and
<code>]</code>, and the beam feathering is turned on by specifying a
direction to the <code>Beam</code> property <code>grow-direction</code>.
<p>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</code> command which specifies the ratio
between the durations of the first and last notes in the group.
<p>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.
<!-- TODO - eliminate "Talking through code" -->
<p>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.
<blockquote>
<pre class="verbatim">
\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] }
</pre>
<p>
<a href="../46/lily-dd902643.ly">
<img align="middle"
border="0" src="../46/lily-dd902643.png" alt="[image of music]">
</a>
</p>
</blockquote>
<p class="noindent">The spacing in the printed output represents the
note durations only approximately, but the midi output is exact.
<!-- TODO - resolve whether or not midi is capitalized - policy -->
<!-- decision needed -->
<p class="noindent">
<h5 class="subsubheading">Known issues and warnings</h5>
<p>The <code>\featherDurations</code> command only works with very short
music snippets, and when numbers in the fraction are small.
<p class="noindent">
<h5 class="subsubheading">See also</h5>
<p class="indent">
<p>Snippets:
<a href="../../../input/lsr/lilypond-snippets/Rhythms.html#Rhythms">Rhythms</a>.
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