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Help with Auto-beaming rules


From: Richard Shann
Subject: Help with Auto-beaming rules
Date: Tue, 08 Sep 2015 12:43:43 +0100

The attached bit of 18th century typesetting shows an 8.[ 32 32] beamed
group and a series of  32[ 32 32  32] beamed groups in a 2/4 time
signature. This is quite typical of the period and is IMHO more legible
than if the 1/32 notes were beamed in larger groups.
Can this be done by auto-beaming rules in LilyPond?
My attempt follows - I have created two bars beamed manually and
followed with two bars which I hope to auto-beam by feeding the first
two bars to  \beamExceptions.
8>< 8>< 8>< 8>< 8>< 8>< 8>< 8>< 8>< 8>< 8>< 8>< 8>< 8>< 8>< 8>< 8>< 8>< 

\version "2.19.5"
MvmntIVoiceI = {
         e''8.[ fis''32 g''] e''8.[ fis''32 g'']
         c'32[ d'32 e' f'] c'32[ d'32 e' f'] c'32[ d'32 e' f'] c'32[ d'32 e' f']
         c'32 d' e' f' c' d' e' f' c' d' e' f' c' d' e' f'
         e''8.( fis''32 g'') e''8.( fis''32 g'')

}
\layout {
    \overrideTimeSignatureSettings 2/4 1/4 #'(1 1) \beamExceptions { 8.[ 32 32] 
8.[ 32 32] |   
      32[ 32 32  32]  32[  32 32 32] 32[ 32 32 32] 32[ 32 32 32] }
}
\score {
 <<
   \new Staff  {\time 2/4  \MvmntIVoiceI } 
 >>
}

8>< 8>< 8>< 8>< 8>< 8>< 8>< 8>< 8>< 8>< 8>< 8>< 8>< 8>< 8>< 8>< 8>< 8>< 

This fails because although the 1/32 notes are beamed in four the dotted
1/8 is not beamed to the following two 1/32 notes.
It is not clear to me from the documentation on the page

http://lilypond.org/doc/v2.19/Documentation/notation/beams#setting-automatic-beam-behavior

whether this should have worked. The relevant rule seems to be

"if a beam-ending rule is defined in beamExceptions for the beam-type,
use it to determine the valid places where beams may end"

where "the beam-type is the duration of the shortest note in the beamed
group. "
The problem for me is that this is a circular definition. Until we know
what the beamed group will be we don't know what the beam type is, and
until we know that we can't apply the rule to decide what notes will be
beamed.

Be that as it may, I would like to be sure that this beaming cannot be
done with a single \overrideTimeSignatureSettings at the outermost
context, that is, that individual passages will need to be marked to
achieve the desired beaming.

Richard

Attachment: autobeam.png
Description: PNG image

Attachment: IrregularBeaming.ly
Description: Text Data


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