Limitation with beat grouping

[Cameron Horsburgh]

Hi folks,

I've had a problem with some auto beaming, and after some discussion
on -user[1] I believe it's a limitation with LilyPond's autobeaming
mechanism. Here's my problem:

I am setting a piece in 4/4 that has many examples of the figure 

  a8 a a a16 a

beginning on either the first or third beats of the bar. The beaming
LilyPond gives me is

  a8[ a a a16 a]

when I would prefer 

  a[8 a] a[ a16 a]

I had a go at writing a rule to get this behaviour but there doesn't
sem to be any way of doing it. This was confirmed by Trevor Daniels in
the discussion on -user.

This raises two questions: first, what should the default beaming be
in this case? I don't see a lot of the one that LilyPond generates,
and I find it reasonably hard to sight-read. Most scores I see seem to
use the one I am trying to get.

Second, the autobeaming mechanism should allow this sort of
construct. The problem is that the beaming between the second and
third notes depends on the length of the fourth and fifth notes. Or,
to quote Trevor,

  You need some sort of back-tracking so that when the 16th notes were
  found the beaming was restarted using a different set of rules.

I imagine the first issue (if it is an issue) would depend on the
second issue being fixed, and I presume that would be a rather
difficult problem to solve. Still, if they are legitimate problems I
think they rate a mention in the bug tracker.

Cheers,



Footnotes: 
[1]  The discussion starts at 
http://www.mail-archive.com/address@hidden/msg46157.html

-- 

Cameron Horsburgh

Blog: http://spiritcry.wordpress.com/