Re: Reverting Beat Grouping Commands

[Trevor Daniels]

Carl D. Sorensen wrote Sunday, April 05, 2009 7:33 PM

> What if we scrapped the current auto-beam code completely, and 
> replaced it
> with a structured beatGrouping, something like
>
> ((denominator (ending-beatGroupings) (subdivide-beatGroupings))
>  (denominator2 (ending-beatGroupings) (subdivide-beatGroupings)))
>
> We might then have something like the following in 6/8 time:
>
> ((8 (3 3) ())
>  (16 (6 6) (6 6))
>  (32 (4 4 4 4 4 4) (8 8 8)))
>
> Then, if subdivideBeams  were set to #t, we could reduce the beam 
> count for
> a given level of beaming at the appropriate point.
>
> I don't know if this is a better solution, but it might improve 
> what
> currently seems to me to be a very awkward system.
>
> One weakness in this approach is that it provides no way to have 
> an
> auto-beam-ending rule for 3/32 beams (but I don't know of any 3/32 
> beams, so
> I don't think that's a real limitation).
>
> David Brobroff's request
> <http://thread.gmane.org/gmane.comp.gnu.lilypond.general/46316/focus=46323>
> could then be met by
>
> ((8 (4) ())
>  (16 (4 4) ())
>  (32 (8 8) (4 4 4 4)))
>
> This would have the downside of requiring a complete redefinition 
> every time
> you changed the time signature, but it would get rid of the 
> current problem
> where you have to revert rules before you can add new ones.  It 
> would also
> put all automatic definitions of autobeam rules in one location in 
> the
> source tree, rather than having them spread across two files.
>
> I don't know if this proposal has merit or not, but it seems like 
> we really
> ought to get to *some* combination of syntax and functionality 
> that we think
> really works.

It definitely has merit!  Let's see if I understand it.
The current (ie in 2.13.1) beam-ending rules are used
only to prevent long beamed runs of 16th and 32nd beams.
Your suggestion easily accommodates all these.  For example,
in 9/4 time there are 16 rules to do this.  These could be
replaced by the far simpler

\set beatGrouping =
 #'( 8 (3 3 3) ())
   (16 (4 4 4 4 4 4) ())
   (32 (8 8 8 8 8 8) ()))

or rather the equivalent in scm/music-functions.scm.  We
could even improve the default by using sub-divided beams,
something we can't do at present.

I can't see anything this can't do.  If by 3/32 beams you
mean beaming 32nd notes in threes, I think it can do this.
For example, in 9/4 you'd need to modify the above to

\set beatLength = #(ly:make-moment 1 32)
\set beatGrouping =
 #'( 8 (12 12 12) ())
   (16 (16 16 16 16 16 16) ())
   (32 (3 3 3 3 3 3 3 3 3 3 3 3) ()))

There was a discussion some time ago about auto-
beaming east-European rhythms.  See
http://lists.gnu.org/archive/html/lilypond-user/2007-12/msg00032.html
It's getting late now, so I'll leave this until tomorrow,
but I wonder if your scheme would handle this?

Trevor