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Re: Limitation with beat grouping

From: Hans Aberg
Subject: Re: Limitation with beat grouping
Date: Mon, 23 Mar 2009 09:47:22 +0100

On 23 Mar 2009, at 01:54, Cameron Horsburgh wrote:

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.

Hindemith, "Elementary Training", p. 18, says that the one you want is more frequent, and that the one LilyPond wants is less frequent though possible. He gives a rule (4) that the two halves of the measure must be recognizable.

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 am not sure what you mean here. Can you give an example?

The problem, as I see it, is tied to the metric interpretation of 4/4, which is ambiguous: it can be taken as a strong beat (metric accent) on 1 followed by weaker on 2, 3 and 4. Alternatively, 3 can be accented more than 2 and 4, but less that 1:
      |   |   |   |
  4a  >   -   -   -
  4b  >   -  (>)  -

Then 4a gets the beaming with the 1/4 note groups together and the second gets the beaming with the 1/2 note groups together.


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