Hans Aberg wrote Monday, March 23, 2009 8:47 AM
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?
See my later note
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.
If this is the accepted standard then there is no
problem with LilyPond as it stands. Either of these
two patterns can be specified by overriding the
current beam-ending rules. What can't be done is to
mix the two stress patterns depending on beam duration.
Trevor
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