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## Re: Limitation with beat grouping

 From: Cameron Horsburgh Subject: Re: Limitation with beat grouping Date: Tue, 24 Mar 2009 08:58:13 +1100 User-agent: Mutt/1.5.18 (2008-05-17)

```On Mon, Mar 23, 2009 at 02:56:48PM +0100, Hans Aberg wrote:
> On 23 Mar 2009, at 11:50, Cameron Horsburgh wrote:
>
>>> 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.
>>>
>>
>> I'm not sure that's relevant---the behaviour happens regardless of
>> whether it starts on beat one or beat three.
>>
>> The problem is that there is no way to tell the beamer to look forward
>> an arbitrary number of notes when deciding whether to beam or not. In
>> this case, the presence of a beam between the second and third notess
>> in the group is entirely contingemt on the presence of a fourth *and
>> fifth* note. If that fifth note exists, there shouldn't be a beam.
>>
>> This is what Trevor means: when the beamer realises there is a fifth
>> note in the group (i.e. it's not four straight quavers) it needs to
>> 'backtrack' and remove the beam between notes two and three.
>>
>> Or have I mnisunderstood you?
>
> See my other post. The normal way to beam is to select a meter,
> including metric accents and subaccents, thus building a hierarchical
> structures of subpatterns, and then let the beaming follow that. Though
> traditionally, one may not adhere to that very strictly, and more than
> one patten may be used, but perhaps not the same engraver in the same
> piece and meter.
>
> Now, 4/4 is an exception to that in the higher number of such patterns
> that can be used. If one then wants to automate what traditionally is
> merely an ad hoc choice, then the problem is to lay down rules for that
> so that a computer program can do it.

And there's the limitation--there's no way to automate this
currently. Currently I have to do it all manually. Not a big job, but
given this is a reasonably common exception LilyPond should provide a
way to do it automatically.

I've also just noticed another thing: the figure

a8 a16 a16 a8 a16 a6

is rendered

a8[ a16 a16] a8[ a16 a6]

which is my preferred option. In fact, I would prefer everything to be
broken to one beat groups *except* for the special case of four
quavers which can appear as one group. It might be easier to write a
rule for that and manually beam the four quaver figure which is far
less common in my score.

>
>   Hans
>
>
>

--

Cameron Horsburgh

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

```