Re: Limitation with beat grouping

[Hans Aberg]

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.

  Hans