Re: autobeams

[Trevor Daniels]

Jonathan Kulp wrote Thursday, August 14, 2008 5:50 AM

> I had a similar problem with an example I was working on for GDP 
> Rhythms, in Notation Reference 1.2.6.2.  If you look at that example, 
> you can see that there's a whole series of 8ths that ought to be 
> autobeamed but are not.  I couldn't even make them beam properly 
> manually.  I ended up sidestepping the issue and removing the extra 
> voice, since that example is only meant to show how to make another part 
> in a different staff begin at the right place after a cadenza.   I don't 
> know why the author of it introduced the complexity of multiple voices 
> in that context.
>
> Regarding your example, there were two ways I could get it to beam those 
> last two 8ths automatically. One was to move the C in the final chord of 
> the bar to the upper voice and allow the multiple-voice passage to last 
> for the entire bar, rather than for only the first three beats.  Here:
>
> \version "2.11.55"
> \relative { \clef bass << {e8 d d c d8 c c4 } \\ {  <c g>4 g <b f>4 <f 
> a> } >>  }
>
> This makes the beaming work, and all the notes are the same, but it does 
> not preserve the original intent of having the final chord <f a c> all 
> in the lower voice.   I'm sure you found that you could manually beam 
> the "d8[ c]" but it doesn't seem like you should have to.
>
> The other way was to leave the <f a c> chord intact in the lower voice, 
> but put it inside the multi-voice << >> and add a quarter-note skip to 
> the upper voice:
>
> \version "2.11.55"
> \relative { \clef bass << {e8 d d c d8 c s4 } \\ {  <c g>4 g <b f>4 <f a 
> c> } >>  }
>
> This does seem like a workaround, though, as it looks like something 
> that ought to work exactly the way you had it the first time.  Anyone 
> else see what the problem could be?

I think the problem is this.  The autobeaming rules define
where beams should start and end, but mainly where they
should end.  The rules are defined in scm/auto-beam.scm
and are applied in a Voice context.  In common time, eighth 
note beams end only on half-note boundaries.  Autobeaming 
only kicks in when one of the defined end-points is reached, 
and in these examples the voice is terminated before the 
next half-note boundary is reached.  The common feature in
the 'workarounds' is to add notes or spacers so that one
of the defined beam end-points is reached before the voice
terminates.

This seems to be a drawback of inserting short parallel
voices which probably merits a mention in the docs (that's 
why I'm answering, Graham :)

I would use your first solution, Jonathan, and simply
insert a \stemDown:

\relative c' {
 \clef bass 
 <<
   { e8 d d c d8 c \stemDown <f,, a c>4 }
 \\
   { <c' g>4 g <b f>4 }
 >>
}

Trevor


> Best,
>
> Jonathan
>
> James E. Bailey wrote:
> > I don't understand this. Why aren't the last two eighth notes beamed 
> > together?
> > \version "2.11.54"
> > \relative { \clef bass << {e8 d d c d8 c } \\ {  <c g>4 g <b f>4} >> <f 
> > a c> } 
> >
> >
> > _______________________________________________
> > lilypond-user mailing list
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>
> --
> Jonathan Kulp
> http://www.jonathankulp.com
>
>
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