Re: Misleading autobeaming in 3/4

[Urs Liska]

Am 17.08.2011 07:15, schrieb Vaughan McAlley:
> Bertrand Bordage wrote:
> > Ok, I'll keep LilyPond's default beaming since it's the usual notation.
> > Thanks!
> > Bertrand
> No! Beam it how _you_ like. Otherwise it’s like using Times font just
> because it’s the Microsoft Word default :-) Just say you’re following
> Debussy...
>
> I ran into a similar problem recently with my first real-world use of
> Lilypond. The music is from Mozart’s La Clemenza di Tito, and I needed
> to follow Mozart’s beaming:
>
> \relative c' {
>      \key f \major
>      \time 3/8
>      \clef "bass"
>      c8^"Default beaming (correct)" (e16 c g e) | c'8 [(\grace { d16[
> c16 b c]} e16 c g e )] |
>      d'8\staccato c\staccato b\staccato c r r |
>
>      \autoBeamOff
>      \times 2/3  { d,16^"Manual beaming" [f a] }
>      \repeat unfold 2 { \times 2/3  { d,16 [f a] } }
>      \scaleDurations #'(2 . 3) {
>          g [ bes c] g [ bes c ] f, [ a c ] |
>          e, [ g c ] f, [ a c ] bes, [ d g ] |
>          c, [ e g ] c [ g e ] c [ bes g ] |
>          f [ a c ] f, [ a c ] f, [ a c ] |
>          f, [ bes d ] f [ d bes ] a [ c f ] |
>          c [ f a ] c, [ f a ] c, [ e g ] |
>      }
>      r32 f, [ a c ] f [ a c a ] f [ c a f ] |
>      r c [ e g ] c [ e g bes ] g [ e c bes ] |
>      r f [ a c ] f [ a c a ] f [ c a f ] |
>      r g [ b d ] g [ b d b ] g [ f d b ] |
>      r c, [ e g ] c [ e g e ] c [ g e c ] |
>      \autoBeamOn
>
>      \set Timing.beatStructure = #'(1 1 1)
>      \times 2/3 { d'16^"\set Timing.beatStructure doesn’t work" f a }
>      \times 2/3 { d,16 f a }
>      \times 2/3 { d,16 f a }
> }
>
> I now suspect \set Timing.beatStructure = #'(1 1 1) didn’t work
> because Lilypond considers the beat to be a dotted quarter.
No, you have to add " \set Timing.beamExceptions = #'()" to clear the 
default rules for the 3/8 time signature.
If you add this at the beginning you don't have to beam manually at all 
in your example:

Try out:

\relative c' {
    \key f \major
    \time 3/8
    \clef "bass"
    c8^"Default beaming (correct)" (e16 c g e) | c'8  (\grace { d16
c16 b c } e16 c g e )  |
    d'8\staccato c\staccato b\staccato c r r |

    \set Timing.beamExceptions = #'()
    \set Timing.beatStructure = #'(1 1 1)
    \times 2/3  { d,16^"Changed beaming"  f a  }
    \repeat unfold 2 { \times 2/3  { d,16  f a  } }
    \scaleDurations #'(2 . 3) {
        g   bes c  g   bes c   f,   a c   |
        e,   g c   f,   a c   bes,   d g   |
        c,   e g   c   g e   c   bes g   |
        f   a c   f,   a c   f,   a c   |
        f,   bes d   f   d bes   a   c f   |
        c   f a   c,   f a   c,   e g   |
    }
    r32 f,   a c   f   a c a   f   c a f   |
    r c   e g   c   e g bes   g   e c bes   |
    r f   a c   f   a c a   f   c a f   |
    r g   b d   g   b d b   g   f d b   |
    r c,   e g   c   e g e   c   g e c   |

    \times 2/3 { d'16^"\set Timing.beatStructure _does_ work" f a }
    \times 2/3 { d,16 f a }
    \times 2/3 { d,16 f a }
}

I admit I also find this chapter of the NR (1.2.4 Beams) somewhat 
confusing: If you're not already into the topic - and that's usually the 
state when starting ;-) - you don't really see what you're missing.
I encourage you to delve into it, try to understand it piece by piece 
while experimenting with small examples. I think it's definitely worth 
the labour.

Two more hints to make your life easier:

1)
You don't have to write out  the \times construct for every group.
Just surround the whole section by \times { } (as you did with the 
\scaleDurations section).
Before this you add
    \set tupletSpannerDuration = #'(ly:make-moment 1 8)
to tell Lilypond to print the brackets and numbers every 1/8th note.

2)
I'd suggest you don't use \scaleDurations here but rather triplets.
Because that's what you have here: triplets without numbers and 
brackets, not a scaled duration.
While it is perfectly valid what you wrote I'd suggest to keep it 
structurally simpler, which makes your code easier to understand (for 
example if you return to it next year). I'd use \scaleDuration only in 
more complex cases such as different tempos (e.g. 3/8 vs 4/8 in 
different staves).
With 1) you have come around the need to write out \times more than once.
But you will also want to add
    \override TupletBracket #'bracket-visibility = ##f
    \override TupletNumber #'stencil = ##f
While this is effectively slightly more text to type, it makes your code 
clearer in terms of structure, because you write what it actually means.

HTH
Urs
> Beam
> exceptions look quite Schemish and involving triplets would be beyond
> me. For the time signature engraver there is no difference between a
> "scherzo" 3/4 or 3/8 or one in three, but for musicians there is a
> difference and maybe it should be easy to specify at the beginning,
> something like:
>
> \time 3/8
> \setBeat 8 % ...or \setBeat 4.
Well, this is \set Timing.baseMoment, isn't it?
> Also nice would be something that parses manual beaming into beam exceptions:
>
> \specialBeaming { r32 f, [ a c ] f [ a c a ] f [ c a f ] | }
> r c [ e g ] c [ e g bes ] g [ e c bes ] |
> \EndSpecialBeaming
>
> Disclaimer: I’m making all of these comments free from any knowledge
> of Lilyponds internals :-)
>
> Vaughan
>
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