Re: Autobeaming

[Hans Aberg]

On 29 Dec 2009, at 22:00, Carl Sorensen wrote:

> > > Does this seem like a feasible architecture?
> >
> > I think a system that determines the [meter] from the time signature
> > is fundamentally flawed. I think in terms of a \meter that can be  
> > used
> > to define the beaming structure. I substructure of that is summed up,
> > and written as a time signature. If one has defined a set of such  
> > time
> > signatures, then one can use that for a lookup.
>
> I believe that is what I am proposing.  Instead of trying to calculate
> beatLength and measureGrouping from the time signature, we set them,  
> along
> with intended beamGrouping.  That way, the meter is determined by  
> the user,
> rather than inferred by the code.

I find the current LilyPond structure hard to cope with when wanting  
subbeaming. Also, some beaming wanted for that was discussed on the  
LilyPond lists in the past breaks the simple idea of beaming  
expressing a hierarchy of metric accents - though I do not want  
anything that. My interpretation of it is like this, though I found it  
hard to express formally:

The smallest units is "in one", where one only has a time segment  
which should be beamed as much as possible - on the time level  
subdivision it expresses.

Then one can repeat that either equally by an integer multiple or a  
"+". For example, 6/8 calls for a "in one" 3+3 division of the time  
unit which is the 1/8th note, which at the same time is the same as 2  
times the dotted 1/4th note. So doing some pseudocode, it might be  
written
  (3+3) x 1/8
or
  2 x 3/8 = 2 x 1/4. (dotted 1/4th)

However, in the first one, the 3's should be "in one", and not be  
beamed as "in three", expressing metric subaccents. So perhaps one  
needs to distinguish between these two types of integers, say write  
"in one" as 3'. Then the first one should be written
  (3'+3') x 1/8

Then take a time signature like 4/4. It has i fact two common  
interpretations:
  (2'+2') x 1/4
  4 x 1/4

Now one might also use tuplets tied to the metric. For example, in  
Macedonian 7/16, one may normally play as
  (3'+(2'+2')) x 1/16
But one may shift to using quadruplets on the 3s divided as 2'+2',  
which one might want to express in the subbeaming. So one might want a  
second rule like
  (3:4 (2'+2') + (2'+2')) x 1/16
So the \meter should have a sequence of such rules.

When writing a time signature, some may want to just adding it all in  
one number, and other want to write a "+", Bartok style. That might be  
described by replacing some of the (..) with [..] on one of the rules.  
For example
  [3'+(2'+2')] x 1/16
would be written as
   7
  16
But there is a problem already here, as one might want to writ it as
  3+2+2
   16
even though the beaming is (3'+(2'+2')). Writing
  [3'+[2'+2']] x 1/16
would strictly speaking lead to a time signature
  3+(2+2)
    16
though it is probably uncommon to have (..) in the time signature.

I think some may then want to write a different time signature than  
what is strictly implied by the beaming.

Together with the defined has defined a \meter structure, one needs to  
also specify how it should be rendered. On the top level, it might  
express a meter change between measures, using various dotted bars  
":", then comes space break, and after that some subbeaming.

So that is roughly how I think about it. - LilyPond has some of it,  
but I think cannot express that hierarchy properly in a suitable human  
interface.

  Hans