Re: Revised autobeam settings patch -- cleaned up debug comments (issue1667044)

[Carl Sorensen]

On 6/16/10 3:18 AM, "Trevor Daniels" <address@hidden> wrote:

> 
> 
> Carl.D.Sorensen wrote Tuesday, June 15, 2010 11:27 PM
> 
>> Description:
>> Revised autobeam settings patch -- cleaned up debug comments
>> in code and eliminated the irrelevant changes in
>> Documentation/snippets just due to running makelsr.py
>> 
>> Please review this at http://codereview.appspot.com/1667044/show
> 
> I've run a few examples through this new code and so
> far it all works extremely well.
> 
> One or two of the default beam settings might be
> improved (while you're changing the beaming, that is - I
> think the behaviour below is probably as in the current
> releases, not introduced in this patch).  The most
> important is illustrated by
> 
> \relative c' {
>   \time 3/4
>   % In 3/4 time never beam an odd number of 8th notes or two
>   % 8th notes in different beats
>   f8 f f f f f
>   f16 f f f f f f f f f f f
>   f32 f f f f f f f f f f f
>   f f f f f f f f f f f f
>   f4 r8 f f f     % incorrect!
>   f8 f~f f f f    % incorrect!
>   d'4. c8 b8. a16  % incorrect!
> }
> 

I accepted your statement of beaming rules, since I'm quite a novice at
beaming.  And I adjusted the the autobeaming code so it would work according
to your recommendations.

Today I've been studying books to see what the references say, because the
new rule I added caused a regression in 4/4 time.

I want to get some clarification.  If I understand your rules correctly, you
believe that 

f4 r8 f8[ f f]

would be incorrect beaming, and that instead it should be beamed

f4 r8 f8 f8[ f]

Ross, however (1970, page 92) shows the first pattern as "Another use of the
beam in 3/4 time", rather than as an incorrect use.

The algorithm I developed to resolve that problem led to the following inT

r8 f8 f8[ f] f8[ f f f]

where we previously had

r8 f8[ f f] f8[ f f f]

Ross (1970, page 91) shows the following as an acceptable beaming in 4/4

r8 f8[ f f] f4 f8[ f]

Which would imply the the previous beaming is correct.

The bottom line is that the new beaming rules solve the first and third
incorrect cases in your example above.  However, the price of doing that is
they split a previously acceptable beam in 4/4 time.

Let me summarize:

OLD                       NEW
3/4
f4 r8 f8[ f f]            f4 r8 f8 f8[ f]
f4. f8[ b8. a16]          f4. f8  b8.[ a16]

4/4
r8 f8[ f f] f8[ f f f]   r8 f8 f8[ f] f8[ f f f]

So are these beaming rules correct, or at least better than the old ones?

> I think here it would be better to break quaver beams
> every beat 

For measures consisting entirely of quavers, beaming in 6 is far preferable,
in my opinion (and we've had this discussion before; we decided that staying
in 6 was best).

Thanks,

Carl