Re: midstaff line = stem shortened?

[Carl Sorensen]

On 4/9/10 4:18 PM, "Mark Polesky" <address@hidden> wrote:

> Kieren MacMillan wrote:
>> Thanks for the in depth and very useful response -- sounds
>> like Lilypond is currently doing essentially the right
>> thing.
> 
> Actually, I don't think it is.  As Carl certainly
> demonstrated, the situation is complicated.  Ted Ross is by
> far the most detailed and specific, but he occasionally
> presents things in a confusing order.  I've attached a file
> in an attempt to clarify the issue.

Mark, thanks for putting this together.  I think this really helps us have
something to discuss.

I'm not sure what you mean by "Ted Ross optional". I'm guessing that's your
interpretation of how he would handle things as implemented in his
exceptions (Examples 1 and 2).

As I read Ross, the stem lengths I quoted before are for standalone stems. I
don't see any discussion of "optional" stem lengths.  Instead, I see
discussion of adjusting stem lengths in order to make sure that "the stem
ends rise and fall with their respective noteheads".  This is only a problem
when we have notes that differ by a half space and their stems also differ
by a half space, so that the stems would be even rather than rising and
falling with the notes.

In the paragraphs that follow, I'll assume we're in a treble clef, because
it's easier to say "b" than "note on the mid-staff line".

In your Ross standard line, there's a problem with the a to b to c going up
and the b to a to g going down.  In both cases, the stem ends are at the
same height, which is cause for an exception to the standard.

In your Ross optional line, you've fixed the problem between a and b going
up.  You've also fixed the problem between b and c going up.  But you've
created a problem between c and d (i.e., you've just moved the problem).
You've also fixed the problem with b to a going down, and by setting the c
going down to 3 1/4, you've avoided a problem at the c to b transition.  But
you've created a problem with the g to f transition.

As you correctly point out, LilyPond violates the Ross standard at c with
the up stem and b with the downstem.  That should probably be fixed.

I think your suggested compromise is a good suggestion, but that it should
be used not as a default stem length, but instead as a stem length
adjustment when the adjacent note is one that requires an adjustment (i.e.
shorten a with an upstem when it's adjacent to a b; lengthen c with an
upstem when it's adjacent to a b; shorten b with a downstem when it's
adjacent to an a; lengthen g with a downstem when it's adjacent to an a).

We already have code to adjust the horizontal spacing when we have
alternating stems, so there is some music adjustment based on adjacent
stems.  I'd prefer to see us make the adjustment only when necessary, rather
than as a general rule.  But I think it would be better to use the suggested
compromise than to stick with the current LilyPond behavior.

But remember, I'm probably the least accomplished musician in the LilyPond
community, so my arguments might not be worth anything.

Thanks,

Carl