Hi, all!
Although I am not an expert regarding chords notation and have
my knowledge merely from talking with musicians and studying a few
scores, I would like to contribute to this discussion, even if the
following may be wrong (end of disclaimer :-)).
1. Although I already heard someone call "Co" as "C Null" (indicating
the number zero), the "o" symbolizes AFAIK a circle:
In <c es ges beses> you have minor thirds stacked upon each other;
the next note after beses would be deses which sounds like c and
hence closes the circle. In fact, I think <c es ges a> or
<c dis fis a> or <c es fis a> could also be regarded as "Co" (but
also as "Ao" or "D#o" or "F#o", respectively), because they all
represent the same concept of stacked minor thirds, regardless of
the actual note names. To avoid ambiguity, I would suggest to take
the note name of the lowest pitch in the chord by default and
append the "o" to it.
A chord like Co may be used for modulation, e.g.:
<c g c' e'> <c ges beses c' es'> <c ges a c' es'> <a, e a cis e>
C Co Ao A
(Probably, there are better examples, but I've just no piano here
to find a better one...)
Here, Co and Ao sound equal, hence, you may leave out the Ao and
just note "C Co A". And therefore, you get Co for <c ges a c' es'>.
N.B.: If you take an Ab7(b9), indicating <as c es ges beses>, and
if you do not play the bass tone as (in German "verkuerzt",
indicated by a slash that is printed across the "Ab"), you also get
a Co.
2. From reading scores with both, fully notated chords and the
corresponding chord names on top of them, I get the impression that
chord names are chosen for easy playing rather than for explaining
harmonics. For example, in a piece ("black orpheus", first half of
second bar) I found (if I remember right) a Bm7(b5), hence
indicating <b d' f' a'>. In fact, harmonically seen, it should
rather be Dm6+ (or whatever you prefer to denote D minor with added
major 6th) with the 6th as bass note (but then they could have
used "Dm/B" instead? Arrgh!).
3. In Jazz arrangements, I repeatedly found that the chord names over
the piano staff only indicate a subset of the chord notes that were
notated in the piano staff itself. From that, I guess, the idea is:
"Look at the chord names. They tell you the notes that should
appear in your chord. But you may play additional notes to make
your chord sound fancier." Mmmh. Perhaps, seen reversely, if
lilypond detects a chord with weird adds, it should just drop them
and only regard the "important" notes of the chord? But what are
important notes and how could you determine them? You probably would
have to make a harmonic analysis which, I think, is beyond the scope
of lilypond as a type setting system... Again arrgh!
BTW., Jan, the correct spelling is "vermindert", not "verminderd" :-),
and "augmented" translates to "uebermaessig" (does Banter not use
"Cueberm"?).
Just a few thoughts...
Bye,
Juergen
