Accordion chords -- a refresher

[David Kastrup]

While we have work happening on chord names, let me mention an old
related issue:

<URL:http://code.google.com/p/lilypond/issues/detail?id=559>
Feature request: support accordion with standard bass

Now since I wrote that request, I have gathered considerable skills
concerning the input side of the problem.

The total picture is still missing enough details.

a) entry of alternating bass material is far too inconvenient when
   simple patterns are concerned (the usual oom-pah style of
   accompaniment is something like c <c' e' g'> g, <c' e' g'>).  I see
   two reasonably "nice" ways, probably both deserving implementation.
   First is very close to German notation: use uppercase letters for
   indicating bass notes, making this C c G, c on entry, or even C c G c
   depending on how much octave-wrapping is on.  The other is a "mixed
   mode" where you'd write c c:M g, c:M (namely having a special letter
   or just 5 for major mode chords, and usual note mode otherwise).
   That's closer to American Accordion Association and Russian notation.

b) chords need to go through a wringer.  Not just the octave wrap is
   something that needs to be taken care of (_after_ any transposition),
   but also major seventh chords and diminuished chords need to have
   their fifth removed by default, both in notation as well as in Midi
   while prospectively parallel written keyboard chords are kept intact.
   So one needs proper ways of messing with chords (and chord names)
   that can use different algorithms and names in different contexts.

c) in the AAA/Russian case, chords get reduced to base note and chord
   type (typeset as an articulation letter on a note/note head).

So maybe while the jazz chord name code is still warm, one can think
about how to deal with the additional requirements interesting for
accordion chord notation.

All the best

-- 
David Kastrup