Keenan Pepper wrote in another thread:
> We should definitely try to get some provision for non-12-equal music
> into the ABC 2.0 standard. In my opinion, the specification of the
> format is more important than the implementation in any particular
> program like abc2midi.
So, here are my 2 cents.
-----
We have, so far:
ABC-2.0
- Only the common accidentals: ^^ ^ = _ __
abcm2ps, jcabc2ps, abc2midi, abcp
- Quartertone accidentals: ^/ _/
abcm2ps, abc2midi, abcp
- Generalized 12-ET semitone divisions: ^1/2 ^3/56 _14/97
- Accidentals with somewhat unclear meaning: __/ ^^/ ^^3/4
abcm2ps (graphical score is not limited to accidental meaning)
- Can use accidentals =m/n like in =3/4c (obscure meaning)
- Accidental ratios have no relation with the audible effect
abcp
- Quartertones can be abbreviated with: ^' ^, _' _,
(BTW, the abcp syntax description is cunfosing)
=====
Then, a basic problem is:
-- How to relate the accidental ratios to the corresponding pitch offset
in a way which can be independent to the 12ET semitones?
For instance, one could use, for 31ET, accidentals like:
(a) ^1/31 ^2/31 ^3/31 ... (to refer to the ET and can use several ones)
(b) ^1/5 ^2/5 ^3/5 ... (a whole tone corresponds to 5 degrees of 31ET)
(c) ^1/ ^2/ ^3/ ... (a compact notation, for manual input)
(d) ^1 ^2 ^3 ... (an even simpler notation, unsupported today)
All the above except (d) can be perfectly used with abcm2ps, because it
only generates graphical scores, not an audio/midi file. But the ratios
above have different meanings for a midi converter like abc2midi.
=====
SUGGESTION:
Premises to maintain ABC syntax consistency:
- Pitches can be only letters a-g and A-G (plus accidentals and octave
indications)
- A microtonal accidental is an ordinal accidental from ^^ ^ _ __
followed by a ratio, as described above (abcm2ps model).
- Derivations of ^^, __ and even = can be used, but some reflexion is
needed to set the precise meaning of the derivated accidentals. By now,
*reserve them* for future definition. (Someone can suggest a definition
just now, of course.)
- Other representations like scale degree number or ASCII versions of
Sagittal accidentals cannot be used in a pure ABC file. One can always
use a perl/ed script or a preprocessor (like abcpp) to convert them to
valid ABC code.
-----
For an equal tempered scale, one can:
- Define the tuning for the base pitches C D E F G A B (pitches C and c
are equivalent mod N, but N doesn't have to be the 2/1 octave);
- Define the number of steps included in a whole tone (C to D); the
number of steps involved in a specific accidental can be represented by
its ratio numerator.
- Assing a numerical identifier to the scale: the denominator of
accidental ratios.
All operations above should be done inside %%pseudo-comments or
I:commands (or [I:command]s).
Then, we can obtain a notation like this, for 3 steps in a whole tone
(e.g. 19ET), and using the ratio numerator for the steps:
=C ^1/C ^2/C =D _1/ _2/D =C
To use several scales simultaneously, one can use the denominator as a
scale identifier (note that derivations of = have a meaning here):
=/19C ^3/24C ^2/48C ^2/31C
Therefore, a default scale has to be set for a section/voice of music.
(BTW, abcm2ps default denominator is 2 in ^/ or ^3/ accidentals.)
-----
Problems
- A problem with the suggestion above is that it is not compatible with
occasional intonation changes, or re-divisions of the current scale,
like in the current abc2midi implementation. They should be represented
using floats in the numerator part (e.g ^0.5/19C), but I am fear this
rather complex notation can be prone to syntax inconsistencies and
ambiguities. (What do you think of that?)
- Irregular scales are not well defined with that generic proposal. Each
scale degree should be explicitly defined, e.g.: =C is 1/1, ^1/C is 60
cents above, ^2/C is 126 cents above, =D is 188 cents above and so on.
- The definition of the accidental glyphs is package dependent: abcm2ps
uses special (user-defined) postscript operators, but what about other
software pieces? How to use special fonts (for instance) in a portable way?
- The suggestion is somewhat complex (perhaps too complicated?).
Cheers,
Hudson
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