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Use better heuristics for chord pitch naming.

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Previously we used a heuristic for choosing pitch names based on the
major scale degree, minimizing radicals. So, for example, in the key of
Gb, we render the 4 as Cb rather than B because Bb is the 3 of Gb. In
other words, we want 1:Gb, 2:Ab, 3:Bb, 4:Cb instead of re-using B. This
is standard practice in western music notation.

When rendering non-diatonic notes we prefered choosing the version that
minimized the radicals. Again in the key of Gb we would choose to render
E as E (the #6) rather than considering it as Fb (the b7) and choose to
render D as D (the #5) rather than E𝄫 (the b6). This was chosen to
reduce the number of unusual radicals like 𝄫.

However, in practice this leads to unusual charts because it is more
common when writing chordal harmony to use the b6 rather than the #5.
Similarly the b7 is far more common than the #6. This is, I think, due
to the prevalence of the major scale and minor scales and the fact that
the minor scale is built from flatting the 3, 6, and 7 of the major
scale. So when thinking in a key-center agnostic manner (like numbers)
we almost always think about these altered scale degrees as being
flatted relative to the major scale, not sharped. Because of this, in
the key of Gb, we would prefer to render a b6, b7, 1 chord walkup as
E𝄫, Fb, Gb rather than D, E, Gb.

This change redefines the heuristic used to name chord pitches to follow
a heuristic that covers all pitches in the octave based on scale degree:
1, b2, 2, b3, 3, 4, b5, 5, b6, 6, b7, 7
This commit is contained in:
Jonathan Bernard
2025-06-02 10:46:56 -05:00
parent d7dd509138
commit e242c1356e
1 changed files with 34 additions and 5 deletions
Download Patch File Download Diff File Expand all files Collapse all files

39
src/pco_chordspkg/ast.nim
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@ -87,14 +87,43 @@ func renderPitchInKey*(
var scaleNames: array[(ord(high(ChordChartPitch)) + 1), string]
if useSharps.isNone:
# If we aren't told to use sharps or flats, we render the diatonic pitches
# according to standard theory (C# in the key of D, Db in the key of Ab)
# but we render non-diatonic notes with flats (prefer the b6 and b7 over
# the #5 and #6).
#
# TODO: In the future, we should also remember the scale degree of the
# chord when parsing. So, for example, in the key of D we would parse Bb as
# the b6 and A# as the #5. The pitch would be the same, but the scale
# degree would differ. This would allow us to preserve intentional choices
# in the chart when transposing.
scaleNames = case key
of A, B, D, E, G:
["G#", "A", "A#", "B", "C", "C#", "D", "D#", "E", "F", "F#", "G"]
of Af, Bf, C, Df, Ef, F:
of C:
["A♭", "A", "B♭", "B", "C", "D♭", "D", "E♭", "E", "F", "G♭", "G"]
of G:
["A♭", "A", "B♭", "B", "C", "D♭", "D", "E♭", "E", "F", "F#", "G"]
of D:
["A♭", "A", "B♭", "B", "C", "C#", "D", "E♭", "E", "F", "F#", "G"]
of A:
["G#", "A", "B♭", "B", "C", "C#", "D", "E♭", "E", "F", "F#", "G"]
of E:
["G#", "A", "B♭", "B", "C", "C#", "D", "D#", "E", "F", "F#", "G"]
of B:
["G#", "A", "A#", "B", "C", "C#", "D", "D#", "E", "F", "F#", "G"]
of Gf:
["A♭", "B𝄫", "B♭", "C♭", "D𝄫", "D♭", "E𝄫", "E♭", "F♭", "F", "G♭", "A𝄫"]
of Df:
["A♭", "B𝄫", "B♭", "C♭", "C", "D♭", "E𝄫", "E♭", "F♭", "F", "G♭", "A𝄫"]
of Af:
["A♭", "B𝄫", "B♭", "C♭", "C", "D♭", "E𝄫", "E♭", "F♭", "F", "G♭", "G"]
of Ef:
["A♭", "B𝄫", "B♭", "C♭", "C", "D♭", "D", "E♭", "F♭", "F", "G♭", "G"]
of Bf:
["A♭", "A", "B♭", "C♭", "C", "D♭", "D", "E♭", "F♭", "F", "G♭", "G"]
of F:
["A♭", "A", "B♭", "C♭", "C", "D♭", "D", "E♭", "E", "F", "G♭", "G"]
elif useSharps.isSome and useSharps.get:
scaleNames = case key
of A, B, C, D, E, G:
@ -112,7 +141,7 @@ func renderPitchInKey*(
of F:
["G#", "G𝄪", "A#", "B", "B#", "C#", "C𝄪", "D#", "D𝄪", "E#", "F#", "F𝄪"]
else: # useSharps.isSome and not useSharps.get
else: # !useSharps (useSharps.isSome and not useSharps.get)
scaleNames = case key
of C, Af, Bf, Df, Ef, F:
["A♭", "A", "B♭", "B", "C", "D♭", "D", "E♭", "E", "F", "G♭", "G"]
@ -348,7 +377,7 @@ let NOTE_START_PAT = re"\{\{"
let NOTE_END_PAT = re"\}\}"
let SPACE_PAT = re"\s"
let CHORD_IN_LYRICS_PAT = re"(\w+)(\[.+)"
let CHORD_AND_LYRICS_PAT = re"^\[([^\]]+)\]([^\s\[]+)(.*)$"
let CHORD_AND_LYRICS_PAT = re"^\[([^\]]*)\]([^\s\[]+)(.*)$"
let BRACED_CHORD_PAT = re"^\[([^\]]+)\]$"
let NAKED_CHORDS_ONLY_PAT = re("^\\s*(" & CHORD_REGEX & "\\s*\\|*\\s*)+$")