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Chord.Parse stacks the natural 9th/11th under an altered one: "C13#11" sounds both F and F#, "C13b9" both Db and D #341
Description
What's wrong
In Chord.ApplyExtensions (Semantics.Music/Chord.cs:437-444), the 13 branch always adds Nine | Eleven | Thirteen and the 11 branch always adds Nine | Eleven. Only the bare 9 branch (:445-451) skips Nine when FlatNine or SharpNine is already set. So an altered tension is added next to its natural version instead of replacing it.
Failure scenario
Probe output against HEAD:
| Input | Tensions | Tones | Problem |
|---|---|---|---|
C13b9 |
FlatNine, Nine, Eleven, Thirteen |
[0,4,7,10,13,14,17,21] |
Db and D |
C13#11 |
… | […,17,18,…] |
F and F# |
C13#9 |
… | […,14,15,…] |
D and D# |
C11b9 |
… | […,13,14,…] |
Db and D |
Anything built on ChordTones inherits the extra notes, Voice() included, so a voicing plays a minor second cluster the symbol never asked for.
The round-trip corpus doesn't catch this because the wrong chord round-trips: C13b9 prints C713b9, which reparses to the same wrong set.
Suggested fix
Apply the rule the 9 branch already uses:
- In the
13and11branches, addNineonly when neitherFlatNinenorSharpNineis set. - Add
Elevenonly whenSharpElevenis not set.
Acceptance criteria
- Tone assertions for
C13b9,C13#9,C13#11,C11b9and a combined one such asC13b9#11contain the altered tension and not the natural one. - Existing
C13,C11andC9tone assertions are unchanged.
Activity
matt-edmondson commentedon Sep 30, 2026
Triage
Semantics.Music,Chord.ApplyExtensions.DetermineQuality), and Chord.ToString() writes an altered tension straight after the root: "C(#11)" prints as "C#11" and reparses as a C# dominant eleventh #336 coversToStringof altered tensions. Consider one Chord-parser PR for Chord.ToString() writes an altered tension straight after the root: "C(#11)" prints as "C#11" and reparses as a C# dominant eleventh #336, Chord.Parse reads "Cm7#5", "Cm#5" and "Cm+" as augmented chords with a major third (Cm7#5 comes back as Caug7) #340 and Chord.Parse stacks the natural 9th/11th under an altered one: "C13#11" sounds both F and F#, "C13b9" both Db and D #341. Not a duplicate.Generated by Claude Code
matt-edmondson commentedon Sep 30, 2026
Covered by #360, which redesigns this bug cluster as a whole. Implement it through that issue rather than individually.
Generated by Claude Code
[minor] Redesign chord symbols; fixes #300, #322, #336, #340, #341, #344