FA-80913 / Music interval and transposition theory / Member archive

Interval quality and number naming: descent judged by sound instead of letters · case 03

B#3 to Cb4 (letters ascend, pitch descends) is rejected, while C4 to B#3 slips through and produces a bogus label.

Member previewVariant 3 · 3 implementations · 8 checks per implementation

Case contract

Input [lower, upper] spelled pitches (letter, # or b accidentals, nonnegative octave). The generic number counts letter steps plus 7 per spelled octave plus one; quality compares the semitone span with the major/perfect reference (compounds add 12 per octave). Perfect class for simple numbers 1, 4, 5: P, A, d, AA, dd; others: M, m, A, d, AA, dd. Descending letter order or unrepresentable quality returns None.

Why this case matters

Pitch spelling and interval arithmetic decide the notes that notation, transposition and analysis tools display or play.

One recorded failure

Sample boundary fixture

This sample comes from the broken implementation of a controlled reproducer.

Boundary fixture	Actual	Expected	Outcome
oracle 6	`"A0"`	`null`	Failed

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