FA-80900 / Music interval and transposition theory / Member archive
Interval quality and number naming: letter position taken from the sounding octave · case 05
Intervals from B#3 are measured as if the B were in octave 4, so B#3 to C4 is rejected as descending.
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 fixtureThis sample comes from the broken implementation of a controlled reproducer.
| Boundary fixture | Actual | Expected | Outcome |
|---|---|---|---|
| oracle 0 | null | "d2" | Failed |
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