FA-81265 / Music interval and transposition theory / Member archive

Diatonic step transposition within a major key: notes below the tonic truncated toward zero · case 05

Notes a few steps below the tonic jump up an octave after transposition (B3 up two steps in C gives D5).

Member previewVariant 5 · 3 implementations · 8 checks per implementation

Case contract

Input [tonic, notes, steps] where tonic is a MIDI reference note. Each note must belong to the major scale on the tonic (else return None). Its scale position is its degree plus 7 per octave counted from the tonic note with floor division (notes below the tonic note are in negative octaves). Move by the signed number of steps and return the resulting MIDI notes.

Why this case matters

Harmonisers and sequence generators transpose melodies diatonically rather than chromatically.

One recorded failure

Sample boundary fixture

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

Boundary fixture	Actual	Expected	Outcome
oracle 0	`[74, 72]`	`[62, 60]`	Failed

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