FA-81018 / Music interval and transposition theory / Member archive

Modal scale spelling from a tonic: steps taken from letter position not scale position · case 03

Non-ionian modes come out as the major scale of the tonic because the pitch advance follows the letter names.

Member previewVariant 3 · 3 implementations · 8 checks per implementation

Case contract

Input [tonic, mode]: tonic is a letter plus optional accidental from "", #, b, x, bb; mode is one of the seven church modes ionian..locrian. The step pattern is the major pattern 2 2 1 2 2 2 1 rotated left by the mode index. Each degree uses the next letter; its alteration is the pitch-class difference from the natural letter folded into -6..5. Return the seven names, or None if any alteration exceeds two or input is invalid.

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 4	`["C", "D", "E", "F", "G", "A", "B"]`	`["C", "D", "Eb", "F", "G", "A", "Bb"]`	Failed

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