FA-80992 / Music interval and transposition theory / Member archive

Key signature and measure accidental resolution: natural sign falls back to the key signature · case 02

In G major, F4 after an explicit natural plays F#4 again because the natural mark (zero) is treated as absent.

Member previewVariant 2 · 3 implementations · 8 checks per implementation

Case contract

Input [fifths, tokens]. fifths -7..7 gives signature sharps on F C G D A E B or flats on B E A D G C F. Tokens are "|" (barline) or letter + optional sign (# b x bb n) + single-digit octave. An explicit sign sets the alteration for that letter in that octave until the next barline (n = 0 cancels the signature); otherwise the signature applies. Return the MIDI numbers (C4 = 60) or None if any token or the signature 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 0	`[70, 70, 70, 70]`	`[70, 71, 71, 70]`	Failed

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