SATB voice ranges (MIDI)

Each of the four chorale/species voices is kept within a comfortable pedagogical range — narrower than a real singer's full range — so student part-writing stays singable and each voice occupies a clearly distinct register: Soprano C4-A5 (MIDI 60-81), Alto G3-D5 (MIDI 55-74), Tenor C3-G4 (MIDI 48-67), Bass E2-C4 (MIDI 40-60). These match audit-satb-voices.cjs's own MIDI convention (`midi('C4')` = (4+1)*12 = 60) and standard college part-writing pedagogy ranges.

A chorale exercise's tenor voice written down to G2 (MIDI 43), below the 48 floor.

Kostka & Payne (Tonal Harmony) and Aldwell & Schachter (Harmony and Voice Leading) — standard college part-writing ranges. Gould's own vocal-range chapter gives broader SOLO-voice ranges (roughly Soprano C4-C6, Alto F3-F5, Tenor C3-C5, Bass E2-E4) intended for real singers in actual vocal writing, not classroom part-writing — Gould's ranges are the right authority for a future 'write a real vocal line' unit.

This rule can be decided from pitches, durations and voices — no layout required. A validator can check it before anything is drawn.