Minor second

This article is about the musical interval. For the printing method see halftone.A semitone, or half-step is a musical interval. It is the smallest interval commonly used in Western music, and is considered the most dissonant. The most commonly written form of this interval is the minor second, notated using two adjacent letter names (e.g. C and D♭), but the augmented unison is also used, both notes having the same letter-name, with one of the notes being inflected by an accidental (e.g. C and C♯).
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