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A semitone, also called a half step or a half tone, is the smallest musical interval commonly used in Western tonal music, and it is considered the most dissonant when sounded harmonically. It is defined as the interval between two adjacent notes in a 12-tone scale (e.g. from C to C â¯).9-tone equal temperament distinguishes between the chromatic and diatonic semitones; in this tuning, the chromatic semitone is one step of the scale (play 63.2 cents (helpÂ·info)), and the diatonic semitone is two (play 126.3 cents (helpÂ·info)).
Definition: A semitone is the smallest musical interval in modern Western music (or, the smallest distance between notes in the chromatic and diatonic scales*). There are two semitones in one whole tone.* A semitone is always a half step; however, it can be called either diatonic or chromatic 1  : Diatonic semitones affect two different note-names; the distance between F and G-flat (pictured) is a diatonic semitone.2  Chromatic semitones name the same note; the distance between A and A-sharp. A semitone is always a half step; however, it can be called either diatonic or chromatic 1  : Diatonic semitones affect two different note-names; the distance between F and G-flat (pictured) is a diatonic semitone.