Semitone

Semitones (also called half steps or half tones) constitute the category of intervals with the smallest size commonly used in Western music, and are among the most dissonant when sounded harmonically. The term refers to the interval between two adjacent notes in a 12-tone scale (or half of a whole step), visually seen on a keyboard as the distance between two adjacent keys. For example, C is adjacent to D♭; the interval between them is a semitone. In a 12-note approximately equally divided scale, an appropriate number of semitones can realize a certain interval (e.g. a whole tone or major second is 2 semitones wide, a major third 4 semitones, and a perfect fifth 7 semitones). In music theory, a distinction is made between a diatonic semitone, or minor second (an interval encompassing two different staff positions, e.g. from C to D♭) and a chromatic semitone or augmented unison (an interval between two notes at the same staff position, e.g. from C to C♯). These are enharmonically equivalent only if twelve-tone equal temperament is used; for example, they are not the same size in Pythagorean tuning, where the diatonic semitone is distinguished from the larger chromatic semitone (augmented unison), or in quarter-comma meantone temperament, where the diatonic semitone is larger instead (see: Interval (music) § Number, for more on interval terminology). In twelve-tone equal temperament, all semitones are equal in size (100 cents). In other tuning systems, "semitone" refers to a family of intervals that may vary both in size and name (see: § Semitones in different tunings, for more). The condition of having semitones is called hemitonia; that of having no semitones is anhemitonia. A musical scale or chord containing semitones is called hemitonic; one without semitones is anhemitonic.