Chromatic scale

Chromatic scale: every key of one octave on the piano keyboard

In Western music, a chromatic scale (or twelve-tone scale) is a set of twelve pitches within an octave, where the interval between any two adjacent notes is a semitone.

If the scale is tuned such that the interval between any two adjacent notes may function both as a diatonic and chromatic semitone (as in the modern 12-tone equal temperament), it provides a practical approximation of acoustically pure intervals in every key, and serves as a superset containing subsets like diatonic scales.

Chromatic instruments, such as the piano, are made to produce the chromatic scale. Other instruments capable of continuously variable pitch, such as the trombone and violin, can also produce microtones, or notes between those available on a piano.

Definition

The chromatic scale is a musical scale with twelve pitches, each a semitone, also known as a half-step, above or below its adjacent pitches. As a result, in 12-tone equal temperament (the most common tuning in Western music), the chromatic scale covers all 12 of the available pitches. Thus, there is only one chromatic scale. The ratio of the frequency of one note in the scale to that of the preceding note is given by ${\sqrt[{12}]{2}}\approxeq 1.06$.

In equal temperament, all the semitones have the same size (100 cents), and there are twelve semitones in an octave (1200 cents). As a result, the notes of an equal-tempered chromatic scale are equally-spaced.

The chromatic scale...is a series of half steps which comprises all the pitches of our [12-tone] equal-tempered system.

— Allen Forte (1979)

All of the pitches in common use, considered together, constitute the chromatic scale. It is made up entirely of successive half steps, the smallest interval in Western music....Counting by half steps, an octave includes twelve different pitches, white and black keys together. The chromatic scale, then, is a collection of all the available pitches in order upward or downward, one octave's worth after another.

— Walter Piston (1987)