Unison

Interval information

Ratio	1/1
Factorization	n/a
Monzo	[0⟩
Size in cents	0¢
Name(s)	missing ?
Special properties	reduced, harmonic, highly composite harmonic
Harmonic distance (log2 nd)	0
Wilson norm (sopfr(nd))	0
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This page is about the interval of 0 cents in just intonation. For the augmented unison, see Chromatic semitone.

The unison is the interval that represents no change in pitch. It has the ratio 1/1, or just the number 1, and a cent value of 0 cents. As such, stacking by it does not change any other interval's size, and it is considered the "default" interval when no movements have been done. Its monzo is [⟩ (an empty prime factorization), which is conventionally written [0⟩.

When commas are tempered out, they are reduced to the unison, so that a unison may represent a functional difference in tempered systems. An example is the difference between the augmented second and minor third in 12-ET, which are the same pitch and thus separated by a unison (which is actually a Pythagorean comma tuned to 0 cents).

"Detempering" the unison is one way to describe straddle/erac tunings.

The unison is associated with the first note of a scale (which is omitted in scale file data due to being the equave-reduced form of the equave itself, which is specified) and is associated with the tonic function and the root of the tonic chord. Additionally, the fundamental frequency of the harmonic series is 1/1.

The tuning system containing only the unison may be called om temperament, 0edo, or single-pitch tuning.