Unison and octave intervals

Unison in musical notationThe unison interval consists of two notes of the same pitch. For example, C and another C note will result in a unison interval. On the picture to the right, an unison in musical notation is shown.

Unison should be distinguished from the octave. While both unison and octave are defined by intervals of the same notes, or pitches, the difference is that an unison is an interval with two notes on the same register when an octave is the same note but on a different register.
Keyboard unison interval Keyboard octave interval
Unison in C to the left and Octave C to the right.

Listen to unison interval (C-C):

Unison is also referred to as a perfect unison and are abbreviated P1. The number derives from the fact that the unison is the first interval, in other words the interval with the least distance (which is none). An alternate spelling is diminshed second.

Examples of unison intervals

A list with unison intervals is kind of superfluous, but to make it extra clear, here are all possible unisons:

Enharmonic notes such as Cb and Fb are leaved out.

Octave

Octave in musical notationA related interval is the octave, which include the same notes as the unison but of different pitches. For example, C and C on the next octave. This could be written out as C4 and C5, meaning C notes on the fourth and the fifth octaves respectively.

Listen to octave interval (C1-C2):

Octave is also referred to as a perfect octave and are abbreviated P8. The number derives from the fact that the distance between the notes are 8 scale steps, if all notes (half-steps) are counted the distance is twelve notes. An alternate spelling is augmented seventh.

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