The INTERVAL between two equal PITCHes or frequencies, that is, the null interval.

Two or more sounds are said to be in unison when they are at the same pitch, although often an OCTAVE may exist between them. For instance, men and women singing in unison are often singing at least one octave apart.

See also: BEATS, TUNING.

Sound Example: Men and women singing in unison, but actually an octave apart.