In music, an octave (Latin: octavus : eighth) or perfect octave is the interval between one musical pitch and another with half or double its frequency. It is defined by ANSI as the unit of frequency level when the base of the logarithm is two.or example, if one note has a frequency of 440 Hz, the note an octave above it is at 880 Hz, and the note an octave below is at 220 Hz.