octave ŏk´tĭv [key] [Lat.,=eighth], in music, the perfect interval between the 1st and 8th tones of the diatonic scale. The upper note of a perfect octave has a frequency of vibration twice that of the lower, and in modern Western notation the two have the same letter name. The octave is the first overtone (see harmonic). The range of the male voice is roughly an octave below that of the female; men and women supposedly singing in unison actually sing in octaves.
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