octave
n. countablen. the distance between two musical notes where the higher note has exactly double the frequency of the lower one. It sounds like the same note but at a higher or lower pitch.
n. the interval between one musical pitch and another with double its frequency. In Western music, this span encompasses eight notes of a diatonic scale.
She can sing across three octaves.
The pianist played the melody in octaves to give the theme a more powerful and resonant sound.
While most human voices span about two octaves in speech, trained vocalists can often extend their range significantly, maintaining tonal clarity even at the extreme ends of their register.
Often used with the preposition 'in' when describing how music is played or 'across' when describing range.