0 the distance between two musical notes that are eight notes apart -- 八度；八度音階
Her remarkable vocal range spanned three and a half octaves. 她的音域達三個半八度，寬得驚人。
For instance, over-blowing on a wind instrument can cause an octave rise, which holds as the pressure is reduced.
That is, three downward harmonic pitches are available, plus four or more harmonics in each octave above the original pitch.
The remainder is given over to a single tonic butterfly in which the second note is displaced downwards by two octaves.
If they start too high, they continually increase the pitch until they reach an octave higher, at which point they simply halve the frequency.
Another tempo change ushers in a closing phrase of classical cues based on a tonic triad followed by tonic tones in descending octave leaps.
The additional decorrelation of the harmonised version guarantees its being perceived as coming from a separate source, even when the interval is an octave.
This solution, which explains the octave doublings as well, seems the most likely, as a brief look at the mechanism of transposition will clarify.
Of the various practical solutions proposed, the one that triumphed was the idea of tuning 12 exactly equal semi-tones in an octave.
