Originally Posted by This Is Not Here
Hey musical people, can someone explain to me what exactly an octave is?
An octave is the distance between two notes, as separated by eight notes. To move "up" an octave is to double the frequency of a note; to move "down" an octave is to cut the frequency in half.
When someone is singing and they hop up to falsetto without changing keys, they're moving up an octave... Because he is doubling the original note's frequency, he's moving to what amounts to a higher version of the same note and he doesn't need the rest of the band to change notes with him. They can stay at the original place on the scale.
Basically octaves are just markers on the scale. 8 notes up or down and you're finding your starting note again, in a "higher" or "lower" form.