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This is Your Brain on Music – Professor Daniel Levitin

Here is a fundamental quality of music, note names repeat because of a perceptual phenomenon that corresponds to the doubling and halving of frequencies. When we double or halve a frequency we end up with a note that sounds remarkably similar to the one we started out with. This relationship, a frequency ration of 2:1 or 1:2 is called the octave. It is so important that in spite of the large differences that exist between musical cultures – between Indians, Balinese, European, Middle Eastern, Chinese and so on – every culture we know of has the octave as the basis for its music, even if it has little else in common with other musical traditions. This phenomenon leads to a notion of circularity in pitch perception, and is similar to circularity in colours. Although red and violet fall at opposite ends of the continuum of visible frequencies of electromagnetic energy, we see them as perceptually similar. The same is true in music, and music is often described as having two dimensions, one that accounts for tones going up in frequency (and sounding higher and higher) and another that accounts for the perceptual sense that we’ve come back home again each time we double a tone’s frequency.

The octave is so basic that even some animal species – monkeys and cats, for example – show octave equivalence, the ability to treat as similar, the way that humans do, tones separated by this amount.

The first two notes of the Harold Arlen melody ‘Over the Rainbow’ … make an octave.