WHY ARE THERE 12 NOTES IN AN OCTAVE?
NOEL GIBSON, BATH
GETTY IMAGES X2 ILLUSTRATION: SEBASTIEN THIBAULT
It’s a combination of biology, maths and physics. If you play a tone with a frequency of 440Hz then you get an A. Doubling the frequency to 880Hz changes the note to an A one octave above. Our ears hear this as essentially the same note, just pitched up. Within this range, certain ratios sound more pleasing than others; the most important being the ‘perfect fifth’ (3:2) and the ‘major third’ (5:4). Dividing the octave into 12 isn’t the only possible system (a lot of folk music uses a five-note octave), but 12 divides neatly by 2, 3, 4 and 6, which makes it easy to construct ratios that correspond closely to harmonious note combinations.