Vocal mistuning reveals the origin of musical scales

Theories of the origin of tonality from the time of Pythagoras onward have assumed that the intervals used in musical scales are defined mathematically based on harmonic ratios. Virtually all such theories are predicated on tunable instruments (e.g. strings), whereas the voice is the most ancestral and universal instrument used to make music. In the present study, we analysed the tuning of sung musical intervals from a familiar song, doing so across both trained and untrained singers. Contrary to the predictions of traditional theories, we found that sung intervals (unlike those of instruments) showed marked overlap with neighbouring interval categories. Furthermore, we found that listeners of these sung productions did not base their aesthetic judgments of singing quality on the precision of tuning of sung intervals. We consolidate these results into a model of tonality based on both vocal and sensory factors that contribute to the formation of sung melodies.