Musical Chords by the Numbers

Abstract: The mathematics of musical intervals and scales has been extensively studied. Vastly simplified, our ears seem to prefer intervals whose frequency ratios have small numerator and denominator, such as 2:1 (octave), 3:2 (perfect fifth), 4:3 (perfect fourth), and so on. While there also have been numerous studies on the mathematics of musical chords, very few of them consider a model that measures consonance/dissonance of a given chord in analogy with this simple-fractions perspective. Our aim is to develop a measure for the consonance of a chord with crucial symmetry features, including invariance under chord translation, inversion, and interval sets. We apply our model to chords in various musical scales and compare it to existing models and empirical studies.