Aristoxenus

Aristoxenus of Tarentum (Greek: Ἀριστόξενος ὁ Ταραντῖνος; born c. 375, fl. 335 BC) was a Greek Peripatetic philosopher, and a pupil of Aristotle. Most of his writings, which dealt with philosophy, ethics and music, have been lost, but one musical treatise, Elements of Harmony (Greek: Greek: Ἁρμονικὰ στοιχεῖα; Latin: Elementa harmonica), survives incomplete, as well as some fragments concerning rhythm and meter. The Elements is the chief source of our knowledge of ancient Greek music.

Source: Wikipedia — https://en.wikipedia.org/wiki/Aristoxenus