[6] Music

The Quadrivium:-
— [4] Arithmetic, [5] Geometry, [6] Music, and [7] Astronomy.

The Quadrivium (which pertains to Matter & Quantity)- the advanced four.

[6] MUSIC OR HARMONIC THEORY —Number in time.

The Quadrivium with Gene Odening, Gnostic Media Podcast episode #050 (start here)

Quadrivium – Number, Geometry, Music, & Cosmology with John Martineau, Gnostic Media Podcast episode #103 (intermediate)

The Elements of Music with Dr. Jason Martineau, Gnostic Media podcast episode #109 (advanced)