The Quadrivium:—

[4] Arithmetic, [5] Geometry, [6] Music, and [7] Astronomy.

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

[4] ARITHMETIC —
Number in itself, which is a pure abstraction; that is, outside of space and time.

[5] GEOMETRY —
Number in space.

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

[7] ASTRONOMY —
Number in space and time.
a. Number
b. Geometry
c. Harmonics
d. Cosmology

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 Golden Ratio with Dr. Scott Oslen, Gnostic Meida podcast episode #108 (advanced)

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