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

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

[5] GEOMETRY —Number in space.

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 Media podcast episode #108 (advanced)