I've been doing some research on the Estonian composer Arvo Pärt lately, known best for his simple yet highly emotive Tintinnabuli compositions. The theory behind it is incredibly dense and difficult to understand (at least for me). If I'm not mistaken, the whole theory behind it is that there are two voices: the T-voice (Tintinnabuli voice) and the M-voice (Melodic voice). The M-voice can be any pitch, and moves stepwise around the tonic note of the scale, and the T-voice is comprised of notes from the tonic triad and can jump octaves.
As per a thesis on this style, "According to Hillier, the relationship between the M-voice and T-voice is predetermined for every piece; moreover, some works are based on “some numerical pattern or by the syntax and prosody of a chosen text. Very often these two ideals are combined.”" (https://digital.library.unt.edu/ark:/67531/metadc271844/m2/1/high_res_d/thesis.pdf)
An entire Tintinnabuli piece is based on the harmonic fundamental and overtones of a ringning bell; for example, the hum tone of a bell is like a drone. The T-voice notes in most Tintinnabuli works come from the centric pitch of the piece, and often have similar characteristic of the minor chord produced by the main partials of the bell's harmonic series. These pieces are also very much based around symmetry and are usually written in Aeolian Mode, and have often been described as being Algorithmic (although I'd rather not generate music).
I'm having trouble figuring out how to actually write one of these pieces though. As I said, explanations of this can be difficult to follow, and there have been numerous theses and papers written by PhD students and academics. Can anyone help me to understand this on a more basic level? Thanks!