It was Luke Fowler's wonderful documentary film Electro-Pythagorus, screened at International House in Philadelphia in 2018, that first brought the music of Martin Bartlett to my attention. Bartlett's work belongs to the second wave of North American experimentalism, when the somewhat ascetic tendencies of Cage and company gave way to a wider spread of influences, from improvisation and pyschedelia to non-Western musical traditions. (Two of Bartlett's teachers were the synthesizer designer Don Buchla and Indian raga guru Pandit Pran Nath.)
One of the obsessions of composers such as Bartlett, James Tenney, and Terry Riley (to name just a few) was alternate tuning systems, and in particular, forms of just intonation (tunings based entirely on whole-number harmonic ratios). A great example of this branch of musical research is Bartlett's 1990 composition Pythagoras' Ghost, a three-movement suite for four electronic wind instruments, of which "Xenomelophilia" is the second movement. (The title is Bartlett's tip of the hat to Harry Partch, pioneer of alternate tuning, who in his Genesis of a Music lamented "xenomelophobia," or fear of strange music.)
In a trance one day, Pythagoras' ghost appeared to me and said: "I'm tired of all the garbled stories about me that are going around—you help me set the record straight and I'll give you some information that'll help you write some incredible music. Nowadays the only thing people remember about me is that stupid theorem, and I didn't invent that; it was the Egyptians. All that stuff about about me discovering musical ratios by listening to blacksmiths pounding metal, for example, is totally wrong. It was really on my trip to Java, where I heard the sounds of the gamelan. I learnt a lot about tuning in India, too. People think I never got further than Babylon; they don't know much about how we got around in those days..."
The pitch information generated by the wind players is converted into just-intonation intervals using a mathematical tool known as the Table of Pythagoras, a array of whole-number ratios that, in Bartlett's words, "makes twelve-tone equal temperament sound like a sick joke." The pitches, in the form of MIDI data, are then fed into a Yamaha TX802 synthesizer (the rackmount version of the legendary DX7) to generate the sounds you hear. For Bartlett, music is the connecting link between mathematics and mysticism: "And the energy is the wind, breath, prana, pneuma, on which Pythagoras' ghost sails through time and space to remind us of beginnings and alternatives."
Further reading: Martin Bartlett, "Relative Ratio Tuning: An Intonational Strategy for Performance Systems," Leonardo Music Journal 1, no. 1 (1991), 71-73.