Composer's notes: “Once I received the commission by HD duo to compose a piece for sax and piano, I asked Michael Duke to select for me his favourite multiphonics for alto sax and send me a recording of them. I analysed the spectra of these recordings, establishing the eight dominant partials for each one. I used these chords as the basic materials for the piece; this is why the work is called Spectrax. I then jammed over these chords in order to extract musical ideas, which I transcribed to the score. The final details of the piece where polished together with HD duo during the previous days to the world premiere at Mexico City in 2015.” Enrico Chapela