Two previously unreleased collages for magnetic tape, both realized at the Studio di Fonologia Muisicale RAI in Milan. These pieces are precious testimonials to Aldo Clementi's intense and ongoing interest in electronic music in the 1960s. The electronic composition »Collage 2« from 1960 was his first experiment with electronic music. »Collage 3« dates back to 1966. It's an electronic collage on »Michelle« by The Beatles.

The composer wanted to replace old concepts and clichés which had become popular and common, through the use of "natural wells of timbre, live and organic, springing from a world of symmetry and fixed blocks." This original idea underwent a drastic transformation when the RAI (the Italian radio) commissioned Clementi to write a longer work. To his initial desire to start from scratch was added the problem of a longer duration. It was only when Clementi had almost completed the piece that he gave it its final title of "Dies irae," owing to the extreme tension that accompanied its composition.