Concret PH

Concret PH is a musique concrète piece by Iannis Xenakis, originally created for the Philips Pavilion at the 1958 Brussels World's Fair and heard as audiences entered and exited the building. Edgard Varèse's Poème électronique was played once they were inside the building.
At 2 1/2 minutes long and focused primarily on density, "Concret PH" was created in the Philips office in Paris or at the Groupe de Recherches Musicales. The only sound source is burning charcoal, cut into one-second fragments, with numerous transpositions and overdubs, a granular texture from which Xenakis creates a continuum. Using slight manipulation, the main techniques were splicing, tape speed change, and mixing. The piece was composed intuitively, rather than being guided by mathematical processes. In the Philips Pavilion, it was projected over 425 loudspeakers through an 11-channel sound system. Xenakis described the effect as "lines of sound moving in complex paths from point to point in space, like needles darting from everywhere."