Courtesy of the fertile mind of Michael Monroe, a tempo canon involving Renée Fleming and Maria Callas's differently paced interpretations of "O mio babbino caro."
A tempo canon is a canon in which the same music unfolds in several voices at different speeds. The classic example in Renaissance polyphony is the Agnus Dei 2 of Josquin's Missa l'homme armé Super voces musicales (1502), in which the lowest voice moves twice as fast as the middle voice and the top voice moves three times as fast:
Tallis Scholars, Gimell 206.
Kyle Gann, in his book The Music of Conlon Nancarrow, sets Josquin's Mass side by side with Nancarrow's canonic studies for player piano, written several centuries later. In Study No. 19, the tempos obey the ratio 12/15/20:
Studies for Player Piano, Wergo 6907.
Elliott Carter, György Ligeti, Steve Reich, and Arvo Pärt, among many others, have used related principles in their music. In the Kyrie of Ligeti's Requiem, the main subject begins with a drop from B-flat to A-natural, but each voice breaks away from the initial note at a different time. An awesome cloud of sound begins to grow:
Jonathan Nott conducting the Berlin Philharmonic and the London Voices, Teldec 88263.
Pärt's Cantus in Memory of Benjamin Britten consists essentially of descending A-minor scales, with the first violins playing sixteen times faster than the double basses:
Dennis Russell Davies conducting the Stuttgart State Orchestra, ECM 817764.
All this reminds me of something I perpetrated in college, in collaboration with Michael Pahre — a self-styled radiophonic composition entitled Ecstatic Radio Fantasia on Robert Ashley's "She Was a Visitor". At one point we set up a race among four recordings of the Tchaikovsky First Piano Concerto; as I recall, Richter won. Michael Vazquez was the lead vocalist for the performance, uttering the phrase "She was a visitor" continuously for forty-five minutes (at one point it became "Cher was a Visigoth"). In this segment he was joined by Douglas Wolk, future author of Reading Comics, who, for unknown reasons, read aloud the printed matter on a Nixon in China radio promo. Bright college days! The Ashley work that inspired this silliness can be found at UbuWeb.
An interesting hyper-canon will ensue if you hit all the buttons on this page in quick succession.