Via All Manner of Thing: “It’s a visualization of a two-part canon from Bach’s Musical Offering. The canon in question exhibits both retrogression and inversion — that is, the theme harmonizes with an upside-down and backwards version of itself.”
The Musical Offering has a very interesting history. From Gene Veith: ‘King Frederick, who enjoyed humiliating his guests, had composed a long melody line full of chromatic scales that was impossible to turn into a multi-voiced canon…and told Bach to turn it into a fugue. Whereupon Bach, on the spot, sat down at one of the new piano fortes and turned it into a three-part fugue. The flummoxed King said, in effect, OK, turn it into a 6-part fugue. A few days later, Bach sent him a 6-part fugue and more than a fugue, “A Musical Offering” that rebuked Frederick and all of his Enlightenment notions with the Christian faith.’
