Shepard tones are notes in multiple octaves, which fade appropriately so that, ultimately, motion goes nowhere: rather resembling a barber pole.
In Gödel, Escher, Bach: an Eternal Golden Braid, Douglas Hofstadter wrote they could be combined with Bach's 'Modulation' or 'Endlessly Rising' Canon (Canon a 2, per tonos: from The Musical Offering).
With existing musical instruments, this would seem difficult. However, just now on YouTube, I discovered Michael Monroe has (re-) created precisely this combination, using MIDI guitars (in 2008)—and, it's beautiful. :)
Fairly seamlessly, his ending connects through to its beginning, if the file is downloaded and the 'repeat' (or 'loop') option is selected (in one's choice of media player).
In case you missed it, the main musical link above is the word, 'combination'!
A more normal performance (or this one on Spotify) gives a subtly aesthetic experience, as well.
Copyright (c) 2010, 2014 Mark D. Blackwell.