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“The 715 Four-Note Chords,” from Chord Catalogue by Tom Johnson

I like to think of “The Chord Catalogue” as a sort of natural phenomenon—something which has always been present in the ordinary musical scale, and which I simply observed, rather than invented. It is not so much a composition as simply a list.

In his Chord Catalogue, Tom Johnson plays every possible combination of notes within one octave. This segment runs through all of the 715 possible combinations of four notes. You can see the score [PDF] here, although the piece is typically communicated verbally by explaining the process through which one can hit every chord—raising the lowest note one semitone at a time, until it hits the second lowest note, at which point that note shifts up and the process repeats. Rests separate each of those short runs. (If you’re curious, there are 8178 possible chords. When you get to the nine, ten, eleven, and twelve-note chords, it gets tough to tell them apart!)

“The mu major chord is something musicically inclined Steely Dan fans have often asked themselves about. Just what is the chord? What does it sound like? Which songs use it?”

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Thing I did not know: the undeniable magnetic power of Steely Dan is linked to the use of a special kind of chord, and this special chord is explored in detail (with audio examples) at this website:

Steely Dan - The Mu Major Chord

(via sass)