In the languid wake of slowed-down Dolly Parton,
Jason Kottke Tim Carmody offers a splendid guide on how to make your own slow jams, with a few of his own to listen to. The trick, he writes, is to remember that music is keyed to specific frequencies–notes!–and failing to scale in accordance with them may produce uncanny results.
Here's the formula for slowing or speeding up a recording to shift the pitch but generally stay in tune:
(2 ^ (semitones change/12) – 1) *100 = Percent Change
So — as one does when procrastinating from remunerative work — I made an Excel spreadsheet.If you want to drop two semitones, you shift the speed down by 12.2462 percent; drop three, you shift by 18.9207 percent, which significantly changes the track.
For your enjoyment, I have already produced Slow Yakety Sax.