Over the past week or so, we’ve posted links to slowed down versions of songs by Frank Zappa and Dolly Parton that have been making their way around the net. This post on kottke.org walks you through the process of slowing down your own music.

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

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. To imitate a 45 RPM record played at 33 1/3, that’s about 25.926, but very few records still sound like something a person actually made at this speed.

There are a series of examples that show off the results. All the examples were created using Audacity. Well done.