The Bohlen-Pierce scale is an alternative tuning system. The typical Western scale is based on an octave (which is a 2:1 ratio) divided into 12 equal parts (in equal temperament). Since we hear frequencies at multiples of two as being the same pitch class, this is a pretty consonant situation.

In a Bohlen-Pierce scale, the fundamental unit is not the octave, but the tritave—a ratio of 3:1. This interval is then divided into 13 parts, resulting in some pretty wild dissonances and resonant frequencies. Apparently there is a lot of math and such behind it, which you can investigate at the Wikipedia page, if you need to know more.

In any case, this video is an arrangement of Pachelbel’s famously consonant Canon in D into Bohlen-Pierce, titled “Canon in J.” Click to about 2:00 if you can’t listen to the whole thing to hear some elaborate, alternative tuning counterpoint!