The choral voices are there in support of a bunch of Da Vinci Code malarkey about secret codes that Bach supposedly was hiding throughout the music. I’m totally uninterested in this idea, whether or not it’s true, but I am intrigued by the possibility that Bach was quoting or adapting pieces of Lutheran chorale tunes. Morimur superimposes the chaconne with the chorales that it’s supposedly quoting. Who knows whether this was in Bach’s mind or not, but it sounds great — and ultimately, that’s the only thing that matters for music.
All are typical phase problems, involving complex signals and interference patterns. With a bit of math at your back, the key is to know how to listen for them and how to fix them.