Something cool about researching stuff that's in the popular press is that people send me new mashups all the time. A friend of a friend sent me this, and I thought it was totally awesome! It's the Cure vs. the Commodores, and it was made by Daniel Barassi. The source tracks are below:
Tonally, it works very well, and required little adjustment. "Easy" was originally in A-flat major. Barassi transposed it up up a half step into A to match the Cure's key. Transposition by such a small interval cause very little timbral change to music, so it can be done fairly imperceptibly.
Structurally, it's quite impressive. The verse-chorus structure of "Just Like Heaven" was retained, making the mashup sound more organic, like a newly-composed song. There are certainly great mashups that don't retain song structure and rely on snippets of samples for their construction. I don't mean to devalue this type of mashup, but the aesthetics are certainly different from those in "Easy Heaven."
The best part about this mashup, in my opinion, is what Barassi did to the tempo of Robert Smith's voice. "Just Like Heaven," by the Cure, was originally recorded at around 151 beats per minute. It's an up-beat song, probably often danced to. I asked a few people where they perceived the beat to be, and this [totally informally and nonscientifically] revealed that the quick pulse of 151 bpm is where the beat is felt. "Easy," by the Commodores, is a laid-back ballad, recorded at between 65-66 beats per minute. The same informal survey method yielded the same results. Barassi didn't adjust the tempo of "Easy" at all for this mashup. The accompaniment remains at the same cool, easy [go figure] tempo. The tempo of "Just Like Heaven," however, was slowed down a bit. Here's where the explanation could potentially get a bit confusing: It sounds like Robert Smith's vocal line was slowed down from 151 bpm to 65 bpm. What? How is is possible to slow down the vocal line by almost 57% and still have it sound fairly normal? Robert Smith isn't singing in slow motion. What actually happened is that Smith's vocal line was slowed down from 151 bpm to around 130 bpm; a 14% decrease. The cool thing, I think, is that our perception of the tempo change is greater, because we feel the beat as being where the Commodores put it: at 65 bpm (and 65 x 2 = 130). Robert Smith goes from singing a bouncy dance number to a lazy slow jam, without actually singing much slower at all. This change in feel to the Cure's song is super dramatic. It's now a completely different genre, even though very little has actually been altered.