We've seen Ciara and Justin Bieber edited on several occasions by several producers, yes, but more often than not, the resulting efforts prove to be worthwhile, so we've no choice but to post them on account of quality. This is the exact case with El. Train's additions to both Ciara's "Promise", and Bieber's "All That Matters", each of which find their way onto a single track, interestingly enough. The UK producer puts together an impressively unified sound with the vocals of either individual, looping them around light synths and understated bass, and the clean sound that ensues has us fans of the final product.
El. Train