A demonstration on the difference between two crossfades. The first is a straightforward crossfade. The second one is a crossfade in which the partials of both tracks are detected, selected (the strongest wins) and then resynthesized.

The normal crossfade:

Crossfading the partials:

To hear the difference listen to the middle of the two tracks (around 16″). While the normal crossfade sounds muddier, the second one retains the same volume and clarity as either track (at least to my ears).