To elaborate on what Steelo said: Dubstep is 99% at 140 BPM, which means a rap tune set to 70 BPM (Most of the slower tunes) will be going the same ‘speed’ just over twice as many bars. Now, I think most of the time the kicks will not sync, because rap doesn’t follow the same drum pattern. However, you could be running a Dubstep tune, and drop rap over it by finding the beginning of a set of vocals in the rap song, cutting out most of the rap’s bass, and boosting the mids a bit to bring the vocals out, and when the timing is right, switch the bass between the two tracks.
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