This is a neurological condition in which stimulation of one sensory or cognitive pathway leads to automatic, involuntary experiences in a second sensory or cognitive pathway. In this case it happens in a very specific way. Colors, Feeling, High Pitched noises, tastes, and many other sensory reactions are all reinterpreted as deeply resounding bass lines. A feeling that inwardly leaves the subject feeling like they are in a mild earthquake though outwardly there is no actual visual accompaniment.
Guy 1: Damn I love dubstep, those heavy bass drops feel so wonderful.
Guy 2: Haha, I don't have to listen to music for that feeling. Bassesthesia is awesome, most of the time anyways.
Guy 1: What the hell is that?
Guy 2: See that hot girl over there? Well, right now looking at her I can feel the rumble.
Guy 1: What about now? She just bent over...
Guy 2: Heh, let's just say the vibrations feel a little too good.
Guy 1: Woah buddy, put that damn thing away! Down Simba!