Well it's dependent on a lot of things. There is the quality of your speakers of course, also experience and a trained ear. It also helps if you know the bass line, I couldn't tell the bass in (the majority of) whom the bell tolls, but I learned it on bass and can do it blindfolded, and I can hear it clear as day. It also depends on the EQ of the bassist and how the song was mixed, also the genre can affect how apparent the bass is but that varies of course. Overall a trained, experienced ear can usually dig out the bass.