i had the same problem too. ive been playing for a year and a half now and the way i beat that was everyday id take time to repitively play all the major notes (E, F G A B etc etc) on it it and try to match my voice to it. matching your voice with it to me, helps not only your ears with the repitiveness but also with i guess internal pitch, your body gets a feel for that note(s). just set aside some time while you practice and youll get better also, just sing somethin random (a note, it really helps i you have a piano/KB around) and try to match the bass with that tone. and pick a slow bassline song or a very repitive one and pick parts out and try to match to that. itll take quite a few stopping and relistening but it helped me
hope this helps