If you wanna take a song and make the bass really low without slowing it you can open it in audacity, duplicate the track so you have 2 sets of it. On the top track, EQ it so it starts to drop off at like 200hz down to 100hz where it cuts off. Do the same on the bottom track, but inverted, so anything above 100hz is cutoff. Then change the pitch of the bottom track. I wanna say -50% pitch change brings it down either a full or a half octave.