This evening I watched a "Legends of Rock" concert on HDTV, and the band John McKay and Steppenwolf played a couple of songs. There was a definite bass line, however no bassist on stage. At first I thought the keyboardist had to be playing the bass line, but several times the camera showed an excellent shot of his hands, and there was no way he was playing the bass line. So...what gives? Can you have a prerecorded bass while everyone else is playing live? I thought it was pretty obvious that the other instruments were being played live, but could they have...?