Just 12 bar blues in C, but what a great bass line. 12/8 time signature, so the beat's on the dotted quarter. Usually Carl plays the middle eighth as a rest (notated as a staccato quarter), but sometimes it's a full quarter note followed by an eighth note. Check out some of the 16th note variations. Harmonically, the first three beats are usually chord tones, but the last beat is more interesting. Lots of half step approach notes.