Does this Brooklyn-based rap duo have something to prove? Certainly sounds like it on Hard to Earn. Leaning toward hard-edged funk and chaotic drumbeats with only the occasional horn, piano, or keyboard loop, DJ Premier seems determined to shake the ''jazz-rap'' label once and for all. In his patented raspy alto, rapper Guru reminds us how long he's been around and compensates for his lack of verbal gymnastics with charm and accessibility. A

