By Stephen Brookes • The Washington Post • September 23, 2008

 If there's one thing Mos Def has, it's ambition. The hip-hop superstar -- who's also an actor, musician and (like all good Renaissance men) a budding clothing designer -- has been trying to invigorate hip-hop by pushing out the boundaries into jazz, R&B and soul. Is it working? The results were mixed Sunday night, when the artist brought his still-under-construction big band, the Amino Alkaline Orchestra, to the Kennedy Center Concert Hall for a show that was provocative and intense -- but often frustrating.

There were some great moments, and Mos Def was in fine form all night, rapping intensely and roaming the stage with the loose, low-key charisma that's become his trademark. But the focus was always on the lyrics and the star, rather than the music; the orchestra was kept in the background, trudging through simple arrangements that didn't break much new ground. And with the exception of trumpeter Keyon Harrold, who delivered some gorgeous riffs in "All Caps," none of the players was given a solo. Too bad. Hip-hop needs to have its range expanded, and a hip-hop big band could be an amazing thing to hear. But if the musicians are straitjacketed, the music probably won't get very far.