Aesop Rock has improved his diction considerably since his celebration of the 9-to-5 grind on 2001’s Labor Days. He no longer swallows whole words while he spits, though his rhymes—generally, metaphors about the neurotic obsessions he shares with Woody Allen (sex and death)—remain willfully dense and obtuse. Aesop Rock’s core constituency prefers its man to retain his air of mystery; there is actually great fun in being able to decode only one-tenth of what the orally fixated emcee is going on about, even with the benefit of a lyric sheet and a dictionary. On last year’s return to form, None Shall Pass, Aesop Rock ditched the nebulous commercial overtures of his recent work in favor of spare backing tracks from frequent collaborators El-P and Blockhead. On “Citronella,” he simultaneously pokes fun at mass media and grouses about the decline of Western civilization. Pop a Prozac and try not to get too bummed. AESOP ROCK PERFORMS WITH ROB SONIC AND DJ BIG WIZ AT 7 P.M. AT THE 9:30 CLUB, 815 V ST. NW. $20. (202) 265-0930.