Here's the Ying Yang Twins [ tickets ] album detractors have been waiting for since the duo exploded onto the scene five years ago with the club-swelling "Whistle While You Twerk." It's the one where, midway through the release, they quit.

To be more precise, in the middle of "Chemically Imbalanced," long-time producer Mr. Collipark gives it up, turning over the disc's beats to Wyclef Jean and Jerry Wonder.

There's an uninspired, Ying-Yang-by-numbers feel about the old-school opening. "1st Booty on Duty" is typical of the first 10 "Imbalanced" tracks, familiarly energetic and empty-minded club bangers. The rhymes are so shamelessly lazy that the song's scheme accidentally turns striking. ("Some of these bitches is real, they hard knock/once you get 'em crunk they start, they won't stop," rappers Kaine and D-Rock drawl.) Here, Ying Yang's lyrics and feel are steeped in southern stripper culture and, predictably, come off tired at this stage of the game. At this point, it's easy to suspect that the group's highly influential 2005 hit "The Whisper Song" was the group's last contribution to hip-hop.

But then the Jean-Wonder collaboration kicks in and the game totally changes. Hip-hop's under-explored connection between Caribbean vibes and black southern vibes gets a full musical workout, beginning with the grunt-inducing party-starter "Water." Live instrumentation and poly-rhythmic, live drumming shift D-Roc and Kaine to the intermittent feel-good roles they're born to play. "In This Thing Still," the album's last track and the group's current single, shows the group is solid at the core, viable without the new collaborators. It's a wild ride. In another era, the last half of "Chemically Imbalanced" would have been released as an EP and considered among the year's best.