It seems highly improbable that a successful film could ever be made using karaoke as a symbol for human liberation, but it’s certain that Bruce Paltrow’s whimsical ensemble piece about six characters who find friendship and love en route to a contest involving their warbling to canned music in a bar doesn’t manage the feat. Alternating between the ostentatiously quirky and the slobberingly maudlin, “Duets” isn’t just off-beat; it goes persistently off-key as well.

The shallow, tone-shifting script by John Byrum intercuts narratives about three odd couples making their way to Omaha, where a karaoke competition is scheduled. The most prominent duo, at least in terms of screen time, is made up of Todd Woods (Paul Giamatti), an overworked salesman who abandons his family to seek freedom, and Reggie Kane (Andre Braugher), an ex-con whom he picks up along the highway and with whom he soon develops one of those unlikely friendships that occur only in the movies. Then there’s karaoke hustler Ricky Dean (Huey Lewis), who reluctantly teams up with Liv (Gwyneth Paltrow), the daughter he abandoned long ago, after returning to Las Vegas for his late wife’s funeral. The final couple, and the one portrayed most sketchily, consists of Billy (Scott Speedman), an amiable but hard-luck cab-driver who leaves his wife after discovering her with another man, and Suzi Loomis (Maria Bello), a free-as-a-bird songstress who persuades him to drive her to Nebraska. The whole notion behind the script is that as these six characters wend their way to the final competition, they learn about themselves and what’s really important in life; the lessons sometimes take the form of knockabout comedy-drama (as when the newly-hysterical Todd absconds with Reggie’s gun and begins employing it much too freely, or when Liv must aid her dad when he’s caught in his hustling scam) and sometimes of mawkishly sentimental mush (as when Reggie teaches Todd about the importance of family or Billy attempts to rescue Suzi from a life of promiscuity in the search for cash). Manipulative moments, crafted to extract both tears and laughs from unwary viewers, abound throughout, but they grow increasingly insistent and shrill toward the close, when all six characters converge in an Omaha hotel where–ever so conveniently–each discovers something about the true meaning of human existence.

“Duets” has been carefully designed to appeal to the worst instincts in the audience: it uses every melodramatic device in the book to make its characters sympathetic, so that viewers will root for them and feel their pain, but it also periodically cuts to other performers in the karaoke bars, whom it portrays as buffoonish clods to get laughs. There’s something deeply cynical and almost contemptuous about the result, even though it aspires to be uplifting. And the constant shifting from one couple to another dissipates whatever emotional impact the piece might have built.

The cast is game but overwhelmed by the contrivances of the script. Giamatti is initially good, when he plays the downcast, lost soul, but soon he switches into the manic mode that made his turns in “Man on the Moon” and “Big Momma’s House” so irritating. Braugher is simply too fine an actor to be doing the schmaltzy material he’s saddled with here, but he goes through it without showing any embarrassment. Lewis is okay as the deadbeat dad, and of course he sings well enough, but Paltrow is curiously pallid as his daughter. Speedman appears to be an attractive, likable fellow, but he’s given little to do here but look either displeased or bemused (an early conversation between him and his erstwhile teacher, who’s been arrested for shoplifting, is very poorly written although it’s obviously intended to be a highlight). Bellows looks great, but her character is barely sketched in. Angie Dickinson appears briefly as Liv’s grandmother, looking well-preserved but tending to shriek.

“Duets” obviously intends to harmonize drama and humor in the same way that director Bruce Paltrow’s television series, “St. Elsewhere,” once did, but the combination doesn’t come off nearly as well here as it did on the small tube. Despite its good intentions and attractive stars, the clumsy comedy and mawkishness of the picture make it little more enjoyable than actually spending an evening in a bar listening to amateurs singing their lungs out to pre-programmed Muzak. And in this case, there’s no alcohol to dull the pain.