Rarely has a dose of maturity suited musicians the way it has Wilco, especially their leader and auteur Jeff Tweedy. On their earliest records, they aimed to reinvent country rock for the '90s, but the music was continually undercut by a smug, smart-ass cockiness; Tweedy seemed all too aware he was a clever songwriter. By 2002's ''Yankee Hotel Foxtrot,'' though, the band was onto something more interesting, murkier, and muted -- ambient alt-country -- that finally wiped the youthful smirks from their faces.
True to the admirable (and frustrating) ways in which Tweedy fiddles with Wilco's sound on each new album, a ghost is born strips away the sonic peach fuzz that encased its cohesive if imperfect predecessor. Looking to break their sound wide open, Wilco (working again with producer Jim O'Rourke, who knows more than a thing or two about avant-garde moves) have made their most audacious and riskiest record to date. One hardly associates the band with interminable, jabbing guitar solos, or with springy electro-pop, or with songs that self-consciously stretch out for upwards of 10 minutes. But that's precisely what we get on the first three tracks: the creepy-crawly ''At Least That's What You Said,'' about a physically abusive relationship; the apparent lure-of-drugs metaphor ''Hell Is Chrome''; and ''Spiders (Kidsmoke),'' which glides from blippy homemade-techno drone to cathartic band rave-up and back again. Maddening on first listen, the songs gradually settle into your brain and make you hear the group in a new light -- as brash sonic architects, not merely rehashers of bits of rock past. Based on a recent performance in New York, these numbers are especially enthralling live; rarely have Wilco seemed like such excitable boys.
The rest of ''a ghost is born'' isn't quite as experimental or always as rewarding, although it has sparkling moments galore. ''Handshake Drugs,'' another song that hints at the pill-popping problems that recently landed Tweedy in rehab, has a pulsating, U2-with-a-hangover groove, and the languid ''Company in My Back'' has a country-road loveliness. The field-of-flowers strings, bouncing-ball pianos, and rock directness that inhabit some of the other songs suggest an openness and vulnerability Tweedy rarely exhibits.
But Tweedy, who has claimed the album was born of improvisation, is also hampered by the same on-the-fly approach. For someone whose longtime strength has been songwriting over all-out adventurousness, many of the more traditional tunes seem, ironically, half finished. The Randy Newmanesque piano pop of ''Humming-bird,'' about a man going to great physical lengths to forget a lover, verges on TV-theme-song coyness, and the emo-lite rocker ''I'm a Wheel'' (another onstage winner) feels like filler on disc. The wind tunnel of feedback that drags the overly frail piano ballad ''Less Than You Think'' out to 15 minutes is pure indulgence.
This is the annoying side of Wilco that never fails to resurface. It wasn't their fault that buying and supporting ''Yankee Hotel Foxtrot'' became a symbol for sticking it to the Man after it was rejected by one major label (Reprise) before being picked up by a tonier one (None-such). But they sure reveled in their roles as industry martyrs. Annoying, also, is ''ghost'''s pretentious lowercase album title and, especially, the way Tweedy, with his Great Plains rasp, actively resists vocal projection, thereby making some of these songs feel smaller than they are. Given that Tweedy was a product of the early alt-rock era, it's no surprise that he still seems caught between wanting to be a cult figure and a pop star, sometimes at the expense of his art. (Tellingly, he ends the album with ''The Late Greats,'' an ode to obscure bands and songs that suggests they are superior to mainstream pop -- sometimes the case, but not always.) As the intermittent highs of ''a ghost is born'' prove, Tweedy can have the whole world in his hand, as long as he wants it.