It’s somewhat worrying when your musical heroes talk about packing their bags during their own zeitgeist. In the New York Times earlier this month, Sasha Frere-Jones quoted Timbaland: “I’m tired of stuff now, even stuff that I do. Coldplay and Radiohead are the illest groups to me. That’s music. Norah Jones is music. I love real music that I can play and never get tired of. The stuff I don’t get tired of is the stuff that’s musical.”

From a critical perspective, it isn’t too surprising when artists fail to really appreciate the very things that make them great. But it can be depressing when someone like Timbaland—who pulled mainstream hip-hop out of the gutter in the late 90s and changed popular music for the better—seeks inspiration from two acts that exemplify everything traditional, comforting and safe about modern pop (Yorke et al excused). “Real” musicians wouldn’t have come up with the android beatbox hiccupping under Missy’s “Supa Dupa Fly” or the schizo, kitchen-sink groove powering Bubba’s “Twerk A Little” or the stoned and surreal erotica of Tweet’s “Oops (Oh My).” If a flawlessly lachrymose, bite-size opera like “Cry Me A River” doesn’t score enough “real” points for people who play instruments, then I’d rather have my music as fake as possible.

Tim is auteur to the bone, his biggest grace and ultimate dilemma. His productions trace a clear evolution, each new single a complete and painstaking reinvention. And they consistently have machines one-upping humans at their game (the programmed rhythm in “Are You That Somebody,” too inhumanly angular and precise for a real drummer’s arms, being my favorite example) while the actual performers vocalize in stark contrast, like any good pop star. Point being that Tim may have started to run out of new ways to augment his friends. (The latest Missy album speaks to that.) If his well does run dry, it’ll be for the same reason DJ Premier is stuck in a profoundly self-serving rut—his goals were reached long ago, his various formulas perfected.

The Neptunes, happily, don’t seem to have that problem. Despite their career running parallel to Tim’s, they always struck me as utterly divergent. I don’t think Pharrell and Chad have ever really cared about the voice in their music (ignoring the former’s penchant for crooning), or about “musicality” by extension, because their tracks don’t seem tailor-made for anyone. “Hot In Herre” may still be their finest moment, with its awesomely self-assured drum break that, especially on the floor, feels like James Brown made into Robocop. As important as Nelly is to that tune, the song is totally autonomous—it grooves ignorant of him or anyone else, satisfied with its own mechanics.

“Milkshake” quadruples the effect, with Kelis confined to the role of a club diva providing the vocal riffs and the real star being the skanking analog low-end. It’s the closest I’ve heard mainstream hip-hop get to house music, where minimal “jack tracks” work more like DJ tools than as complete pieces of music, and the human presence is fully mechanized in between pulses of the drum machine. Appropriately, Kelis sounds so bored in “Milkshake” she’s practically disembodied. It’s both mind-numbingly sterile and addictive, another fully functional product. The Neptunes don’t offer a particularly idyllic vision of pop in their assembly-line tracks, but they at least point to genuinely new directions.

But in between things like “Milkshake” and producing rock bands, the Neptunes are barely contained by hip-hop as a genre. In truth, “In Da Club” is the only joint from this past year still in my head, all mainstream and sewage-level underground productions of 2003 considered. That song, and 50 Cent, are redolent of hip-hop’s gradual ascension more than two decades in the making. They say 50 signaled the return of the hardcore thug emcee, the embodiment of the streets and the real and Tupac Shakur. But his rise reminds me more of Pac’s death, an epochal event everyone had to accept as fact. “In Da Club” defies real criticism; it simply is. As if to prove everything he said on 2001, Dre came up with the most monolithic hip-hop beat I’ve ever heard, whose blank, perfect handclaps and minor-key stabs herald Judgment Day, 50’s arrival. Eminem was right when he said they were “juggernauts of this rap shit / like it or not.” The song chugs along inexorably, wiping out any sense of forward propulsion—it only makes you want to stare downwards and crush the floor while 50 mutters commands in everyone’s ear.

With his bullet-riddled slur plastered over the track, flow has never mattered less in hip-hop. 50’s skills don’t matter—indeed, they seem impossible to gauge—and the beat hardly needs to try. It’s a suitable metaphor for the idea that hip-hop, at least the way we know it now, has few places left to go. Maybe that’s why Tim says he’s tired—not just bored, but completely run down by the music.