Sheldon "Shay" Haley, left, and Pharrell Williams, right, team in N.E.R.D. with the M.I.A. Chad Hugo, who also records with Williams in the Neptunes. The side gig has become a big deal. (Carolyn Cole / Los Angeles Times)

TALK about a tour manager's worst nightmare.

Chad Hugo had missed his flight from Virginia, skipped rehearsal and wasn't picking up the phone. Worse still, with less than an hour until show time it appeared the 32-year-old multi-instrumentalist and superstar pop producer wasn't going to be anywhere within three states of the Big Apple in time for a taping of "Late Show With David Letterman," where he was scheduled to perform with his gold-selling hip-hop/rock/new wave group N.E.R.D.

Inside Midtown's Ed Sullivan Theater on a recent Monday, the news of his absence provoked two divergent reactions: astonishment and near total apathy.

It's a lot for a band like N.E.R.D. -- a self-described "niche" act on the cusp of a potentially paradigm-shifting mainstream crossover -- to land the kind of broad cultural pedestal provided by "Late Show." And several of the broadcast's producers seemed incredulous that Hugo should be M.I.A.

Meanwhile, N.E.R.D. tour support staff and band mates Sheldon "Shay" Haley and Pharrell Williams barely registered Hugo's absence. Their attitude wasn't so much "The show must go on" as a dismissive whatevs.

But then, Hugo and Williams have become well versed in each other's peccadilloes. Over the course of a 14-year recording career, they have come to rank among the most elite hit makers in R&B, hip-hop and pop.

Their other group

WORKING under the professional alias the Neptunes, the Virginia Beach, Va., natives, who have been buddies since middle school, have crafted multi-platinum hit after hit for an eclectic roster of major stars, including Britney Spears ("I'm a Slave 4 U"), Snoop Dogg ("Drop It Like It's Hot") and Gwen Stefani ("Hollaback Girl"), in addition to several songs on Madonna's new album, "Hard Candy."

And since 2001, after the release of N.E.R.D.'s forward-looking debut, "In Search of . . ." -- a record that helped break down musical walls and infuse mash-up culture in hip-hop at a time when the genre's abiding aesthetic was defiantly homogeneous -- Hugo has skipped out on tour dates and promo duties pretty much at will; a keyboard tech is always at the ready to serve as Hugo's understudy (as he eventually did for the producer-musician on Letterman). It got so chronic, N.E.R.D. entourage members joke about making a cardboard cut-out of Hugo for photo shoots (such as one Hugo blew off for this story).

Which wouldn't even have been a problem if not for the fact that the group was about three-quarters of the way through the highest-profile tour of its career, performing as an opening act on Kanye West’s Glow in the Dark tour, which concludes in Cincinnati this month. And that band members describe N.E.R.D.'s genre-blurring new CD, "Seeing Sounds" -- which equally recalls P-Funk and the Beatles, Metallica and the Isley Brothers, Gary Numan and Curtis Mayfield, sometimes in the span of a single song -- as an exercise in creative cohesion, band unity and a statement of renewed "purpose" for N.E.R.D.

On "Seeing Sounds" there are political manifestoes and odes to voyeurism (the Curtis Mayfield-esque "Love Bomb" and the '60s-tinged "Window," respectively), a funk banger called "Kill Joy" that's reminiscent of the Red Hot Chili Peppers, and even a seven-minute opus, "Sooner or Later," that features Williams singing in his trademark falsetto and rapping over crescendos of guitar, synthesizers and crashing beats. The album's lead single, "Everyone Nose" -- with its unforgettable chorus shouted by Shay: "All the girls standing in the line for the bathroom!" -- takes aim at badly behaved celebutantes on the Paris-Britney-Lindsay axis of empty celebrity.

"Until now, I've been living my life just to have fun," Williams, 35, said in the back of a Cadillac SUV inching through traffic on the way to "Late Show." "But now, having a vertebrae of creativity is more -- not even challenging, but more fun. You realize there's an actual statement to be made. Now we're these creative guys that have a purpose."

To emphasize that the men of N.E.R.D. are on the same page, Haley noted that Hugo's failure to make the gig was a relatively isolated incident. "Chad's been a lot more of a part of this album," Haley said. "The first two albums, he wanted to stay home and be more of a family man. This time out, he's only missed two shows. "

Encountered much later the same night at a downtown nightclub, where he stood quietly nursing a beer, Hugo put a different spin on what went into making "Seeing Sounds," due out June 10. "We had anger, quiet angst," Hugo said. "We had something to get off our chest. And we wanted to show we could do it as a band."

The notion of hip-hop as a "hybrid" cultural expression is nothing new. From the genre's inception, DJs have repurposed the break-beats of existing records and rappers have liberally cribbed from TV jingles, cartoon theme songs, movie dialogue and refrains from classic R&B. As far back as the early '80s, rock 'n' roll guitar and song structure began to influence rap, coming to an apex in 1986 with Run DMC and Aerosmith's groundbreaking collaboration, “Walk This Way.”

Enter N.E.R.D. in 2001. A "side project" of the Neptunes, "In Search of . . ." went certified gold by the Recording Industry Assn. of America while leaving rap purists scratching their heads and incidentally prompting a run on trucker hats -- Williams' signature headgear.

N.E.R.D.'s live instrumentation and electroclash-rock-funk simply wasn't the stuff any self-respecting hip-hop head was expecting at that time from the production duo responsible for rap anthems like Nelly's "Hot in Herre," Mystikal's "Shake Ya Ass" and Noreaga's "SuperThug." N.E.R.D. burst on the scene pledging allegiance to the dork (its name, an acronym for "No one Ever Really Dies," reaches for an air of mystique while remaining squarely in the geek realm).

The group's 2004 second album, "Fly or Die," didn't perform as well as its debut, selling just more than 400,000 copies. But now, with sales of hip-hop music falling off steeply over the last three years after three decades of steady growth, rap purists are looking outside the genre's boundaries for hip-hop's future.

To wit: the successes of hip-hop's most esteemed lyricist Jay-Z and the nu-metal band Linkin Park's "Collision Course" mash-up EP (which hit No. 1 on the national album sales chart in 2004) and super producer Timbaland's genre-hopping "Timbaland Presents Shock Value" (on which he collaborated with rock acts including the Hives and She Wants Revenge to the tune of more than 1.1 million albums sold domestically). As well, the eclectic duo Gnarls Barkley landed two Grammys last year and unleashed what is perhaps the decade's most infectious single, "Crazy," in 2006 by channeling a singular blend of hip-hop beats, psychedelic rock and hot-buttered soul.