Timberlake. Producers. Black Eyed Peas. 'Stronger.'

"Pop music" has long had the most vague of definitions. Unlike rock or hip-hop or country, it has never been characterized by sonic, ideological qualities. It exists in accordance with popular-and more recently-technological demands. The No. 1 hits of the 21st century were and still are defined by information conglomeration and overload. The sound of now isn't a single aesthetic, but a tangled mess of them.

In the mid- to late '90s there was a tug of war for No. 1 between Hanson (1997's "MMMBop") and Ricky Martin (1999's "Livin' la Vida Loca"), as well as Mariah Carey (1997's "Honey") and Will Smith (three weeks at No. 1 with 1998's "Gettin' Jiggy Wit It"). In the end, everything blurred seamlessly. Rappers turned to singing (OutKast's 2003 No. 1 "Hey Ya!"), singers turned to rapping (Gwen Stefani's 2005 No. 1 "Hollaback Girl"), and many of the decade's biggest hits, such as Usher's 2004 No. 1 "Yeah!," fused the two.

This blur was inevitable. Music is now recorded directly into the same boxes from which it's consumed. Producers share similar software setups and plug-ins while listeners and artists all seem to be tapped into the same global playlist. Niche genres that were once difficult to access-like European dance music and hyper-local underground hip-hop-now fill the same iPod space, and both have left their share of fingerprints on what is in fact a new non-genre.

Kanye West absorbed the French house of Daft Punk with his 2007 No. 1 "Stronger" while Justin Timberlake adopted the syrupy sounds of Southern rap on his 2006 chart-topper "My Love." This musical evolution seems quaint in terms of one-world, post-race idealism, but the inevitable sameness of it all can prove frustrating. Live instrumentation, and just about anything resembling rock music, is scantily heard in the new menagerie.

It has become trite to suggest that pop music is created not by its stars, but a team of mythical studio dwellers. But one look at the charts of the first decade of the 2000s and it's hard to deny the power of the unseen hand. Of the last 15 No. 1 singles-from artists like Katy Perry, Rihanna and Wiz Khalifa-11 of them were helmed by one of three producers: Dr. Luke, Stargate or the Smeezingtons. Earlier in the decade, Timbaland and Polow Da Don held the same baton for Timberlake and Usher. Producer-driven chart dominance certainly isn't rare-Phil Spector's dominance in the '60s and the hot-and-cold reign of Jimmy Jam & Terry Lewis during the '80s and '90s come to mind-but it's now the norm.

This is a disconcerting trend. It was once the producer's job to accentuate the character of the artist. But now producers mold songs in their own image. The vocalists on these records often feel interchangeable. Smeezington Bruno Mars' vocal contributions dominate B.o.B's No. 1 "Nothin' on You" and vastly outshine the rapper's talents. A popular YouTube video cuts back and forth between two recent Dr. Luke No. 1s-Ke$ha's "TiK ToK" and Perry's "California Gurls"-and asks if they're "the same song."

The rise of vocal plug-in Auto-Tune was one catalyst for this charge, whether used for pitch correction or misused to create the singular robot tone. While a few hitmakers pushed the technology to bizarre and artful extremes (Lil Wayne's mechanical gargle on the No. 1 "Lollipop," for example), more fell to cliché. Not only are most stars singing to aggressively similar instrumentation, many of them are doing so with nearly the same voice. Auto-Tune is a grand leveler.

If any group is equipped to thrive in today's landscape it's the Black Eyed Peas, a once mediocre troupe of hip-hop purists who flourished when they added European dance pop elements (and a white girl) to their equation. With a formula that transcends race, gender, genre and the continental divide, the quartet held the No. 1 spot for a record-breaking 26 consecutive months in 2009 with the one-two punch of "Boom Boom Pow" and "I Gotta Feeling." The act's production impresario, Will.i.am, is also its frontman.

Yet pop stars and starlets remain media darlings and childhood heartthrobs. They overcome any homogeneity in the musical landscape by more firmly asserting their characters. Personas are magnified by the 24-hour news/online feed. Lady Gaga's meat suit style sense may make as much of an impact as any of her mega-hits. West is as well-known for critiquing George Bush and bum-rushing Taylor Swift's acceptance speech as he is for his 2005 No. 1 "Gold Digger." The data stream that strips away musical identity exaggerates personal identity. As ever, pop music eats itself-and pop culture lives on.