It started as a challenge.
Jordan Roseman, a.k.a. DJ Earworm, was bored. So in 2007, he decided to raise the stakes, assigning himself a daunting task: to combine the top 25 pop songs of the year into one. Could he slice and dice 25 seemingly disparate tunes to create a single song that would stand on its own — an impossibly catchy "earworm" that embodied the spirit of the original songs, yet carried his own spin?
The first "United State of Pop" instantly made an impression. And in the time since, Roseman's cumulative year-end mashups have become an annual tradition. They're played on the radio like the pop songs they've transformed, and have racked up millions of views on YouTube; 2009's "Blame It on the Pop" has tallied nearly 48 million all on its own.
Each edition of the United States of Pop tells a different story; together, they form a revealing study of contemporary pop music. In making the mashups, Roseman has been analyzing pop music trends and tropes on a micro level.
When I recently caught up with Roseman by phone, we talked about how music has evolved since he started the experiment, what each year's top songs say about American culture, and the way he views his own relationship to the United States of Pop.
If he does his job right, he told me, the United States of Pop will reflect people's experiences that year, evoke nostalgia, and reveal some greater truth about the state of music. "What I think [the mashup] should be is not the point," he insisted. "It’s never the point." Really, he said with a laugh, each United State of Pop is just "a funhouse mirror."
2007 and 2008: The United State of Pop figures itself out
In 2007, Roseman was just looking for something new to do. "I had put out a mashup of these songs from all different eras, and I was wondering, 'What if I put out a mashup that was just all current hits?'" he says. As he was playing around with some of the year's catchiest songs — including Rihanna and Jay Z's "Umbrella" and Justin Timberlake's "What Goes Around Comes Around" — he realized that many of his choices already lined up with the Billboard year-end chart. So why not widen the scope?
When I asked him why he chose to work with the top 25 songs versus any other number, Roseman answered with the audible equivalent of a shrug. While he finds 25 to be a "nice number," the reason the initial 2007 mashup contained 25 songs — instead of, say, 15 or 20 — was that he wanted to use the piano melody from the Fray's "How to Save a Life" for his outro. With that, Roseman had the final puzzle piece for what, in his words, was a "cool party trick."
"I was still learning how to put things together, and in a way things were less challenging because I just let things be out of key where I wouldn’t do that today," Roseman told me. For proof, he pointed to Chris Daughtry's "Home," which is in a different key and has a harder "rock" sound than many of the pure pop songs to come out of 2007. "Rock 'n' roll is tough sometimes to mash up," he said, thanks to inextricable guitars. But as far as the top Billboard charts go, he went on, "there is no rock 'n' roll [anymore], so we don’t have to worry about that."
In 2008, he opted for a more downtempo mashup by using the backing instrumentals of Coldplay's "Viva La Vida" to underscore songs like Katy Perry's "I Kissed a Girl," Lil Wayne's "Lollipop," and Pink's "So What." The result is a sweeping, sometimes melancholy mashup that swells and loops, until it finally fades into the distance.
"I didn’t know whether people would bite my head off for being so mellow," Roseman told me with a laugh. "But at the same time, it was my second one, so there was no expectation." After all, he went on, "I never told people I was going to do more than one."
So when his head remained stayed safely attached to his body after 2008's release, Roseman decided it was time to crank things up to 11.
2009: "Blame It on the Pop" crystallizes how the United State of Pop can reveal greater truths about pop music
I asked a few of my fellow Vox staffers to name their favorite DJ Earworm mashup, and with just a couple of exceptions, the overwhelming consensus was 2009's "Blame It on the Pop."
While the "party tricks" of 2007 and 2008 achieved their baseline mission of combining their component songs in a way that wouldn't seem totally nonsensical, "Blame It on the Pop" was the first mashup that became a pop song in its own right. With help from the Black Eyed Peas' "I Gotta Feeling" pulsing behind Beyoncé's "Halo," Lady Gaga's "Just Dance," and Kelly Clarkson's "My Life Would Suck Without You," "Blame It on the Pop" builds and drops, dancing with abandon.
Not coincidentally, "Blame It on the Pop" is also Roseman's favorite mashup to date. While his 2007 and 2008 compilations allowed him to refine his aesthetic and elevate the United State of Pop beyond the "mixtape," 2009 was the year he figured out what, exactly, he wanted his experiment to yield. "I was like, 'Okay, this could be a summation of how we feel,'" he said. "It could be a celebration of the year." And so his focus shifted from trying to have fun for himself to trying to use that aforementioned "funhouse mirror" to reflect the audience's year instead of just his own. "['Blame It on the Pop'] actually is a song that has a relationship to the audience rather than just me," he said. "I got much more of a feeling of responsibility to relate to the zeitgeist."
Aside from the musical lessons he learned, though, 2009 is the year the United State of Pop became a mashup phenomenon. Quite simply, it changed his life. "There’s no comparison to what my career was like beforehand and afterward," he told me. "I feel like I never made such a leap forward. Even if I were to match it, it wouldn’t be that leap forward."
2010 through 2013: Partying gets a little more complicated
As Roseman got more comfortable with the mashup format and with Billboard's charts, pop music started to move on from the straightforward party anthem that defined it from 2007 through 2009. If there's one major trajectory for this past decade in pop music, Roseman told me, it's ditching overt artificiality for songs that feel more "authentic."
Since he started the United States of Pop in 2007, Roseman says, "we've had two major movements: EDM and an organic kind of vibe, which is how I would define this decade. People want this feeling of authenticity now. When I started, they wanted more artificiality, for want of a better word. Not that it’s any realer now. But it feels realer."
He then pointed to Lady Gaga as a specific example of how meticulous, overtly slick production has fallen more out of favor in recent years. "There’s reality underneath it, but on the surface it’s all artifice. And that is not at all where we are now," he told me. "Now people want to strip it down; they want it real. They want to know that you came up by yourself through the internet, and that you’re just like them."
You can hear it in 2012's "Shine Brighter," which isn't his strongest mashup but is nonetheless one of his more interesting ones because it sits at the crossroads he's talking about.
Roseman calls 2012 "our last big shift ... when we went from sort of EDM to this sort of Sam Smith–dominated, Ed Sheeran, adult contemporary vibe."
"Shine Brighter" features a whole mess of pulsing electronica clashing up against what Roseman repeatedly referred to during our conversation as "adult contemporary." Kesha — who had made her name with the unapologetically thumping beats of 2010's "Tik Tok" — transitions to rhythmic, strumming guitars in her 2012 hit "Die Young." Fun's "We Are Young" crescendos into Nicki Minaj's "Starships." As Rihanna wails over "Diamonds," Gotye mourns for "Somebody That I Used to Know," and Adele "Set[s] Fire to the Rain" Flo Rida and Psy dance right on by.
By the time 2013 rolled around, Roseman had begun to notice a darker undercurrent in pop music, something he tried to bring out for what he calls a "protest song" about consumerism. That year's mashup, "Living the Fantasy," features Lorde's "Royals," Miley Cyrus's "Wrecking Ball," Avicii's "Wake Me Up," and even Taylor Swift's EDM attempt "I Knew You Were Trouble." Roseman admits it didn't quite hit the mark he wanted it to — "I think the lyrics are really tight, but the feeling didn’t quite get there" — but that the motivation behind aiming for a "darker place" came out of 2013's more conflicted songs.
2014 and 2015: Pop starts winding down
After stumbling a bit with 2013's more message-driven mashup, Roseman went back to leaning on the music for the 2014 edition. Interestingly, this proved his theory that holding a "funhouse mirror" to the year in pop can be much simpler, and much more revealing, than an interpretation. "Do What You Wanna Do" (my personal favorite) dances like no one's watching with Nicki Minaj's acidic interjections on "Bang Bang," a swelling peak based on Charli XCX's "Fancy" chorus, and even Idina Menzel reminding us to "Let It Go," courtesy of the Frozen soundtrack. But it still teeters on the edge of a minor key with Tove Lo's depressed ballad "Habits (Stay High)," Hozier's crooning "amen," and John Legend's pleading "All of Me." (Not for nothing: I can't stand any of these songs outside this mashup.)
"Do What You Wanna Do" is also one of Roseman's most tempered, melodic mashups since 2008's "Viva La Vida" — which reflects today's more temperate charts.
In Roseman's view, pop music is currently dominated by "soft, adult contemporary stuff, like Ed Sheeran or Adele. Some of Adele’s new album  just sounds like melodramatic ballads from the '70s."
But he also says that pop is returning to what he calls "retro-funk," noting, "We've got groups like Maroon 5’s 'Sugar,' or the Weeknd’s 'I Can’t Feel My Face,' some Jason Derulo stuff, Daft Punk’s 'Get Lucky,' 'Blurred Lines' … it’s all just comfortable retro-funk that feels like it’s from the '70s or early '80s. You can tell it’s from today, but it so refers to another time."
You can feel that funk beat in 2015's ambitious — if scattered — mashup, "50 Shades of Pop," which pulls from the year's top 50 songs instead of the traditional 25. But the prevailing feeling, even with acts like Sheeran and Fetty Wap going up against each other, is that Bruno Mars could come sliding into the room at any minute with a tailored suit and a wink. At its core, 2015 was a smooth, funky jam — and one we've heard it before.
Roseman told me that very little of today's most successful pop music is going to "make the older generation freak out," usually a given no matter what the trend. (See: rock 'n' roll, techno, hypersexual pop, rap.) Even dubstep master DJ Skrillex, he pointed out, has teamed up with Justin Bieber to create more "soothing" EDM (though to be fair, this definition of "soothing" is probably not universal). A prime example is Drake's "Hotline Bling," a smooth and melodic hip-hop song that "is almost adult contemporary, right there. It’s just mellow ... it's not abrasive in any way."
Roseman conceded that there is still a jagged edge left to some popular hip-hop. "[Nicki Minaj's] 'Truffle Butter,' there's still some shock value going on," he said. "But even in that, the shocking, explicit hip-hop still has this comfortable, luxurious vibe to it."
In fact, the pointed raps in "Truffle Butter" are built atop a slowed-down version of Maya Jane Coles's 2010 house song "What They Say." The song is purposely smooth. It flows. And even if there's shock value to it — Google the title at your own risk — its primary objective is not to shock you out of your seat. It would rather slink across the stage, confident and lush, and creep up on you when you least expect it.
Just about the only artist Roseman identified as breaking this "soothing" trend for 2015 was — to no one's surprise — Rihanna. "It took me so many listens just to figure out what is going on with [the "Bitch Better Have My Money"] rhythm," he told me, with the triumphant tone of someone who had solved a seemingly impossible puzzle.
But even Rihanna stripped down her usual brashness at least once this year, to sing for Sir Paul McCartney's gently strumming guitar on "FourFiveSeconds."
As for 2016? Probably "more of the same."
When I asked Roseman if he has any predictions for what 2016 might bring, he sighed a little; he didn't exactly sound resigned, but he didn't sound excited, either. "It would be more of the same," he said. "Obviously, Adele is going to have hit after hit after hit after hit ... [so] more retro-funk, more adult contemporary, some slightly weird, psychedelic hip-hop."
"I’m always surprised at how old whatever the new thing is, is," Roseman told me with a chuckle. "I feel like after many decades of real music revolutions, we keep on recycling more and innovating less."
And while he concedes that this view might be coming from him as "a grumpy old man," Roseman insists that the decade he's spent working in pop music has leaned heavily on older traditions. When I asked why he thinks that is, he took a second to clarify his thoughts before declaring, "Certain times call for comforting music. Music that isn’t too challenging and just kind of takes you to a safe place."
"That's what you think 2015 is?" I asked.
This time, he didn't hesitate. "That," he said, "is what I think this decade is."