Five minutes into Girl Talk’s October concert at the Starlight Ballroom in ­Philadelphia, about a hundred audience members have crowded onto the stage and are dancing as a dry-ice haze seethes around them, strobed by colored lights. Girl Talk himself–a.k.a. Gregg Gillis, a 27-year-old former biomedical engineer from ­Pittsburgh–bends over a laptop on a table at the front of the stage, a white bandanna around his head. About 15 minutes in, a shirtless young man leaps onto the table. His furious dancing loosens a cable plugged into Gillis’s laptop, and the music booming through the club’s P.A. speakers abruptly stops. “The people dancing on the table are not helping anyone,” ­Gillis says into his microphone, as he ­fumbles with the cables taped to the floor. Booing from the audience finally shames the accidental saboteur off the stage.

Such are the perils of live performance in the age of the mashup, a fledgling art form that, like Gillis’s shows, blurs the boundary between creator and consumer. A mashup is a digital recombination of musical elements extracted from different recordings–say, a vocal line from one song, a piano part from another, a drum pattern from a third. Some observers trace the form’s origins to avant-garde experiments with tape loops in the 1970s, others to the “sampling” of existing recordings in 1980s rap. But the mashup is a distinctly 21st-century phenomenon, made possible by the proliferation of digital music files and the increasing quality and accessibility of software for manipulating them.

Gillis may be the most popular mashup artist in the United States. He’s opened for Beck. He’s performed at the rock festival Lollapalooza. His MySpace page gets more hits than that of indie-rock sensation Wilco. When he tours, he packs good-sized clubs–like the Starlight Ballroom, where more than a thousand people pressed toward the stage, dancing.

Part of Gillis’s appeal is the sheer number of samples he combines in his mashups. Wikipedia lists 24 sources for “Play Your Part (Pt. 1),” the first track on his latest album, Feed the Animals. “Play Your Part” begins with a vocal by the hip-hop group UGK, paired with an instrumental track from the Spencer Davis Group’s “Gimme Some Lovin’.” About 42 seconds in, the rhythmic chant “Pump that shit up,” from a song of the same title, succeeds the UGK lyric, and a few seconds later, “Gimme Some Lovin’ ” drops out. The looped fragment “Pump that shit” continues over a drum sample from a song by the Louisiana R&B singer Cupid. The vocal drops out, but the drum beat continues as the signature synthesizer arpeggios of Pete Townshend’s “Let My Love Open the Door” enter. New samples succeed each other for another three and a half minutes, taking in the work of rappers Ludacris, Birdman, and T.I. and the bands Twisted Sister, Rage Against the Machine, and Temple of the Dog–among others.

Girl Talk Concert
October 9, Starlight Ballroom, Philadelphia

Feed the Animals
Girl Talk
Album available on illegalart.net

DJ Earworm Mashups
djearworm.com

A good mashup can revivify the familiar by placing it in a new context, and for the crowd in Philadelphia, that’s what Girl Talk’s work appeared to do. Cheers went up when recognizable instrumental lines entered the mix. Audience members sang along with sampled hip-hop lyrics and danced with an enthusiasm that the source songs probably wouldn’t have inspired on their own.

/files/22845/TR_mixAudio_R2.swf

The console above offers a way to simulate the creation of a music mashup. Six vocal lines and six instrumental tracks have been extracted from their original contexts. Their pitch and tempo have been shifted so that, for the most part, they can be seamlessly recombined. (There are a couple of exceptions, reminders of how difficult matching musical tracks can be.) Click a dial to add or subtract a given track from the mashup mix.

Interactive by Conrad Warre and Alastair Halliday.

Vocals
ABC: How to be a Millionaire (Fry, White) Dazz Band: Let it Whip (Andrews, J.R./Leon “Ndugu” Chancler) Diana Ross: Love Child (Deke Richards/Pam Sawyer/R. Dean Taylor/Frank Wilson) Fergie: Glamorous (Bridges, Christopher/Stacy Ferguson/Jamal Jones/Elvis Williams) Katy Perry: I Kissed a Girl (Cathy Dennis/Lukasz “Doctor Luke” Gottwald/Max Martin/Katy Perry) Robin Thicke: Magic (Gass, J./Max/Robin Thicke)

Instrumentals
Daft Punk: Around the World (Thomas Bangalter/Guy-Manuel de Homem-Christo) Exposé: Point of No Return (Lewis A. Martineé) Falco: Der Komissar (Falco/Robert Ponger) Rick James: Superfreak (Rick James/Alonzo Miller) Bees Deluxe: Roll Over Stockhausen (Warre) Sister Sledge: We are Family (Bernard Edwards/Nile Rodgers)

But among Gillis’s fellow mashup artists, the response has been tepid. “The stuff he’s putting over the top of a track seems to be like, ‘Oh, remember this tune, remember this tune, remember this tune,’” says Tim Baker, who hosts a music-themed podcast called Radio Clash. “It’s like you’re trying to watch TV, and someone is sitting there switching the channel every 30 seconds.”

“Form requires repetition,” says Jordan Roseman, who makes mashups under the sobriquet DJ Earworm. “You listen to any pop song on the radio: the elements repeat themselves. They go away, you miss them, they come back, and you welcome them. And just when you’re getting sick of them, it goes somewhere else. And just when you start to miss them again, they come back.” Girl Talk, however, simply discards each of his samples after it’s played for 30 or 40 seconds.

He also tends to pair instrumental tracks with hip-hop vocals, as the analysis of “Play Your Part (Pt. 1)” might suggest. “In the mashup community,” says Luke Enlow, a mashup artist from New Hampshire who releases music under the name Lenlow, “that’s kind of seen as a cop-out because it’s very easy to do, because you don’t have to worry about keys matching.”

Gillis doesn’t deny that hip-hop mashups are easier to do; he just considers that irrelevant. “What the Ramones play isn’t very difficult to play,” he says, referring to the New York band widely credited with launching the punk-rock movement. “I think of playing the computer as a very punk exercise.” He also invokes the figure of Joe Satriani, a rock guitarist renowned for his blisteringly fast solos. “Joe Satriani is not necessarily more important than [Nirvana’s] Kurt Cobain just because he can wail on the guitar better,” Gillis says.

It’s a common pattern in music history, however, that at the moment of a popular form’s ascendancy, its most ambitious practitioners begin to move in a more esoteric direction. The sidemen who played in Benny Goodman’s small ensembles at the height of swing are one example; the Beatles and Beach Boys in the mid-1960s are another. Mashups haven’t yet achieved the type of cultural prominence that jazz and rock did in their heyday, but if there’s a similar transitional figure in the current mashup scene, it could well be Roseman.

Roseman double-majored in music and computer science at the University of Illinois, and because he can analyze the harmonies in his raw materials, he can see key clashes looming a mile away. He doesn’t have to rely as heavily as his peers do on trial and error to find samples that fit together musically.

He’s also more skilled than many at acquiring raw material in the first place. The digital files from which mashups are made are rarely complete recordings; they’re usually isolated vocal or instrumental tracks. Recently, it’s become more common for recording artists themselves to release disaggregated tracks to encourage mashup artists to remix them. Sometimes record labels will leak the tracks unofficially, to drum up publicity. Sometimes engineers spirit raw tracks out of the studio: once they’re posted online, they rapidly propagate through the mashup community. Disaggregated tracks can also be found in surround-sound recordings and video game software. But if no such option is available, mashup artists have to try to extract the material they need from complete recordings.

Roseman wrote a book, Audio Mashup Construction Kit, that has a 40-page chapter called “Unmixing,” about isolating vocals and instrumentals. One of the tricks he describes is to find a section of a song where an accompaniment figure repeats for a few bars before a vocal comes in. Software can then, effectively, subtract the repeated figure from the final mix, isolating the vocal line.

It’s Roseman’s artistic instincts, however, that set him apart. Like Girl Talk’s mashups, Roseman’s generally sample multiple songs: his biggest hit, “United State of Pop,” borrows elements from all of Billboard’s top 25 songs from 2007. But rather than string his samples together in long chains, as ­Gillis does, Roseman gradually layers them over each other, adding texture and building momentum as a song progresses.

A good example is the hypnotic “Stairway to Bootleg Heaven,” which borrows tracks from seven different recordings. The heart of the mashup is the juxtaposition of an ’80s Eurythymics song and a cover of Led Zeppelin’s “Stairway to Heaven” by, of all people, Dolly Parton. On its own, the unlikely and surprisingly effective pairing of synthesized rhythm section with fiddle and mandolin would be enough for a memorable mashup. But Roseman goes further, adding a minute-and-a-half introduction that combines a piece by performance artist Laurie Anderson with a song by the synth-pop band Art of Noise. Toward the end of the mashup, a sample from the Beastie Boys’ “So What’cha Want” adds urgency, and at the song’s climax, Pat Benatar’s “Love Is a Battlefield” enters in double time. Throughout the mashup, as a kind of connective tissue, a sample from the Beatles’ “Because” floats in and out, spectral and mysterious. Although several of the recordings Roseman samples sound dated if not risible on their own, the combination is sublime.

Roseman hasn’t enjoyed nearly the popular success that Gillis has (though his work is by no means obscure: “United State of Pop” was one of the 100 most-played songs on pop radio for several months in 2008, and his remarkable mashup of Kanye West’s “Love Lockdown” and Radiohead’s “Reckoner” met the approval of West himself, who posted the accompanying video on his website). Still, if the question is whose mashups we’ll be listening to 20 years from now, I know who I’d put my money on.

Larry Hardesty is a Technology Review senior editor.