Imagine old, bald Pete Townshend shuffling gingerly onstage as a synth burbles up behind him — “Let My Love Open the Door.” Now imagine the rapper Pimp C already on that stage, in a white fur suit and hat, holding up four fingers to show off his bling. A kick line of girls in black minishorts walks it out for DJ Unk, who’s rapping about a kick line of girls, then Levon Helm appears on a drum riser to chirp out “The Weight.” Also onstage: Jay-Z, Black Sabbath, Rick Springfield, Kesha, Bruce Springsteen, Miley Cyrus, the Ramones and Tupac and Biggie Smalls (both back from the dead) and hundreds more. In the audience are a few thousand fans jammed together beneath a blinding light show, waving their arms as rolls of toilet paper and explosions of confetti fall around them. You sense they’re feeling the same freedom, daring and camaraderie that they might at a house party when someone’s parents are away. This is pretty much the state of affairs at a Girl Talk show these days.

Girl Talk is the stage name of the 29-year-old Pittsburgh native Gregg Gillis.

In November, Gillis and his label, Illegal Art, released the fifth Girl Talk album, “All Day,” as a free download. Within 24 hours, several sites had posted annotations of “All Day,” cataloging the samples on the album —there are 373 of them. Download traffic was so heavy that MTV News ran the headline “Girl Talk Apologizes for Breaking the Internet” — hyperbole, but not far from the truth. Illegal-art.net reports that “All Day” was downloaded so often that the servers crashed. In Girl Talk’s honor, Pittsburgh declared Dec. 7, 2010, “Gregg Gillis Day.”

All this excitement is focused on a performer whose instrument is a laptop. Girl Talk songs are mash-ups: chunks of other people’s songs combined into new ones: the Rolling Stones and the rapper Wiz Khalifa, Ice Cube and Devo. The mash-ups sound ironic to the ironically inclined and like pure joy to the joyfully inclined, and for both camps they’re fun to dance to. These are not just a collection of other people’s hooks; Girl Talk has created a new kind of hook that encompasses 50 years of the revolving trends of pop music. Sometimes cynicism is a hook, sometimes the hook is﻿ humor, angst, irony, aggression, sex or sincerity. Girl Talk’s music asserts all these things at once.

On Dec. 3, Girl Talk inaugurated the new Stage AE concert hall in Pittsburgh, filling the arena on two consecutive nights. (Despite the fact that there are no instruments onstage, Girl Talk can sell tickets as fast as some of the stars he samples.)