The 2012 Lollapalooza lineup to be announced Wednesday reaffirms that the culture of DJs and electronic artists is catching up with rock as a live attraction on the lucrative summer festival circuit.

Two of the rock headliners for the Aug. 3-5 festival in Grant Park -- the Red Hot Chili Peppers and a reunited Black Sabbath – have a retro feel. Also playing closing slots on the main stages will be the Black Keys and Jack White, two acts that update classic, guitar-based blues and rock from the '60s and '70s.

But for an increasing number of fans in a key Lollapalooza demographic – those in their late teens to mid-twenties – the dance music acts are the primary draw. Continuing the increasingly heavy dance-music theme of past summers, two electronic acts for the first time will headline the main stages: 22-year-old Swedish DJ/producer Avicii (Tim Bergling) and French electronic duo Justice.

The big music story at last year's festival was the explosive growth of dance-music acts such as Skrillex and Deadmau5, and this year the Perry's electronic stage will once again be moving to a bigger location in Grant Park to accommodate the burgeoning fan base, Texas-based promoters C3 Presents have said. Among the headliners at Perry's will be DJ/producer Bassnectar, coming off two sold-out shows scheduled next weekend at the Congress Theatre, and singer Santigold, who is scheduled to release the follow-up to her acclaimed 2008 debut album in a few weeks.

Nostalgia remains a big theme on the rock side of the Lolla spectrum. Besides the Sabbath set, which (according to C3) includes original members Ozzy Osbourne, Tony Iommi, Geezer Butler and Bill Ward, two other notable reunions are being staged: Texas avant-punk group At the Drive In, which broke up in 2001, and the Afghan Whigs, the Greg Dulli-led Cincinnati band that also imploded in 2001.

Think you've seen and heard some of this lineup before? You have. The Chili Peppers return to headline Lollapalooza for the third time, having done it previously in 1992 and 2006. Also making at least their second visits to the festival are the Black Keys, Jack White (who appeared previously with the Raconteurs), Miike Snow, Bloc Party, the Temper Trap and Delta Spirit.

Only a smattering of world-music acts are represented, including Brazil's O Rappa, Chile's Los Jaivas and Mali's Amadou & Mariam. You'll also have to dig pretty deep to find hip-hop, represented by Childish Gambino, Doomtree and Macklemore & Lewis.

In its early years during the '90s, the festival became a stepping stone for a large number of cutting-edge rock acts toward wider recognition. That role has diminished in recent years as Lollapalooza has reinvented itself as more of a mainstream festival for rock, while the electronic component has restored some of its youthful vitality.

This year's lineup boasts at least a dozen up-and-comers aiming to broaden their audience. These include Canadian artist the Weeknd, alternative R&B vocalist Frank Ocean, British folk-soul singer Michael Kiwanuka, blues guitarist Gary Clark Jr., soul-rockers Alabama Shakes, Merrill Garbus and her band Tune-Yards, and singer-songwriter Sharon Van Etten.

Also on the bill: Florence + the Machine, Passion Pit, the Shins, Sigur Ros, Fun., M83, Franz Ferdinand, Metric, Dawes, the Temper Trap, Die Antwoord, Mona, the Growlers, the Gaslight Anthem, Hey Rosetta!, JEFF the Brotherhood, Band of Skulls, Anamanaguchi, SBTRKT, First Aid Kit, Tame Impala, Wax, the Walkmen, FIDLAR, JJ Grey & Mofro, LP, JC Brooks & the Uptown Sound.

Milo Greene, Neon Indian, Dum Dum Girls, Kopecky Family Band, Washed Out, the Jezabels, Aloe Blacc, Trampled by Turtles, Yuna, Bear in Heaven, Walk Off the Earth, Blind Pilot, Animal Kingdom, Chairlift, Dev, J. Cole, the Black Angels, the Sheepdogs, Yellow Ostrich, the Dunwells, GIVERS, DJ Mel, Polica, Empires, Bombay Bicycle Club, Kevin Devine, Wale.

Dry the River, White Rabbits, Helena, Haley Reinhart, Imaginary Cities, the Head & the Heart, the Devil Makes Three, Overdoz, the Big Pink, Oberhofer, Ambassadors, Twin Shadow, the War on Drugs, DJ Zebo, the Tallest Man on Earth, Chancellor Warhol, Toro Y Moi, O Rappa, Laura Warshauer, Dr. Dog, Bowerbirds, Red Oblivion, Of Monsters and Men, Orchard Lounge.

Perry's stage: Bassnectar, Santigold, Skream & Benga, Totally Enormous Extinct Dinosaurs, Kaskade, Little Dragon, Star Slinger, Calvin Harris, Porter Robinson, Nadastrom, NERO, Sub Focus, DJ Nihal, Madeon, the White Panda, Knife Party, Zedd, SALVA, Zeds Dead, Paper Diamond, Kid Color, Big Gigantic.

Tickets ($230 for a three-day pass) are on sale at lollapalooza.com. Specific days for each act will be announced at a later date, at which point single-day tickets will go on sale. Last year, 270,000 fans attended over three days, a Lollapalooza record.

greg@gregkot.com