Tool is a band of mystery, of brooding, unsettling rhythm and words of anxiety and decay. But singer and part-time vintner Maynard James Keenan seemed oddly vulnerable Saturday as he waved a crutch from the shadows during the band's headlining set at the Epicenter Festival, apologizing repeatedly for injuring his leg recently while harvesting grapes.

"I want to make sure you get drunk and run into each other," Keenan joked to fans at the Fairplex in Pomona, explaining why Tool didn't cancel. "All I ask for is acknowledgment of my sacrifice."

No apologies were needed for hard rock fans gathered for Epicenter's full day of loudness from varied genres. The festival was co-sponsored by KROQ-FM (106.7), and the lineup represented the harder side of the station's playlist, from the marquee names of Tool, Linkin Park and Alice in Chains to the rising locals Atreyu and Hollywood Undead.

Opening with "Jambi," Tool played a 90-minute set heavy on atmosphere, as shuddering waves of sound unfurled over the crowd. There was thundering prog guitar from guitarist Adam Jones on "Stinkfist" as a ghostly skull-like image undulated behind him. Tool remains an intensely visual live band, with video, lasers and ominous clouds of fog, though the visuals are never used to glorify the players as personalities, only to embellish the music and the band's obsessions with the elements of fire, water, earth and flesh.

Tool, Linkin Park and a revamped Alice in Chains will anchor a new addition to the summer festival circuit.

Dubbed Epicenter, the rock-focused event is scheduled for Aug. 22 at the Fairplex in Pomona and also will feature Australian metal act Wolfmother and Tom Morello's latest project, Street Sweeper Social Club.

Hip-hop artists Atmosphere and Aesop Rock also are scheduled to perform at the all-day event, as are Hollywood Undead, Atreyu and Sonny.

Conduct a cursory YouTube search of  “Exile” + “MPC," and you’ll see the Echo Park-based producer/rapper wielding his Akai MPC sampler as a weapon -- delivering clavicle-snapping drum smashes in a way that transforms the machine from a producer’s best friend into a potent live instrument.

Coupled with his surprisingly adroit rhyme skills, Exile’s stage shows and DJ sets rank among the most entertaining in recent rap memory -- particularly when paired with his partner-in-crime, Warner Bros.-signed Blu.

Best known for producing 2006’s acclaimed collaboration with Blu, “Below the Heavens,” Exile emerged as a viable creative force in his own right on this year’s “Radio,” a found-art opus that found him re-configuring taped snippets of everything from old commercials to evangelical sermons to Alan Watts. Sewing them into the fabric of an instrumental hip-hop album in the vein of J Dilla or Madlib, “Radio,” firmly establishes the Garden Grove-raised producer as one of the West Coast’s leading lights.

With DJ Day in tow, Exile -- the beatmaker born Aleksandr Manfredi -- will perform in-store for "Radio" on Saturday night at Fat Beats. He will be doing his 2 MPC / 2 Turntable Set. There will be 10 cases of Colt 45. Good times will be had by all. He chatted with Pop & Hiss to preview the show.

The band has a new singer and is recording a new album.

The daily ritual is always the same: nine guys kneeling around a pile of money in Studio B at Henson Recording Studios in Hollywood, shouting, cheering and moaning as a pair of dice rolls across the carpet, delivering moments of euphoria and defeat. The members of Alice in Chains are among the group, briefly distracted from their final week of sessions for the band's first album of new material in nearly 14 years. Against the wall is an impressive row of vintage electric and acoustic guitars. Incense is burning and a U.S. flag hangs over a sound partition. But for the moment, the rock will have to wait.

Guitarist Jerry Cantrell looks up from his pile of cash and smiles. "Compared to how we used to have fun," he says, "this is pretty tame." The low-stakes game is Left, Center, Right, and many $5 bills change hands before it's over. The day's winner is producer Nick Raskulinecz, laughing now as drummer Sean Kinney grumbles something about the man's take of "two hundred bucks in the last two games."

The real challenge is still ahead, as the three surviving members of Alice in Chains -- Cantrell, Kinney and bassist Mike Inez -- work to complete new songs as a band for the first time since the death of singer Layne Staley from a heroin and cocaine overdose in 2002 at the age of 34. Their album, still untitled and set for release mid-September on Virgin/EMI, will be another case study of a major group continuing after the loss of a key member. AC/DC managed the transition successfully back in 1980, while others have failed to match their earlier triumphs, including INXS (whose search for a new singer was turned into a 2005 reality TV show) and classic rock acts Queen and the Doors.

"I don't think we ever intended to do anything," says Cantrell, 43, his thick, blond beard marking the months of preparation and recording that has gone into the new album. "With the passing of Layne, all possibility of that went out the window, probably in my mind and everyone else's too."