Candice Glover, Angie Miller, Amber Holcomb, Kree Harrison

It's a gorgeous spring Saturday in Hollywood, but instead of soaking up the sun at the pool of the Sunset Marquis, the final four American Idol contestants are tucked away in the hotel's basement recording space, NightBird Studios. When Angie Miller fails multiple times to hit a particularly high note in the Jessie J song "Who You Are," an assistant brings her a second mug of steaming green tea. "I'm so blowing up my voice ­today!" Angie says to producer Beau Dozier. "You need to make magic with this song." After finishing her cup, she tries again, this time nailing the note and the subsequent runs — and causing Dozier to lean back, exhale and say, "She really wants to win this thing."

And in order to win American Idol, there's no slowing down. Once the lights go out on the Thursday results show, the ­contestants who make it through immediately begin planning their next performances. (Fridays involve song-selection meetings with vocal coaches, followed by Saturday studio sessions to record that week's iTunes downloads.) On this particular day, it's evident that vocal fatigue has set in not only for Angie, but also for Candice Glover, Kree Harrison and Amber Holcomb. As they sing, Candice and Kree start second-guessing themselves ("My voice is gone, so I think I'm singing off-key," Candice admits), while producer Siedah Garrett criticizes Amber for "lacking energy and feeling."

Then there are the critiques from mentor and Interscope Records chairman Jimmy Iovine, who spends hours with the contestants. This week, Iovine targets Angie for occasionally oversinging, Kree for her poor song selection and Amber for her inability to connect with the audience. But he says Candice has the most daunting task. "She has to protect that very, very big voice, and that's almost out of her control. These girls are singing three times a day, four days a week."

Overall, Iovine is impressed. "This is the first year that there are four kids behaving like pros [in the studio]. But they tend to oversing. They have to save their voices."

There are moments of levity among the pain and suffering, such as when Kree interrupts her "A Whiter Shade of Pale" with a coughing fit. "Hairball!" she says with a laugh ­before launching into a spot-on ­imitation of judge Nicki Minaj. "Your vocal was A-plus-plus!" she mimics, much to the producers' delight. "You were everything!"

One of these singers will hear similar words when she is crowned the winner of the Fox reality show on May 16. And the young women insist there is no time for cattiness. "We genuinely love each other," Kree says. "They're like my sisters, so whatever happens is going to be amazing."

American Idol airs Wednesdays and Thursdays at 8/7c on Fox.

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