The singer confesses Carrie Underwood's voice gives him goosebumps
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Michael W. Smith had a wish list when he was putting together the lineup on his latest Christmas album, and toward the top was Carrie Underwood. Though the Grammy-winning Christian singer was already a fan, he was still blown away when Underwood actually stepped into the studio to record her part.

“What a moment – it made my hair stand up a little bit,” Smith tells PEOPLE of the star’s powerful performance on "All is Well," an original Christmas song he wrote. “In my entire life, I’ve never felt that way in the studio. When she sang it the first time, we were plastered against the wall. Usually you’re like, ‘That’s great, but let’s just try it again,’ but I remember pushing the talk back button and we just said, ‘Wow.’ And she says, ‘Well, I m just getting warmed up.’ And I go, ‘Really?’ You just don’t hear people sing like that. Her pitch is just impeccable.”

Underwood is just one of the dream team of singers Smith duets with on The Spirit of Christmas, his fourth Christmas album. The Nashville-based singer brought in other country star neighbors like Little Big Town, Vince Gill, Jennifer Nettles and Lady A to help out, too. However, snagging the most surprising name in the mix, U2 frontman Bono, meant calling in a favor to a longtime friend.

“I’ve known Bono for 12 years,” Smith says. “We got to know each other because we had a passion for Africa and the AIDS epidemic and we got to work with the ONE Campaign. Whether we ever got to do anything together musically wasn’t on my radar. I figured it was probably impossible and I always wanted to preserve the friendship.”

But Smith’s co-producer, Robert Deaton, urged him to reach out. “I thought, ‘That’s a tall order. And I don’t want to infringe on friendship.'” Then they came up with a unique idea for the Irish rocker – a recitation rather than a singing part – and Smith sent a note to his friend.

“He emailed me back and said, ‘Sounds interesting.’ It came down to the wire, but deep down inside I had this hunch that he’d do it.” The result is a hushed reading of “The Darkest Midnight,” a traditional Irish Christmas carol. “He whispers and it’s haunting and beautiful,” Smith says. “I think he had a blast doing it. In an email a couple months ago, he said, ‘I love the whispering – it reminded me of Christmas morning.’ He got into it.”

See below for a behind-the-scenes look at Smith’s The Spirit of Christmas: