"I would describe Bono's singing as 50 percent Guinness, 10 percent cigarettes — and the rest is religion. He's a physical singer, like the leader of a gospel choir, and he gets lost in the melodic moment. He goes to a place outside himself, especially in front of an audience, when he hits those high notes. That's where his real power comes from — the pure, unadulterated Bono. He talks about things he believes in, whether it's world economics or AIDS relief in Africa. But the voice always comes first. That's where his conviction lies.

He has so many influences. You hear Joe Strummer, Bob Marley, Otis Redding, Elvis Presley, even John Lennon. And he has the same range as Robert Plant. It's amazing, the notes he has to go through in the first lines of "Sunday Bloody Sunday." But it's filtered through this Irish choirboy. The Joshua Tree shows the mastery Bono has over his voice and what he learned from punk, New Wave and American musicians like Bob Dylan. In the quiet moments of "With or Without You," you can imagine him sitting under the stars. Then, when he comes back to the chorus, all of a sudden it's a hailstorm.

A lot of Bono's free-form singing comes from the band's rhythms and the church-bell feeling of the Edge's playing, the way the guitar sings in that delay. Bono can glide vocally through all of that. But it's very natural. And he's not afraid to go beyond what he's capable of, into something bizarre like his falsetto in "Lemon." In "Kite," on All That You Can't Leave Behind, he belts it out like he's crying with joy.

I never had the feeling he was manipulating the power of his voice to show off. They say a submarine never goes in reverse. That's Bono, always looking for a new way of singing something. That's one thing I learned from him: Never rest. Keep learning and be a good listener. That's the spirit of singing — and he definitely has it."