Bono has confessed he struggled to write U2's new and 'personal' album.
The rocker and bandmates The Edge, Adam Clayton and Larry Mullen Jr released 'Songs Of Innocence' for free to iTunes ysers on September 10, but found composing the tracks difficult as they had to revisit and rehash old memories.
Bono said in an interview with Rolling Stone: "We wanted to make a very personal album.
"Let's try to figure out why we wanted to be in a band, the relationships around the band, our friendships, our lovers, our family.
"The whole album is first journeys -- first journeys geographically, spiritually, sexually. And that's hard. But we went there."
One particular track - 'Iris' - sees Bono open up about his deceased mother Iris Hewson, who passed away when he was just 14.
He explained: "Forty years ago, my mother fell at her own father's funeral, and I never spoke with her again.
"Rage always follows grief, and I had a lot of it, and I still have, but I channeled it into music and I still do. I have very few memories of my mother, and I put a few of them in a song called 'Iris.'"
Collaborations on the album include Lykke Li, Danger Mouse, Paul Epworth and Ryan Tedder.
"I think having them around really helped.
"Some of the music out there now that people call pop, it's not pop - it's just truly great. And we wanted to have the discipline of the Beatles or the Stones in the Sixties, when you had real songs. There's nowhere to hide in them: clear thoughts, clear melodies."
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