The new album by Irish rock band U2 is now "70% complete," bassist Adam Clayton told Q magazine, via Digital Spy.

The album, titled "Songs of Experience," follows "Songs of Innocence," which was given away in early September to hundreds of millions of Apple subscribers. The album before that, "No Line on the Horizon," was released in 2009.

"The 30 percent that we're missing I think we will be able to generate relatively easily," Clayton said. "But the amount of energy it will take to refine the perspective of those songs is hard to predict."

Acknowledging that the manner in which "Songs of Innocence" made its way to the fans was polarizing - some didn't like that the album was downloaded to their devices without permission - Clayton said "Songs of Experience" might be released in a different way.

"Y'know what, depending on how long it takes to be completed, there may be a whole new delivery method invented by then. I think we just have to wait and see," he said.

"There'll be a bit of water under the bridge before we get to that point. But yeah, I think it would be a bit predictable to do the same thing," the bassist surmised. "The law may have changed by then, and we'll have to find some other way of doing it."

It was earlier reported that U2 guitarist The Edge said the tracks on both "Songs of Innocence" and "Songs of Experience" were the product of four years of recording sessions, according to Music Times.

"Early on it became obvious that we were working on two separate albums," The Edge told Rolling Stone. '"The majority of the unfinished songs are worthy of becoming part of 'Songs of Experience' and some are already as good or better than anything on 'Songs of Innocence.'"