Foo Fighters have amassed five and-a-half hours of music for their next album, which is about to go into pre-production, NME.com says.

Frontman Dave Grohl said the band has been recording new tracks for its follow-up to 2002's "One By One" in California.

In a statement on the group's official website, Foofighters.com, he said: "Having a year to write and demo things at your own pace sure makes for better songs."

As previously reported, the band's next release will be a double album, with one disc acoustic and the other rock.

Talking about the concept, Grohl said: "The idea comes from the fact that we've always explored both dynamics, just not to their fullest potential. Why not get heavier? Or quieter? Why try and cram all of that onto one CD? Why not make two albums, and call it one?"

In addition to prepping the new album, Grohl played several benefit concerts for U.S. presidential candidate John Kerry in July and August, and recently assumed percussion duties for the next Nine Inch Nails disc.