Linkin Park’s new album has been a “challenge.”

Singer Mike Shinoda - who spoke about his band’s much-anticipated follow-up to 2007’s Minutes to Midnight - said the album was taking so long because they were trying out a different style of music.

“We make records as a challenge to ourselves. And the challenge this time is: ‘Nobody else is making a record that sounds like this, only we can do it,’” Mike explained MTV.com. “It’s been going great, I feel like it’s an entirely different process and an entirely different style of music than anything we’ve done before. It’s hard to place. People keep asking me, ‘What does it sound like?’ and it’s hard to describe. When people hear it, they’re going to have a tough time saying that it falls into a category.”

Despite the changes, the 32-year-old performer says Linkin Park have not forgotten those who helped them with their success over the past 13 years.

“The album is going really well - we decided to go with Rick Rubin again, he’s been in the studio with us. And we’ve been working in a different studio than we did the last record in, we decided to go back to the studio we did Hybrid Theory and Meteora in,” Shinoda said.