Mick Jagger says his new SuperHeavy project set out to sound different from the outset -- but even they weren't quite sure what that meant until they got together and started playing.

"It came together because [the Eurythmics'] Dave Stewart had an idea to do a slightly different project, not a kind of rock or folk or [something you can put] into a single iTunes category," the Rolling Stones singer tells IHeartRadio." And I said, "Yeah, but what's it going to sound like?' And of course nobody really knew. To be honest, we really didn't know what it was going to sound like until we got in the room."

And while SuperHeavy -- which, in addition to Jagger and Stewart, features pop-soul singer Joss Stone, reggae star Damien Marley and Indian composer A.R. Rahman -- didn't know what sound they were going after, they seemed to know what they weren't going for on their self-titled debut album, which recently dropped (check out Ultimate Classic Rock's review here).

"The thing is that in popular music ... you do get a lot of repetition and people like repetition, people are comfortable with repetition," he continues. "So to do something that isn't [comfortable] is always difficult and not always appealing to everybody, because people when they listen to it have to work a little harder that they would."

Jagger concludes: "As soon as you step out of the norm that you've established -- especially somebody like myself who has been doing this for a very long time -- people go, 'what on Earth is that?' So it's hard for the performer to do, and it's hard for the listener to accept."