The Edge says U2 felt the need to "double down" on 'Achtung Baby'.

The 60-year-old bassist has reflected on the band's mentality going into their iconic 1991 album, and compared it to their mindset as they wrote their 1981 sophomore record 'October'.

He told Guitar World: "I think we all felt by the end of 'The Joshua Tree' [1987] and 'Rattle and Hum' [1988] that there was a sort of weight of expectation amongst U2 fans, and maybe within ourselves, that kind of sense that we had established a sound, a thing, and it started to feel restrictive.

"It started to feeling like we were being forced to repeat ourselves, or at least that seemed like the logical thing for us to do. So we did the opposite.

"We doubled down down, and really rolled the dice again on innovation and doing something very different and outside of our comfort zone."

The Edge noted that striving to do something different had long been at the heart of the group, which is completed by Bono, Adam Clayton and Larry Mullen Jr.

He explained: "I think our main creative axiom early on was to innovate, and to not sound like other acts, although we inevitably were part of a movement of bands that were thinking in those ways.

"So there was some borrowing of thoughts. But the need to be different and do our own thing serves us well."

Just like 'October', Edge noted how 'Achtung Baby' was made with an open mind to all kinds of possibilities.

He added: "Assuming that, as we had done with 'October', when you really do put yourself in that sort of position where you don't know what you're up to, where you really have to use imagination and resourcefulness as your main kind of get-out-of-jail cards, that it will bring out of you unexpected things and bring you to unexpected places.

"That was the sort of spirit in which we went into the writing of that record."