British pop star Adele is convinced her voice is completely different to when she started her career as her vocals changed after her throat surgery and during her pregnancy.

The Rolling In The Deep singer had to cancel a number of concerts and take a break from music so she could undergo surgery on her vocal cords in 2011.

Adele went on to make a complete recovery, and she admits her voice was not the same after the operation.

"At the very beginning (after the operation) it changed, it was very clean," she tells talk show host Graham Norton. "Obviously I used to smoke quite a lot, so all the scars that my voice had from most of my life were gone (after the surgery), it was like a brand new voice.

"I can sing a lot higher than I used to, and also a lot lower than I used to... and now someone's going to challenge me and I won't be able to do it!"

The singer reveals her voice changed again after she fell pregnant with her son Angelo, and her different sound was showcased in her James Bond theme tune Skyfall.

"Also in pregnancy my voice got a lot lower, which is why Skyfall is so low. I couldn't get up there for (the high notes in) Skyfall."

During the chat with Norton for upcoming TV special Adele At The BBC, the singer goes on to admit she nearly quit music for good following the huge international success of her 2011 album 21.

"I just got really worried that I was never going to make anything that anyone liked again," she adds. "It was just being self-critical of myself, it was nothing else other than that. And also I started to wonder, maybe 21 being so successful is enough for everyone? But I realised it wasn't enough for me."

Adele made a return to music in October (15) with the release of her comeback single Hello, which hit the charts ahead of the launch of her new album 25 this month (Nov15).

She explains that the songs on 25 are vastly different to the heartbreak anthems of 21 because she has grown-up a lot since then.

"I was so open (in the songs on 21)... and I hurt people's feelings with that..." she admits. "Being so honest, and being a bit more immature then than I am now, I was like, 'I don't care, like, he broke my heart, whatever', and stuff like that. So I felt quite bad about that...

"I have a lot of different things going on now. I have a family that I love, and I'm a lioness, and I want to protect them, and stuff like that. So I'd also like people to interpret these songs how they want to, rather than me shoving it down their throats."

Adele has a young son, Angelo, with her partner Simon Konecki.

The show, Adele At The BBC, airs in the U.K. on Friday (20Nov15).