Photos: 2011 American Music Awards
Justin Bieber performs at the 2011 American Music Awards at the Nokia Theatre in Los Angeles on November 20th, 2011.

Justin Bieber's growing up, but vocal producer Kuk Harrell says he's not ready for "the adult game" just yet.

"The only conversation we've had about Justin's album that we're about to do is it's really important that it's the proper transition because we've seen him [with] 'Baby,' now we're watching him grow up," he told MTV News. "There's a record in between."

However, he said the 17-year-old star's current release -- the Christmas album "Under the Mistletoe," which bowed at No. 1 on the Billboard 200 -- is an "important" preview of what fans can expect from the next album.

"It gave everybody the opportunity to hear him, see him and get used to his voice changing," Harrell said. "That was a huge thing going into this album. We were able to get a running start on where he's at vocally 'cause it's a natural thing. When his proper album comes out, everybody's going to really be looking at that."

Bieber's next album, dubbed "Believe," is expected next summer. His manager, Scooter Braun, told the Hollywood Reporter last month that the teen star would be taking a hands-on approach to his new material.

"He's pretty adamant about writing a lot of [the album]," Braun said. "And he played me some stuff that he's been doing on his own. He wrote this amazing song that sounds like a Jodeci record. I'm really excited for him. This kid can sing his ass off. He's coming into his own."