They're no strangers to belting out a tune or two, but Justin Timberlake and Anna Kendrick admit they were nervous when it came to recording songs for new DreamWorks Animation, Trolls. But, as they tell Gemma Dunn, they're convinced the movie hits all the right notes

Justin Timberlake has always wanted to oversee a motion picture soundtrack - but penning songs for DreamWorks Animation's Trolls, he admits, had a far richer appeal: serious dad points.

"I feel like I'm going to have a lot of terrible dad behaviour come Christmas time," quips the 35-year-old actor and singer, who doubles up as executive music producer on the movie, as well as lending his voice to Troll Town's grumpiest resident, Branch.

"But I don't care, because even if it's falsification, I just want him to love me because I gave him all the merchandise from the movie."

The 'him' in question is 18-month-old Silas Randall, his son with wife Jessica Biel, and the doting dad credits fatherhood for inspiring Trolls' hit theme song, Can't Stop The Feeling.

"It changes everything. I would have never written a song like [that]," he recently said of the summer smash during an appearance on America's Today Show.

The Memphis-born star is on good form - as is his co-lead, comedy genius and Pitch Perfect star Anna Kendrick, who plays fellow troll Princess Poppy, an eternal optimist.

"He's our musical overlord, as someone described him today," says 31-year-old Kendrick.

"You were like, 'Oh God, he's going to call himself that for the rest of the press tour!'" Timberlake retorts. "I should have made them put that on the ending credits... 'Musical overlord'."

From the creators of Shrek - Trolls, based on the ugly-loveable dolls of the same name - boasts an impressive ensemble cast, including Christopher Mintz-Plasse, Zooey Deschanel, Jeffrey Tambor and James Corden.

It's an irreverent comedy about the search for happiness, and just how far some will go to get it.

Laughing in unison throughout our chat, it's clear Timberlake and Kendrick had a lot of fun making it.

"It was honestly one of the best experiences I've had," says Portland-born Kendrick, whose credits also include 2012 comedy What to Expect When You're Expecting and musical fantasy epic Into The Woods.

"It's so uncomplicated, in terms of the production, that you get to do your best work, which always feels nice. You're completely uninhibited and you also get to try all the jokes you want," she continues. "And the directors are really nice and laugh - even if it's not funny. So that made it fun for me!"

The 3D computer-animated film promises to transport audiences to a colourful, wondrous world, home to the overly upbeat Trolls, who have a constant dance in their step and a song on their lips - unlike the comically pessimistic ogres, known as Bergens, who try and achieve a little of the Trolls happiness - by eating them.

Trouble ensues when the Bergens invade Troll Village, leaving sassy-yet-adorable Poppy and the overly-cautious Branch to set off on a journey full of adventure and mishaps to rescue their friends.

"I hardly felt like the person to play the happiest Troll; sugary sweet isn't really my forte," notes Kendrick with a giggle. "I warned Mike [Mitchell, the director], Walt [Dohrn, the co-director] and Gina [Shay, the producer] that I might lead Poppy down a feistier path. I think I used the term 'spark plug'."

When the film-makers assured the actress that her vision for Poppy was in sync with theirs, she embraced her inner Troll with a vengeance.

"Each time I stepped into the recording booth and was greeted with a picture of Poppy's smiling face, I couldn't wait to add some fire, sarcasm, sass and determination to her," Kendrick recalls. "That's what makes the difference between a relentlessly happy character that's a little irritating, and one that really comes to life."

Similarly, Timberlake was only too happy to embrace the disgruntled Branch.

"Branch isn't much of a people person," notes the actor, who's previously starred in the likes of Friends With Benefits alongside Mila Kunis, and 2010's The Social Network. "He's a hardcore survivalist and a huge contrast to all the other Trolls. He doesn't connect with anybody.

"I thought playing Branch's sarcasm and pessimism would be a lot of fun, even though I'm generally not like that - at least not after I've had my morning coffee."

While Timberlake puts the characters' constant needling down to "flirtation", Kendrick sees it more as a triumph for Poppy, stating: "Poppy loves Branch because she loves everything and everyone. And that annoys Branch even more, which is a bonus."

It might be a musical animation, but the Trolls team are certain the movie's going to appeal to adults - especially those who remember the dolls from their own childhoods (they were originally popular in the early-Sixties, and had a resurgence in the Nineties) - as well as children.

"I remember all the girls in school had the pencil-toppers or some sort of troll with the jewels in the belly, and we used to steal them to flirt with them," recalls Timberlake of his schooldays.

Kendrick nods in agreement - but troll-craze flashbacks aren't the only thing the co-stars agree on. They both admit, despite each owning an impressive set of lungs, they'd get nervous every time they were required to sing.

Timberlake insists this is a good thing though, as it means you care.

"It would be weird if I didn't feel slightly nervous," Kendrick shares first. "If I was just like, 'Oh hi, yeah Justin, I don't need your notes, I got this', that would be weird."

Laughing, Timberlake - who has scooped nine Grammy Awards during his extensive music career - adds: "I've got to say, singing True Colours, specifically, I felt really nervous about too. I feel like it's slightly different [to the] way I've become comfortable singing.

"There's something more theatrical about it," he elaborates. "And we all want it to be as great as it can possibly be."

Trolls opens in cinemas on Friday, October 21