Richard Madden may have had no problem portraying all sorts of horrible acts in Game of Thrones, but singing in Rocketman was another matter.

"Richard Madden said to me, 'I'm not singing,'" soundtrack producer Giles Martin tells UCR. "I went, 'What?' He said, 'I'm not singing.' It was the first thing he said to me. I went, 'You are singing.' He said, 'I'm not.' I said, 'You'll be fine.' He goes, 'I don't sing.' I said, 'You'll be fine.'"

Madden portrayed Elton John's former manager and lover in the film, memorably belting out "Honky Cat" in a duet with star Taron Egerton. That's a long way from Game of Thrones, where Madden starred as Robb Stark – heir to the honorable lord of Winterfell – until the bloody Red Wedding in the penultimate episode of its third season.

Madden told E! that he "felt naked" while singing in Rocketman. Later, speaking with Jimmy Fallon, Madden quipped: "Thank God for autotune!"

Nevertheless, Martin told UCR that Madden "was great. It's amazing once they let themselves go, but it still required huge amounts of work."

Madden wasn't alone in dealing with inexperience at singing on camera. In fact, Celinde Schoenmaker, a Dutch actress who plays Renate Blauel; Rachel Muldoon, who plays Kiki Dee and sings "Don't Go Breaking My Heart"; and Egerton were the only ones on the soundtrack with backgrounds in musical productions.

Listen to Taron Egerton and Richard Madden Sing 'Honky Cat'

Martin says his approach with all of them was on personalizing their approach. "It's hard to stereotype in a way, but actors are so used to taking direction that you need to find the truth in their vocal – because otherwise they're singing in the third person," he said. "You get the slightly 'show tune' effect, do you know what I mean? It's very Broadway – 'I'm so confident. I'm singing a song' – and for me, what makes a great singer is their personality coming through. And I suppose that's one of the great decisions we made, not to get Taron to do a vocal impersonation but to sing as himself. Because what makes a good actor is they bring their own personality, or a part of it, into the role."

In this way, Martin said actors are easier to deal with than musicians, who tend to arrive with a hard-and-fast point of view. "In the studio, you can say, 'Would you try this?' and a singer won't necessarily get it," he said, "but an actor will tend to get it, but magnified by 400. ... So yeah, actors take direction much faster."

All of it was in service of an offbeat decision to have Madden and Jaime Bell (who plays John's long-time songwriting partner Bernie Taupin) sing with Egerton. Some of the songs themselves were changed in subtle ways.

Rocketman director "Dexter [Fletcher] said to me, 'Hey Giles. I had an idea. Why don't we have Bernie singing 'Goodbye Yellow Brick Road?' to Elton, because he's exasperated,'" Martin said. "I said, 'I love that idea. That's kinda cool.' And then, once you go there, you then realize that it can't just be the song. It wouldn't make any sense. He's angry, he's pissed. And then the arrangement evolves around that."

A lengthy collaboration with Egerton brought out new shades of meaning in his performances, as well. They drilled down into the most minute of details.

"With Taron it was very different because we spent so long working together," Martin said. "We were together for 18 months on this, which is longer than most producers work with singers on a project. So, we had a relationship where there was a trust to what we did. We'd often listen to Elton's original, and then I'd try to get him to re-listen for the phrasing. It's kind of a forgotten thing now, but the most important thing about singing is how you phrase your words, not how you sing your notes. Everyone thinks about vowels, but it's really consonants that are the most important thing."

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