Hildur Guðnadóttir composed ‘Joker’ soundtrack before the film was shot

Icelandic composer Hildur Guðnadóttir created the soundtrack for “Joker,” which opened earlier this month and is now the biggest R-rated film in history. She wrote most of the score beforethe movie was shot.

Her music was based on feelings she had after reading the script. “I really loved the script. It really resonated strongly with me,” she tells Press Play.

Guðnadóttir knew the Joker as a character when she was growing up in the early 1980s. But in director Todd Phillips’ film, she saw an emotional side of the Joker that she hadn’t envisioned before.

“I just thought it was a fascinating take on his character. It kind of struck me -- the way that he's just misunderstood by society, and he's really just trying his best to fit in. He doesn't understand why he doesn't fit in. And he doesn't understand where he came from… and why he’s feeling what he’s feeling,” she says. “And then as he understands more about his background, his lack of upbringing, this rage that's just lying under there, it starts to come forward and swallow him, really. I thought it was a really beautiful story.”

She says she sympathized with the Joker and wanted to get inside his head, and from there make music out of his journey.

One scene came to life thanks to Guðnadóttir’s music: when Joaquin Phoenix (who plays the Joker) is dancing in the bathroom.

“It's this kind of transformational scene where he becomes the Joker… But he told me a few weeks ago… that he was having a bit of a hard time getting into the character and finding this transformation,” Guðnadóttir says. “And the director started playing this music to him on set. And so this scene… is Joaquin’s response to the music. He's actually doing a real time interpretation of the music.”

Guðnadóttir also recentlywon an Emmy for her music in “Chernobyl,” HBO’s five-part series about the worst man-made accident in history, when the Chernobyl Nuclear Power Plant in the Soviet Union exploded on April 26, 1986.

She went to the actual power plant where the series was filmed -- to record sounds to include in the music.

“I wanted the radiation, which was really important, that the music would be the voice of the radiation,” she says. “And so I went into the power plant just to explore what it was. I recorded the room tones, and machinery, and just anything that I heard -- really for quite a lot of hours. And then, of course, I spent six months going through those recordings and molding those sounds into musical elements.”

A bright person, but dark music

Guðnadóttir’s music sounds ominous, but she describes herself as a cheerful person who smiles and laughs a lot. So where does the darkness come from?

“I guess the darkness of my music is best explained by… every person has a dark side and a bright side… The outlet for my darkness is best suited through music,” she says.

Growing up in a family of musicians

Guðnadóttir began playing the cello when she was 4 years old. Her father is a clarinet player, composer, and teacher. Her mother is an opera singer.

“My mother kind of half chose the cello for me as when I was a child… She says that she had a very strong intuition when she was pregnant with me that I would become a cellist,” Guðnadóttir shares.

--Written by Amy Ta, produced by Alex Tryggvadottir