Musical biopics are remain a compelling watch, in no small part to the flawed and talented characters at the heart of the stories. Ethan Hawke is Chet Baker in Born to Be Blue, Don Cheadle is Miles Davis in Miles Ahead, but perhaps the most fascinating transformation is English actor Tom Hiddleston taking on famed country singer Hank Williams.

Written and directed by Marc Abraham, I Saw the Light chronicles the professional and personal life of the beloved and plagued American musician, with all the good, and definitely all the bad.

“I felt a duty to play him honestly, I felt a responsibility to committ to his truth,” said Hiddleston during an interview at the Toronto International Film Festival. “I knew I had to put myself through the paces he put himself through, get under the skin of who he was, treat his flaws with compassion, and try to feel the things he felt because he a self destructive headlong life. He packed so much in such a short time.”

Hiddleston isn’t the only one playing a character of whom opinions and actions are varied. His costar Elizabeth Olsen, also joining in Toronto last fall to promote the film, is Audrey Williams, Hank’s wife, and a controversial figure in her own right.

“She was a notoriously disliked person,” said Olsen. “It’s sad. She has a daughter who is still alive, she speaks highly of her. All she really wanted was her to be treated with respect, she knows probably that her mother wasn’t popular. You try to not judge her and have compassion and sympathy for her. She wanted so badly her own career, she was great business mind; he didn’t have a business mind at all.”

“She was in a hard relationship with a man that she loved who was an alcoholic. They loved each other and they couldn’t figure out to communicate, and that’s really sad. You try and go into from that standpoint.”

Another challenging part for the cast was of course the singing. Hiddleston holed up with musician Rodney Crowell, practicing across five weeks to prepare for the part, sometimes as long as 12 or 13 hours a day.

“It was a pleasure, and it was challenging,” said Hiddleston. “I was trying in a very short time to get close to Hank who had 25 years to practice, it was the most joyful challenge. You cannot get close without enjoying it.”

The most important part of singing, both actors confirmed, was finding the sincerity in the music and lyrics. While you can never exactly duplicate the sound, you can indeed feel the words and express the feelings that go into them.

“Why it is so powerful, it’s something that sound does, that you cannot speak about,” explained Olsen. “There is not language to show how music makes you feel when music connects with you, its another form of communication, and everyone has a different relationships with every singer, every sound. To me its magical, if you can penetrate someone with sound, that’s a whole other thing.”

“I think it is the most directly emotional medium,” echoed Hiddleston. “Artists who sing are more naked and more vulnerable and more raw. If you sing, it is so raw, and has to be so personal. It will not travel unless it’s deeply felt and committed to. Music is the most directly emotional art form, it’s like an arrow to your heart.”

“People sing when the language of the spoken word is no longer sufficient to express the depth of what they’re feeling.”