Joaquin Phoenix and Lady Gaga didn’t worry about singing off-key every once in a while. That’s because the “ Joker: Folie à Deux ” stars were mostly concerned with delivering performances that felt honest and true when it came to pulling off their elaborate musical numbers.

“It was crucial to me that we never perform the songs in the traditional way of a musical,” Phoenix told Variety for a cover story on his “Joker: Folie à Deux” director Todd Phillips. “We didn't want vibrato and perfect pitch.” Instead, the duo “let the emotions guide them” and primarily focused on “being true to the moment.”

The film is a sequel to 2019’s “Joker,” which grossed $1 billion at the box office. In the follow-up, Phoenix once again plays Arthur Fleck, an aspiring stand-up comic who is in the psych ward after murdering a talk show host (Robert De Niro) on live television while dressed as a clown. Arthur’s shocking act of violence has inspired a wave of followers, including a fellow patient, Harleen “Lee” Quinzell (Gaga), better known in the comics as Harley Quinn.

Lee and a band of discontented Gotham residents believe Arthur's alternate personality, the Joker, is a kind of visionary. But things escalate drastically when Arthur and Lee find themselves in a chaotic dance of insanity. However, the film isn't a conventional musical – only Phoenix and Gaga's characters sing and dance, and many of their performances exist within their troubled minds. “Some of the music is imagined, some of it's in the scene,” Gaga explains. “It breaks the mold.”

Phillips saw the music, which includes covers of songs like “Get Happy,” “That’s Entertainment” and “For Once in My Life,” as a form of dialogue. “It’s simply Arthur struggling to express himself, so he sings his feelings instead,” he explains.

On set, the collaborators pondered why their characters would choose to sing instead of speaking.

“We questioned what would make two people burst into song in the middle of a conversation?” Gaga says. “Where does the music come from when only the characters can hear it? Neither Arthur nor Lee are professional singers and they shouldn’t sound like they are (unless it's a fantasy). We wanted to convey their shared madness in a way that felt real. I believe we all have a personal connection with music, a soundtrack for our inner emotions. A score that only we can hear. That's what we tried to capture for Arthur and Lee. The music within them.”

Capturing the “music inside them” demanded an unconventional approach. Instead of having Gaga and Phoenix sing to a pre-recorded track, the actors performed everything live, accompanied by a pianist who played off-camera. During editing and post-production, these takes were blended into one cohesive number and the actors later re-recorded portions of the songs. It was a demanding process that Phillips calls a “nightmare,” but one that was crucial to the outcome.

“Especially for Joaquin, a large part of it is about feeling the moment as it unfolds,” Phillips explains. “You can't pre-decide that in a studio three weeks before shooting.”

Both Phoenix and Gaga commend Phillips' willingness to take risks. “He’s bold and thrives on new challenges,” Phoenix states. “He’s exceptional at resolving problems on the spot.”

Gaga appreciated Phoenix's collaborative approach. “As a filmmaker, I don’t think he would ever force a specific emotion. He's more interested in exploring these two characters,” she says.

“Joker: Folie à Deux” will make its global debut at this year's Venice Film Festival before arriving in theaters on October 4th.