Christopher Navarro

Christopher Navarro, an ADR mixer who worked on four of this year's nine Oscar-nominated best pictures, in his studio at Audio Head sound studios in West Hollywood. (Bob Chamberlin / Los Angeles Times / February 25, 2014)

Growing up, Christopher Navarro used to listen to himself talking on a hand-me-down Kmart cassette tape recorder, then re-record his voice until he had perfected the audio clip.

Now 38, the Northern California native channels his childhood pastime in his career as an automatic dialogue replacement mixer, meaning he re-records dialogue by actors in a sound studio during post-production.

Though his name won't be read among the official Oscar nominees this Sunday, the ADR mixer for Audio Head and the Formosa Group has his work in four of the nine best picture contenders: "Gravity," "12 Years a Slave," "Her" and "The Wolf of Wall Street."

FULL COVERAGE: Oscars 2014

"I'm the guy behind the curtain," Navarro said at the Audio Head sound studio on the Lot in West Hollywood, the site of what is said to be the first ADR stage here in the 1920s.

Sporting a ponytail, bandanna around his head and rings galore, Navarro walked around the sound studio pointing out where directors, sound editors and actors — Joaquin Phoenix, Scarlett Johansson and Chiwetel Ejiofor, to name a few — have delivered their lines.

Last weekend Navarro was part of the team that won a Cinema Audio Society sound mixing award for "Gravity," but when asked about his favorite of this year's Academy Award nominees, he couldn't pick just one. Here is a rundown of the ADR mixer's experiences working on the Oscar-nominated films.

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Movie: "Gravity"

When: April to October 2012.

"As far as I knew, it was just going to be one day in May," said Navarro, who was approached by people with whom he had worked in the past. The project turned out to be long term. "They had already been working on it for three years before they called me."

The film was one of the longest projects he has ever worked on, Navarro said. Almost all of the dialogue needed to be added in post-production because the film's setting — outer space — required absolute silence in the background.

FULL COVERAGE: 'Gravity'

The takeaway: Navarro liked "being part of the conversations … and hearing some stories about what is going on behind the scenes," noting it was especially interesting to see George Clooney and director Alfonso Cuarón review their notes.

"They were going over discussions of character development between George and Sandra's [Bullock] characters," Navarro said, adding that actor and director didn't rewrite the story in post but they did finesse "a little here and there."

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Movie: "Her"

When: April to September 2013. "Any time you get longer-term projects going on, you get to be more involved with the people and develop more of a relationship," he said of the Spike Jonze film. "It was a lot of fun."

FULL COVERAGE: 'Her'

The takeway: Although ADR often involves replacing just one line of dialogue at a time, Navarro said, the ADR for "Her" required stars Phoenix and Johansson to play out whole scenes. "We had both of them here at once," Navarro said.