Christopher Nolan explains why you might have trouble hearing the dialogue in 'Oppenheimer'

• Sometimes it's hard to hear what people are saying in Christopher Nolan movies.
• He told Insider the reason for that is he doesn't do additional dialogue recording, known as ADR.
• "I like to use the performance that was given in the moment rather than the actor revoice it later," he said.

For most of his career, the one criticism Christopher Nolan has routinely faced for his movies is that you sometimes can't hear his characters' dialogue.

This hiccup has been most obvious when the lead actors are wearing masks, like when Tom Hardy played the villain Bane in "The Dark Knight Rises" or John David Washington wore an oxygen mask in the time-traveling spy thriller "Tenet."

But some words are muffled even when characters have nothing covering their mouths. Though not as jarring as in some of his previous films, Nolan's latest movie "Oppenheimer" still has some indiscernible moments.

Turns out, there's a reason for this.

Nolan shoots his movies with gigantic Imax cameras, which aren't fully soundproof. (However, Nolan did tell Insider there have been improvements with the technology in recent years.)

"There are certain mechanical improvements," he said. "And actually, Imax is building new cameras right now which are going to be even quieter. But the real breakthrough is in software technology that allows you to filter out the camera noise. That has improved massively in the 15 or so years that I've been using these cameras. Which opens up for you to do more intimate scenes that you would not have been able to do in the past."

Though the director admits you still have to "choose your moments" for using the Imax cameras.

For example, Nolan said he purposely didn't use the 15 perf-70mm camera for the dialogue-heavy Oval Office scene where J. Robert Oppenheimer (Cillian Murphy) meets President Truman (Gary Oldman) because it's noisier than other cameras.

But there's a bigger reason why there can be dialogue issues in his movies — and it's a purely stylistic choice: Nolan doesn't have his actors come back after filming and do additional dialogue recordings, known as ADR, in post-production.

It's a tool that virtually every TV and movie utilizes. The way it works is an actor goes into a soundproof booth long after a scene is filmed and reads lines over again so they are more clear. Nolan refuses to do this for his movies.

"I like to use the performance that was given in the moment rather than the actor revoice it later," he said. "Which is an artistic choice that some people disagree with, and that's their right."

Nolan's sound mixing choices don't seem to be hurting his movie's box-office performance.

As half of the double-feature phenomenon "Barbenheimer," "Oppenheimer" has become not just one of the biggest hits of the summer movie season, but is also well on its way to becoming one of Nolan's largest box-office earners, having already grossed over $400 million worldwide.