Christopher Nolan has explained why some audience members may have difficulty hearing the dialogue in Oppenheimer.

• READ MORE: ‘Oppenheimer’ review: Christopher Nolan’s mind-blowing biopic hits like a bomb to the brain

The movie, which stars Cillian Murphy as Robert J. Oppenheimer — the real-life American physicist who played a pivotal role in the creation of the atomic bomb — has received rave reviews and become a box office hit, but some fans have raised complaints about the film’s sound quality.

Nolan’s films have long been criticised for hard-to-hear dialogue, with The Dark Knight Rises and Tenet being two notable examples. However, the director has now revealed that there are a couple of reasons why you may struggle to hear some of the speech in his films.

Firstly, Nolan uses large IMAX cameras, which aren’t fully soundproof. Speaking to Insider, the director explained that improvements have been made to the technology in recent years, but that they haven’t been fully perfected yet in terms of their noise levels.

“There are certain mechanical improvements,” said Nolan. “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.”

The director admitted, though, that for the film’s dialogue-heavy scenes, he refrained from using the 70mm camera due it being noisier than others.

But there’s a bigger reason why some people may struggle to hear the dialogue in Nolan’s films, and it’s purely down to a stylistic choice: the director doesn’t have his actors come back to do Additional Dialogue Recordings (ADR) in post-production. Their lines are simply recorded on set.

“I like to use the performance that was given in the moment rather than the actor re-voice it later,” he said. “Which is an artistic choice that some people disagree with, and that’s their right.”

In a five-star review of Oppenheimer, NME wrote: “Not just the definitive account of the man behind the atom bomb, Oppenheimer is a monumental achievement in grown-up filmmaking.

“For years, Nolan has been perfecting the art of the serious blockbuster – crafting smart, finely-tuned multiplex epics that demand attention; that can’t be watched anywhere other than in a cinema, uninterrupted, without distractions. But this, somehow, feels bigger.”