Not long ago, producer Giles Martin wasn’t sure four-track-era Beatles albums like Revolver could be properly remixed. The tech, he said then, wasn’t there yet.

“That’s a good example of, ‘How do we do that?'” Martin told Rolling Stone in 2021. “How do I make sure that John [Lennon] or Paul [McCartney]’s vocal isn’t just in the right-hand speaker, but also make sure that his guitar doesn’t follow him if I put it in the center?”

Martin tried earlier versions of separation software when completing 2016’s remix of The Beatles: Live at the Hollywood Bowl, another album originally produced by his father George Martin that had guitars and voices on the same track. But Giles didn’t feel the tech wasn’t advanced enough to make similar separations in a studio recording’s quieter, more controlled setting.

Then came The Beatles: Get Back. Peter Jackson was handed hours of additional footage from the production of 1970’s movie version of Let It Be, but much of it was ultimately unusable because of sound issues. So, the director developed an automated-learning process for his WingNut Films Productions with an audio team led by Emile de la Rey.

Suddenly, whispered asides originally filmed by Michael Lindsay-Hogg could be heard. Offhandedly recorded practice sessions could be cleaved into a broad stereo spectrum.

“So what John and George [Harrison] used to do is, if they were in a conversation, they would turn their amps up loud and they’d strum the guitar,” Jackson told Guitar Magazine in 2021. “They’d just be strumming, not playing anything, no tune. So, all Michael’s microphones were recording was this loud guitar, but you’d see the Beatles talking, having some private chat.

“What we’ve been able to do with computer technology and artificial intelligence-based technology is we’ve been able to strip the guitars off now,” Jackson added, “and expose the private conversations that they had.”

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Jackson was also able to include stunning footage of rehearsals from Twickenham Studios that had previously existed only in unmixed mono form. Martin zeroed in on those musical advancements, which would be critical to continuing the Beatles’ remixed and expanded album series further back into the ’60s.

“There’s no one who’s getting audio even close as to what Peter Jackson’s guys can do,” Martin told Rolling Stone, in an interview published on the day his long-awaited remix of Revolver was announced. “The simplest way I can explain it: It’s like you giving me a cake, and then me going back to you about an hour later with flour, eggs, sugar – and all the ingredients to that cake haven’t got any cake mix left on them.”

Dubbed “demixing,” this breakthrough involves teaching a computer program to recognize individual instruments so that they can be isolated. “In fact, we taught the computer what John sounds like and what Paul sounds like,” Jackson told Variety in 2021.

“So we can take these mono tracks and split up all the instruments so we can just hear the vocals, the guitars,” Jackson added. In the film-editing room, “you see Ringo [Starr] thumping the drums in the background but you don’t hear the drums at all. That that allows us to remix it really cleanly.”

Martin ended up facing one final obstacle: Jackson’s demixing technology was still proprietary. Luckily, they share a certain musical passion.

“They won’t anyone else use it — they may do eventually – but Peter’s such a big Beatles fan, he’s willing to help out,” Martin told Rolling Stone. “I quite like that in a way, that the Beatles are still using technologies that no one else is using. It’s really groundbreaking.”

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