Skip Lievsay, an unassuming-looking guy in his mid-60s with highly trained ears, stood before the stacks of speakers and giant movie screen in his office, fussing quietly. Lievsay is one of the preeminent sound designers working in film today, and whatever he does, he does it quietly, as if his personal volume dial operated in inverse correlation to the often noisy task at hand.

On this midwinter afternoon, he was meeting with one of his effects editors, a similarly soft-spoken young man named Larry Zipf, about a film they had been hired to work on: Miles Ahead, a forthcoming Miles Davis biopic directed by and starring Don Cheadle.

The two men stood with their arms crossed and heads cocked at the same angle, reviewing a scene in which a sound cue they had designed had gone awry. The sound, originally of vintage tape decks turning, had ended up evoking a sci-fi odyssey rather than a jazz biopic. One of the problems, it was agreed, is that to the untrained ear, 1970s tape decks sound a bit like lasers.

On screen, Cheadle entered an elevator and pushed the button for the lobby. The button emitted a soft, innocuous beep. "That's a good beep, Lar," Lievsay muttered. "Good beep."

As he said so, Cheadle-as-Miles leaned against the wood-paneled elevator wall, eyes closed. Suddenly, the elevator swung open to reveal a dark room of Miles' imagination, filled only with a piano, a horn, and a spotlight. The moment was intended to feel surreal, as though you were entering Miles' mind, but as the door began to swing, a deep rumble erupted into a volley of zings and swishes — those troublesome tape decks — as if the scene had plunged into a battle in outer space.

Lievsay hit Pause and turned to Zipf, shaking his head. No good.

For research, Lievsay had spent a few months reading biographies and listening through all the recordings in the Miles Davis estate. The film is set in the 1970s, "which is Bitches Brew Miles," Lievsay explained, a period when Miles favored improvisational rhythms and electric instruments over traditional jazz. The research had led to the idea of experimenting with recording equipment of the sort that Miles would have used.

They had got their hands on some vintage tape decks and spent an afternoon recording the sound of them playing forward and backward, clicking and scrubbing. But when Zipf edited the sounds and played them underneath scenes from the movie, the result sounded like Battlestar Galactica, not old-fashioned music equipment. Lievsay sighed. "Probably because sound editors used to use tape decks when they needed space sounds. Bet you Battlestar Galactica was tape decks." He threw the noises out and started over.

It is a central principle of sound editing that people hear what they are conditioned to hear, not what they are actually hearing. The sound of rain in movies? Frying bacon. Car engines revving in a chase scene? It's partly engines, but what gives it that visceral, gut-level grind is lion roars mixed in. To be excellent, a sound editor needs not just a sharp, trained ear, but also a gift for imagining what a sound could do, what someone else might hear.

Lievsay is one of the best. He won an Academy Award in 2014 for his work on Gravity. Goodfellas, Silence of the Lambs, Do the Right Thing — his work. He is also the only sound editor the Coen brothers work with, which means that he is the person responsible for that gnarly wood-chipper noise in Fargo, the peel of wallpaper in Barton Fink, the resonance of The Dude's bowling ball in The Big Lebowski, and the absolutely chilling crinkle of Javier Bardem's gum wrapper in No Country for Old Men. Jonathan Demme, who first worked with Lievsay on The Silence of the Lambs, put it concisely: "He's a genius."

Despite Lievsay's influence, you have probably never heard of him, and this is no surprise: Lievsay and his team are only a few members of the legions of people involved in film production who go about their painstaking, essential work far from the public eye. Lievsay is not a household name, but he is famous among people who are.

His expertise, fittingly, is what can't be seen — sound, yes, but also everything else that sound is to the human mind: the way we orient ourselves in relation to spaces, to time, to each other; the way we communicate when language fails; the way our ears know, precognitively, when the dark room has someone lurking in it or when a stranger will be kind. He orchestrates the levels of human perception that most people either fail to examine or lack the ability to notice at all. His job is to make you feel things without ever knowing he was there.

THE MONSTROUS COMPLEXITY of Lievsay's work — the quest to make films sound the way the world sounds — may not be immediately apparent. When a movie finishes shooting, it enters the labyrinthine world of post-production, in which the best takes are selected and spliced together into reels — roughly 20-minute segments of film that are worked on and then stitched together. Each reel goes through picture editing (for such things as visual continuity and color) before being handed off to the sound supervisor, who oversees all the various elements of sound design, editing, and mixing.

At the beginning of this process, editors remove the audio recordings taken during filming and break down each scene into four sonic elements: dialogue, effects, music, and Foley, which is the term for everyday sounds such as squeaky shoes or cutlery jangling in a drawer. For every scene, each of these four elements needs to be built and then edited separately, and at WBNY, the New York production company Lievsay runs with fellow editor Paul Urmson, each gets its own dedicated editor. Then, Lievsay or Urmson takes the team's work and layers it to make scenes that sound like the world sounds.

Consider the scene at the end of No Country for Old Men when Bardem's character has a car accident. After the crunch of impact, there are a few moments of what might be mistaken for stillness. The two cars rest smoking and crumpled in the middle of a suburban intersection. Nothing moves — but the soundscape is deceptively layered.

There is the sound of engines hissing and crackling, which has been mixed to seem as near to the ear as the camera was to the cars; there is a mostly unnoticeable rustle of leaves in the trees; periodically, so faintly that almost no one would register it consciously, there is the sound of a car rolling through an intersection a block or two over, off camera; a dog barks somewhere far away. The faint sound of a breeze was taken from ambient sounds on a street like the one depicted in the scene. When Bardem shoves open the car door, you hear the door handle stick for a moment before it releases. There are three distinct sounds of broken glass tinkling to the pavement from the shattered window, a small handful of thunks as he falls sideways to the ground, his labored breathing, the chug of his boot heel finally connecting with the asphalt — even the pads of his fingers as they scrabble along the top of the window.

None of these sounds are there because some microphone picked them up. They're there because Lievsay chose them and put them there, as he did for every other sound in the film. The moment lasts about 20 seconds. No Country for Old Men is 123 minutes long.

Sound mixes are notoriously stressful, in part because they come at the very end of a film's production. They are also hard on the senses. Imagine sitting in a dark room watching a movie in four-second intervals. Repeat this until the hours stretch into days, then weeks. Life becomes a series of stuttering noises stretching into eternity, punctuated only by complaints about the "chunkiness" or "creaminess" or "washiness" or whatever-ness of a fly's buzz.

The impact a tiny aural cue can have on the brain's understanding of narrative is astonishing. On the third day of the mix, Lievsay and Zipf were breezing through a scene of Miles dropping in on his wife Frances' dance rehearsal when Cheadle paused them. The scene sounded a little too dreamy. Cheadle wanted a more matter-of-fact sound.

Lievsay nodded and fiddled for a moment. When he replayed the scene, something small but extraordinary happened. I had watched this scene somewhere between one and two dozen times, but this time I noticed something I'd never seen before: a young woman passing behind Frances with a stack of papers in her hand. Lievsay had given her footsteps. Without the footsteps, I'd somehow never seen her; now, I saw her, and her presence — along with a few other tweaks by Lievsay — suggested bustling in the room, people at work, things happening outside the eye contact forged between Miles and Frances. I didn't exactly hear the difference: I just saw the scene differently.

IN ORDER FOR that edit to be possible, Lievsay needed the footsteps of that young woman close at hand. He needed not just any footsteps, but ones that sounded like they were made by a low high heel of roughly the sort that women would wear in the mid-1970s, crossing a wooden stage. This kind of noise — one that requires precision, but that is intended to blend into the background — is called Foley (for Jack Foley, who first came up with a process for adding quotidian noises, such as footsteps, to films in the 1920s).

When Lievsay reached for that girl's footsteps, he wasn't going back into some old library — he was reaching into the library of Foley designed and created specifically for Cheadle's film. The Foley house, also known informally at his studio as "the sound castle," where these sounds are made, is in New Jersey, just over the George Washington Bridge from Manhattan. It is not so much a castle as a warehouse crammed with more stuff than can be adequately described here.

Marko Costanzo, the antic "Foley artist" who works there, takes evident joy in giving tours of the soundstage and the treasures he stores there: a bin full of Zippo lighters; a bunch of swords ("from when we did Crouching Tiger, Hidden Dragon"); barrels; bicycles; baby carriages; one area devoted to different kinds of indoor flooring and another devoted to outdoor ground cover; a pool ("we built it to do the sounds for the raft in Life of Pi"); a child's Easy-Bake oven. "I beg people not to take things to the dump, but to bring them to me instead," said Costanzo, grinning and spreading his arms wide.

Costanzo's job is to replicate every sound that might reasonably be produced in a film, while his colleague, engineer George Lara, directs and records. Lara, tucked into a sound booth, announces the cue to Costanzo ("skin on cloth") and pulls up the clip for him. Costanzo watches once to rehearse, positions his two microphones to approximate the distance and reverb needed, and then does it for real, eyes locked on the screen. They work up from the easy things like "hand on hair" (for which Costanzo, bald as an egg, has a menagerie of wigs) to the harder cues: the sound of a tiger's feet scraping wood or the sickening thwap-clunk of a gallows releasing.

"You make every single sound?" I asked Costanzo.

"He performs it," Lara gently corrected me.

Costanzo changes into shorts before recordings to ensure that the microphones won't pick up the sound of a trouser hem rubbing against his shoes. On the morning I visited, he changed while watching his first cue: a woman knitting. He carefully selected two pieces of wood from his collection, tapping them once or twice to get the right sound, and then executed the taps again in time — with gusto — for the recording.

If sound editors are the secret backbone of movies, this is one of their secrets. That glorious slap Cher gives Nicolas Cage in Moonstruck before yelling "Snap out of it"? Not Cher at all. Likely as not, that was a mustachioed man standing in his socks in a warehouse in some suburb of New Jersey.

Excerpted from an article that originally appeared in The Guardian (U.K.). Reprinted with permission.