How Audio Post Production Works

By: Dave Roos
Films like Tim Burton's Batman require extensive editing of audio, including voices and special effects.
© Terry O'Neill/Getty Images

Batman looks down from a Gotham rooftop into the dark alley below. We hear the sounds of the big city: cars whizzing by, sirens wailing in the distance, indistinguishable voices calling to each other from the street. The Joker and his henchmen enter the alley dragging a helpless Vicki Vale. We hear Vicki's muffled screams, the Joker's evil cackle and the scrape of Vicki's high heels across the pavement.

The movie score swells as Batman dives from the rooftop. We hear the metallic whir of his zip line and his leather cape snapping as it cuts through the air. Then comes the fight -- the punches, grunts, thumps and slams punctuated by blaring horns and sharp percussion from the soundtrack.


On the screen, this scene takes less than a minute. But behind the scenes, professional audio post production engineers worked hundreds of hours to make sure that every snippet of dialogue, every scrape of a shoe, every tiny detail of background noise, every sound effect and every second of the film score are perfectly blended to create a cohesive and powerful cinematic experience.

Audio post-production editors won't ever be famous (they don't even give them speech time at the Oscars), but the work they do is crucial to film and television productions. A screenwriter can come up with the funniest dialogue in the world, but who's laughing if the audience can't hear it? A digital animation team can design dazzling characters and expansive virtual worlds, but often it's the audio details -- the ruffle of the character's clothes, the wind through the digital leaves and the subtle hints of the musical score -- that make the world come alive.

The tools of audio post production can be as low tech as a fist and a sirloin steak (for the most realistic punches) or as high tech as a sprawling mixing console powered by the latest digital editing software.

What are the different roles and responsibilities of an audio post-production team? And how does digital technology help post production engineers do their work faster and better than ever? Read on to find out.


Different Aspects of Audio Post Production

boom mic
Boom mics record the actor's voices, which are then edited during audio post production.
© Gregg Segal/Stone/Getty Images

In film and TV, the audio portion of a project is recorded separately from the video. Unlike your home video camera, the film or video cameras used in professional productions don't have built-in microphones. Instead, all dialogue is recorded with either a boom microphone (those long sticks with the fuzzy mics on top) or a tiny, wireless lavalier mic that can be hidden in an actor's clothing. Most other audio -- like ambient background noise and music -- is added in post production.

Post production refers to all the editing, assembling and finalizing of a project once all the scenes have been shot. Audio post production begins once the editors have assembled a locked cut of the project. A locked cut of a film contains all of the visual elements -- selected takes, special effects, transitions, graphics -- that'll appear in a film's final cut.


With the locked cut in hand, the audio post-production staff can start spotting the film for sound. Different members of the post production team look for different things:

  • The dialogue editor examines every line of spoken dialogue, listening for badly recorded lines (too quiet, too loud, jarbled, et cetera) or times when an actor's voice is out of sync with his lips.
  • Sound effects designers look for places where they'll need to add ambient background noise (honking cars in a city, tweeting birds in the country), and "hard effects" like explosions, doors slamming and gun shots [source:].
  • Foley artists look for places to fill in details like footsteps across a wood floor, a faucet running, the sound of a plastic cup being placed on a marble countertop, et cetera.
  • The music editor looks for inspiration to either commission original music or buy licenses for existing song use.
  • The composer, if he's already hired, looks for places where original music would add to the on-screen moment.

If the dialogue editor needs to replace or re-record unusable pieces of dialogue, he'll ask the actors to come in for an automated dialogue replacement (ADR) session. Here, the actors and editors synchronize the newly recorded dialogue with the lip movements on the screen and mix the audio smoothly into the existing recording.

Foley artists -- named after the pioneering audio and effects man Jack Foley -- use an eclectic bag of tricks to reproduce common sounds (a wooden chair for a creaky floor, cellophane for a crackling fire, a pile of audio tape for a field of grass, et cetera) [source: The Art of Foley].

Sound designers and effects editors spend much of their time collecting libraries of ambient natural sounds. They record the sound of Monday morning traffic and save it as a digital file for later use. They record washing machines running, children playing and crowds cheering. You can also buy ready-made libraries with all of these sounds. But some of the best sound designers like to create entirely original effects.

Ben Burtt, sound effects designer on the original Star Wars movies, used a distorted elephant bellow for the roar of a tie fighter. And the famous hum of the lightsaber? A blend of TV static and a 35mm projector [source:].

The most important job in audio post production is the mix, where all of the sound elements of a project are balanced and blended together. Typically, this job is shared by a dialogue mixer, effects mixer and a music mixer [source:]. The final copy of the composite soundtrack is delivered either on optical film stock, as a digital file or both.

Now let's look at some of the systems and software used in audio post production.


Audio Post Production Systems and Software

Sound engineers combine a film's dialogue and sound effects in a post-production studio.
© Piotr Powlietrzynski/Photographer's Choice/Getty Images

Film and TV editing is an entirely digital world. No one sits around splicing film stock anymore. Even if a project is shot on film, it'll be digitized for editing and laid back onto film for distribution. The same is true for audio post production. The nice thing about digital audio editing technology is that there's a product and system for every budget and skill level.

For the home studio, everything can be done on a single computer without fancy control panels or consoles. You can buy a basic version of Pro Tools, Adobe Audition or a similar digital audio workstation (DAW) and do all your recording, editing, mixing and exporting using the software's built-in functionality. Pro Tools doubles as a MIDI (Musical Instrument Digital Interface) sequencer, so you can even record a soundtrack straight into the software using a MIDI controller or live instruments.


Professional audio post production studios add another level of control by using large digital editing consoles. All of the knobs and faders on the console control specific elements within a DAW like Pro Tools or Nuendo. For many editors, it's faster and easier to manipulate knobs and faders by hand than to constantly be reaching for the mouse and keyboard.

Here are some features of DAW software for audio post production work:

  • Handles an unlimited amount of separate tracks for the same project. This is especially advantageous in mixing a big project with different Foley recordings, sound effects, dialogue, background noise, music, et cetera.
  • Tracks the audio to a built-in video feed. This is critical for timing the placement of effects and music.
  • Allows for tons of different automated pre-sets. Each separate audio recording session requires different levels on each track to create a balanced recording. DAW software makes it so you only have to set those levels once. Once they're saved as pre-sets, you can just click a button and return to the desired settings. This works with the large consoles as well. Click a button and all of the knobs and faders will return to where they were two Wednesdays ago.
  • Cleans up bad recordings. Maybe a plane flew overhead when your hero was saying his big line, or the air conditioning unit in the grocery store was buzzing too loud. DAW software includes special filters and tools for cleaning up clicks, pops, hums, buzzes and all other undesirable background noise.
  • Endless plug-in options. Plug-ins are small software add-ons that allow for additional tools and functionality. They can be special effects plug-ins, virtual instruments for scoring a movie, or emulators that reproduce the sound of classic analog instruments and equipment.
  • Graphic interfaces for placing sound recordings in the 5.1 surround sound spectrum. By moving a cursor back and to the right, you can make it sound like a train is approaching from behind the audience.

And what's the deal with THX, Dolby Surround Sound, DTS, Ultra-Stereo and all those other fancy terms? THX is a standard developed by George Lucas to ensure that how a film sounds in the studio is how it'll sound in the theater. Both soundstages and theaters can be THX certified. The rest are technologies for encoding a film's final audio, and each requires the purchase of a special license. Different encoding technologies allow for more surround sound channels and apply to either optical or digital soundtracks (for more details, check out How Movie Sound Works).

For more information on audio post production and related topics, check out the links on the next page.