In a film, no sound is a coincidence.

Every shot, every angle, and every sound is deliberate. Each of the three elements of a soundtrack—dialogue, music, and effects, including sounds that don’t occur in nature—is recorded and evaluated. In the editorial phase of production, as the director determines which dialogue performance is the best among multiple takes, thousands of edits are made to produce the final dialogue track that we hear in the theatre. The score is recorded, then cut into thousands of pieces to match the pace and feel of the movie’s final cut. From footsteps to rustling skirts to bellowing dragons, sound effects real and mythical are designed and recorded, often combining the most unexpected sounds to enhance the movie’s hyperreality.

Finally, it’s up to the rerecording mixers to blend those components in a way that represents the film’s drama. They create the illusion that sound is occurring where the action is happening, whether it’s looming ahead, passing you by, or approaching you from behind. Because it’s impractical to set up microphones where they will be visible in a close shot or pick up a lot of extraneous noise, the mixers recreate the soundscape by carefully placing sounds that were created in editing, with the help of giant mixing consoles.

The effectiveness of the illusion of a sound’s location depends in part on our sense of hearing. We assess the timing, loudness, and frequency of sounds. We also take into account visual stimuli and oursense of body position and effort of movement (known as proprioception) to judge where the sound originates. In fact, visual input can override the other senses.

You can get an idea of how your brain works to process and make decisions about multiple inputs when you watch a movie shown in 3D with surround sound. Try watching the film without moving your head; now try looking all over the screen, allowing your head to move and follow the action. You may notice more sounds or feel more aware of their presence in space.

If that movie happens to be The Hobbit: An Unexpected Journey in 3D, pay close attention to the ponies. From whinnying and snorting to hoofbeats and the jingling and creaking of bridles and saddles, even the subtler effects are deliberate. They not only help make the ponies’ fidgeting presence more lifelike in a scene, they also heighten the air of danger. And as Wargs’ jaws are snapping overhead, you feel just as threatened as Bilbo Baggins in that tree; it doesn’t matter that you’ve never met a Warg. Your perception of sound located with action makes for a richer emotional experience of the story.

 Find how the sound team sweeps you into an epic quest to reclaim the lost Dwarf Kingdom of Erebor from the fearsome dragon Smaug, and get director and producer Peter Jackson’s behind-the-scenes look at intensive final preparations for the premiere at the Embassy Theatre in Wellington, New Zealand—even as production wrapped hours before the press preview.

What scene made you most aware of sound around you?