Sound and image run simultaneously — lip-sync, footsteps, door slams. Recorded on-set or post-synced with precision.
Sync means: sound and image run in exact temporal agreement. The actor speaks, their mouth moves, we hear the voice at the same moment—or a door slams shut, and the bang occurs simultaneously. This is a constant technical challenge because image and sound can drift apart again and again during production, editing, and mixing.
On set, sync is routine: the sound recordist records while the camera is rolling. Slates and timecode are the tools to know later which sound recording belongs to which picture take. The biggest pitfall is in dialogue recording—lip sync is mercilessly visible if the sound is shifted by just two or three frames. The eye forgives asynchronous footsteps more easily than a lip that moves before we hear the word. Requirements differ in documentaries and feature films: with doc interviews, one can often work with some tolerance, but in feature film close-up dialogue, synchronization must be perfect.
In editing, sync becomes a technical obsession. The editor places the audio track precisely on the visual moment. For dialogue, we often zoom in on the lips and shift the sound millisecond by millisecond until it fits. Tools like sync software help, but the editor's ear and eye ultimately decide. With foley—the sound effects recorded afterward—this becomes very practical: sound is placed with precise timing, step by step, hand movement by hand movement.
Often, the problem is not the original sound recording from set, but the mix. When background atmosphere, music, and dialogue come together, synchronization can suffer due to volume balancing and effects. A good sound mixer maintains spatial and temporal accuracy while shaping the sound. Sync is not perfection for perfection's sake—it is the basis for the viewer not being pulled out of the story, but unconsciously believing in the film's reality.