The Purpose of Placeholder Audio
In the early stages of film editing, the primary focus is on rhythm, pacing, and visual storytelling. A picture editor needs to assemble scenes and sequences to see if they work, but they cannot do this in silence. They need the actors’ dialogue to understand the timing of line delivery, the length of pauses, and the overall flow of a conversation. Scratch dialogue—often called a ‘scratch track’—serves this exact purpose. It is a low-quality, temporary audio track that is synchronized to the picture, providing an essential guide for the editor to build the scene around.
Its quality is secondary to its presence. The audio might be noisy, echoey, or filled with off-mic sounds, but as long as the dialogue is intelligible, it allows the editor to make crucial decisions about which take to use for a particular moment, where to place a reaction shot, and how to pace the cutting. It’s a foundational tool that allows the editorial process to move forward without being delayed by the more time-consuming process of audio cleanup and final mixing.
Sources of Scratch Dialogue
Scratch dialogue comes from various sources on set, none of which are intended for the final film. The most common source is the on-camera microphone. Most professional cinema cameras have a built-in microphone whose primary purpose is to record reference audio directly onto the video file. This audio is not high-quality, but it’s perfectly synchronized and provides an immediate, usable scratch track.
Other sources include:
- Boom Mic Spill: The boom microphone is highly directional, but it still picks up sound from other actors in the scene who are ‘off-mic’. This audio is not clean enough for the final mix but can be perfectly adequate for a scratch track.
- Unused Lavalier Feeds: An actor’s lavalier mic might be used for their lines but will also pick up the other actors in the scene.
- Editor or Director Recordings: In some cases, such as with animation or visual-effects-heavy scenes that are created without live actors, the editor or director might record themselves reading the lines to provide a temporary guide for timing.
Its Role in the Editing Workflow
The scratch track is the picture editor’s working copy of the sound. Once the picture edit is ‘locked’—meaning no more changes will be made to the timing of the visuals—the project is handed over to the sound department. The sound editors will then discard the scratch track and begin the meticulous process of conforming the high-quality production audio. They will use the original, isolated microphone recordings (ISOs) from the production sound mixer’s files, cleaning them up, and mixing them. If any lines are unusable, they will be replaced with ADR (Automated Dialogue Replacement). The scratch track has served its purpose and is completely replaced by the polished, professional dialogue track in the final mix.