Professional-quality sound editing is crucial to a finished film. While not all films can afford a dedicated sound editor, with some effort, it’s possible to edit sound yourself. The minimum requirements are a copy of Pro Tools (or a comparable Digital Audio Workstation, though Pro Tools is the standard in the film industry) and patience. Sound editing is primarily concerned with:
In this short guide, we will go over the basics of completing each of these tasks. Before we begin, it’s important to note that sound editing is NOT the same as sound mixing. Audio mixing is concerned with blending the levels on all the tracks in a sound mix, as well as adding effects such as compression and reverb. The last step of audio mixing for film is exporting the sound locked to the video in both stereo and surround versions; mastering is a subset of sound mixing that deals with optimizing a sound mix for a variety of listening environments. Sound editing goes hand-in-hand with video editing, and is focused on proper timing and seamless assembling of all sound in a film.
Counterintuitively, the more common cause of audio sync issues lies with changes in the video frame rate. It is crucial that the frame rate be standardized between recording and every stage of editing (standard frame rates for different media are available here). It will save time during editing if the audio is synced during the production process, which can be achieved through the use of a cable following S/PDIF or TDIF protocols linking the camera and the sound recorder. A full breakdown of the terminology and consumer/professional variations is available here.
Sound devices with syncing capabilities are significantly more expensive, so many low-budget productions choose to synchronize the audio later from external microphones with the internal camera audio in the editing stage. Sometimes, a perfect sync actually sounds hollow because it ignores the time sound takes to travel across a room and destroys the illusory space between the audience and the camera’s subject. Possible corrections for this include the use of reverb as a plug-in (though we won’t get into that, as it’s more of a mixing topic) and manually un-synchronizing the audio, delaying it 5-15 milliseconds, a change that isn’t noticeable to the ear but can be psychologically effective.
Clicks and pops arise in audio when two non-adjacent clips are placed next to each other. The jump in the signal between them leads to a percussive sound. The issue is resolved by creating a short crossfade between the two clips. You’ll want to create an equal-power rather than an equal-gain crossfade for a smoother transition (there’s science behind that, but just trust me on it). Often, projects with many dialogue, music, sound effects and Foley tracks, called audio stems in the sound world, and a complicated video edit will have thousands upon thousands of cuts in the audio. It’s not always possible to manually crossfade every single transition, especially when on a deadline.
The best way to deal with clicks and pops, in my opinion, is to solo out tracks one at a time and use your ears, with the volume turned up. Any audible clicks should be immediately dealt with; on the other hand, if you can’t hear a click with the track soloed, it will almost certainly be fine in the final mix. Clicks and pops occur at every stage of editing, as every video pass implies a new audio edit, and are generally still being removed during the final mixdown.
Foley is the overdubbing of (generally naturalistic) sound effects to a production in post. Hiring a Foley artist for a day is well worth it for verisimilitude and will often resolve many of the issues related to production noise. ADR generally sounds terrible unless great attention is paid to it, which means rerecording the actors in a proper sound studio with prep time to get them into their roles and significant attention paid to ensure that the artificial reverberation of their voices matches the room in which the scene was originally recorded. In other words, unless the film has a proper budget for it, ADR often leads to less rather than more professional-sounding audio.
Properly placing ADR and Foley is a time-consuming task, with attention needing to be paid to both sync and the contextual flow of the audio. For the placement of the music, it’s best to work with a dedicated music editor. If this isn’t possible, oftentimes, film composers are also competent music editors. The flaw with this, though, is that they tend to over-prioritize their own contributions. This is often resolved during the rerecording mixdown session.