The term "MOS" is used, on a slate, when a scene is filmed without sync sound (or any sound).
What MOS orginally stood for is still up
Motor Only Sync! Suffice it to say that if someone asserts that it is "Mit out Sound" and yet they have never worked with interlock distributors or multi-duty camera motors.
Hence, that's why I maintain that "Mit out Sound" is descriptive of the *result* (from the point of view of a non-technologist), while "Motor Only Sync" is descriptive of the *process* (from the point of view of a technologist).
Edited excerpts from discussion thread "MOS original meaning"
Archived discussion threads:
Other terms are On-location Sounds and Direct sound
Sound recorded at the actual location of principal photography, whether on-stage at a movie lot or on-location. It can be difficult to get usable dialogue or other sounds at time of filming, especially on-location.
Background sound such as honking horns or shouting people or even the noises of the film crew itself can obscure dialogue or otherwise produce an effect that the director does not want in the sound of the film.
Outdoor locations can be especially difficult
due to the very limited control the film-makers have of the environment.
On the set the location recordist (listed as production mixer) tries to record dialog as cleanly and crisply as possible, with little
background noise (a high signal-to-noise ratio). A boom operator, usually suspending the microphone above and in front of the person speaking, tries to get it as close as possible without letting the microphone or its shadow enter the frame.
An alternative to a mike suspended from an overhead boom is a hidden lavaliere mike on the actor's chest, which is either connected to the tape recorder via cables or wired to a small radio transmitter also hidden on the actor. But dialog recorded from below the mouth must be adjusted later to match the better sound quality of the boom mike. And radio mikes can pick up stray sounds like gypsy cabs.
While on the set, the sound recordist may also ask for a moment of silence to pick up some "room tone" (the sound of the location when no one is talking), which must be combined with any dialog that is added during post production (with reconstructed room reverberation) so that it matches what is shot on the set.
We don't usually notice the sound of the
breeze or a motor hum, but their absence in a Hollywood product would be
quite conspicuous. The set recordist may also capture sounds distinctive
to a particular location to give the post production crew some sense of
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