In short, all spaces have a unique sound to them. Take a moment to stop and listen to the space you are in right now, what can you hear?
You might hear the hum of lighting, the low rumble of an air conditioning unit. Each space has its own unique sound characteristics.
When you hear a sound recordist ask for some ‘room tone,’ what is actually happening is they are capturing a sound print of the room, it’s 30 seconds to a minute of audio which the sound designers can use later in post production as part of the noise reduction process.
We can take the capture noise print and apply it to our noise reduction process, for example in Audition, we can tell the software what noise print we want to identify and remove from the audio we are working on.
The end result is that we produce a video with less background noise, because we have been able to capture and isolate unwanted background noise.
When you are on set next, take a moment to stop, and record some audio of the room you are about to film in, have everyone be as quiet as possible. (‘quiet on set.’)