Room Tone

We plan to use an external microphone whilst filming in order to achieve a high quality sounding product. We will be editing in sound bridges and cutaways throughout our trailer so we want the dialogue and diegetic sound to be as crisp as possible. One thing we were told to consider when recording a scene with sound was background noise. Every room or location (including different dimensions within the same location) has it's own unique background noise, so to avoid the issue of differing aural signatures during editing, this silence is normally recorded at a location for usually around 30-60 seconds. This is known as room tone. Once this is done, the editor can insert the room tone under any cutaway shots and you are left with a smooth soundtrack. Here are a couple of videos I researched to help me understand room tone.