Such a noob I am HA, forgot all about room noise during this filming project. However I Wonder how important it really is. I mean all you are recording is, well science pretty much, is this truly necessary?
All you're recording with your camera is "science pretty much", is that going to stop you being a filmmaker? As to room tone being necessary, that depends on what your audience will be listening on and whether or not you want your audience to feel involved with your film. If your audience is watching your film on a laptop or smartphone then unless your dialogue is very noisy, you probably won't need room tone. However, if your audience is using headphones, has a half decent sound system or heaven forbid see your film in a cinema (say at a film festival) or you want to make a film approaching professional standards then you will most definitely need room tone!
None of my takes has just plain silence, But I do still have access to some sets I am done filming in. I mean can't I just go back now and records the silence?
First off, your takes do and will always be packed wall to wall with room tone, it will be under all your dialogue (and therefore unusable) and in lot's of tiny chunks between the dialogue. With time, effort and the know how, it is sometimes possible to manufacture room tone from all these tiny chunks.
Second off, you can't go back now and record silence because it's impossible to record silence! The vast majority of people never experience silence in their entire life (or even before it). The few who do, have been in an anechoic chamber and the first time inside one is usually an uncomfortable experience because the brain cannot accept the existence of silence and starts to do strange things, which culminates after a few minutes for some people being physically sick, although they usually leave before it gets to that stage!
At the most fundamental level we have to use room tone because you have to understand that the human brain is a pattern matching machine. If you are editing lines of dialogue correctly, you will end up with areas where there is no sound then, when the next line of dialogue comes in, it comes in with it's room tone. The brain is used to dialogue starting and stopping but room tone starting and stopping is completely alien and will immediately destroy any atmosphere you are trying to create and force your audience to become uninvolved in your film. BTW, the audience doesn't have to be able to consciously hear the room tone cutting in and out, just a subconscious awareness is enough to drag them out of your scene/s!
Room tone is created by inaudible sounds and vibrations interacting with the air molecules and acoustic properties in a room and yes, this is science! When your shoot your film your camera's sensor detects and converts photons reflected from whatever you're pointing your camera at, this too is science and without it you could not make a film! Acoustic properties vary enormously from room to room and are also greatly affected by what is in the room; furniture, decorations and even people absorb or reflect certain frequencies. So every room has a different sound and even the same room has a different sound anytime something inside the room is moved/changed. Humans are very sensitive to subliminal changes and different types of room tone. Blindfold someone and take them into a room; a kitchen, toilet, gymnasium, warehouse or basement for example and within a second or so, they will have a pretty good idea of what sort of room they are in, even though they are probably not consciously aware their brain is analyzing the room tone to give them the answer. Good filmmakers use this fact to go beyond just the fundamental requirement of avoiding room tone cutting in and out and use it as a manipulation tool in audio post to make the audience believe they are in the space they are seeing in the films visuals.
You can just go into any old room and record room tone but then you'll have room tone which doesn't precisely match the room tone on your production sound and and may not even match the acoustic space in your visuals. Not only are you risking the pattern matching functions of the brain registering the difference between the room tones but you're also risking your room tone subconsciously contradicting your visuals. Either of these eventualities will stop your audience feeling involved in your film!
As a member of the public you can ignore the science of silence (or the lack of silence) but as a film maker you cannot, not if you want to be a decent film maker one day!
Forced air conditioner wind through AC vents is the greatest contributor, followed by the gentle hum of fluorescent lights and computer fans. Room size, window/wall ratios, and general furnishings also alter the sound.
These are all background or ambient sounds, NOT room tone, room tone should not contain any of these sounds you mention! And, room size, windows/walls/floors/ceilings, furnishings, etc., don't "alter the sound" of room tone, they define it.
G