Sound Versus Noise by Barb Karg, Rick Sutherland, & Jim Van Over
The difference between sound and noise is like the difference between a daisy and a thistle — they're made of the same basic stuff, but you don't want both of them in your bouquet. The inherent difficulty in excluding all noise is that no recording equipment is perfect. Couple that with the abundance of ambient noise surrounding us no matter where we are, and you've got a host of issues to conquer.
System Noise
For decades it has proven impossible to eliminate all the system noise that results from imperfections in recording equipment. Because of these inherent flaws, both microphones and analog tapes add a noticeable background hiss to any sound recording. Fortunately, the new generation of digital recorders and DAT tapes reduces equipment noise to negligible levels.
Ambient Noise
Everywhere we go, we're surrounded by ambient noise. Fluorescent lights, chirping birds, the hum of a refrigerator, and the distant drone of traffic are a few examples of the natural and continuous sounds of our everyday environment. On one hand, you want to get rid of them as much as possible; on the other, you want to be sure to record them.
When filming anywhere except in a completely controlled soundstage, you cannot help but have background ambience or room tone. Because the ambience is unique to that location, be sure to record several minutes of room tone, with no dialogue, movement, or anything that'll interfere with the pure background noise. This will prove invaluable at the editing stage, by providing you options if it becomes necessary to rearrange synchronized sounds.
Other than recording a track of room tone, you want to minimize ambient noise as much as possible. One way to do that is redubbing. Also called looping or automated dialogue replacement (ADR), this is the process of recording or replacing voices during editing, long after the film is done. It's a difficult task at best, and one that soaks up precious editing time and money.
A far easier way than redubbing to get around ambient noise is by using a highly directional microphone. When properly positioned, this microphone will pick up the dialogue or other sounds you want while minimizing background noise.
It may also be necessary to muffle the cause of the noise. Refrigerators, for example, can be turned off during shooting. Film cameras not only make a lot of noise as they sprocket the film past the gate, but they're often close to the subject, and therefore close to the microphone. In order to avert this problem you'll need to invest in specialized camera covers called barneys and blimps. If you're keeping it simple, try throwing a blanket over the equipment. This usually works well enough, as long as you remember to remove it between takes to keep the camera from overheating.
