Environmental noise is that which exists within the recording environment. For example, if recording outside, the wind can be a significant source of noise, as can cars, planes, and helicopters that are travelling within a few miles of your location. Inside, common sources are air conditioners, vents, power supply fans, fluorescent lights, and doors opening and closing. In short, in any place that has people, you will likely find a lot of noise. Of course, if you are outside, you will have to contend with a whole chorus of natural sounds as well (crickets, frogs, birds, leaves, etc.). In any case, it's hard to escape noise.
One particular problem with environmental noise is that our minds are trained to filter it out automatically. We often do not realize just how much noise surrounds us because we are all the time ignoring it, focusing only on those sounds that are important to us. This can be a problem when trying to determine how suitable an environment is for recording because one must pay close attention to all of the sounds one hears. It can also be a problem when listening to a recording to determine its suitability. Unless you are in a sound-proofed environment while you listen, you might mistake recorded ambient noise for noise simply attributable to you current environment. For example, if the recording picks up the slight buzz of a plane, you might be tricked into thinking that what you are hearing is, in fact a plane flying outside your window several miles away. This can be especially problematic with today's high fidelity digital systems, which can reproduce even the subtlest of sounds.
Another particular difficulty with environmental noise is that it often takes the form of low frequency compressions. An example is when a door somewhere else in the building is allowed to slam closed. Low frequencies have a tendency to travel easily through solid structures. So, the several rooms in the building between your recording environment and the slamming door may make little or no difference at all.
What To Do
The first thing you can do to help reduce the noise problem is to carefully choose your recording environment. Take the time to listen carefully within the environment in order to pick out any potential trouble spots. Also, when recording, try to monitor from outside of the environment, such as from a different room. That way, you will be more likely to recognize environmental noise in the recording that your mind might otherwise filter out.
Another thing that can be done is to carefully choose the placement of the microphone. Miking close to the sound source will provide a much higher signal-to-noise ratio. Otherwise, the noise floor (the average amplitude of the noise in the recording) will quickly overcome the sound source itself. When placing the microphone, remember to adjust the record levels accordingly in order to avoid clipping or distortion due to an overly strong signal.
If you have plenty of time and a bit of money, and plan to do a lot of recording, you might also consider building a sort of recording booth. Surprisingly, this can be done relatively cheaply if you have access to a few materials. Here's how:
With that, you should be able to achieve a reasonable isolation booth for recording without a lot of background noise. Even so, you will still have to be cautious of any activity that is taking place just outside that might cause problems.
Last modified 4/26/97.