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Amateur Recording
Part 2. Environmental Noise

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.

[Waveform of a helicopter]
Waveform of a helicopter in the distance.

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:

  1. Find a room that you can set up in. Plan on making this a permanent establishment if you can.

  2. Find all of the air conditioner vents in the room and immediately remove the grills from each. This alone will cut down significantly on the air conditioner noise (though it will not help if the air conditioner itself is in the same room).

  3. Using temporary office cubicle walls (the kind covered with what looks like carpeting), construct a small room within the room. Try to locate it in the center of the room, and include a roof on the cubicle by simply laying an extra cubicle panel across the top of the structure. Make sure that no part of the structure comes in contact with any of the walls or the ceiling of the outer room. This leaves nothing but air between the inner and outer rooms (excepting the floor, of course), which is a much better insulator for sound than solid matter.

  4. Finally, place the microphone and maybe a table and chair inside the booth. If possible, keep most of the recording equipment on the outside so that the recording process can be monitored from the outside and to cut down on any noise that may be caused by the equipment itself. This is especially important if using a desktop computer or anything else that has a power supply fan. If you must include a lamp, be sure that it is not a fluorescent light or one that buzzes when it is on.

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.

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    [Return to Top] Copyright 1997, Mark R. Johnson.
Last modified 4/26/97.