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WPI Technical Theatre Handbook: Compressors and Limiters
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Compressors and Limiters

Quite frequently, microphones will be used in a theatre application. These mics may be on the actors, or elsewhere. One frustrating aspect of running sound for a show in cases like this is that often the volume level will not be loud enough at times and too loud at other times. This can be due to many factors, most of which involve the actors. This problem can be practically eliminated through the use of a device called a compressor/limiter.

A compressor/limiter reduces the dynamic range of an audio signal. Simply put, it makes quieter things louder, and louder things quieter. Several controls are available, such as attack and release times, threshold levels, and compression ratios. There are two main schools of setting compressor controls; one dictates that some calculations be made, while the other follows the ``fiddle with it until it sounds good'' methodology.

The calculation scheme is rarely used when the compressor is being used on an input such as a microphone. Since compressors/limiters can be placed on the output stages of sound boards, they are often used to protect the speakers and amplifiers from excessive peaks. Setting the compressor such that the sound may not rise above a certain level is fairly easy, and in this sense the compressor is merely acting as a limiter. However, finding the level that won't destroy the speakers isn't necessarily easy, as there are many factors to consider. This is where the calculations can come in. Needless to say, they are beyond the scope of this book. Consult the Yamaha Sound Reinforcement Handbook or a competent audio engineer for more details.

The best way to get a feel for how a compressor works is to hook one up and insert it on a microphone input on a sound board. Adjust the attack, release, threshold and ratio until the sound seems fairly natural. Try moving the microphone closer and farther away while speaking into it. With appropriate settings, the ill-effects of an person speaking quietly at one moment and yelling the next, or moving closer and farther away from the microphone can be reduced.

next up previous contents index
Next: Noise Gates Up: Signal Processing Equipment Previous: Equalizers   Contents   Index
Steve Richardson 2000-07-06

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