Improvement Plan
Compression falls under the broader category of dynamics processing. The term “dynamics” refers to changes in loudness level, so dynamic range is the difference between the softest and loudest sounds that a source produces, or that a track contains. A dynamics processor’s purpose is simply to increase or decrease a signal’s dynamic range, which alters how the levels fluctuate within that range. Types of dynamics processors include gates, expanders, limiters, levelers, and compressors.

A compressor is a type of dynamics processor that “squeezes” a signal’s dynamic range—that is, it reduces the difference in volume, or level, between the loudest and softest parts of a performance. The process of reducing volume is called gain reduction. Properly applied, gain reduction makes a performance sound more consistent from beginning to end. For that reason, compression is a great remedy for a performance in which the levels fluctuate too widely.

By reducing dynamic range, a compressor also allows for the processed signal’s overall level to be raised—that is, become “hotter”—resulting in increased loudness without pushing the signal’s loudest parts into distortion. Bringing up the overall level has the additional benefit of making lower-level sounds louder than they were before compression. The result is that subtle nuances such as mouth sounds and ghosted notes—as well as burps, string buzzes, and snare rattles—are louder, clearer, and easier to hear.

Of course, you may not want to make burps, string buzzes, and other incidental performance sounds more audible. Therefore, apply compression only when musically appropriate—when the end result will sound better than what you started with.

You can always add compression after a track is recorded (during mixdown), but sometimes it is desirable to use compression during the recording process. That approach has several potential benefits. For one, a compressor makes it easier to capture usable tracks when recording an instrument with a wide dynamic range. Moreover, solving level-fluctuation problems during tracking frees you from having to solve them at mixdown. That, in turn, leaves more time and brain power—not to mention gear—for focusing on the mix’s creative aspects.

For those recording to any digital medium, using a compressor during tracking ensures that sounds are encoded at a higher level. Because more bits are used, better bit resolution results. Furthermore, by putting a lid on peaks, the compressor also helps avoid digital clipping on extraloud notes. For those recording to analog tape, compressing during tracking allows the signal level to be raised higher above the noise floor, which results in an improved signal-to-noise ratio.

Tricks of the Trade

You can make the lead vocal sound so urgent that listeners dial 911.

In addition to problem solving—smoothing out rough performances, improving digital resolution and signal-to-noise ratio, avoiding digital clipping, and the like—you can also employ compressors in numerous creative applications. For example, a compressor can dramatically change the envelope of a sound in much the same way an envelope generator works in a synthesizer. That and other compression tricks can give a vicious attack to a lackluster snare drum, add crunchy edge and sustain to a mild-mannered electric guitar, make a lead vocal sound so urgent that listeners will dial 911, or pump up an entire mix until the band sounds like it’s exploding out of the speakers.

BACK | NEXT

Reprinted with permission from Magazine, February, 2001
© 2001, Intertec Publishing, A Primedia Company All Rights Reserved