Compression is a useful tool for many musicians. Whether your a bassist playing a difficult line, or a guitarist that uses a wide range, compression can turn any line with inconsistent dynamics into a divine melody. That being stated, many musicians don’t fully understand how to use a compressor, or don’t know how to use it to their advantage, which can potentially cause havoc to a signal and make you sound worse than you started.
Compression modifies a signal by lowering the volume of a signal when it reaches a threshold volume. It is used to keep inconsistent dynamics in check, and maintain a constant signal level, which is useful for guitarists that use a lot of legato (hammer-ons, pull-offs, tapping) and sweep picking, or guitarists that switch between single-note lines and chord lines. The technique these playing styles require makes it hard for a musician to play consistently within the same volume, which can be overcome, but with difficulty (the cleaner a guitar sound, the more these inconsistencies stand out). Although practice in this area is important, it’s good to have a fail-safe for performance, and that fail-safe is compression.
Using compression can be both benign and malevolent. Too little and the signal remains uneven, but too much and unwanted sounds become more prevalent. For this reason it’s important to know the basics of a compressors function.
Important variables of a compressor:
The ratio is how much the compressor affects the signal once it has reached the threshold. A signal affected by a 2:1 ratio at 6dB will leave the compressor at 3dB, cutting it in half. A ratio of 3:1 will reduce the same signal to 2dB. Compression at a ratio of 10:1 or higher is considered “limiting”, because it limits the signal from going greatly beyond the threshold.
The threshold is the point of volume at which the compressor acts upon the signal. A threshold of 6dB will act upon any signal at the volume of 6dB and beyond. A relatively high threshold can be used with limiting to stop a signal from overloading an amp or effect pedal, but if the threshold is too low it can cause unwanted muddiness.
Attack is the speed at which the compressor lowers the volume of a signal, after the threshold is achieved, to the amount defined by the ratio. The faster the attack, the more consistent the signal, and the slower the attack, the more natural it sounds. It’s important to find a point between these two extremes of speed to produce the compression your playing needs.
Release is essentially the opposite of attack. This defines how fast the signal is returned to it’s normal volume level after it leaves the threshold. A fast release sounds more consistent, and a slow one sounds more natural.
Gain is simply an extra volume boost most compressors provide to make up for the loss of volume during compression. Too much gain can overload an amp, and raise the noise level of a signal (That fizzing, popping, whirring sound your cables can pick up from electronics).
The use or misuse of these variables can drastically change how good a compressed signal sounds. Too much threshold and the signal loses all dynamic quality, and the signal moves closer to the volume of unwanted noise. Too fast or slow of an attack, and the signal loses it’s natural sound. It’s important to understand and balance these variables to create a compression that works for your playing style.