A compressor (a.k.a.dynamic processor) is designed to automatically control the volume or dynamics of the sound traveling through it. Compressors can improve the intelligibility of vocals and control where instruments are placed in the overall mix.
Understanding the Parameters
To understand how to properly use a compressor you will first need to understand the parameters of this piece of outboard gear. Obviously, I have no idea what make or model you may be using, but I can still touch on the five main elements of compression: threshold, ratio, attack, release and gain or gain make-up.
“Threshold” sets the point where compression begins. Turning your threshold knob to the right will raise the dB level where the compressor kicks in. Turning this knob to the left has the opposite effect. In a high-threshold setting you will only be compressing the upper decibel levels of your audio signal. As you lower the threshold, more of the audio signal will be compressed. Setting your threshold knob to the center position is a good place to begin. Then use your ear as you raise or lower the threshold.
“Ratio” is the difference in decibel reduction from the input signal to the output signal. Your compressor’s ratio knob typically ranges from 1 to 10. For example, setting the ratio at 2 creates a 2 to 1 ratio (2:1). This means that if 2 dB of signal enters the compressor above the threshold setting, 1 dB exits the compressor. A 4:1 ratio lets 4 dB in and 1 dB out. With these two parameters we can now adjust when we capture the signal and how much we compress it.
“Attack” controls how fast the signal is captured and operates in milliseconds (ms) — 10-25 ms would be a very fast attack. This is good for removing the sibilance or ‘sizzle’ from a vocal, making it more intelligible. Slower attack times have a multitude of uses. Use your ears.
Once you have captured the audio signal you have to decide when to release it. The “release” knob will adjust that. Also calibrated in milliseconds, a faster release time will cause the compressor to follow the signal closely so that rapid input changes (ratio) will not be lost during compression. Slower release times smooth out the overall compression effect. The dynamic process of compression will reduce signal level. As a result, many manufacturers add a gain control to their compressors in order to add back level.
Making It Work
Now that we have a pretty good idea about what a compressor does and how to operate it, I would like to share some of my settings with you. If I am compressing an exuberant preacher, I will set my attack time to fast, my release at medium and ratio from 4:1 to 5:1. For my singers, I set my attack time to medium, release to medium and ratio from 2:1 to 4:1. Should I have an acoustic guitar, I will set my attack to medium, release to medium and ratio from 3:1 to 4:1. If I’ve got a bass guitar, I will attack the signal fast and release it fast at a ratio of 4:1 to 6:1. Kick and snare drums will be attacked and released fast at a 4:1 ratio. Should I have a lively brass section, attack and release times are set to fast at a ratio of 5:1 to 7:1.
This should give you some actual settings that you can use when compressing your preachers, singers or instruments in your house of worship. Lastly, be sure to connect your compressor through your channel inserts if you are working on one particular audio signal. Or take your main mixer left and right outputs and connect them directly into the inputs of your compressor to compress the entire mix.