Decide what you want the compressor to do
There are a few basic rules to setup any compressor with any number of different parameters.
To set up a compressor
- start with knowing the two basic uses of a compressor
- decide which use you want for your job at hand.
Using the Compressor as a Limiter
This way of limiting the signal to the threshold values is known as limiting.
A limiter will require a theoretical compression ratio of infinity:1. Any input signal above the threshold is reduced to zero, preventing the output signal to move past the threshold value. But in real life, any ratio above or around 10 is close to true limiting.
Compressors are often referred to as compressor/limiters because most compressors have enough ratio range which will allow us to use the compressor as a limiter.
Why use a compressor as limiter?
The main reason to use a compressor as a limiter is to control excessive peaks. To do this, you need to set the threshold fairly high and use a high ratio in the vicinity of 10:1.
Setting the threshold fairly high means that the signal will not kick the compression into action, most of the time. But, when a peak occurs, it will be reduced firmly based on the high ratio we set.
When using a compressor as limiter, a fast attack and release time is best, so that the peaks are acted upon fast while once the signal goes below the threshold, the compressor immediately disengages. If the sound appears to reveal level pumping, lengthen the release time until the pumping does not sound like a problem.
Using the compressor to 'thicken' the sound
If you use the compressor to bring up the level of the low sounds, it will sound as though the input signal has been thickened a bit, made a bit more solid, substantial, strong and present.
If you want to use a compressor to thicken up a sound:
- set a low ratio – 2:1, or even less. This means any signal above the threshold will be cut to half while setting a higher ration of 6:1 would have cut the signal by 1/6th.
- set the threshold quite low so that you still get between 6 and 12dB of gain reduction showing on the meters. We want most of the peaks to be affected. Even small peaks can activate the compressor, cutting the signal over the threshold by a mild ratio of 2:1 or so.
- A longer release time gives you a smoother sound, but decide based on what you feel most appropriate for the situation you have.
Setting up the compressor
Ratio Decide on whether you want to thicken or limit and set the ratio accordingly. Around 10:1 for limiting, around 2:1 or lower for thickening. In the case of pop mixes, many of the instruments or vocal groups may be given a higher ratio of compression.
Threshold Adjust the threshold control to show 6-12dB of gain reduction on peaks. This is a good starting point.
If you want audible pumping, bring the threshold even lower to bring more gain reduction. Else if you want to be subtle with your compression, back off the threshold, raise the threshold value, have less gain reduction.
Release Always adjust the release time to be as short as possible, while avoiding pumping. We want the compressor to stop acting on the input signal as soon as the signal goes below the threshold.
Attack Start with a fast attack. Lengthen the attack if you are working with percussive sounds or other sounds which will benefit from the initial hit or strike passing through. Listen to the result. Set the attack just long enough to let the sound have the percussive quality while the high-frequencies don't sound like they undergone gain modulation.
Vocals and other smoother sounds can have a faster attack setting.
Try the above settings on your compressor. Also try the use of a compressor as a limiter. If you use a software compressor, next time you open your project, add a compressor to an audio track, try its effect with smooth and percussive kind of sounds. Once you have some good initial settings, adjusting to your needs becomes an easy task and the sound of your mix will show obvious improvement.