At a basic level a compressor has 5 main controls which we can group into 2 groups that allow us to easily navigate and control the behavior of our automatic volume fader.
The 1st group is called our Fader ‘Triggering’. It consists of our Threshold, Ratio, and Sidechain controls.
These controls tell our automatic volume fader ‘when’ to move down, and ‘how much’ volume to subtract when it does.
The 2nd group is called our Fader ‘Speed Properties’ It consists of our Attack and Release controls.
These controls tell our automatic volume fader ‘how fast’ it should move when it is triggered by the incoming signal.
Fader ‘Triggering’
The controls in this section allow our automatic volume fader to know ‘when’ and ‘how much’ to push down the volume of the incoming signal.
Threshold
Threshold tells the volume fader ‘when’ to start decreasing the volume of our incoming signal. Signals which rise above our threshold cause our automatic volume fader to move down, thus decreasing the volume of our sound.
Signals which remain beneath our threshold cause our automatic volume fader to do absolutely nothing.
Ratio
Ratio is ‘how much’ our automatic volume fader will move down in response to the incoming signal when threshold is exceeded. This means when the volume of the sound is louder than our threshold setting, then the ratio determines ‘how far’ down the compressor will move our automatic volume fader.
The higher our ratio, the more our automatic volume fader moves down in response to an incoming signal which goes above our threshold.
The lower our ratio, the less our automatic volume fader moves down in response to an incoming signal which goes above our threshold.
The difference between a high ratio and a low ratio is like the difference between gravity on earth vs. gravity on the moon.
When you jump on earth you get pulled down right away, but when you jump on the moon, you go higher and you get pulled down slower and more gently.
It’s the same with our ratio control. The lower our ratio, the more gently our volume fader pushes down. The higher the ratio the more aggressively our volume fader pushes down.
Fader ‘Speed Properties’
Attack
Attack is ‘how long’ it takes our automatic volume fader to move downward when the threshold is exceeded by our incoming signal.
So for example, with a 10ms attack when our incoming signal exceeds the threshold of our compressor, it means that our automatic volume fader takes 10ms to decrease the volume as determined by our threshold and ratio controls.
Once our attack is complete the volume fader will continue subtracting volume until the incoming signal gets quieter and falls beneath our threshold. Once this happens our automatic volume goes into the release phase.
Release is simply the time it takes for your automatic volume fader to move back up to 0 volume reduction.
Release
Release is ‘how long’ it will take our automatic volume fader to return back to its original position of 0 volume reduction.
The release phase happens only when our incoming signal has fallen beneath the threshold we’ve selected.
So with a 10ms release, it would take our lowered automatic volume fader 10ms to return back to its original level.
If as the compressor is completing its release timing the incoming signal goes above threshold, then the compressor will re-enter its attack phase until gain reduction is achieved again.
I know it’s kind of redundant, but nobody ever explained what happens if your release isn’t allowed to finish before the compressor is retriggered.
Makeup Gain
Since our automatic volume fader functions by reducing the volume of the sounds, often the sounds we treat with compression can become quieter.
Makeup Gain allows us to restore our instrument to its original perceived volume level.
However there will be situations where you’ll be using compression to only reduce the volume of a sound whenever it gets too loud.
This is because you’re using the compressor as a volume sentinel who’s only job is to viciously slap any overly loud sounds back into lower volume territory. This is one of the easiest and most natural ways to use your automatic volume fader.