If you have a DAW such as Logic Pro, Pro Tools, or Cubase, and so forth, you may have begun to explore things called audio plugins. Within those audio plugins, you will usually find some called “compressors” and ask what they even do in the first place, how do I use it, and why is it necessary? In this post, I will help you understand why compression is important when it comes to audio and how to best use it in your tracks.
What is Compression Used For?
Compression is widely used in the music world to control the dynamic range of audio. For example, a song can have very soft parts such as the finger picking of a guitar and then when it gets to the chorus, the guitar player starts strumming heavily and it gets louder. When listening to a song, we want to be able to hear all parts of a song clearly without having to turn up the volume when it is soft and then lower the volume when it is loud. To put it in simpler terms, compression tames an audio file so that the loud and soft parts are heard equally and are more consistent throughout the track.
Breakdown of the parameters and how to use them
Threshold: This determines how loud a signal has to get before the compressor will start to work. The lower the threshold, the more audio gets compressed. The higher the threshold, the less audio will get compressed.
For example, if you set the threshold to -20db and the audio signal reaches that limit on the input or goes beyond it, the compressor will start to compress. This is all the threshold knob does. It either allows more or less audio to come in depending on where you set it.
Ratio: The ratio knob determines how much audio is going to be compressed after it reaches the compressor. For example, if we set the compressor at a 2:1 ratio here, that means that for every 2 decibels of audio that go above the threshold we set, the compressor will “compress” or tame half of that amount before it reaches the output.
To put it even simpler, the higher the ratio the more dramatic the compression is going to be. Lower ratios are more subtle and less aggressive. However, if you set the ratio too low it won’t really allow the compressor to do its job. I would recommend sticking between a 2:1 to 4:1 ratio for basic compression.
Attack: This determines how fast a compressor will trigger and tame the audio. The faster the attack, the more it will reduce the initial peaks of a source and round out the sound. The slower the attack, the less it will focus on the initial peaks of a source and therefore cause it to sound bigger and “punchier.”
Too much attack can make a source sound less natural and more processed but too slow of an attack can cause some of the harsh peaks of a source to not get compressed and make the source sound uneven in dynamics. So the key here is to find a good balance between fast and slow.
To accomplish this - focus on what you are trying to compress. Is it an instrument that has a lot of initial attack on it like a snare hit for example? If so, then you might want to set the attack more on the slower end so it doesn’t lose character and sounds punchier. If it’s a vocal track on the other hand, then we might want to have a little bit faster of an attack so that we can focus on taming the initial peaks of the vocal and make everything more consistent so that it fits better in the mix.
Release: The release knob works hand in hand with the attack. It determines how fast or slow a compressor will stop compressing. The faster a release, the more of a “pumping sound” the audio will have. The slower the release, the more controlled the dynamics will be.
Too fast of a release can sound unnatural and too slow of a release can cause the compressor never to turn off and can make a source not sit well within a mix. A tip here is to set the release so that the compressor releases with the tempo of the song or before the next beat hits. This will give you the most even and natural sound.
Knee: I wouldn’t worry too much about this parameter for basic compression but this setting controls how hard or soft the compression is going to work.
Generally I’ll keep the setting on a softer knee so that the compression is as smooth as it can be.
Depending on the compressor plug in you are using it could either have a knob like the one here or a switch from hard to soft knee.
Output/Makeup Gain: This setting essentially controls the amount of gain you’d like to make-up on the output after compression is done.
Since the loudest parts of the audio coming in are getting reduced after it gets compressed, it will usually be lower in volume by the time it reaches the output. A simple way to use the make-up gain is for every decibel of audio compressed, then that is the amount of gain to make-up when the audio goes out. This brings the audio back to a better overall volume.
For example, the meters on the compressor will tell you how much is being compressed. Notice that the meter below is peaking around -3db. This is the amount of gain I will add on the make-up gain when the audio goes out.
RECAP
The threshold controls the amount of audio allowed into the compressor.
The ratio determines how much the compressor will compress after the audio comes in.
The attack controls how much of the initial peak the compressor will tame
The release controls how fast or slow the compressor will turn off and stop compressing.
The make-up gain allows you to “make-up” or increase the gain that has been attenuated by the compressor.
That’s all the basics of compression!
I hope this info was helpful. Compressors are valuable tools when used properly. I encourage you to record a few things or even use the stock samples within your DAW and spend some time messing around with these settings on the compressor. Using compression might seem tricky at first but the more you use it and see how each setting works the more you will get comfortable. My advice would be to go light with compression at first because it is really easy to get carried away and over-compress a track. Less is more!
Just to help you even further I have created what I call my Quick Start Guide To Compression to make using compression even easier on your tracks. There is even a “cheat” sheet at the end giving you some great starting points for different instruments you might be using in your music.
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