Audio compression is ESSENTIAL in producing and mixing world-class music (of any genre, but particularly EDM genres), and alongside volume and equalisation (and our ears), compressors are arguably one of the most important mixing tools we have at our disposal.
In this post, I explain all the core controls that decent compressors have (Threshold, Ratio, Attack, Release, Output Gain and Knee), and how they work, and then go through 4 examples of why, where and how you might want to compress...
Compressors are also one of the most abused and misunderstood tools (*sad violin music*), but don’t feel sorry for them…. they will CRUSH the life out of your mix if you give them half a chance. This post and video will help you avoid ever doing that to your mixes again.
Here is what we'll cover:
1. What compressors ACTUALLY do.
2. Using compression to tame peaks in volume.
3. Using compression to fatten a sound.
4. Using compression to create excitement.
5. Using compression to glue sounds together.
I also made a video (at the bottom of this post). It covers the same stuff, but also shows audio examples, so I recommend watching it as it's probably easier to hear/see compression in action than merely read about it!
1. What Compressors ACTUALLY do.
Compressors are just volume controllers. A bit like having an elf on the mixer, riding the volume fader up and down in response to the audio signal entering it. Filthy little elf.
All compressors have threshold, ratio, attack, release knobs. Decent ones also have soft/hard knee and output gain. Here's what they do:
Threshold: Sets the level above which the signal is compressed. so if it's set to -4dB, only audio louder than -4dB will be compressed.
Ratio: The extent to which the audio above the threshold is compressed. A 1:1 ratio won't compress it at all (i.e reduce it's volume). 1:2 will halve the volume. 1:4 will quarter it, etc.
Attack: This determines the speed at which the compression is applied. So a very quick attack will compress the signal straight away, whereas a slow attack will let the first part through without compressing it.
Release: As you'd expect. A quick release will stop compressing the signal quickly (i.e. stop reducing the volume of anything above the threshold), and a long release won't.
Soft/Hard Knee: Determines how smoothly the signal is compressed above the threshold. If a hard knee, the full compression ratio is applied to EVERYTHING above the threshold. The softer the knee, the more gentle the transition from non-compressed to fully compressed. Visually, it would be kind of like two colours either having a sharp line between them, or a smooth gradient.
Output Gain: When you compress a signal, it reduces it's volume. The output gain is just used to make-up that volume at the end of the compression process.
Here are the 4 main reasons to use audio compression:
1. Taming the peaks of a signal.
If you have a vocal with some loud parts and some soft, you can pull the loudest parts into check to avoid clipping. Generally gentle settings on the threshold and ratio. Season with attack and release to taste.
2. Fattening a sound.
Basically making it more sustained and squashed, which allows it to sound louder and fatter without clipping. Short attack, long release. Tip: Don't do this on everything, and do it for a good reason! Can kill a mix's dynamics if abused.
3. Adding energy.
Great for percussive stuff. Longer attack (to let the transients through, like a drum hit) and longer release.
4. Glueing sounds together.
If got a layered sound, some light audio compression can "gel" the layers together and make them sound more cohesive.
Other uses would be sidechain compression, buss compression, parallel compression, mastering, etc. but all based on those 4 ideas.
Hope you enjoy, and let me know in the comments if I've missed anything / been unclear, or if you just plain find it useful!