Dynamic compression is a common ingredient in all mixing as much as it’s a subject of debate. Many studio buffs argue about correct use of compression and there are forever new techniques and tips on how to get the most out of your studio’s mysterious tool. But why are compressors so important? I hope to shed some light on this fairly basic concept that tends to confuse so many.
What Is Compression and How Does It Work?
This is the very basics of compression so if you’re a bit more advanced, you may want to skip this section.
In its most basic form, a compressor is an automated volume fader. The way it works is that all volume that exceeds a certain threshold is turned down. This means that the overall volume can be turned up so you can clearly hear the quieter parts of sound source without the louder parts being too loud.
There are many parameters that you can change on your compressor that alter how it affects the sound source.
Threshold: This controls the limit at which the compressor becomes active. A higher threshold means that only very loud sounds are turned down, where a low threshold will affect much more.
Ratio: This determines how much the sound exceeding the threshold is turned down. With a 2:1 ratio, a sound that exceeds the threshold by 10dB will only output at 5dB above the ratio. With a 10:1 ratio, it would only be 1dB output.
Attack: This determines how quickly the compressor reaches it’s full gain reduction once the threshold is exceeded.
Release: This determines how quickly the the gain returns to full once the threshold is no longer exceeded.
These are the most basic descriptions that I could come up with but there is plenty of literature all over the internet that goes a lot more in depth with the function and controls of compressors.
Uses of compressors
There are many ways that compressors can be used and there are compressors are better than others for each type of compression.
Levelling: This is where you are simply trying to level out louder sections of the source to the quieter ones. It could be in trying to get all the kick drums hits to be at the same level, a vocal to be consistent throughout the performance, or getting the your whole mix to be heard with the quieter parts dropping out less.
Adding Punch: This is almost the opposite of the normal function of a compressor, but if you slow down the attack enough, you can actually expand the sound envelope of a sound. This technique can be used to boost the strike of the sound and then have the compressor kick in to pull down the sustain.
Limiting: A limiter is just a compressor that has a high ratio. Usually a ratio of 10:1 or higher is considered to be a limiter. Limiters usually use a fast attack and release and a high threshold. Limiters are usually used in the mastering stage in order to get a track louder while ensuring they never hit zero dB which would cause digital clipping.
Why Use Compressors?
This is where this gets a little more interesting and we learn why we should use compressors in our mixes.
Most people agree that a well compressed signal sounds better, but most people can’t explain why. There's a lot of anti-compression people out there right now that are fighting compression in music, but many of them don't know what they're talking about. Many people confuse digital file compression with dynamic audio compression and see them as the same thing, but they are completely different. I'm also not talking about the “loudness wars” slamming of modern tracks which is essentially an epidemic of music that involves over-limited in order to make it comparably louder than other tracks, at the detriment to its musical integrity. I'm just tackling artistic compression.
The reason that we find a compressed sound more appealing than a more dynamic sound has to do with the anatomy of our ears. On the journey from our eardrums to our brain, sound waves go through three different biological compressors (and 4 EQs) in the middle and inner ear. One of them, the cochlea, even acts as a multiband compressor. These natural compressors work together to give us an amazing hearing range and help us decipher different frequency bands. The difference between the quietest sound we can hear and the limit at which our eardrums rupture is approximately 100,000,000,000,000:1. This makes the pressure of the loudest sound 100 trillion times bigger than the quietest sound.
Here’s a more in depth article on the functions of the ear.
What does this have to with mix compression? Why would we need compression in our mix with so much natural compression? I'm glad you asked! Sounds that are louder in our ears are subject to higher in-ear compression. Therefore, we associate loud music with more excitement and intensity. So, when we hear a mix that’s been compressed, it sounds loud and exciting, even if the actual volume isn't that loud.
The problem is, when some mixing engineers pull up a compressor on certain tracks, they don't have a vision of why they want to use the compressor. I
It's been said time and time again, but always check that your compressor isn't adding any extra volume to your track and just check, using the effects bypass, that your compression is making the track sound more exciting. If it's not, change the settings or ditch it. This is also a good argument for mixing at low level, as you aren't being distracted by your in ear compression. If it sounds exciting at low level, it'll sound amazing loud.
How do you use compression? What is your favourite compressor? Has this article made you rethink your use of compression? Let me know in the comments below.