What is Compression?
Compression can be very confusing, but in its most basic sense, it makes loud noises quieter and quiet noises louder. By squashing the very loudest signals down, we’re able to bring up the level of the quieter noises to match. It’s what our ears do naturally, otherwise we wouldn’t be able to hear whispering and our eardrums would burst every time a noisy motorcycle rode past.
Compression is crucial in music, so you can clearly hear every part of the mix and don’t get deafened by any volume spikes. Without compression, you wouldn’t be able to mix music because the volume fluctuations of different instruments would make it impossible to get a good balance.
Alongside EQ, compression is the most important part of mixing and mastering music — it’s what allows each instrument to find its place in a balanced mix. But studio compressors can be very complicated, so we’re here to demystify some of the most common terms you’ll see.
Threshold is simply the level at which your signal will start to compress. Everything below the threshold will remain uncompressed, and everything above it will have the compression applied.
Sometimes referred to as “makeup gain”, this controls your overall volume. When a compressor is applied, it makes the loudest parts of the signal quieter, so to compensate, you add makeup gain to bring the volume back up, as well as making the quiet parts louder and more audible than before
This is the amount of time it takes for the compression to apply. A slow attack will allow your signal to pass uncompressed for a moment, allowing the initial transient through. Something like an MXR Dyna Comp pedal has a slow attack, making it great for guitarist who want to retain their dynamics while adding some extra sustain to their notes. While the 1176 Studio Compressor is known for its fast attack that will compress the front end of every note, which has the highest volume peak already.
As you might have guessed, this is the opposite of attack. It determines how long a note is compressed for before it lets go — basically controlling the amount of sustain. A fast release will allow the signal to naturally decay quickly. This is especially important for drums, which are very percussive, so you don’t want to add unnatural amounts of sustain. Whereas, a guitarist might want a slow release for a solo, to hold long sustaining notes (think David Gilmour).
This refers to the amount of compression that is applied to your signal. For example, a fairly subtle 2:1 ratio simply means that for every 2dB your signal goes over the threshold, it will only add 1dB of volume after compression. So 3:1 compression would mean you would need to go 3dB over the threshold to add 1dB of volume. You might even see ∞:1, which will limit your signal — meaning that once your volume reaches the threshold it won’t get any louder at all.
This is an especially useful feature if you just want to add subtle compression without losing the attack of your note. Blend will combine your uncompressed (or dry) signal with your compressed signal. This way, you can add your compression to taste without compromising your dry signal. In recent years, this has become especially popular on guitar compressor pedals, and is extremely hand to have!
You won’t see this on many studio compressors, but it’s worth knowing about anyway. While most compressors will apply compression immediately to when the attack time is set, some will ramp up their compression. The knee controls this ramp up. So, if you set a 5:1 ratio, instead of it instantly compressing at 5:1, you could slow the knee, which would control the amount of time it reaches 5:1 — it might start at 2:1, then 3:1 etc. until it reaches 5:1.