Many people think that compression is the key to great results when mixing. Compression is a very useful tool but it will not fix a bad mix. The truth is you need to know how to build a good mix before you apply compression.
What is compression for anyway?
A compressor is used to control the dynamic range of a signal, closing the gap between the loudest and quietest sounds. This helps prevent clipping or distortion, controls transients, and keeps things from jumping out in the mix.
Compression can be corrective or creative.
An example of corrective compression would be using it to smooth out the spirited playing of the bass player or a wildly dynamic singer who goes from a whisper to a scream.
Examples of creative compression are using compression to create loudness or to add the particular characteristics of the compressor to color the track or mix. A little compression on the overall mix can increase headroom when mixing live sound, and compression can help to pull a mix together.
But there are several things you want to do before adding compression and the last thing you want to do is slap a compressor on every single input.
Where to begin.
Two things that will go a long way in crafting a great mix are optimal gain on your inputs and EQ.
Start with great sounds and make sure you have a good strong signal level into your DAW or mixer. After that, if you need a little corrective compression you can add it pre or post EQ depending on the desired result.
Apply EQ. EQ is one of the best tools you can use for creating a great mix. EQ will sculpt your sounds, remove muddiness, add punch and clarity, and can even be used as an effect. Proper EQ will do wonders for your mix.
After applying EQ, work to balance the levels of all instruments and vocals. Use panning, EQ, and level adjustments to place things in the stereo image. If your mix isn't sounding good at this point, you need to go back and fix the problems before moving on to things like compression and effects.
Once you have completed all of the above, your mix should sound pretty good. This is the time to apply creative compression but use it sparingly. If you don’t know how to use it correctly, best to avoid using it because the mix would be better off without it. Overuse of compression will suck the life right out of your mix. Improper adjustments of the compressor’s settings (threshold, attack, release) can create unwanted and unnatural artifacts.
As with anything, start with a good foundation to set yourself up for success. That foundation is great sounds, optimal input signal to your DAW, mic-pre, or mixer, and EQ where needed. Rather than trying to use compression to fix a bad mix, learn how to create a good mix first and you'll have much better results.