Compression Basics

Remember in the last lesson I said EQ’s are my favourite thing in the world, well, I think my second favourite thing would be a compressor. If I were stranded on an island, but could have 2 things, it would be an EQ and a compressor. I’d be pretty happy with that. The 2 most powerful tools you have as a mix engineer are EQ and compression. Get them right and your mixes will sound great. Get them wrong, and you can guess how the mix will sound. But if music is an art, how can there be a right and a wrong?
Because music isn’t just an art. It’s also a science. It’s a combination of waves along a time grid. When combining these waves, there’s certain things you can do that will make them combine smoother, not clash with each other, and just sound more natural.

A compressor reduces the dynamic range of an audio signal. It makes the quiet parts louder, and the loud parts quieter.
Have you ever watched a movie... and had to turn up the volume to hear the dialog, but then turn the volume down when there’s a loud part? If you have done that... then you were being a compressor. Thankfully, us audio geeks have this automatic tool that does this for us... we just have to dial it in.

When recording a song, the natural volume fluctuations of our voice, or instrument playing, are much to extreme to sound good in a mix, or sound good when amplified. Compression is almost always needed, on every track. But, too much comprehension will take away the feel of the song... so there’s a delicate balance between keeping the life in the sound, and getting the best volume level.

(Let’s take this drum beat for example as I use drum sticks on this table. The feel comes from the dynamic changes. If I compress it so they are all the same volume, it sounds like this. There’s no life left.)
If I were to play a drum pattern on a bongo, with some hits being loud, and others are soft. When we listen back to it, it will sound good, and you will hear all the hits just fine.

It sounds great without any compression because it is the only thing you hear. Let’s add some simple piano chords to it. Now, without compression, the quiet hits are lost, they’re not heard, and the harder hits seem too loud for a nice balance. So with just a bit of compression on this drum part, you can hear the quiet parts, and the loud parts aren’t harsh, and it still has its life. If I overcompress it.. it’s louder, you can hear it more clearly, but the life is gone.
You need to be careful of ear fatigue and poor room acoustics when using compression.
Ear fatigue will cause you to not notice the life being lost little by little.. as you compress more and more because it keeps getting louder, and therefore, fooling us to think it sounds better. If you do an A/B comparison of 2 identical sounds... if one is louder, it will always sound better. I do a lot of microphone testing, and its imperative that I match the volumes perfectly, because an inferior microphone can beat a better microphone if it is just a little bit louder when listening back and forth. So, be aware of that as you keep dialing the compressor up more and more. Trust your ears... only a little bit. Also trust your meters. If the vocals sound good, but you see the gain reduction meter slamming like -20db of gain.... you might be over-compressing and not hearing it. Most of the time, over compressing will sound like a pumping, or an unnatural feeling. Better quality compressors are capable of providing more compression before it is noticeable. The attack release settings can also be used artistically to shape the sound.
First let’s look at the logic compressor, (Fig.1).This is a pretty standard layout. You have your threshold, ratio, attack, release, and make-up gain. All of these controls are important to sculpt to sound perfectly, but the most important 2 controls are the threshold and the ratio.