Breaking Down Compressors (Or Compression For The Rest Of Us)

If you ever get into mixing music in the studio or in a live venue, you’ll need to know what a compressor is and how to wield it with precision.

But when you first start out, compressors can seem a bit scary. They have lots of knobs with weird names (“soft knee” anyone??) and it’s hard to know if you’re making the track better or worse with each virtual tweak.

This week I want to hit the topic of compression head on by breaking down a typical compressor so you see how truly simple (and powerful) of a device it is.

This Is All Your Compressor Does

Before we dive in, let’s just be clear about what a compressor does in the first place.

At it’s most basic (and I love basic) a compressor is simply an automatic volume fader control device. It can literally turn down loud stuff automatically and give you a more even volume throughout. That’s it!

Why is that helpful?

Well most music is very dynamic, meaning it gets loud and soft with great variety throughout a song. This can make it hard for an instrument or vocal to be consistently heard and felt throughout in a final mix. Compression, can help you get that nice, consistent, up front sound you’re after.

To be fair, compressors are used for more than just volume control. They can give something more energy or more sustain. They also can act as tone shaping devices.

But for today, let’s look at the knobs and tweakable settings on a typical digital compressor plugin so you can feel right at home and in charge!

Threshold

The most important knob on a compressor in my opinion is the threshold. It’s the knob that actually allows compression to take place or not (and how much).

It makes absolutely no difference whatsoever how much you’ve tweaked the other settings on the compressor, if the threshold is set at 0db (or the top) then no compression is actually happening.

Threshold is the volume at which compression kicks in. It’s like a “master control” on the whole darn plugin.

Turn it down a tiny bit, and the compressor will only affect the loudest peaks of the track. Turn it down a lot more, and you’ll get even more squash to your signal.

A great rule of thumb for natural sounding compression is to turn it down and watch your “gain reduction” meter until you’re seeing around -3db to -4db of gain reduction.

Ratio

Another knob that works in tandem with threshold is the ratio. The ratio knob controls how hard the compressor hits when signal crosses the threshold.

A 1:1 ratio means the signal isn’t turned down at all. It’s a flatline. A 2:1 ratio tells the compressor to turn down any signal that crosses the threshold in half. (For example if signal crosses the threshold by 6db of volume, a 2:1 ratio would turn that signal down to only 3db above the threshold.)

The higher the ratio, the more squashing you get. Basically you can play with the ratio and threshold knobs together to get as much or as little compression as you like.

Attack And Release

If threshold and ratio control how MUCH compression (or volume being turned down) is happening, then the attack and release knobs control how fast the compression kicks on and off, thereby affecting the tone.

The faster the attack setting, the quicker the compressor pounces on your audio when it crosses your set threshold. And the faster the release, the quicker the compressor resets or “lets go” of the signal.

Attack and release are game changers because they basically change how your compressor sounds and what it does to the audio.

The best suggestion I can make is to keep attack and release in the middle as a starting point, and then experiment with much faster (and slower) settings, noting what affect they have on your track in question.

You’ll soon discover what sounds cool on what type of audio (and what doesn’t).

Makeup Gain

The last compressor setting I want to address today is makeup gain (or sometimes simply “gain”).

With all this turning down of the signal (because remember, that’s all a compressor is meant to do), you’ll have a much quieter track than when you started. The solution? Simply turn it back up a bit.

Thankfully for us, engineers were smart and put a simply output gain stage at the end of compressors to “makeup” any lost volume or gain.

If your compressor is on average turning down your snare drum (let’s say) by 4db with every hit, then it’s safe to say you can turn the makeup gain knob up around 3db to 4db. The goal is to level match it to the original signal going into the compressor.

The difference, though, is that now you have a much more consistent signal coming out of the compressor, than you had going in. – Which is the whole point of compression.

Forget The Rest For Now

While many compressors have other settings like knee, key input, etc, ignore them for now. All that matters for 90% of the time are the four main settings I’ve shown you here.

In my next post I’ll give you a little demonstration of how these four elements can give you the power to totally control your audio.

In the mean time, I’d love to hear from you what has been the most frustrating or confusing thing about using compression during your mixing adventures. Share your thoughts below!