Finally, it’s part two of the compression tutorial. Building on what we learned in the first one, we are going to look at some of the really useful and slightly more complex things you can do with the concept of compression. Today we’re going to talk about side-chain compression

Headroom

You’ll often hear the term “headroom” when talking about mastering. Headroom is the area between the peak of a sound and 0 dB which is as loud as a sound should be.

Look at what happens when you play the same sound on top of itself.

Here is two tracks playing the same drum hit together.

See how the space has shrunken almost in half? Why do we care about this? Again, we never want to go over 0 dB. When we have lots of instruments playing, we fill up this space quicker.

If a bass kick drum has some of the same frequencies as the bass guitar, they either clip by using up all the headroom or it will just loose some of its clarity. You won’t hear the bass drum clearly since the bass guitar is overwhelming it.

How do we fix this? Well, using compression we can divvy up how the headroom is used slightly. We don’t want the bass guitar to disappear, but do usually want to hear the kick drum a bit more in the moment it hits than the bass guitar. Using side chaining, we can give the kick drum a quick moment to shine thru without losing the bass guitar.

Side-chaining compression for mixing

Side chaining is more recently associated with the thumping electronic sound often called “ducking”. We will talk about that soon, but the more subtle and useful use is used to fix the above scenario.

Side chaining is using data from one sound to drive the compressor for another. Here’s our kick and a pad.

We put a compressor on the bass guitar. And side chain it to the kick. Every DAW handles side chaining differently so we aren’t going into how to do that. Usually it’s just a simple setting to pick the track that drives the compressor.

So now, whenever the kick drum hits, it turns the compressor on for the bass drum. We set it super tight so only for a quick moment the bass guitar drops out when the kick hits the hardest. Now the headroom is being utilized but the frequencies they have in common won’t overlap each other so much. The moment goes by so quick you can’t even hear the bass drop out unless you solo it. But it’s enough to lower the peaks when too many low frequencies are hitting.

Now the kick drum shines through the bass guitar just a little more than it would otherwise.

Side chaining as an effect

Now we come to the famous “ducking”. The same exact thing is happening as explained above but with a much higher attack level. When the kick hits the pad drops out quite a bit and then swells back up. The result? The kick and beat come flying through in a big way and make you want to pump your fists.

Here is the uncommpressed version:

Now here it is with some strong compression, the kick is driving the compression against the pad track:

You can see more on how DJ Cutman uses side-chaining here.

Next time we’ll be looking at the multipressor, which combines the compressor with EQ, useful for mastering.