You may have heard about sidechain compression as a tool used to get your kick drums pumping through the mix, especially in EDM. But what is sidechain compression, how does it work, and how can you use it in your mixes?
Let’s say your kick drum sounds great on its own, but it isn’t cutting through the mix quite enough. You don’t have any more headroom to turn up the kick—if you do, you’ll either have to limit your mix so much that it sounds awful, or you’ll have to deal with the rest of your mix being really quiet. What do you do? Why isn’t your kick cutting through if it sounds great on its own?
The problem is masking. As I discussed in an earlier article, if two instruments occupy the same space at the same time, you won’t be able to hear them both. The term for that is “masking”—sounds covering each other up.
Sometimes you want sounds to blend and run together, but often you want separate things to sound separate. A kick drum is an example of a sound you definitely want to cut through the mix, rather than blending in with everything else—especially in EDM or hip hop (or current pop music, which is strongly influenced by EDM and hip hop).
A kick drum takes up a lot of space in the frequency spectrum.
Not to mention, if it’s distorted, it might have some “gritty” harmonics a little above each of these regions. In other words, a kick drum can potentially have important content in almost the entire frequency spectrum.
So there are a lot of potential instruments in your mix that might mask part of your kick. The vocals or guitars might mask the click of your kick. The knock might be masked by some of your lower instruments. And the bottom of your mix—below 150 Hz—will often be masked by the bass.
Masking from the bass is the most important problem to deal with, because that’s the most important frequency range for a kick drum.
Remember, these are your basic options to deal with masking that I discussed in the arrangement article:
For reasons I won’t get into now, panning low-frequency instruments is a bad idea if you want your mix to sound clear and as loud as possible (in other words, if you want your mix to sound good). Using reverb on bass instruments is also not a great idea, and it won’t even work that well for these purposes (it’s hard to change the perception of where bass frequencies are coming from, so reverb won't be effective in pushing the bass into the background).
Ideally, the solution is to have a kick drum and bass that never hit at the same time. Or if they do play at the same time, they don’t have overlapping harmonic content, so that they don’t step on each other’s toes. Try to solve your masking problems as much as you can using those techniques--rewriting parts to eliminate unnecessary overlap, and using EQ to cut out any unnecessary overlapping harmonic content from the kick and bass.
However, in most mixes you can never eliminate all masking between the kick and bass. You’ll probably want your bass and kick to play at the same time at least sometimes—they often sound really good together.
The idea behind sidechain compression is that you briefly lower the volume of your bass part whenever the kick drum comes in. That gets the bass out of the way for just long enough to hear at least the attack of the kick drum clearly. And since the kick would have masked the bass part anyway, you usually don’t miss hearing it for a short amount of time.
Reducing the volume of the bass REDUCES masking, but doesn’t eliminate it. Only muting or aggressively high-pass filtering the bass would completely eliminate masking. But sidechain compression is a good compromise solution that allows you to achieve more mixing clarity without sacrificing the music you wrote and the sounds you worked hard on. As I already mentioned, if you’re smart about your drum sample and bass selection and you write the parts to clash as little as possible, a dab of sidechain compression is enough to get your kick popping out of the mix.
Sidechain compression is fairly simple to set up. Before you begin, make sure you have a compressor plugin that allows you to use sidechaining. Some examples of these plugins are C1, RCompressor, and H-Comp from Waves; Fabfilter Pro-C; and Native Instruments Vintage Compressor. One free compressor plugin with sidechaining is the MDynamics plugin from Melda Production.
The first thing you’ll need to do is send the signal from your kick track to a bus. Make the send a pre-fader send, and set the send level to 0 dB. Making the send pre-fader allows you to change the volume of the kick later without changing the amount you’re sidechain compressing the bass. Setting the send level to 0 dB just ensures that you’re sending a strong enough signal for the compressor to detect.
If you’re using Logic or another DAW that automatically creates aux tracks when you send to a bus, you’ll want to set that aux track to have no output.
Now put the compressor you want to use on the track where the sidechain compression will be applied—let’s say the bass.
(You could also put the sidechain compressor on a bus and route multiple tracks to that bus, so they’ll all be sidechain compressed together. An extreme use you may find interesting would be to route every single track and effect return except for the kick into one bus, and sidechain compress that bus to the kick.)
Now the important part—if you’re using a compressor plugin that supports sidechaining, there should be a menu in the top bar of your plugin that says “Side-Chain” or “Key,” or it may have a key icon. Set that sidechain to be the same bus where you sent the kick signal. Now the compressor is detecting the signal from that bus rather than the signal from the bass track—but the actual compression will still be applied to the bass.
Start with the compressor with a fast attack (10 ms or less), fast release (50 ms or so), and pretty large ratio, say 5:1 or so. Now play a part of your song where the kick and bass play at the same time. Set the threshold low enough so that you get around 6 dB of compression on the bass every time the kick hits.
You should be able to hear the compression, or at least you should hear the kick pop out a bit more than it did before. Now you can tweak the compressor settings to your taste. Be careful, it can be easy to overdo sidechain compression at first. Sometimes a little bit goes a long way.
A lot of electronic music relies heavily on sidechain compression. Here are two very famous examples of songs that use a lot of sidechain compression.
Notice the pumping sound when the kick comes in.
You can sidechain compress less for a more natural sound. If your sidechain compression is subtle enough, you can make your kick pop out of the mix a bit more without making any noticeable difference to the bass.
Or you might want to sidechain compress more. Besides allowing the kick to cut through the mix more, of course, using more sidechain compression may make your mix sound more modern. You may just want to imitate the sound of EDM producers you like who use heavy sidechain compression.
One producer I like who uses this modern sidechain compression sound a lot is Galimatias. Notice the sidechain compression on the kick when the drums come in around 40 seconds.
Sidechain compression can also make your mix sound more exciting. When you hear really loud music—like at a loud concert or club—your ears use a natural form of “limiting” to protect your hearing. That limiting happens more on the loudest parts, like kick drums. So sidechain compression can emulate this effect, and make you feel like you’re listening to loud, exciting music even when your mix is at a quiet volume.
Try out sidechain compression the next time you’re mixing a song, and see how you like it. Please let me know if you have any questions about these techniques in the comments. Also, what are some of your favorite songs that use heavy sidechain compression?