Compressing the bass when the kick hits
Over the last handful of years, I’ve noticed the term “sidechaining” being used like it’s the password to get by that big bouncer at the city’s hottest club. Even people who admit to not knowing what it is keep saying it. “I think I’ll have to sidechain the kick. It just needs it, you know? Then, maybe I’ll sidechain the bass because I can’t have it flatlining.” Meanwhile, I’m furrowing my brow and being slightly too judgy.
Sidechaining can be a great solution for some routine mixing problems, or it can shake the foundation of an otherwise solid sound. If you’d prefer to be in control of your sidechain activities and avoid self-sabotage, do read on.
First, let’s review what happens without special sidechaining in a typical “compressor plug-in on the bass” scenario. The bass signal is what causes the plug-in to compress. If the bass level goes above the compressor’s threshold, the plug-in compresses. If the bass level falls below the compressor’s threshold, the plug-in stops compressing. The same truth applies to compression on any other instrument. Whatever signal goes through the compressor is the signal that triggers it.
The core idea behind sidechaining is to use one signal to trigger a processor on a different signal. It’s as if one signal is the key to unlock and activate an effect on another. As a result, some devices (software and hardware) use the term “key input” while others prefer the label “sidechain input.” Understand that a device’s key input (sidechain) is not mixed with its processed audio output. Some processors have a cool “key listen” mode, which allows you to monitor the sidechain signal, but once you turn off that mode, the sidechain will no longer be audible.
How would some fancy sidechaining change the typical bass compression scenario? Let’s see! If a kick drum is used as the sidechain/key source for the bass compressor plug-in, then every time the kick hits, the plug-in will compress the bass.
Wacky as that may seem, it can be quite useful when trying to get the kick and bass to cooperate. If the fundamental concept of sidechaining makes sense, the next step is to make sure you can make it happen.
The Sidechain Setup
Let’s stick with the kick and bass scenario for the first example and break down an average sidechain setup into bite-size morsels. The following steps don’t necessarily need to be done in the order given, but they are in a nice, logical layout. Open a session and follow along!
1. Insert a compressor plug-in on the bass track. Since not all compressors have sidechain functionality, you might have to look through a few until you find one that has a key input or sidechain section.
2. Dial in a decent starting point for your compression parameters—ratio, attack, release, and threshold; those are up to you.