You’ve probably heard someone mention that they use sidechain compression to make something like a kick stand out and pump through the mix. But what is it, and how do you use it? Sidechaining is when you use one sound source, or track, to trigger a plugin or effect. This effect is then placed on, and is therefore affecting, a separate track.
You can choose to sidechain any effect on any tracks. But it’s often done with compression, so that’s what we will discuss here.

The concept of sidechain compression can be difficult for new engineers to understand. But, most of my students seem to understand it when I use examples involving ducking. Ducking is when you cut the volume of one sound source when another sound source enters your mix. The first example I use is that of radio DJ’s. Have you ever noticed that the music cuts in volume as a DJ comes back onto the radio and begins to speak? This ducking effect isn’t done by the DJ manually as they enter. It’s most likely sidechain compression, with the DJ vocal “track” as the source that’s controlling compression that’s affecting the music “track”.

The other example is your cell phone. Have you ever been playing music in the car using your cellphone and gotten a text or other notification that sends a beep through your phone? If you listen, you’ll notice that the music lowers in volume as the beep is played for the notification. This is another example of ducking that could be done through sidechain compression.

So now that you understand the concept, let’s discuss how we do it in Pro Tools. Here are some basic steps you can follow with any two sound sources:

  1. Pick the track that will trigger the compression (track 1)
  2. Pick the track that will be affected by the compression (track 2)
  3. Place your favorite compressor on track 2 
  4. Place a send at unity out of track 1
  5. Open the compressor plugin that’s on track 2 and select the matching send source to the right of the key icon
  6. In the same plugin, make sure the sidechaining is enabled by activating the sidechain key button as pictured (if present)
  7. Tweak your plugin parameters as desired

So there you go! You might use this technique, for example, to reduce your bass volume whenever the kick drum sounds, thus bringing the kick out in the mix. You can sidechain with any plugin that has that key input parameter. So go out and experiment, and let me know how you like to use this technique!

Questions? Comments? As always, please share in the comments section below!