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The Many Splendors of Sidechaining

by Philip Nichols, iZotope Contributor October 26, 2021

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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 sidechaining 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.

This article references a previous version of Neutron. Learn about Neutron 4 and its powerful features including Assistant View, Target Library, Unmask, and more by clicking here.

Learn how to use sidechain compression in your mixes with the new oscilloscope view in Neutron.

The Concept

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.

Follow along and set up your sidechain in your DAW with Neutron, included in a free trial of a Music Production Suite membership. 

The Sidechain Setup

Let’s use a kick drum and snare drum scenario 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 that has sidechain functionality on the drum bus. iZotope Neutron has a compressor with an all-new oscilloscope view to dial in a perfect sidechain. 

Neutron's compressor on the drum bus
Neutron's compressor on the drum bus

2.  As we play the track before applying compression, you’ll see oscilloscope in action, displaying the waveform of the material.

Neutron oscilloscope view
See the waveform of the material with Neutron's oscilloscope view

3.  Dial in a decent starting point for your compression parameters—ratio, attack, release, and threshold; those are up to you. By bringing the threshold down, you can see how the accentuated attack is being represented by a sharp spike at the beginning of the waveform. We can now see a visual representation of the attack in the oscilloscope view as well as hear it. 

bringing down the threshold in neutron pro
You can see how the accentuated attack is being represented by a sharp spike at the beginning of the waveform

If you increase the ratio, you’re going to see a sharper spike for the transient. If you alter the attack, a higher value will show more of the transient passing through unaffected, and a lower value will show less. 

If you alter the release, a shorter setting will make the tail of the waveform appear larger, as the compressor is leaving it unaffected, whilst a longer setting will also compress the tail, and it will appear smaller.

altering the release parameter in neutron pro's oscilloscope view
A longer release setting will also compress the tail and it will appear smaller

4. Add the compressor to the music bus to feed the kick and snare into the sidechain input of the compressor. 

adding compressor to the music bus
Add your compressor to the music bus to feed the the kick and snare into the sidechain input of the compressor

When the sidechain is in use, you will see a purple display on oscilloscope, so you know straight away you’re side-chain mode. Neutron will also give you some default settings when you engage the side chain to get you to the right sound even quicker.

Select the sidechain button in the center of Neutron's compression parameters to turn on sidechain compression

On the regular display, you’ll still see the amount of compression being applied on the orange trace, but you’ll now also see the sidechain input coming into the plug-in in purple. 

display settings in neutron pro oscilloscope view
You'll now also see the sidechain input coming into the plug-in in purple

5. Play the track and begin to play with the parameters. As you would expect, altering the parameters of the compressor will change the waveform in oscilloscope, ensuring you can see exactly how the compression is affecting your sound. 

changing parameters in neutron pro sidechain oscilloscope view
Viewing the waveform in the oscilloscope shows you how compression is affecting your sound

Once you’ve got the routing and standard configuration taken care of, you can delve into some routine uses for this nifty process.

Common Applications

Typically, sidechains will only be found on dynamics processors such as compressors, gates, and dynamic EQs (though you may find exceptions). So, focus on threshold-based audio effects. To get started, here are some frequently-encountered situations that can benefit from sidechain processing.

  • Bass drowning out the kick: Using the configuration detailed in the previous section, the bass will be compressed each time the kick hits. As a result, the kick will be more audible than the bass during those hits. This can be a great way to get the kick to punch through a bit more, especially if your kick and bass share the same frequency range.
  • Drum overheads with overwhelming snare: Toss a compressor on the overheads, then send the snare (close mic) to its sidechain. Every time the close-miked snare is played, the snare-heavy overheads will be attenuated. If there is significant kick bleed in the close snare mic signal, use a high-pass filter on the sidechain to minimize it!
  • Bright guitars covering up the lead vocal: Insert a dynamic EQ or multiband compressor on the offending guitars. Set it to subtly turn down or compress the frequency range where the vocal is present and bright. You know what’s next; send the vocal to the sidechain! Whenever the vocal is heard, the guitars will get just a little bit “mellower.”
  • Lots of bleed in the kick out: Put a gate on the “Kick Out” track. Assuming that the “Kick In” track doesn’t have excessive bleed, send it to the gate’s sidechain. Now, the kick track without bleed controls the gate on the bleed-heavy kick. The bleed in the “Kick Out” won’t open the gate!
  • Fiending for some ‘80s snare reverb: Set up a reverb plug-in on a spare channel. Insert a gate directly after the reverb plug-in. Send the snare track to the reverb channel and to the sidechain of the gate. Ho ho ho, dear readers. What happens as a result is not for seekers of the subtle. Each time the snare plays, the gate will open and let the reverb be heard, and the gate will close after each crack of the snare. So, the existing of snare signal triggers the reverb, and the lack of snare signal stops the reverb (abruptly or gently, depending on the gate settings). Wild and nostalgic!

Start using sidechain compression

As long as you have sidechain-capable processors and an unfaltering faith in the power of signal well-sent, the fruits of the sidechain tree are yours for the taking. Pull up some tracks and enjoy! You can also use sidechaining for some pretty creative mix effects

Try out sidechaining in your mixes with Neutron, included in a free trial of iZotope's Music Production Suite Pro membership. 

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