Sidechain is a term that gets used a lot in modern music production.
It’s a key part of many common production techniques in electronic music.
But it’s not easy to understand sidechains if you’ve never dealt with them before.
Even if you’ve used the most common sidechain technique, you’re probably only scratching the surface of what’s possible using sidechains.
In this article, I’ll explain everything you need to know about sidechaining and six ways to use it.
What is a sidechain?
A sidechain is an extra input to an effects processor that’s not part of its main signal path.
Sidechain inputs are typically found on dynamics processors like compressors and gates.
In these effects, the sidechain signal is fed to the processor’s detector circuit—separate from the signal the effect acts on.
In this setup, the compressor is “listening” to the sidechain to decide how to affect the main signal.
The advantage is that the sidechain can be processed differently from the main signal path to get better results from the effect.
That might not sound very clear, but the best way to understand sidechains is through examples.
Here are some of the most common ways to use sidechain inputs:
1. Stop a compressor from compressing lows too much
Sidechain inputs were developed to solve a common issue audio engineers face with compressors.
Loudness, dynamics and the intensity of audio signals are all related. On top of that, your own perception of sound has a big influence.
Fletcher-Munson curves explain why a sound can seem louder or quieter based on its frequency.
But there are similar issues with audio signals. A compressor relies on the strength of the input signal to decide how much to reduce the level of material above the threshold.
A compressor relies on the strength of the input signal to decide how much to reduce the level of material above the threshold.
The low end information in a sound is often stronger than other parts of the frequency spectrum, even if you don’t hear it that way.
That means setting your compressor’s threshold isn’t easy for instruments with a lot of bass.
Excessive lows trigger the compressor’s gain reduction before it can act on the quieter material higher up.
The solution is to use the sidechain input. In this example, you would insert an EQ in the compressor’s sidechain and use a high pass filter to reduce the amount of bass the compressor is “listening to.”
Now the compressor won’t act too much on the lows and let all that powerful bass through!
2. Sidechain ducking
This is the classic kick and bass sidechain effect that took over electronic music in the early 00s.
It’s still a key ingredient in many subgenres of EDM.
To get the ducking effect, insert a compressor with sidechain input on your bass or pad synths.
Next, send the signal from your kick track to the compressors sidechain input.
Now the compressor is listening to the kick drum. Every time it hits, the compressor will reduce the gain of the bass or pad track with a satisfying whoosh.
If the threshold and ratio are set to extreme settings, it produces a pumping effect that enhances the rhythmic feel of a track.
3. Trigger a gate with different signal
Noise gates are some of the most helpful tools in mixing.
But just like compressors, changing the signal in the detector path with the sidechain input makes them even more useful.
Here’s a classic example.
When you use multiple microphones to record a drum set, some of the sound from the kit will bleed into the close mics on each drum.
That’s OK, it’s part of the natural sound of recorded drums. But if the spill is too intense it’s often better to reduce it with a gate.
Unfortunately, it’s difficult to set a gate’s threshold correctly when the bleed is nearly as loud as the drums.
This problem happens all the time when you record a bass drum with an inside and outside microphone. It’s worth it since the inside mic captures the intensity of the beater and the outside mic gets the natural sound of the drum head.
In this setup the outside mic will capture more bleed and may not respond well to gating.
However, if you use the inside kick drum mic as the sidechain input, the gate will use this cleaner signal to decide when to let material through.
Now it’ll be much easier to set the threshold to gate the spill properly.
4. Trance gate
The example above shows why sidechain inputs were originally added to gates and expanders, but there’s more creative effects you can do with them too.
This one is sort of like the opposite of the sidechain ducking trick.
Insert a gate with sidechain input on a sustained sound like an ambient synth pad. Then send a percussion track to the gate’s sidechain input.
A drum machine pattern or looped sample works great for this.
Now the gate will open and close based on the rhythm of the percussion track.
This effect was a mainstay of trance music in the 90s.
5. De-esser
If you’ve been following along closely you might have guessed which sidechain trick I’ll show next.
De-essers are an important effect in any good vocal chain. They help reduce the negative effect of sibilance in a vocal recording.
Sibilance means the harsh “S” sounds that can sometimes sound distracting with certain singers and microphones.
Sibilance means the harsh “S” sounds that can sometimes sound distracting with certain singers and microphones.
But a de-esser is simply a compressor with a pair of filters in the sidechain that restrict its effect to a narrow frequency band where the sibilant “S” normally occurs.
You can use any compressor as a de-esser by using a high and low pass filter in the sidechain to make the compressor act on the S’s only.
Hot tip: Sibilance is most distracting in the upper-mids and highs, between 2.5 kHz and 8 kHz. Experiment with filtering out everything outside a narrow part of this range to isolate the sibilance.
6. Upward expansion
I’ll go back to percussive material for this example since it works so well with expansion.
An expander is a less aggressive form of a noise gate. You can think of it kind of like a compressor in reverse.
With upward expansion, when the signal level goes above the threshold, the expander boosts the signal instead of attenuating it like a compressor.
One fantastic way to use an expander’s sidechain on percussion is to get a more punchy sound from room mics.
Room mics add a lot of realism but sometimes they take away from the sense of impact of the close mics.
To fix it, send each close mic to a bus and use that as the sidechain input to a gate inserted on the room mics.
Now the room mic channels will get a slight boost every time the drummer hits a kick, snare or tom.
Tailor the threshold, ratio and attack and release time dial in the effect to emphasize the hits nicely.
Sidechain gang
Sidechaining is a powerful tool when you know how to use it.
It’s also responsible for one of the most essential sounds in modern electronic music production.
Now that you know these five sidechain tips, get back to your DAW and start dialing in some dynamics.