So, an article focused exclusively on audio sidechain. To be honest, it doesn't get any more nerdy. Because of that I'm enjoying it more than any other topic in this ongoing mix series!
Let's start off by talking about the rough mix. Which is to say, the mix that you receive as a mixer at its current state, before you get involved with it. This should of course be used as a reference, since it offers lots of valuable insight (sometimes all of the insight that you get!) into how the artist/producer actually wants the track to sound. Sometimes it sounds really good to begin with! Now this may be the time where you start to think to yourself, "hey, what can I even do to enhance this track, and make it sound better?"
Let's talk about some of those nerdy things that we as producers or mix engineers can do to add that last solid 10% to an already nice-sounding mix. Call it "bring out the details" or "make it 3D." In addition to placing things in spaces using reverb, we can manipulate the dynamics, and that's what I will talk about in this guide about All Things Sidechain.
Gates: The Basics and Beyond
A noise gate controls the volume of the parts of an audio signal that fall below a certain threshold, either reducing it to total silence or just lowering it by a few dB. Basically, it acts as the opposite of a compressor, which reduces the volume of the loudest parts of a signal, above a set threshold. Gates are incredibly versatile tools that can be used in various ways to shape the dynamics of a mix, and even as a sort of indirect quantizer. You will see.
Expanding Sounds
One creative use of gates is to expand sounds and accentuate transients. For example, you can use a gate on a reverb channel or a room mic channel to make the reverb or room mic pop out when the kick and snare hits.
By sidechaining the gate placed on the reverb with the signal from the kick and snare, and setting the release and attack settings to taste, you can achieve a lively, dynamic reverb effect. The gate doesn't close completely but attenuates the signal by a few dB when the sidechain signal is not loud enough, effectively expanding the reverb on the transients of the kick and snare. This technique can also be applied to pads or synth sounds to follow the rhythm of the drums, or maybe a bass line.
Tightening Sounds
Gates can also be used to tighten two or more sounds together, such as aligning guitars or bass with drum hits. If a synth or bass isn't tight enough with the drums, you can sidechain a gate with the drum signal placed on the synth or bass. This allows you to reduce the volume of the synth or bass on either side of those drum hits. Adjusting the gate parameters can make this effect as subtle or as drastic as you want it to be.
Another application is tightening up backing vocals that extend too long, or enter before, the lead vocal. Sidechain a gate on the backing vocal track using the lead vocal as the trigger, and the gate will open and close according to the lead vocal's timing.
Creating Special Effects
For special effects, gates can create staccato notes for pads or strings, often referred to as the "trance gate" effect. Sidechain a rhythmic instrument like a hi-hat or drum machine to a synth pad, choir, or any other sustained sound, so that the sound only plays staccato along with the rhythmic signal. If you don't want to hear the rhythmic instrument itself, send the sidechain signal as "pre-fader" and pull its fader down. The signal will still be sent on to the gates input.
Cleaning Up Noisy Tracks
Sometimes regular gating doesn't effectively remove in-between noise, such as loud hiss between drum hits with full-on heavy distortion. In such cases, sidechain the gate with a clean version of the drum hits. This way, the gate only opens when the actual drum hits are playing, providing a much cleaner result compared to regular gating.
Sidechain Compression: Sound Design and More
Now let's head into sidechain compression. At its most basic level, sidechain compression means you are sending a copy of one signal (e.g., a kick drum) to the sidechain input of a compressor on another track (e.g., bass). This causes the bass to duck in volume when the kick plays, making the kick more audible and prevents a messy low-end. Generally speaking, I recommend going with the fastest attack settings possible here.
High-Pass Filtering the Sidechain Signal
Using a high-pass filter (HPF) on the sidechain compression signal can make the ducking effect cleaner and faster. For example, if the kick drum is longer and sort of extended, the bass might take too long to duck out of the way. By applying an HPF on the sidechain circuit, only the clicky part of the kick drum (its higher frequencies) triggers the compressor, resulting in quicker and much cleaner ducking.
Some compressors also offer a full EQ section for the sidechain circuit, allowing you to really shape which frequencies trigger the compression. This can be useful for fine tuning how the compressor reacts.
Creative Sidechain Compression
Entire genres of music have been shaped by creative applications of sidechain compression. For example, you can drastically sidechain the volume of sustained melodies or sounds to rhythmic pulses that are not your actual beat, creating dynamic and interesting effects.
Instead of using a 4/4 kick drum to trigger the sidechain, use sequenced trigger pulses that are not audible in the mix but still influence the volume of the melody or pad. And if you are lucky enough that your DAW allows it, you can sidechain parameter destinations other than volume and compression, such as the pitch envelope of a synth, from the audio signal of another track, for unique and wonky results. The sky is really the limit here!
Specialized Tools: Trackspacer and Masker
I try my best to avoid mentioning specific plugins in this series of advice, but Trackspacer by Wavesfactory is a fairly unique tool worth noting.
It operates by taking the sidechained signal and analyzing its frequency response. It then applies an inverted EQ curve to the input signal, effectively ducking only the relevant frequencies rather than the entire signal. This selective ducking affects the sound you are trying to duck only in the frequencies that clash with the sidechained signal. This can be really useful for creating space and clarity in a mix.
When cranked, Trackspacer produces a filtery and phasy sound. But applied subtly, it becomes a decent tool to reduce frequency masking. One thing I often do when mixing and mastering involves placing Trackspacer on my top level instrument bus and sidechaining it to the main vocal bus. This allows the vocals to come through just a little bit more without overly compressing the instruments.
The reason I feel confident mentioning Trackspacer specifically is that a free plugin alternative called Masker has recently become available. Masker operates on the same principles of inverse EQ, providing similar functionality for those who can't or don't want to try Trackspacer.
Multiband Sidechain Compression
Multiband sidechain compression allows you to duck only specific frequency ranges of a signal. This technique is similar, but not identical, to the previous method but in a more manual way. For example, if you want to duck an instrument when the bass hits certain frequencies, you can use one of the bands on a multiband compressor set to react on an external sidechain source. This way, only the frequency range that you specified for that band is compressed, leaving the rest of the instrument's frequency spectrum untouched.
Takeaway
I hope these ideas and concepts inspire you to experiment and go wild with sidechain in your own productions or mixes. These techniques can enhance the dynamics throughout little places in your mix and really add that extra dimension. By creatively using gates and compressors, you can achieve an interesting and moving sound. Keep trying things out and push the boundaries!
Happy mixing! Don't forget to always listen to new music. Or, go check out patrikskoogmusic.com if you are wondering how collaborating with a mixer to complete your tracks might work in practice, from an artist's or producer's perspective.