Pro Tools Tutorial – The Art of Side Chain Processing

Welcome to a new MusicTech series. Mike Hillier guides you through today’s most cutting-edge and effective production techniques, and kicks things off with side-chaining in Pro Tools…

We’re often asked about specific production techniques here at MusicTech, and not necessarily those specific to particular DAWs. So, in response, we’re starting a new series about some of today’s most commonly-used (or indeed secret!) production techniques – those that are both defining genres and making music what it is today. We’re illustrating them with Pro Tools but even if you don’t own that DAW you should be able to use the techniques shown within your software of choice…


To kick things off Mike Hillier is talking side-chaining and ducking and diving…

Dynamics processors, both hardware and software, often have an additional “side-chain” input which can often go overlooked, but can be used to achieve a variety of advanced production techniques. In broadcast, compressor side-chains have long been used to achieve a ducking effect, reducing the level of the music while the DJ is speaking. This same trick has also been used in music production, for instance to duck a guitar part while the vocalist is singing. In the dance world, especially, this technique is incredibly popular, ducking the instrumental parts in response to the kick drum – it’s a technique that has been used for a while now but also one that is still very popular.

By sending the kick drum to the side-chain of a compressor placed across an instrument, the instrument can be made to pump in response to the kick. This creates a moving rhythmic dynamic, turning even the most static pads into exciting sounds. It also creates more room for the kick drum in the mix, which is why it is so popular in the dance scene, where a strong kick drum is, as ever, essential to the mix.

One of the most famous users of this technique is Daft Punk, who use the side-chain of an Alesis 3630 – a notoriously dirty-sounding analogue compressor. However, you don’t need a hardware compressor to get similar results and many software compressors, including the Dynamics III plug-in in Pro Tools, have a side-chain that can be triggered from a kick drum to get a big pumping synth sound. Be careful with what you send to the compressor to be pumped though. We often hear artists sending their entire instrument buss to be pumped through the compressor, when a couple of simple choice elements would make for a far more exciting and interesting sound.

Another common trick for side-chain dynamics is to beef up the sound of kick drums with a gated sine wave. This time the kick drum is sent to the side-chain of a gate rather than a compressor. A sub-harmonic frequency is then sent to the gate’s audio input, which can be tuned to the key of the song, or to add depth to the fundamental of the kick. Now when the kick drum crosses the gate threshold the gate will open, letting the sub-harmonic sine wave through, and then close again once the kick drops below the threshold, ensuring the sub-harmonies are only present at the same time as the kick drum.


By carefully setting the attack, hold/hysteresis and release controls on the gate it is possible to shape the amplitude envelope of the sine wave to closely resemble that of a kick. Fast attack and slightly slower releases will produce the most natural sounds, although if you set the attack too fast you will create a high-frequency ticking sound as it opens, which may or may not be useful in accenting the kick drum.This same trick can be used on toms and, by substituting a pink noise waveform for the sine wave, it can be used on snares too. It can also be used to create an automated gating effect on other instruments.

Try gating a synth or vocal part to trigger off the hi-hat rhythm. The textures that you can create with these sounds can be quite interesting, and don’t always need the original sound to be present in the mix. Using the hi-hat to trigger a gate on a synth, for example, can be used to replace the hi-hat pattern entirely, or as a substitute for it in a different section of the song.

This effect is often easier to produce, and more natural sounding than using a pattern sequencer, or automation to control a gate. We have recorded tapping on a desk to use as a trigger for a gate on many occasions, knowing the desk tapping channel will never reach the final mix itself.

Getting a Pumping Sound

1: Send the instruments you want to pump in time with the kick to a group buss. It’s best not to send everything, but to specify specific sounds that will benefit, such as bass and pads.

2: On the kick track add a mono send, but don’t bother bringing the return back on its own aux channel. We’re just going to use it to control the compressor side-chain.

3: Add an instance of a dynamics compressor/limiter (here it’s Dynamics III in Pro Tools) to the group buss. And in the side-chain key menu at the top left select the kick SC buss we created.

4: The side-chain is now routed to the compressor, but the compressor is still not listening to it. In the side-chain section at the top right, click the key icon to engage the side-chain.

5: The threshold control will now respond to the incoming side-chain. Set the ratio at 4:1 and lower the threshold until you’re getting a fair amount of compression (6-12dB).

6 Finally set the attack and release to time the pumping effect to the rhythm of the track. A fast attack will bring the signal down, quickly making room for the kick, while the release should be timed to create a rhythmic pumping effect.

Beefing it up with a Sine

1:Add a new mono Aux channel next to your kick, and add an instance of (in Pro Tools) Signal Generator followed by Dynamics III Expander/Gate.

2: Set the Signal Generator to a sub-harmonic sine wave. You can tune this to your track, but is best around the 30-50Hz range.

3: Similar to the side-chain compression earlier, set your dynamics gate to key from the kick SC channel and enable the side-chain.

4: We want to completely gate the signal when the kick isn’t triggering it, so set the Range to full (-80dB) and the ratio to 100:1

5: Set the threshold to trigger only on the peaks of the kick, so that the gate isn’t open for very long. This enables us to better shape the sub kick with the attack and release.

6: Finally, when setting the attack and release we’re controlling the speed at which the gate opens and closes, allowing the sine wave through in response to the kick. This shapes the envelope of our new sub kick.