Studio Tips With Ant LaRock: Issue #4 [Sidechain Compression]

Words By Ant LaRock
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Finally, a topic that I'm sure we can all agree, is as fun as it is useful!

Side Chain Compression

Side Chain compression is a form of audio compression that works when an external source or “trigger” engages a certain amount of amplitude reduction on an audio track. In simpler terms; when one thing hits, the other thing gets quieter. This is particularly useful in the world of electronic music as we have our loudest element of the track, our kick drum, hitting on every beat for almost the entire song. In genres like House and Techno, you can keep plenty of space in your song for you big-ass kick drum to shine through. I know there is a couple of automatic side chain type of effects out there but this month we are focusing on setting up and utilizing our own sidechain compression in both Ableton Live and Logic Pro. When you set up your own sidechain compression in your DAW, you will have much more control of the effect and the process is pretty simple.

It is very common in House, Tech House, and Techno, that your tracks are lead by a kick drum and a bass line. They will be the loudest and most present parts of your song. The challenge is that both of these musical elements sit in the same low frequencies of the audio spectrum. If your bass line is hitting at the same time as your kick drum, the sum of both parts is very loud, if not “clipping” (distorting), when all of the elements of your song come together. The most common workaround for this is sidechain compression. When the kick drum “triggers” the compressor, the volume of the bass line “ducks”, thereby reducing the overall volume and preventing your low end from clipping your track.

So what do we need to get started? We need a compressor plugin, a “trigger” and an audio track that needs to be side chained or “ducked”. In Ableton Live, we will be using the Glue Compressor (Fig. 1A) that comes stock with version 9 and up and in Logic Pro, we will use the stock Logic Compressor (Fig. 1B)

Fig 1A

Fig 1A

Fig 2B

Fig 2B

Firstly, we need to set a “trigger” or the source audio that will engage these compressors to “duck” the audio. Most commonly the “trigger” is set to the kick drum but I tend to use a muted audio track with a rimshot drum sample to trigger the compressor. Reason being, if your side chain compressor is set to your kick, and you remove your kick drum for 16 bars in your breakdown, your audio will come screaming back full volume during that breakdown. To me these are the wrong dynamics to have in the more subdued part of the track like a breakdown. So I set another, constant trigger to a four-to-the-floor pattern or the same place that your kick drum traditionally goes in House, Tech House and Techno

(Fig. 2A). The same technique applies to both Logic Pro and Ableton Live. I find that the sharper transient of the sound, the more effective the side chain compression will be so I tend to use the Rimshot from a Roland TR 707 drum machine as the sound has a very sharp transient that the compressor recognizes quite easily. This sample comes stock with both DAW’s

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After we set the pattern for the trigger source, in this case our TR 707 Rimshot, in Ableton Live we can simply mute the track. In Logic Pro we can set the output in the channel strip to “No Output”. This simply makes it so that we cannot hear this “trigger” audio as the track is playing. This track can be minimized and forgotten for the rest of our production, as long as the trigger spans the length of our entire song.

Next, we need to set our compressor on the audio track that we will be sidechaining or the track that we want to “duck” when the kick drum hits. In Ableton’s Glue Compressor there is a tiny expand arrow in the upper left-hand corner of the plugin that opens the side chain section, where you need to click the “Sidechain” button to engage it (Fig 3A). Even simpler in the Logic compressor, in the upper right-hand corner, click on the button that says “Side Chain” (Fig. 3B)

Fig. 3A

Fig. 3A

Fig. 3B

Fig. 3B

Now we need to set our side chain source in both plugins to the muted “trigger” track that we created earlier. In Glue Compressor, under the “Audio From” tab, click the drop-down menu and select the track with our TR 707 Rimshot. In Logic Pro, the upper right-hand corner, click the drop-down menu for Side Chain and locate your “trigger” track there. Now your compressor is almost ready to work...

As you hit play on your project, slowly drag down the knob in either compressor labeled “Threshold”. This threshold function is the audio level, that when crossed, the compressor starts to work, in this case, what level the “trigger” starts to “duck” the volume of the audio track. So as you bring that threshold level lower and lower you will see a more dramatic “ducking” effect. Visually you will see the meter in both compressors start to jump as the kick hits, as you lower the threshold knob. In turn, your kick drum will be left with less and less competition and be given more space to really punch through on your tracks. The lower your Threshold level, the more “ducking” or reduction in volume will occur. Again, this is particularly handy when applying to bass lines or samples that tend to sit in the lower frequencies.

The other secondary functions on the compressor have a dramatic effect as well. The “Attack” on both compressors is in milliseconds and this is how quickly the side chain compression takes effect. The lower the attack time, the sooner it will start, creating an accurate and fast triggering of the compression. The higher the attack time, the lazier or slow triggering the effect will be. I tend to keep the attack times around 1 millisecond, so quick and accurate to make sure the kick drum has substantial room as soon as it hits. As a fair warning, if the attack time gets pushed too low, usually below 1 millisecond, a clipping of the audio may occur.

A further secondary function to address is the “Release” time. This is how quick the compressor allows the audio to return to full volume after the trigger source engages it, again, this is set in milliseconds. Have a play with this one but generally, you would like your audio to spring back to life at a fast to medium pace as to not make the side chain effect sound very obvious. If the release time is set very slow, the audio may never return back to full volume once it is triggered, thereby reducing its overall volume through the entire track and making this side chain process moot. I also keep this setting at around 1 millisecond as I do not want parts of my audio track to be reduced in volume after the kick hits. For example, I want my bassline to be right back to full volume immediately after the kick hits so that all of the notes will be heard between the kick drums.

Lastly, we have “Makeup”. Makeup is a gain boost to compensate for the loss in volume due to compression. Again, experiment with this function but if the makeup gain is pushed too much, the overall volume will have been boosted, even when the trigger engages the side chain, that it may make this whole process moot as well. I find a slight bump to the Makeup gain of 1dB to 2dB is helpful to fill out the audio track that we are “ducking” but this is definitely to taste.

Part of the fun of this process is to find the settings that work for you both technically and creatively. The more I experiment with sidechain compression, even after all of these years, I find new applications for it. I sprinkle it on hi-hats and even vocals from time to time to apply interesting dynamics to otherwise flat sounding samples. The possibilities are endless and again, the fun comes from experimenting. Get sprinkling.

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