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This is a description of how I use side chain compression in Logic Pro 8.
The concept is very similar in most other sequencers.

EDIT [2009/12/06]:
Leave a comment on this post and receive a download link to my original Logic Pro source file used in this tutorial. Have a closer look at the settings or use it as a starting point or template for your own production.

The most common use for side chain compression is to make more room for your instruments in the mix by letting a key input signal trigger a compresssor or limiter.

I use side chain compression mostly on bass/subbass tracks triggered by a kickdrum (commonly called kick/bass compression or bassducking) to either make that well-known “pumping effect” or just mix the bass in louder and get some extra dB in the mix.

In most cases I use two kickdrum tracks, one “main” kickdrum, and a second kickdrum (on which I can use different EQ and envelope settings) to trigger the bass compressor. Using that extra kick for the bass compression instead of the main kick keeps the compression on the bass line if the main kick isn’t playing, say in the intro, break, etc.

The basic tutorial:

• 1. Create a new audio or instrument track for your main kickdrum. (Kick1)
• 2. Create a second track for a kickdrum which is going to control the bass compressor (Kick2 (SC)). You can simply duplicate the first track.

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• 3. Create a Bus channel (called “SC input” in this screenshot) and set the volume of this Bus channel to “- infinite dB”, the lowest volume possible. (don’t mute the track!)
• In this example I used Bus11 (as I most often use Bus 1 to 10 for aux send/return Effects, and the rest for sub-mixes and side chain voodoo, etc.)
• 4. Set the output channel of your second kick (Kick2 (SC)) to the Bus channel you just created.
• 5. Create the bass line track.

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• 6. Insert a compressor at the very end of the chain on the bass line track.
• If you want some additional effects to your bass sound, add them before you insert the side chain compressor. You could – and probably should – use some EQs on your bass.

Compressor settings

• 6.1. Set the compressor´s external sidechain input to Bus 11. You set the external sidechain input in the upper right corner.
• 6.2. Set the attack between 0 to 5ms to compress the bass immediately/fast.
• 6.3. Set the knee to hard (0.0) to trigger the peak of the signal.
• 6.4. Set the ratio between 10 and 40, depending on how much compression you want. – The more ratio the more pump in the bass line, which might be just what you want.
• 6.5. Set the release time depending on how long you want the bass to be compressed, usually quite short, e.g. 20 – 50 ms.
• 6.6. Set the threshold level between 5 and 20, depending on how much compression you want.
• 6.7. Try different settings for Circuite Type/mode and attack/release time to fine tune the pumping effect/compression.

Here are some demos for comparison:

• The plain, uncompressed Bass:

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• The same Bass side chain compressed using the compressor settings above:

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• Kickdrum and uncompressed Bass:

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• Kickdrum and side chain compressed “pumping” Bass:

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For now, I’ll leave you to experiment.

Try different compressor settings and/or input signals and different envelope settings of your triggering Kickdrum.
You could also experiment using side chain compression on other tracks, eg. on strings/pads, vocals or a submix.

SideChain Compression Tutorial – Source file

Don’t forget to leave a comment and get the original Logic Pro 8 file I used in this tutorial!

I hope this helps.

Feel free to contact me with any questions or comments. I will try to respond to all comments as soon as I am able to.