Side-Chain Compression for Kick Drum & Bass Guitar

Side-Chain Compression for Kick Drum & Bass Guitar

Using Avid Pro Tools Recording Software

By Chad Berton - June, 7, 2013

A.  What Is Side-Chain Compression?

To Put it simply, side-chain compression is a technique that uses the audio signal of one source to trigger the compression of another.  This helps reduce the output gain of your instrument in direct correlation with the the input signal of your outside source.  In this blog we discuss using a KICK drum to trigger the compressor on a BASS guitar.  The same procedure can be used for any variety of instruments.

In dance music especially, the KICK and BASS tend to live within common low end frequencies.  Using this technique helps allow the KICK to punch through the mix by reducing the gain of the BASS every time the KICK attacks.  Producers also use this technique as an effect within their mixes to creating a pulsating sound that gives the mix an undulating push & pull feel.  In these cases, the producer may use the KICK to also trigger compression on other instruments within the mix.

B.  How Is It Applied?

(You can begin with a session that you have already created if you like.  In my example, I have created a new session in Pro-Tools.)

                                                                                                                                 

I.  Setup Your Audio Tracks 

First I will create two new Audio tracks in our Pro-Tools session.  We label one of them KICK, and the other one BASS.  In a real session, we would then go ahead and record our instruments to their respective tracks.    


(In this example we don't use any audio.  I'm just showing you the basic setup on   how to use this technique in Pro-Tools.)

II.  Send Your Kick Track Through BUS 1  

Once you have your KICK and BASS tracks recorded, make sure you are in the MIX window in your Pro-Tools session. Directly below the insert section, at the top of your channel strip is the SEND section.  Open up one of the sends on your KICK track, and in the drop down menu, select BUS 1.  This will open a window that looks like the picture here, showing a fader that controls the signal going through BUS 1.  This will be the signal path we will use for the KICK drum to trigger the compressor that we have already inserted onto your BASS guitar track. 
Directly above the fader section is a line of three buttons labeled: [SAFE] [PRE] [FMP]
Click the button in the center labeled: [PRE]. 
By doing this, you are sending the signal into the BUS, pre fader.  Meaning that the signal is routed to the BUS before the Volume fader, and therefore it is not affected by volume changes in the mix.  
 Now only the BUS fader controls the amount of signal being sent to the compressor.
 Next, click on the BUS fader and slide it up to around zero db to send your audio signal through the BUS.

III.  Insert Your Compressor Into The Bass Track

Next, we'll need to insert the compressor into the BASS channel.  Bring your pointer up to the top of the channel strip on your BASS track, and click on one of the channel inserts.  From there, a drop down menu will open, and you can select a compressor from within the dynamics menu heading.

In this example, we have selected the Digirack Compressor / Limiter Dyn3 Plugin.  You may choose whatever compressor you like.  But since this plugin comes standard with Pro Tools, I thought it was better to use for this lesson.


 IV.  Set Side-Chain Input On Compressor

On the upper left hand side of the Dyn3 compressor plugin there is a small icon that looks like a key.  Next to it is a drop down menu that allows you to select the input for the side chain source.  Since we've already established the SEND on our KICK track to go through BUS 1, we need to open up this drop down menu and select BUS 1 here as well. 

 

V.  Activate Side-Chain Input

On the right hand side of the same plugin window is a box labeled, "Side-Chain".  In this box you'll see the same key symbol as you saw in the upper left.  This time around it is a button.  Click this button to activate the side-chain on the compressor.  Now the compressor will know to look to BUS 1 for the input signal.  There are a couple of other controls in this box, but we'll leave those alone for this example, since they have to do with Hi and Low-Pass filters, which aren't necessary at this time.  

 

 

VI.  Adjust Compressor Settings

From here you can adjust your compressor settings, such as Threshold, Ratio, Attack & Release.  I generally start with a very low threshold so that the effect of the compressor is overtly audible.  Then, I gradually back off until I get the amount of compression I'm looking for.

From there it's time to experiment.  For the pulsing / push-pull effect of dance music, you need to adjust your release time to match up to the BPM of your song.  There are formulas for converting milliseconds to BPM which were used a lot in calculating delay times before digital syncing of delays became common in today's DAWs.  These same formulas can be applied to the release time of your compressor to help match the BPM of your song, but remember, not all compressors act in the same manner, and  you'll likely need to do some manual tweaking to get the pumping effect to fall on the beat.  


VII.  Link For Release Timing Calculator

A good resource for converting BPM to MS is:  http://web.forret.com/tools/bpm_tempo.asp

They have a free online calculator where you can enter your BPM, along with the time signature of your song, and it will give you the amount of millisceconds that happen between beats at that speed.


Now you're ready to go and do it all yourself.  I hope this little tutorial was helpful.  Now go out there and create!

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