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If you have listened to Electronic Dance Music, or EDM, then you have probably experienced the "pumping" sounds that move along with the groove of the track. What's happening here is that the audio signal (usually a synthesizer) is being "ducked" when another signal (usually a kick drum) is sent.
There are times, however, when you want to maintain the "pumping" sensation without another audio signal being heard. Today, I will show you how to do this with the "Silent Sidechaining" technique. While I am demonstrating this method in Logic, you can achieve the result in most every DAW.
First, set up a new Software Instrument Track. This will be your Sidechain signal.
Next, change the output of the new Software Instrument track so that it is sending its signal to a bus. I have chosen Bus 1, but you may pick any available bus you would like.
Change the Output of the bus to "No Output." This is is absolutely necessary so that we do not hear the signal of the sidechain.
Your sidechain bus should now look like this.
Next, we need to select a software instrument that will actually generate the sidechain signal. Since this signal will never actually be heard, I have chosen the Klopfgeist Metronome.
Now that we have our sidechain bus set up, we need to put a signal into the channel. I have drawn four quarter notes into the piano roll. This is a pretty typical pattern for the popular House music "pump." Repeat the pattern for as long as you would like.
In Logic, you can copy or repeat a section easily by first clicking and holding the region you wish to repeat, then pressing the Option key while dragging. The cursor hand will display a "+" when Option-dragging. Let go of the mouse to place the copied region.
Now that we have a pattern repeating for several bars, it's time to actually affect an audio signal. I have recorded a simple pattern using the ES2 synthesizer. The original audio can be heard below.
Place a compressor on the signal you wish to "duck" (here, it is our ES2). From the Sidechain menu in the upper right, select the bus on which you have placed your "silent" Software Instrument signal (the Klopfgeist in our case).
Set the attack and release settings to taste. For EDM styles, you generally want fairly short attack and long release times, so as to let the signal really swell. Don't be afraid to have higher-than-usual ratios, either. The circuit type depends on the track/sound you have, but I tend to like either VCA or Opto style compression on my synths.
Here is the original synth line.
Here is the Sidechained synth line.
As you can hear in the examples, this technique is very audible. In Electronic music, sidechaining is something that the audience can easily identify, as opposed to more subtle techniques such as filter modulation or reversed reverb, for example.
Sidechaining is certainly not limited to EDM, though. In Pop music, try using the sidechain function on your compressor to duck the bass to allow for the kick drum to punch through. In Rock music, when you need the vocals to really cut through the mix, you can sidechain the snare so that it is not as present when the singer is belting out the chorus.
There are limitless uses for this technique. Try a few out!