If you listen to any club-oriented music these days, you're probably intimately familiar with the sound of sidechain pumping by now. The trendy technique consists of strapping a compressor with extreme settings over and instrument and using the compressor's sidechain input to use the kick drum track to trigger the compressor instead of the track being processed. The result is a rhythmic sucking/pumping (get your mind out of the gutter) in time with the music. It adds a certain extra level of energy and indeed sometimes artists sidechain every instrument except for the kick and vocals. It can also be useful in keeping your kick drum and your bassline from overlapping too much frequency wise, thus giving you a cleaner low end. If you're not that well versed in using a compressor, however, it may be frustrating trying to get the effect working properly.
So today, I'm going to show you how to simulate the effect from within your synth itself. I'll be using Spectrasonic's Trilian, but just about any well-appointed soft synth should be able to pull the effect off without too much effort.
1. Fire up your DAW and insert an instance of Trilian or whatever synth you choose.
2. It defaults to a simple "init" patch, a simple, non-descript sawtooth wave with an organ-style amplitude envelope. From the EDIT page, go ahead and turn the MIX slider for LAYER A down to about 1/4 of the way (say, -14.3 dB or so). We don't want the level all the way down because sidechaining doesn't totally silence the sound it's squashing, it just lowers it significantly.
3. Trilian and Omnisphere's default patch already uses LFO 1 for vibrato, so let's select LFO 2 to keep things simple. Here's where we're going to set it up to create the pumping effect. Set the waveshape of LFO 2 to the ascending sawtooth wave. This will give us that "rising and dropping off suddenly" effect produced by a signal sidechained with a kick.
4. Set LFO 2's mode (right below the waveshape) to LEGATO, so the pumping continues no matter what you play.
5. Click the SYNC button so it lights up. Since this is a rhythmic effect, it's important that the LFO is in sync with your host's tempo.
6. Now we need to set the LFO to the proper speed. With SYNC activated, LFO 2's RATE will let you select specific note values. Set it to 1/4 for quarter note.
7. Finally, we have to do the actual assignment of the LFO 2 to modulate our AMP level. So in the modulation section, select LFO 2 as your modulation source and AMP -> AMPLITUDE as your destination. Push both sliders all the way up.
If you sustain a note now, you should hear the trademark pumping sidechaining is known for. For an even more current sound, try sending your sound through an amp or bitcrusher effect.