1 stereo track for the synth to duck
1 stereo track for the kick (used as ducking signal)
3-channel bus for the SC3 plugin
Output 1 & 2 (left & right) of the synth track go to input 1 & 2 of the SC3 bus
Output 1 or 2 (left or right) of the kick track goes to input 3 of the SC3 bus
And this is the important (and counterintuitive) bit
(Tested in http://qtractor.sourceforge.net)
@macinnisrr please don’t attribute side chain compression to get the pumping effect to David Guetta… this is a technique that has been around since early house music and possibly even Georgio Moroder (although with although the enhancers, in 70’s disco that kind of kills the bass a bit)…
@Peter7k… If you can handle the Ardour 2 interface, Mixbus has sidechain compression built into it’s busses… It’s really simple, easy and sounds really good… and hopefully the V3 version will be out soon.
@linuxdsp … please please please update or create a compressor that has a sidechain input… I’m sure I’m not the only person who has emailed you in the past about this… 
BTW (I’m a very happy customer of quite a few of your products)…
@allank: apologies :-). I wasn’t implying that he invented it. I could just as easily have said Daft Punk for a reference closer to my time. I just suggested Guetta as he’s a well known modern producer who employs pumping heavily.