Sidechain EQ trick

Quite a common trick in "pop" mixing is to set up an EQ that will reduce frequencies that might clash when two sounds are present at the same time.  The classic example of this is a bassline and a kick drum - when the drum hits you want to cut out the lowest frequencies of the bassline.  I'll explain using that as an example.

The main trick is to use a SouthPole and an Inverter to turn the SouthPole from a lowpass to a highpass filter.  I learned this on the mulch-discuss mailing list years ago, all credit to the long forgotten contributor there. :)

You need to have the clean kick and basslines heading to the sound out or a mixer or whatever - what I'm describing is additional signal routing.

Send the bassline to the SouthPole's first input and the kick to the sidechain input.  Put the base resonance of the SouthPole to zero and leave the base cutoff at its lowest setting.

Send the SouthPole's output to an Inverter.

Mix the output of the Inverter with the clean bassline signal, however you'd usually do that.  For example, send them to the same input on a Mixer contraption.

On the SouthPole, turn up the SC follower cutoff knob.  

That should be it.   In my case I put the knob at about 0.5 and made the SC smoothing faster / shorter.

I hope that makes sense. :)