something i found that makes things quite clear...

- Load up a kick into channel 1.

- Load up a bass into channel 2.

- Create a group channel track (Group 1 until you rename it), open up the mixer, and add C1-sc on the last port of the groups inserts rack.

- Go to the kick on the mixer, and open the sends1-4 rack (as if you was going to enable a send effect). Click in the first port, and select Group 1. Make sure you've enabled the send, and then click the button next to enable - Pre-fader. Set the pre-fader to 0db. This will mean that the original unprocessed signal of the kick will be the key for the bass' compression, and no matter what level you adjust the kick, the bass will still compress the same.

- Now open up the kicks Channel Settings window - the little 'e' in the kicks mixer strip. From the Channel settings window of the kick, look near the top right corner and there will be a black drop down menu. Select 'routing'. Then pan the send of the kick (below it) to far left. Close the kicks Channel settings.

- From the main mixer window again, pan the bass far right, and then route the Output of the bass straight to Group 1. Now you should hear the bass coming only through the right speaker, while the kick comes through in stereo but far louder on the left.

- Go to the Group 1 channel on the mixer and open up the C1-sc. Select Key Mode 'L > R' and compress your bass how you want. I go for a ratio of 3.0:1, threshold at about -15 to -20, attack at 0.01ms and release at 50ms.

(now you should hear the bass being compressed, but still only coming through the right speaker, while the kick comes out in true stereo)

- On the main mixer, right click on the Group 1's panning and choose 'Stereo Dual Panner'. Two sets of panning should be there now. Take the pan from the right and bring it back centre (leave the left where it is). Bass should now be back where it's meant.