First, create a stereo group, and put the 'Waves C1 comp sc' plugin on it. Then route the bass track to the group (at maximum volume, ie 0dB on the bass fader) and use a PRE-FADER aux send to get the kick to the same group (at maximum volume, ie 0dB on the aux send), with the bass on one side and the kick on the other - hard left and right. I assume you know how to route an aux send to a group. You can pan the aux send of the kick channel to one side of the group by clicking the 'Send display modes' button above the list of sends to see the routing of each send. This means that the bass goes through the group to the outputs, and the kick goes both through the group, and directly to the outputs - and the level of the kick fader DOES NOT affect the kick level going to the group.

Basically the idea is to use the compressor to reduce the level of the group when the kick drum hits... since the bits inbetween the kicks are uncompressed, the effect of this is that the parts of the bassline that fall at the same time as the kick get reduced in volume compared to their level between kicks... if you see what I mean!

So... you send the tracks to the group in their different ways, panned on opposite sides as I said. Pan the group to the centre so that the kick and bass come out of the group in the centre of the stereo field - ie. the group output is in mono. At this point the group will be outputting both the kick and the bass - the kick will probably seem far too loud. Don't worry!

Set C1 'Key mode' parameter so that the side with the kick is doing the compressING and the side with the bass is being compressED, eg. if you have kick L and bass R, set it to 'L->R'. Now the kick channel will no longer play through the group, and the bass channel will be compressed - not by its own dynamics, but by those of the kick. This is called 'sidechaining', where the dynamics of one sound are controlled by the dynamics of another.

Now you can start compressing. Take the kick fader down to zero so you only hear the bass - don't mute the channel though as this might mute the send too. Set the ratio to about 8:1 and adjust the threshold so the gain-reduction meter shows, say, 12dB of compression - this is a lot but it makes hearing what's going on easier. Make the attack as fast as you can - this means the compressor reacts instantly to the kick. You should now be hearing the bass drop in level every time the kick drum hits. Now adjust the release time so that the bass comes back up in level as soon as possible after the kick has finished; this depends on the shape of the kick, the speed of the bassline and how much 'pumping' you want to hear.

You can try EQing the sidechain by clicking the 'EQ Mode' button on the compressor controls until it says'Sidechain'; the compressor EQ now affects the sidechain (ie the kick drum). You can hear the effect of this by clicking 'Sidechain' button in the 'Monitor' section - you will now hear only the kick. If you take all the bass out of the kick here, the compression on the bass will react faster, as it is now reacting only to the 'click' of the kick. To hear the bass again, click 'Audio' in the monitor section.

Once you have got the bass pumping nicely it's time to balance it with the kick. If you've set things up correctly you can change the levels of the bass (using the group fader) and the kick (using its channel fader) as much as you like without affecting the compression. Set things up so that the level of the bass between kicks is good compared to the kick (I try and aim for maybe 2dB lower than the kick, but it's a matter of taste). Now listen to the level of the bass during the kick drum. If it's too low, you need to reduce the compressor ratio (eg to 6:1); if it's too loud you need to compress more. Try experimenting with the Release control.

And that, my friend, is (as far as I can tell you) how to cross-compress the bass with the kick using Waves C1.

Happy tweaking!