Help: Need to noise gate track based on another track

Apologies if this is super obvious. I'm a bit of a newb with buses, and I think that's what's required.

Here's what I'm looking to achieve:
- Drum track on track a (Session Drummer)
- Synth or audio output on track B 
- Track B gets muted whenever track A hits

I've fought with compressors and the Cakewalk compressor/gate effect on track B's audio channel, but can't figure out how to gate based on a different track's level.

Help? 

Put a Sonitus gate on the synth track

Create a send in the drum track and route it to the sidechain input of the gate

Switch gate to 'duck' (if you want to mute when there's a hit, if you leave that setting it will mute when there's no hit). Adjust threshold and timing to taste.


Don't need a buss per-se.

Have fun!
Child

Rothchild, Nice guitar sound on "If These Are the Good Times."