One signal controlling the noise gate of a second signal?

[wvnl]

I'm currently breadboarding a project which has a guitar signal, plus a second continuous generated signal. These are being mixed at a later stage, but what I'd like is to have the guitar gating the 2nd signal before I mix them.
i.e the 2nd signal is only present when the guitar is playing.

Haven't really been sure what direction to look in for something like this so any ideas would be great!

 

[DailyDovetails]

I haven’t built one yet but I’m pretty sure you could use the sidechain function on the muzzle to do this. Just plug the guitar into the side chain and then the other signal into the in and out.

 

[Harry Klippton]

Lots of noise gates already have a key input yeah? As dailydovetails mentioned, the muzzle does. I have some dbx 363x units with a keyed input as well

 

[wvnl]

ah thank you, I'm realising I wasn't very specific! - I'd like to build this into a pedal, so I'm looking for circuit solutions rather than external units

I will look at the schematics of both of these though, and see if there's anything I can get from them