When I record drums I will usually place a bottom snare microphone. My 'go-to' microphone for bottom snare these days is AKG C414 however it can be anything else depending on what the song need. Once in a while I would receive a mix session recorded without the bottom snare microphone. The bottom snare microphone captures the sound of the snare-wire rattling when the drummer hit the snare. Sometimes I need the high-mids and high frequencies from that microphone to process it with a harmonic distortion plugin such as the Softube Saturation Knob to get the snare cut through the mix. So if I really want a bottom snare microphone, I will setup a gated noise track. This concept is similar to gated reverb for snare.
Before I discuss how it's setup, listen to the results with and without gated noise at the link below. The audio clip consist of 8 hits of the snare without the gated noise and the same 8 hits are repeated with gated noise follow by a snare roll without gated noise and lastly the same snare roll with gated noise.
Click this link to listen: https://soundcloud.com/eugenenks/snare-with-gated-noise
Here is how I did it in Protools:
Step 1: Create an Aux Track and insert the Signal Generator plugin follow by the Dyn3 Expander/Gate (it can be any gate plugin that have side-chain and look forward function). I selected pink noise in the audio clip example above but it can be white noise or any plugins that generate noise. Ultimately you have to let your ears be the judge.
Step 2: Create a Bus Send on the snare track. This will be the key input for the gate plugin.
Step 3: Set up the gate plugin and mix the gated noise track with the snare track to your liking. Usually I will set the attack time to the fastest and work on the hold and release time to ensure the gate plugin work with the snare smoothly. I will spend most of the time tweaking the look-ahead parameters to get the optimal results. Depending on how the snare is played through out the song automating the threshold will help to ensure the gated noise track work more naturally.