Don't be lazy and just slap Slate Trigger on your audio track and assume its not going trigger accurately. IT WON'T!!
...is from Midi. Period! Here's why
This might take a bit longer than triggering off of your audio but, trust me, its worth it! Now, there are a few ways you can create the midi. Some DAW's even have some build in tools to achieve this, like Cubase but we're going to focus on two 3rd party tools available to everyone. Slate Trigger and Toontrack Superior Drummer 3.
Firstly, you want to instantiate Slate Trigger on your drum audio track, like your snare top mic track.
click play and adjust the input so that the louder hits touch the top of the transient display window
Adjust the Detail control so all the snare hits are outside the bounds of the two lines. Orange indicators will appear to give you a visual that the transient has been detected
If you are not getting the orange indicators on hits you know to be snares, adjust the sensitivity control until you pick up all your hits. Better to get more hits now and delete some later than trying to manually add missed triggers
play through the entire song to enable slate trigger to detect all the hits
Once that's completed, drag the midi to a new track in your DAW. Click and hold the "Drag on Track" button under Midi Capture
Now move your instance of slate trigger down onto the new midi track (or instantiate a new one), click settings, make sure Midi In is enabled and the note corresponds to the midi note exported by trigger.
NOTE: This might be just for Reaper users but the midi note C1 in Reaper doesn't trigger if slate is set to C1. I have to set slate to C0
Now, of course, check through all your midi and make sure there is no mis-triggers and everything looks clean.
Here is a video where i explain exactly how i do all this