The term "trash mic" refers to a microphone used to record anything including vocals, guitars, or as detailed in this tutorial, drums. This mic can be lo-res by design or have the trashy effect created by the engineer while tracking or during the mix by using guitar pedals, a wah pedal, a plug-in, or anything else that will render a distorted and chaotic-sounding result.
Placing the Mic
Because a trash mic is a "personality" transducer, you can feel free to experiment with placement. When used around a drum kit the mic can be put on the floor in front of the kit, under the snare, positioned on a stand over the drummer's shoulder, or tucked over the kick drum pointing at the side of the snare. There are no rules to be broken because this mic is an extra added attraction used along with other traditionally placed microphones.
Taking Out The Trash
The trash mic can and should get out of control, but that doesn't mean you can't limit its presence in the track. By using an expander/gate which is side-chained from desired sources like kick and snare, you can clean up the signal allowing only selected parts of the trash track into your final mix. It all starts with putting an expander/gate, such as Avid's DYN 3 or Fabfilter's Pro-G onto the trash track's insert, then setting up a bus from other tracks that are "invited" into the DYN 3's key input. Once it's all working, it's a matter of adjusting the threshold, range, and release controls until you achieve the desired result.
Watch this free tutorial to see and hear all these tips in action.