Q: “What is the Strip Silence function in Logic used for?”
A: Strip Silence literally strips silence from an audio clip which divides an audio region into smaller pieces and replaces the original region by these new slices in the Arrange window. Among many things, Strip Silence is an excellent “destructive noise gate” for stripping unwanted side noise from a vocal or acoustical instrument track. But you can also use this function for “splitting” something like a drum track or loop and then changing the song tempo!
How? First, understand that Strip Silence works by detecting audio levels. Detecting beats with this function will therefore work best when working with percussive material that has clearly defined attacks (long cymbal sounds or the like will disturb the beat detection).
Start by importing a drum loop to the Arrange window and set the loop to match the tempo of the song.
Select the region and call up the Strip Silence window by pressing the default key command Ctrl+S. Tweak the threshold and other parameters until the loop appears to be split accordingly. The preview will help you find the best settings for the particular loop.
After confirming with OK, the long drum loop of the Arrange window will be replaced by the smaller beat regions (If Strip Silence did not detect some loop split points, you can cut them by hand.).
The result are single beat regions that are fixedly bound to their bar position. You may now increase or lower the tempo and the drum loop will stay in time.