I was playing around with GarageBand's Lounge Jazz Drum loops this morning and noticed that the ride cymbal had the wrong timbre for the loop -- you hear too little sizzle and too much ring for such a laid back groove. I set about to change it.
To do so, I double-clicked on the loop to bring up the editor and dragged and selected the notes found at D# 2 (the location of the ride cymbal). By default their velocity was set to 101. The "sizzle" sample for that sound ends at a velocity setting of 95 and the "ring" kicks in at a setting of 96.To fix the mix I simply entered 95 into the Velocity field, pressed Return, and I had a groove that sounded much more natural.