This is just the briefest of introductions to each of these subjects, intended only to give you a basic idea of what's necessary for different tasks, and perhaps whet your appetite for more information. From here you might move on to books or magazines, or just go to your local music shop and have a listen to some of the equipment mentioned here. Nearly all of it is widely available (I'm not covering the high-end electronic music area, where custom-built equipment is the norm and degrees in math or music theory are perhaps just a bit too useful. I do know of some sites, though, if you're interested in that.).