What does half-time/double-time mean? Like if you had 4 bars, each bar with a whole-note, what would happen if you switched to half-time? Double-time? Or does it only have to do with the drum beat and not the melody?
it's just a way of describing if something happens twice as fast or half as fast as something else. usually used to talk about drums, for example a common drumbeat would have the snare (or "backbeat") on beats 2 and 4. but then if you go "halftime" then the backbeat would be only on 3. the beat would be moving half as fast