>>1839845With brass instruments, you make sound by buzzing your lips into the mouthpiece. If you change how tight your lips are, you can get different pitches. However, bugles can only get a small set of notes (this is why all bugle calls use the same few pitches)). Trumpets add valves, which allow for more notes to be played. I have no experience playing brass instruments, but going off of what I know, I'd assume trumpets are harder to play.
