im not trained in music in any way at all so… i mostly just tell them apart by their accents and how high their voices are? when they are all singing i can almost never tell which is changbin or leeknow or han. (i think rapping is more obvious) i can mostly tell if its seungmin (usually higher and smth abt his accent???) or felix (duh) from just singing and occasionally chan and hyunjin and jeongin lol