It’s usually all visual or sound based. Usually there are visual or audio cues that tell you when the right time perform an input is. After that it’s just practice to get the timing down.
If you’re having difficulty with something, I’d recommend going to the games’s community to get some help with setups.
Just something to keep in mind if you aren't currently. It's pretty important to play on the type of screen the game was meant to be played on.
I used to think a lot of NES, SNES, and even PS1 era tricks were impossible until I ditched the crappy LCDs I used to play on in favor of a small CRT.
It's not impossible to learn tricks on a display with input lag, but it's certainly a lot harder.
Letcha in on a little secret: nine times out of ten when someone says something is frame-perfect, it really isn't.
Pssh, 10 to 30 frames is frame perfect! It's perfect for those 10 to 30 frames! =P
In the case of sotn we can use a few things to either confirm the correct frames or increase our chances of success. We can pause the game by pulling up the map and take as much time as we need to visually confirm. We can set up our position so that the next action needed has a set frame window. Often we can tell after failing a trick if it was early or late by side factors like Alucard's behavior and by feel. So it's a combination of things. Nobody is manually reacting to anything in 1/60th of a second. Muscle memory and homework.