I haven’t got to the point where I feel my Sukui (upstroke) is natural enough for me not to focus on it when playing. Currently I play it when the notation tells me to. As a guitarist, I am well aware of how much easier it is to play fast parts when alternating between down and up strokes with the plectrum.
However, in some slower songs I feel like there is no need for a sukui. Or the other way around, “if I am supposed to do sukui here, why not in all these other places?”.
I notice the difference in sound, but as a beginner such subtle changes in the sound is not in the scope of my concentration as I am more focusing on the technique.
My main question is, if you compose or play a song that has no notation, what would you say tells you when to perform sukui or not?