Selection: offline Fade-in & fade-out

Hi SL community.

I’m SL 8 Pro owner.
I need to apply offline amplitude fade-in and fade-out on single frequency or freq. range selections even on single or multiple layers.
I have not found any simple and faster solution but using the eraser tool through decreasing or increasing hardness and attenuations which is not the right way.
Does offline fade-in and out functions already exist or not?
Regards.
Gustavo.