For use with the built-in mics the H4 has three gain settings, L-M-H. I just set mine to M for the pub session and forget it. On my HiMD recorder I was forever fiddling around with the manual rec level and never seemed to get it any better than the default. You just need to avoid digital clipping at very loud bits, that's all. If you were using a slightly low level you can fix this with your editing program. It isn't something to get too stressed about. But you can fiddle with it manually if you really want to! None of these gizmos have manual settings that are easy to get right when you're on the fly.