Originally Posted by solitario
If I'm not wrong the right way for recording is with a high input signal before it clips.
This is true for Analog recordings, in the Digital World it is no longer necessary. In fact, it is a good idea to leave a bit of headroom for whatever post processing you want to do.
A good recording level in the Digital world is setting the level to somewhere around -18dBFS.
That been said, it seems like the UX1 does not have a gain control for the instrument input. If you 're getting a signal that is too low, then I would suggest getting a Boost Pedal of some sort to increase the level of your Bass' output.