Bass Rider.

Bass Rider keeps a bass part at a steady level by riding its gain automatically, the way an engineer would work a fader. It is not a compressor, and that distinction is the whole point, because the attack, tone, sustain and dynamic feel of the instrument are left alone. It runs in real time with no added latency, works live as well as in the studio, and writes an automation track you can edit afterwards if one phrase needs a different hand.