I have some questions that may be noob-like for the bass. I'm able to play but there's some technical stuff I just can't seem to find information for. 1. What is active and passive pick-up? 2. How do you activate active (if that is what you do)? 3. I've been looking at my amp and I can't seem to find the purpose of 3 knobs on there that say Low, Mid, and High. 4. I have 2 knobs on my bass. One is volume, the other I'm not sure. If the amp has gain turned way up, if I turn one way, when it gets all the way to the other side, the sound seems to come from the amp. If I turn it away just a little bit and all the way over, it sounds like it comes from the bass. If the gain is lower, when the knob would make it seem sound was coming from the amp, sound seems to come from the body. In the other direction it sounds like it's coming from the head. Can someone tell me when this knob may be? Thanks in advance.