MXR Bass Compressor Pedal - Professional Bass Guitar Effects Pedal for Musicians | Perfect for Live Performances, Studio Recording & Practice Sessions

I use it as a mild dynamic range compressor, it generally is on for the E string and sometimes the A.The effect is subtle, evens out the note volumes and adds a little to the sustain the way I have it dialed in. You can use a compressor for other things, but that's what I wanted it for. Another reviewer said a compressor on bass is better felt than heard, that's exactly right, it makes you seem like a better player, and makes it easier on the sound guys because your peak volume is more consistent.I had to front-end it with the MXR-M81 preamp since I have a passive bass. This pedal is not intended to be used as a preamp from what I can tell, it adds some hiss and doesn't have enough gain to be effective for that purpose, my bass couldn't even light up the lights on highest gain. But if you hit it with line-level inputs it shines.It appears to draw power from the moment you plug in to the input jack, turning on bypass does not appear to stop current draw like the tuner and preamp pedal do, so keep that in mind when you are figuring battery life. I learned this the hard way. A nice feature is when the battery dies it silently goes into bypass mode. A few of the LED lights stick on for a while as a low battery indicator, but it's already in bypass mode when you see that.My settings are 12:00 for input, output, and attack, 3:00 for release, and 4:1 ratio. My low E string hit hard will almost light up all the LEDS, the A string not so much, and the D and E hardly at all, so mostly it stops the E from overpowering the rest of the strings. When played softly I don't hit the limit so my soft dynamic range is still accessible for expressiveness o soft parts, and cleans me up a bit on the loud ones. I love this pedal and won't play without it now. Wish I had bought it years ago.