I've just spent a few hours listening to compressors and here's my take on them.
1. Floor noise:
With those three, the Cali is most silent and the Keeley is the loudest. None of them make noise in a disturbing way and all are well within the expected parameters, but the Cali is a clear winner.
2. Controls:
The Keeley only has three knobs which makes is easiest to set up. No worrying about a HPF sidechain and attack/release times. Just set the amount of compression and where it should begin. The MXR is hardest to set because there is that tiny fraction of a thought of merely touching the knob that already covers the distance between too much and too little. The good bit is that those knobs are very stiff and when you found your setting, they stay like that through packinng up your pedalboard, transporting it and setting it up again. The Cali has a bigger range of a sweet spot on those knobs. The pots just ooze quality when you twist them. I like how they made attack and release a single knob where you can find your preferred position quickly.
3. Seeing what's going on:
The MXR has a LED meter that tells you how much gain reduction is actually happening.
The Keeley has two LEDs, where one is a bit redundant because the other one will tell you all you need to know.
The Cali has that big light which pulses when you pump notes hard. I guess it's a matter of preference but all pedals tell you what's going on. The MXR gives you the most detail while the Cali does it in the most elegant way.
I owned an Aguilar TLC once and that had no visual way of telling you what it does and that made setting it up properly a nightmare for me.
4. Finally - The sound:
The Keeley IS the most transparent. It really behaves like a limiter. Set your amount (and you all were right, I was using way too much) and your spikes will be gone, the volume levels even out but the sound is not really touched. The MXR adds a little of color to the whole process, but it also is rather clean. When you compress hard, it gets a little harsh on the ears and lower notes have a tendency to distort or fart out.
The Cali gets you a fat, warm and soft tone. When you play hard, the attack is a bit softer and when it lets go, there is also a rounded off edge to the character. I don't think that this will suit players that favor the bridge pickup and use fresh rounds with a pick, but I have no such bass handy to test that thesis. I'm playing with boosted lows and a six string J style bass with the neck PU on full and the bridge PU turned up just enough to cancel the single coil hum, strung with flats, and the described character of the compression suits that style quite well.
With the Ratio and Att/Rel knobs set around 11 o'clock and the HPF knob set around 1 o'clock, I have the comp activating mostly when I play the E, A and D strings between 3rd and 9th fret, where the sound has the most beefy content.
It might be already quite clear between the lines, but there is a favorite pedal for me here.
I should write favourite, because it's made in the UK. I set out looking for a comp that's transparent and learned that I like it when it colours my sound, as long as I like the colour.
I'll keep that Cali, it makes me grin.
