The equally lovely @Osiris put me on to optical compression. I knew very little about compression at all really but after a few hours chat and some demos he saved me £££s and a lot of frustration by calmly and patiently explaining optical compression until I pretended I understood him. I began the hunt for an optical compressor and very luckily, @Osiris' first (I think) recommendation was the Effectrode PC-2A. I play in an acoustic duo, I play fretted and fretless basses built by our own resident genius @Jabba_the_gut. TBH I'm still not really sure what the hell the compressor is doing, really, I just know there is something missing when it's not on. @Osiris can define in technical/science terms what it does but as far as an description as to exact changes in tone... I dunno. I turn the peak and gain knobs down so I cannot 'hear' any tonal change but still it's quietly doing something mysterious that I can't do without. It is good with the fretted bass but, lord, with the fretless... I play through the compressor and a preamp straight into a QSC powered speaker, the PC-2A adds this organic warmth that it really is difficult to define, which is why I'm going round in circles repeating myself. I wouldn't play either bass without it but for fretless it's a must have.