I'm a long time compression lover/user. In fact, it's the only effect I'd keep if I had to pare down to just one. I've gone thru a few of them (not as many as some of you but a fair amount, to be sure), but I've never used one that had a sidechain or HPF built in. The only two that I'm aware of are the Empress and the Apex. The Empress comp has an input for sidechain and, as I've read, one can wire up a cap into a 1/4 slug and use the circuit as an HPF. The Apex only has the HPF option, and it's built-in on a variable pot. My question is: When and why would one want an HPF in a compressor? I understand that having the HPF causes the compressor to ignore the lowest frequencies and allows the comp to primarily react to the frequencies above whatever point you've set it to. But *why* someone would want that is what I'm wondering about. In my experience, it's the higher strings (and their corresponding frequencies) that I'm trying to get to pop out more... I'm never short on bass. So I compress my signal in order to bring the bassier notes down to a level that's more even with the higher ones. It seems to me that having an HPF in a comp would achieve the opposite effect - which is cool if that's what you're going for, but I've never played a bass that lacked in low end and needed to have only the db reduction in the highs. *shrug* I haven't been able to find a video that does a really good job of showing the difference between a traditional compressor and one that uses an HPF... plus, I suspect it's probably more of a "feel" thing than an audible thing, but as I said, I've never tried one. Can anybody provide some insight?