Any way you push it, any way you pull it it sounds great. There's a reason why these cost as much as they do. They sounds great, are built to last and have been used by professionals for 50 years.

I love these equs they sound great the reason for four stars instead of five is because I bought two and one of them came in DOA and had me questioning in the quality built because I recently bought API high and low pass filter 500 series and one of the two of those was broke so I'm not sure what's going on here with that being said after both the units got replaced now they sound great but still brings up some concerns on quality control

If you're going to pick an outboard EQ for your arsenal, this should be your first one. Amazingly musical and stunning in how clear and rich it is on every source. It has a crazy powerful low end and arguably one of the best mid-range character tones out there (yes, the highs are beautiful too). The build quality is superb - solid aluminum knobs and every setting is detented for easy recall. It's one of the more pricey EQ's for the 500 series but worth every penny. I can't wait to get my second one!

This is my second favorite EQ. The API550B can be a fantastic surgical tool. It can cut without making your sources sound hollowed out, and it can boost to bring things forward without over dominating.

Been using these at studios for years and always wanted one for my own. Sounds great, easy to use, repeatable settings. Just get it, you'll use it on everything.

I really didn't want to spend this much money on an eq when there are so many eq's out there. I heard it was great so finally just got it any way, thinking by the best and don't look back. I won't! This is the most musical eq I've ever used. It it is so detailed and instead of just boosting frequencies you like, it is like musical surgery getting rid of the nasties in your track. Used in conjunction with a good preamp (I chose the 512c) you can get your microphones dialed in and sounding so wonderful with just the details you want. This unit give me the control on the way into my DAW so that I don't have to do much if any eq'ing in software. I've used it with different mics, and it brings out the greatness in all of them. I will never sell this eq, it's just that good.

Let's face it people, API has been the "go to" people for great professional sound since before I started giging. I'm happy that other companies are producing 500 series products with success, but it's not API. I've been playing off api products since the early 90's in studios and have had great success with these units. I have two of these beauties in my lunchbox that I use for my bass stack (you read it right) for live sound. Don't be intimidated by the looks or price. These units are very easy to set, they sound so wonderful and once you play off this you will be chasing this sound untill you buy a pair! I know because I did. I chased this sound to no avail. As far as price goes my bass stack sounds like God and I know it. I do not need to improve my sound anymore or look for other products that claim they do just as good if not better. When you get a bassist that loves thier sound as much as I do it's just the right thing to do at any price. I will play through these for the rest of my life and will never have any regretts.