I am not a bassist, but record a lot of electric bass at home. This pedal really helps with getting my performance right at the source. I also like using it to compress lead notes for a mild Holdsworth-ish sound and sustaining cleaner electric guitar sounds. I have been looking for a compressor that operates more like a studio compressor for a while and this is it.

There are two basic circuit types of compressor, a compression-limiter type and a more overt compression-sustainer type. The Pro unit is more a limiter type and is extremely transparent. It can be used later in the chain more like a mastering compressor. Set moderately you can't hardly tell it is on, till you switch it off. Pretty much every thing you have heard recorded is mastered through a slight limiter-compressor during final mix down and mastering. The Pro unit is a very useful multiple position compressor you can place to just polish the final tone more end of chain after gains or even in the loop. Or up front to just add that bit of thickening and leveling the compressor does. The Auto feature is just amazing. Most do not understand how to adjust release and attack, having the auto feature be able to detect and alter that without changing knobs is great and unique. Basically with compressors, less is more, keep the ratio about 4:1 at the highest for guitar, when attack goes up, release goes down and vise-versa. They are adusted in reverse tandem up and down, one goes up the other opposite. Part of the problem with players hating compressors is how they are adjusted. Add the soft or hard knee and it has it all. Those who hate overt compressors will love the Pro unit. If you are a country player that wants that overt squeeze (chicken pickin) and Ross/Dynacomp pedal like compression, this is probably not your best choice. But if you want a more subtle, transparent, studio quality compression-limiter this is just a great unit. It's been around a few years but still one of Keeley's flagship units.

I just received it today, from Sweetwater. It works good, but it is tiny. You would never know that from the Sweetwater pictures. Also, the two page instructions are written in tiny text. You almost need a magnifying glass to read them. Also, the four "rubber" discs for the bottom, are stick-on. It is tiny, the instruction text is tiny, and the bottom disks are stick-on, all for only $!

So, once upon a time, I didn't believe in the power of the pedal. I'm a bass player, and I believed that the best tone was a pure one, relying on the powerful pre-amps my active basses have in them and relying on my head for complete tonal control/shaping. I have learned, and, boy, am I glad that I did! This pedal is absolutely fantastic. I mean that in the most literal sense. The amount of tonal variance you can squeeze out of this puppy, while maintaining an even, professional sound is head spinning. I run this at the end of my loop, taking advantage of the limiting compression to send that perfect signal to my boogie machine. I run the MXR bass compression at the front of my chain for even more shaping/tonal control. What's different about the pedal from 85% of the other compression pedals I see on the market, is that it's a compression "LIMITER." Which is exactly what you need at the end of your pedal loop. It's called the "Pro," for a reason. This little box can give you the most professional sounding, even tone. I can't speak well enough about it. There's a terrific video floating about on Youtube that features Robert Keeley himself talking about this pedal and showing off its sonic capabilities. That video sold me on this pedal, and I'm absolutely happy that I stumbled upon it. If you're on this page, reading the reviews, don't over think it. BUY IT. You can thank me later!

Robert Keeley is the expert in compressors and this has all you will ever need. Being able to see when the compression kicks in is so essential. The compression is subtle but you can tell it's working. It's not like a Dynacomp although you can use the auto function to get close to that sound. Overall, it's worth the price.

I use this in a house of worship with very 'live' acoustics. Three things I love: 1. A fast attack eliminates the string noise from the bridge pickup in my Taylor, and takes the amplified sound of my Lowden to another level of warmth & clarity. 2. Using 4:1 soft knee compression tames the strident treble frequencies and aids in feedback suppression so that I can get full, round bass notes without having to notch them out with EQ. 3. The sum of all the parts is a full, string-to-string balanced acoustic sound: strummed or finger picked. I've been chasing this sound for 30 years and found it! Worth every penny.

Title says it all.

An all around great compressor that can be used in a lot of different ways.


There is lot of control with this thing, which is fantastic if you know how to use a compressor... Less so if you're not familiar with them, especially if you don't know how to set the attack and release.

The attack and release relationship is crucial to all styles of compression, whether it's super squashed or transparent. Spend some time with that relationship and it will shine.

Top loading inputs so you can put it side by side with other pedals, love it.

For being 9v it still has a ton of headroom and is quiet.
I compared it to my Origin Effects Cali76 CB and i couldn't hear any noise difference between the two.

The Keeley Compressor Pro is a highly versatile compressor in any situation or style of playing.

For those of you that know what a compressor can do after the distortion pedal (guitar knob volume cleanup), this does the trick. I wanted a "3rd" channel for my Mark 5 35. I use a distortion box that is well known for it's ability to clean up but needed to boost the volume of the clean up while taming the loudness of the cranked guitar. Works perfectly. Set it forget it. After some spending a bit of time with this, I was able to have the same setting used after the pedal even with the pedal off. Pure clean sounds have the extra bit of oomph without getting dirty.

Robert Keeley and company is a huge disappointment. I ordered a Keeley Compressor Pro and while I was waiting for it to arrive, I got on robertkeeley com I looked for technical data on the unit. There was little to be tendered, so I sent an email asking about input and output levels, input and output impedances, and the power-in specifications. It's now two weeks later and nothing from Keeley.

The unit arrived from Sweetwater, and I was immediately struck by the poor build quality. Poor finish on the paint job with blotches. Poorly machined metal case. This thing looks like a high school electronics project. The graphics don't line up with the hole punches for the knobs, so you can't even see where you have the knobs set. Hard to believe this thing sells for $... (and without the power supply to boot).

I bought this for my bass, but it works fantastic on my guitars as well. This is my first compressor limiter (I have a couple compressor sustainers) and the Keeley Compressor Pro is fantastic. It's versatile and sounds great. I was surprised at how great the auto attack/release function is. I highly recommend this compressor.

Great pedal enjoy it way more then even my Kealey 4 knob, let's face it everyone knows that pedal. It's a keeper, between both wet and dry and every other option you can obtain with an all in one, get it you will not be disappointed!

I've been playing guitar for over 40 years - live and in the studio; from 100W stacks and monster pedalboards to nothing more than a mic'ed 4W combo with compressor & volume pedal. Along the way, I've owned and used quite a few compressor pedals.

The Keeley Compressor Pro is, hands-down, the best compressor pedal I've used to date. It's dead quiet, accurate, very versatile, and doesn't kill your tone. The Threshold LED and Compression LED meter provide good visual feedback, too.

Those experienced with studio rackmount VCA, diode, and similar compressors, will feel right at home with the controls. In fact, the controls are more accurate than some studio compressors I've used. If you're not familiar with attack, release, etc., it's not rocket science. So a little time spent will go a long way to learning the nuances of the compressor. And, if you'd rather not mess with it, the "Auto" switch provides program-dependent control of attack & release.

What's more, Robert Keeley and crew are very customer-oriented, personable, and provide top-notch customer support. So, rest assured, you won't be left hanging out in the breeze, should you encounter a problem with the unit.

Lastly, I'm providing my feedback, based upon my unbiased, personal experience with this compressor, other Keeley pedals, and Robert Keeley Engineering. Something I believe the two previous reviewers can't say.

Most Transparent compression pedal I've ever owned.

a good starter comp for studio use.

Not a bad comp, not a great one either, but does keep levels in check well enough. Not too transparently though.
As it's a non tube based unit, it has some issues with fullness of tone/fidelity; but still sounds OK for the most part.
So from a comp point of view it works well. From a tonal perspective, less so I think.
The attack and release is less than transparent as well. Not ultra smooth in either direction imo.
I also have an Effectrode PC-2A comp which IS a vacuum tube output, and it seems a better comp all the way around, but the Keely has it merits in variance of applied compression curves, over the Effectrode.
If I had to choose, it would surely be the Effectrode. But the Keely what I'll use for practice, and save the tube in the Effectrode for performance needs. So the Keely can be a bit more economical perhaps, if you don't mind the attack/release being slightly visible.
That would be it's only better point I think.