Empress Effects Compressor Review – Best Studio Grade Compression Pedal?


The Canadian pedal gurus at Empress Effects are well-known for making exceptional products, a couple of their diverse offerings being the Vintage Modified Superdelay, a digital delay pedal of high regard, and the Empress Effects Heavy, a beastly extreme metal distortion pedal. Attaining to similar top tier build quality, the Empress Compressor is their take on a fully-featured, studio-grade guitar compressor pedal. It’s an FET compressor (think of rack mount compressors in the Urei 1176 vein) similar in design to Empress Effects’ own ECM-519 Compressor (a 500 Series module that expands upon the pedal). It also has a few surprises in its arsenal that set it apart from your run-of-the-mill compression pedal.

The Empress Compressor is an exceptionally well-rounded little unit feature-wise, offering a lot of possibilities beyond the OTA (Operational Transconductance Amplifier) based 2-knob compressors of old. It provides deep control over your compression with Attack, Release, & Input (similar to threshold) knobs and offers 3 different Ratio settings for mild to heavier compression. It even has a dedicated Mix knob for true “New York” style parallel compression. Surprisingly, the Empress Compressor also features a dedicated Sidechain TRS input for external fine-tuning of your compression via an EQ or filter; or you can feed an external audio source into the Sidechain to trigger the compressor. Handy LEDs for Metering let you monitor the gain reduction, input, or both at once.


All-in-all, the pedal looks very promising. Here’s a deeper feature rundown before we dig into our Empress Compressor review.


  • All Analog Signal Path – no digitals in here!
  • Extremely Transparent – Add dynamic control without altering the original tone of your instrument
  • 3 Compression Ratios – 2:1, 4:1 and 10:1 ratios offer lots of flexibility
  • Attack and Release Control – allows for ultimate control over the compression characteristics
  • Mix – Blend uncompressed signal in with the compressed signal for parallel compression, New York Style!
  • Metering – Meter either gain reduction, input, or both.
  • True Display LEDs – Bright multi-color LEDs always let you know what the Compressor is doing.
  • Bass – Works great on bass!
  • True Bypass – The Empress Compressor employs true bypass, so you can be sure that it’s not affecting the signal when disengaged.
  • Small Size – The enclosure measures approximately 4.5″ by 3.5″ by 1.5″, which is delightfully small when considering all the features packed into this unit.
  • Beautiful Case – It has a sparkle you can’t deny!
  • Powered by 9-18VDC power adapter (current draw: 100mA).

Visit Empress Effects for more info about the Empress Compressor.

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Sound & Performance:

The Empress Compressor evokes a sense of pristine sound quality from the moment you engage the pedal. It was intended to be as transparent as possible and delivers on that promise. If you’ve had issues with Ross style compressors that add too much of their own character to your overall sound, you’ll be pleased with how this pedal preserves your guitar’s tone. And it’s pretty quiet, too, which can make or break a compression pedal when it comes to studio grade performance.

The Input is the key to determining how much compression is applied to your guitar signal. It functions similarly to a threshold style control, but instead of simply adjusting a volume threshold, it increases the input level going into the compression circuit. At extreme levels you might notice a hint of saturation but without the added color that comes from transformer-equipped FET compressors. The Empress Compressor retains signal integrity even when applying massive amounts of compression.

Empress-Effects-Compressor-Review-Best-Studio-Grade-Compression-Pedal-03Generally, you’ll stay with the lighter 2:1 or 4:1 Ratios for mild compression amounts and maybe kick it up to 10:1 if you’re going for some heavy country-style twang. The 2:1 setting is great for barely there compression; it’s mainly for nearly unnoticeable compression that just catches stray peaks here and there. The 4:1 setting is still transparent and unimposing while covering basic compression needs. It’s a solid default setting for evening out your overall level without losing too much dynamic range. The 10:1 Ratio gives you a more squashed sound that isn’t quite as extreme as limiting but still more than adequate for heavier squeezing. Of course, you can crank the Input on 10:1 and significantly flatten your signal if you have the twisted urge to do so.

Empress-Effects-Compressor-Review-Best-Studio-Grade-Compression-Pedal-04I typically appreciate having Attack & Release controls on a compressor, and they’re especially useful when you have such an accurate array of Gain Reduction LEDs like the Empress Compressor’s Metering provides. The Attack knob goes from an insanely fast 50us (microseconds) to 50ms. The Release ranges from 50ms to 1 second. This is well within the musical range for most purposes, and even if you’re not too experienced setting attack and release times, the visual Meter indicator will help you achieve a solid sound for your needs. (I generally find Attack settings around the 10 o’clock area to be a good starting point. Fully counter-clockwise values choke pretty hard. Then set the Release to taste.)

The Mix knob blends the wet (compressed) and dry (uncompressed) signals for parallel compression. While this “New York” style of compression was typically reserved for studio use on percussion tracks, it’s been finding it’s way into guitar pedals more frequently. Essentially, the Empress Compressor’s Mix control allows you to achieve a fatter, less noticeably compressed signal with added sustain while ensuring that the original character of your source material (i.e. guitar) remains intact. That’s especially apparent with this pedal as the compression is already more transparent than most. It’s especially fun to crank up an extremely compressed signal (try 10:1 with a high Input!) and blend that in with your dry guitar sound. Extra versatility for the win.

Sidechain Compression

Empress-Effects-Compressor-Review-Best-Studio-Grade-Compression-Pedal-05Okay, this is a pretty big deal as the Empress Compressor is currently the only pedal I know of that offers sidechain compression which is facilitated by a dedicated jack on the left side of the pedal. The jack is actually a TRS input. One of the tricks this allows is to let you split your signal into another effect, like say, an EQ or a high pass filter, so that you can have the compression only be triggered by certain frequencies. Bass players in particular may find use for that handy feature.

You can also use a dedicated audio source to control the compressor. One technique is to use a kick drum to duck your guitar or bass whenever it hits. This helps to keep low-end frequencies from conflicting and mudding up your mix. This technique is very popular in certain styles electronic dance music, and now similar rhythmic pumping effects can be achieved in real-time by feeding your drummer’s kick into the Empress Compressor. You can even experiment with running a sidechain kick from a DAW (Digital Audio Workstation) like Ableton Live into the pedal’s sidechain input. It’s a lot of fun. I’m also waiting to see a band use the Empress Compressor to split their singer’s live vocal to the sidechain to apply a little ducking to that lead guitarist who’s always noodling through song verses. A sidechain input happens to be my single most wanted feature in any so-called “studio style” compression pedal, and I’m glad the Empress Compressor finally fills this void.


Another nice little touch are the 3 options for LED metering that the Empress Compressor provides: Input, Gain Reduction, & Both. Gain Reduction is most useful, but it’s nice to set it to Both as well to see how the compression responds to the input signal. The green Input LEDs collide with the red Gain Reduction LEDS for yellowish orange hues when they overlap. And let’s face it… it just plain looks cool. Style counts for something, right?

The only minor thing I could wish for with this pedal would be a variable Ratio knob. The default settings are fine for most uses. It’s only when applying the sidechain compression function that I sometimes want to vary the compression with a Ratio setting somewhere between 4:1 & 10:1. But this is a minor concern as it’s a situation that most guitarists will never find themselves in. Besides, you can also adjust the volume of the audio source you’re feeding into the Sidechain beforehand. The 2 Auto Modes from the later released ECM-519 might have been handy to those who’d rather not fiddle with Attack & Release controls. But this pedal is very easy to dial in, so that doesn’t hurt it either. Other than those possibilities, this pedal is perfect in every other way and one of the best guitar compression pedals around.

The Empress Compressor is another standout pedal from Empress Effects. Let’s see the final result.



The Empress Effects Compressor is among the best studio grade compression pedals available, living up to its claims of pristine transparency and versatile functionality. The Mix knob offers parallel compression for blending in compression with your dry signal. The Metering LEDs give you an accurate visual cue of what’s happening. The Empress Compressor is also the only true studio grade compression pedal to offer a dedicated Sidechain input, certain to be put to creative use by some musicians. If your old 2-knob compressor isn’t cutting it anymore, this beautiful FET comp may be what you’re looking for. It’s an all-around outstanding pedal in all regards.

That concludes our Empress Effects Compressor review. Thanks for reading.


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Keeley Electronics Compressor Pro Review – Best Studio Grade Compression Pedal?


Keeley Electronics’ most famous pedal is the C4 Compressor, a Ross Compressor inspired gem that is still one of the best compressor pedals available today. Not content with having just one outstanding pedal in that category, Keeley released the GC-2 Limiting Amplifier, a dbx 160 style pedal that offers studio flavored compression/limiting. Now comes the Keeley Electronics Compressor Pro, the pinnacle of Robert Keeley’s long-standing experience making quality compression pedals. And this is a pedal that more than lives up to the expectations I had for it.

The Ultimate Keeley Compressor Has Arrived

Keeley-Electronics-Compressor-Pro-Review-Best-Studio-Grade-Compression-Pedal-02Keeley Electronics first showed the Compressor Pro and Winter NAMM 2014. While I knew this would be a pedal to keep an eye on, it would be yet another long year before Keeley would show it again at Winter NAMM 2015 in near-complete form. It was finally released shortly after, and now Keeley Electronics is making compression pedal history all over again.

The Compressor Pro shouldn’t be mistaken as simply an upgraded “Pro” version of Keeley’s original C4 Compressor as it actually has more in common with the GC-2 but with a greatly increased feature-set. The Compressor Pro features the same THAT Corp. 4320 chip, 1:1 through Infinity:1 Ratio range, and similar Gain & Threshold controls to the GC-2. In addition to the GC-2’s default Hard Knee setting, the Compressor Pro also offers a Soft Knee option for smoother compression. There are also dedicated Attack & Release controls and a convenient Auto mode for allowing the Attack & Release to respond naturally to your playing without being affected by the values of their respective knobs. A handy row of Gain Reduction LED’s and a Threshold indicator LED also gives you a visual indication of what’s going on.


Warning: Playing this Compressor Pro
will cause ambient tones,
perfectly mastered tracks,
and addiction to Keeley gear.

You’ve been warned!

A summary of specs and features is below. Then onward to our Keeley Electronics Compressor Pro review to find out if it’s the best compression pedal around.


  • Device controls for Threshold, Ratio, Attack, Release, Gain, Knee, & Auto.
  • Compression LED Display – 7 Segment LED display for fast and accurate metering of compression and gain reduction.  Gain Reduction Levels of -1dB to -20dB are indicated.
  • Threshold LED Indicator – Bi-Color LED to indicate when compression is initiated and released.
  • Exact RMS Analysis (ERA) – Senses the true RMS value of the input program material such as your guitar, bass or drum machine.
  • Hard/Soft Knee Compression – Hard Compression for limiting or adding sustain, soft knee or Komfort Kompression for gentle compression, keeping performances lively and natural sounding without potential phase issues in parallel, or blending style compression.
  • Auto Mode – Program dependent Attack and Release times.  Set to Auto ON for worry-free performance and automatic Attack and Release times.
  • True-Bypass – No tone or signal loss when OFF.

Visit Keeley Electronics for more info about the Compressor Pro.

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Sound & Performance:

While there have been a few times a pedal I was excited about let me down, this is one of those situations where a pedal met and surpassed my expectations. The first thing I noticed about Keeley’s GC-2 is just as apparent here, the Compressor Pro is incredibly transparent. While old CA3080/LM13700 based Ross/Dyna Comp style compressors (including the C4 Compressor for that matter) seem to add a little something to your tone – and that’s arguably part of their charm – the Compressor Pro is on par with the most transparent compression pedals available. That’s due in part to being a VCA (Voltage Controlled Amplifier) compressor which are generally known for their quieter, more transparent performance when compared to the aforementioned Ross/Dyna Comp/C4 style of OTA (Operational Transconductance Amplifier) compressor. Then there’s also the fact that Keeley went all out with a THAT Corp. 4320 chip and other premium components. But beyond the compression type and spec-sheet hype, the bottom line is that the Compressor Pro is more comparable to a studio grade compressor in terms of sound quality (and features) than nearly any other compression pedal out there.

Keeley-Electronics-Compressor-Pro-Review-Best-Studio-Grade-Compression-Pedal-04One of the key things I like about the Compressor Pro are its Ratio options as I wish more guitar pedals would include a full Ratio range. Most of the knob’s range is dedicated to more subtle Ratios with fully counterclockwise to noon ranging from 1:1 (no compression) to a still moderate 4:1. Once you cross noon you’ll reach 5:1, 10:1, and then jump to Infinity:1 for extreme compression and limiting. As I mentioned before, the Compressor Pro is all about transparency. (That should be the key buzz word you get out of this review: “transparency”.) Even at the heaviest “brick-wall” setting of Infinity:1, the Compressor Pro doesn’t crush your tone into oblivion when it clamps down. For most front-of-signal-chain purposes though, most guitarists will probably have the Ratio knob set somewhere to the left side of half-way for subtle compression and around noon or a little higher for moderate to slightly heavier amounts of compression. If you need heavier squash for chicken pickin’, the 10:1 Ratio has you covered.

Keeley-Electronics-Compressor-Pro-Review-Best-Studio-Grade-Compression-Pedal-05The Threshold knob determines the volume level your signal must exceed before the compression kicks in. You’ll get a visual indication from the Threshold LED when that happens. You’ll also see the row of 7 red Compression LEDs illuminating to show you how much gain reduction is occurring. These visual indicators will be especially beneficial for those new to using guitar compressor pedals. Even advanced compression users will benefit because the rhythm of the lights will help you set your Attack & Release times with greater confidence. I personally like having the combination of audio & visual feedback when using more complex compressors.

Keeley-Electronics-Compressor-Pro-Review-Best-Studio-Grade-Compression-Pedal-06Having independent Attack & Release controls, the Compressor Pro is already more in line with a studio rack compressor than your typical guitar pedal. What’s more is that the Auto switch lets you bypass the knobs’ settings for a responsive attack and release that varies depending on the input source. Basically, if my understanding serves me correctly, the compression will vary depending on the dynamics of your playing for a very responsive and musical feel. You’ll notice the Compressor Pro responding differently when you’re playing single staccato notes or letting chords ring out. I spent plenty of time adjusting the Attack & Release and switching to Auto mode while monitoring the gain reduction LEDs and listening to how the pedal responded. Simply put, Auto mode sounds great and will most likely produce better results for your playing than all but the most experienced compression users would dial in via the Attack & Release knobs. For many guitarists I imagine this becoming their default setting regardless of how competent they are at dialing in their attack and release times.

The Knee switch is an essential addition to attenuating your compression for a variety of uses. Basically, a soft knee is curve for a more gradual attack while the hard knee is abrupt. For guitarists, the Soft Knee will typically be your setting of choice as this yields a smoother, more natural compression curve. Bassists may prefer the Hard Knee when trying to achieve a tighter, more consistent level. The Hard Knee setting is also what you’ll most likely use when using the Compressor Pro for hard limiting duties. Also, if you’re using fast Attack times in general and are really trying to tame any unruly transients or volume spikes, the Hard Knee may be what you need.

Compressor Pro vs GC-2 vs 4-Knob Compressor


Compressor Pro vs C4

And that brings me to the Compressor Pro vs GC-2 Limiting Amplifier vs C4 4-Knob Compressor comparison. Basically, Keeley’s classic 4-Knob Compressor is a pedal you’d put in the front of your chain for attenuating your signal before it hits anything else. While it’s a pretty clean compressor that preserves the nature of your instrument, it does enhance your sound with subtle qualities of its own, more noticeable at higher Sustain settings. The Compressor Pro on the other hand, does not; it keeps the sound of your guitar essentially untouched. Again, it’s about “transparency”. While the C4 has its long-standing reputation as a pedal used by many professional guitarists and is arguably still quite transparent in its own right (especially when compared to lesser Ross influenced pedals), the Compressor Pro is simply truer to its namesake in that it is more akin to a rack-mounted unit than a stompbox. If you want dynamic control and sonic presence without a hint of coloration, the Compressor Pro is the winner.

Compressor Pro vs GC-2

The GC-2 Limiting Amplifier is an anomaly as there aren’t too many guitar pedals that have a focus on limiting (although the terms compression and limiting are similar and often interchangeable). Essentially, the GC-2 is more like a Compressor Pro Lite as it is based off the same THAT Corp. 4320 chip and has similar limiting abilities. The GC-2 also compresses similarly to the Compressor Pro’s Auto mode. Now I absolutely love the GC-2 as an end-of-chain pedal for its brick-wall limiting. If you specifically need a pedal for that purpose alone, the GC-2 is still a great choice as the extra Attack/Release controls and Soft Knee option may not be as necessary to you. But if you want the versatility of having an ultra-transparent and more versatile front-of-chain compressor OR an end-of-chain limiter, the Compressor Pro covers both duties. Again, the C-Pro wins.

There’s not really much else to say here. The Compressor Pro sounds outstanding and features almost everything you could possibly want in a pedal. The only thing I could wish for is a side-chain input as that would make it even more ideal in the studio (or in my Ableton Live automated guitar rig as I feed audio signals into an external side-chained compressor during performances). But the Compressor Pro greatly exceeds the utility, sound quality, and feature set of most compression pedals while remaining relatively compact in size and should be one of your top considerations if you’re looking for an outstanding compressor for your pedalboard. The Auto mode in particular is so good that I almost wish Keeley would make yet another 3-knob compressor (Keeley Compressor Pro Compact anyone?) that just has Gain, Ratio, & Threshold knobs (like the GC-2) and a Knee switch. For those who just leave Auto mode on all the time, a Compressor Pro “Lite” would be yet another enticing Keeley compression pedal. But the extra versatility of the Compressor Pro makes it one of the best all-around compression pedals out there.

The Compressor Pro proves that Keeley Electronics is still a force to be reckoned with in stompbox compression.



The Keeley Electronics Compressor Pro is a supremely transparent studio-grade compression stompbox. This pedal is hard to beat when it comes to transparent pedal compression. The Compressor Pro also has a complete range of studio-style controls including an innovative Auto mode for greater ease of use. The Hard/Soft Knee options and extended Ratio settings also make the Compressor Pro equally well suited for standard guitar compression or hard limiting duties. I can also imagine some engineers finding handy use for this pedal in the studio for a wide range of compression duties. Not only does the Compressor Pro get my vote as the best pedal Keeley Electronics has released to date, but it’s one of the best compression pedals ever created. Try it and hear for yourself.

That concludes our Keeley Electronics Compressor Pro review. Thanks for reading.


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