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The Ultimate Guide To Guitar Compressor Pedals
Compressors aren’t sexy. They’re not on the “yeah I guess I’ll get one” level of tuners, but they’re certainly not dreamscape emulating reverbs or super rare overdrives that cost a lot of money.
But if you walk into a studio, one of the first things the engineer is going to try and geek out over is their compressors. And then they’re probably going to send your guitar through one, or use a good plug in during mixing.
Why the disconnect?
When I have nothing better to do with my time (so often) I wonder why we’re OK using compression in the studio but not on our pedal boards. Sure the types of compressors have some differences, but how can something that has the same name be on such opposite sides of the “need” spectrum?
How Do Compressors Work?
Compression, by definition, means to “press together” or “force into less space”. If you’ve ever worn compression socks, compression sleeves, or a compression shirt, you know the literal and physical meaning of forcing something into less space.
In our context, compressors compress an audio signal into a more finite space. Take a look at the below image. It shows an audio signal moving along at various wave lengths. Some are really quiet (low) and sound are louder (high).
This is just the nature of your signal. Now take a look at the parallel horizontal lines at the top and the bottom. These are the threshold lines. We’ll talk more about threshold a little later but for now just remember the visual.
When you increase the threshold knob on a compression pedal, you’re bringing these two lines closer together. Consequently, you’re also “squashing” the audio signal. So the lowest (quietest) part of the signal gets raised up, and at the same time the highest (loudest) part of the signal gets brought down.
Most compressors will have a gain knob to make up for the volume drop you’ll inevitably have.
How To Use A Compressor
Ron Swanson would tell you to use it however you want to, it’s a free country after all.
This same answer is how I’d recommend using any pedal. It’s your music and your art, make it how you want to.
But if you’re looking for some jumping off points, there are a few common ways they’re used.
Country Pickers
Take a listen to any Alan Jackson era Country song with a guitar solo and you’ll hear this in action. You can actually go back pretty far into the history of country music and hear it, but Alan Jackson is the man and you should listen to his tunes!
What’s fascinating about the way Country players use compressors is how they use them in a tonal way as much as they do in a functional way. The tight squeeze the compressor puts on the tone kills your pick attack and squashes your harmonic frequencies into something much smaller.
That tone is really cool when used correctly.
Country players didn't traditionally use much (if any) gain. Since they’re soloing with a crystal clear clean tone, they need the compression to add sustain. The more overdrive you have the less you’ll need help with sustain. But the less overdrive you have, the more help you’ll need with sustain.
Which perfectly segues into the next use.
Funky Strumming
Funk is another mostly clean tone based genre. And those players often have a hard time being heard in a mix, especially with the "in between” setting on Strats.
Compressors add just enough oomph to bring the guitar out a little more.
Clean Picking
Not to be confused with Country Picking! I’m talking about Midwest Emo type of clean playing. Something that can help your softly picked extended chords get brought up a little and pair better with the louder strummed rhythms.
If you set your compressor just right you can help bring these softer parts up without changing your tone.
Solos
I’m not talking Revv Red Channel solos, I'm talking light gain solos. Gain naturally adds sustain to your signal. But if you’re playing Pink Floyd solos with low output pickups and light gain, you might need more sustain.
So a lot of people will use a compressor for this. When they do, it’s barely noticeable. You won't hear it or feel it in the tone. But you will have just enough added sustain to let those big step and a half bends ring out.
Where To Put Compressors In Your Signal Chain
This is another topic that deserves and will get its own article. In that article I'm going to give you the Ron Swanson treatment and encourage you to experiment. However, one thing that you wont find much success in is putting your compressor after your overdrives.
Compressors should always be before your overdrives.
Remember, compressors are going to bring up quiet things. So that tiny bit of hiss or hum your overdrive is naturally creating is going to be amplified as soon as you turn that compressor on.
I think there’s value in hearing these things so you should try it just to see what I mean.
What Do The Controls On Compression Pedals Do?
Different compressors may have different options, but these are pretty universal across compressors. We’ll first look at the big three controls you’ll find on pretty much all compression pedals, and one that’s not always included but it's vital to understand.
Threshold
Let’s start with threshold since we’ve already talked about it. Threshold is those two horizontal lines on either side of your signal. When you turn the threshold knob on your pedal up you’re bringing those lines closer together. Like the walls in the famous trash compactor scene in Star Wars.
With the threshold all the way off (or the pedal not turned on) those lines aren’t there.
This is the primary function of the compressor. The quiet parts get louder and the louder parts get a little quieter. If the threshold is turned all the way up the space between the lines is very small. A hard pick and a soft pick won’t have much of a different sound.
Attack and Release
The attack is how quickly the pedal responds to your signal, or how quickly the threshold comes in to squish your signal. The quickness varies by pedal and your settings will vary by application, but it can range up to 300ms. If you want your tone to be more nuanced you would set it to a slower attack.
Release is the same idea but in reverse. It’s how quickly (or slowly) your signal returns from the threshold once you stop playing. How quickly the compressor stops doing its job. Slow attack and release will retain much of the nuance in your tone. Quick attack and release will not.
Gain/Volume/Make Up Gain
This along with the previous two are what you’ll see on most compression pedals. Since there is a certain level of bringing your...level down, you need some makeup gain to bring your overall volume up. Gain in this context doesn’t refer to clipping, but clean volume. It’s symmetrical in nature, so it turns up all of the frequencies it received equally.
Ratio
The ratio setting is mostly reserved for studio compressors, and is the most misunderstood part of compression. It’s rare to find on guitar pedals, but it’s an integral part of compression as a whole.
The ratios start at 2:1 (two to one), and can go infinitely mathematically. Normally you’ll see this stop at 25:1 and technically anything past 10:1 is considered a limiter.
Here’s how it works. Let’s take 2:1, the lowest setting (except for 1:1 which is no compression...). For every 2dB that goes over the threshold, only 1dB will sound out. In 4:1 for every 4dB that goes over the threshold, only 1dB will come through.
The higher the first number is, the more aggressive the compression is going to be. And the stronger the compression, the quieter your end signal will be and the more makeup gain you’ll need.
Amp Compression
Amp compression occurs when you push an amp past it’s headroom. It can’t get any louder than it’s at. When you try to go past that point it 1) distorts and 2) starts to compress.
If you have a power attenuator, or the ability to crank a low watt amp up, try this experiment.
Crank the volume of your amp little by little. On most low watt amps once you get 80% there you’ll get some natural overdrive. As you turn the volume up you’ll notice more gain than volume, and you should start to hear your amp compress a little.
When your amp is at high noon, you can lightly strum and strum hard and notice a lot of difference in the dynamics and volume.
When it’s cranked though, it doesn’t have any more room for volume. That’s the upper limit of the threshold.
Now, put an overdrive in front of the cranked amp. Gain all the down, tone wherever, and start to turn up the level. You’re not going to get any more volume, because your amp is still at its max limit. You’ll get more gain and you’ll hear the amp compress everything you play.
I do want to point out that gain and compression are two different things. However, on amps with smaller rectifiers/lower headroom as your output reaches its limit the amp will clip (distort) and compress at the same time.
What Compression Pedals Are Good?
There are a TON of compression pedals available, but here are a few that are popular among guitarists.
Keeley Compressor Plus
Robert Keeley is one of the most respected pedal builders, and his compressors are no exception. If you want a bells and whistles compressor the Compressor Plus is a great option.
MXR Dyna Comp
The MXR Dyna Comp is as simple as it is iconic. With just two knobs it’s a perfect compressor for people who want to quickly set their pedal and start playing.
JHS Pulp N Peel
I can’t talk about compressors without talking about JHS. The Pulp N Peel is based on the Dan Armstrong Orange Squeezer. Like the Keeley, it has a lot of bells and whistles for the guitarists who like to fiddle with settings.
Whatever You Pick, Just Get One!
If you made it this far I’m probably preaching to the choir at this point, but it’s worth saying. Every guitarist should own a compressor. I think most people either hear it only in country music and assume that’s all it does, or gets one and aren’t quite sure how to use it.
There are a ton of ways to use them without them impacting your tone, and a lot of tutorials on the interwebs. So hopefully this has demystified them a little and you’re inspired to go out and buy one.
And then after that you can get back to buying your 14th delay.