If there is one effect out there than seems to cause guitarists the most confusion, it’s definitely the compressor. I read plenty of people on the Seymour Duncan Forums asking about them. What do they do? Do I need one? What do the controls do? Is it even working?
The compressor is one of the most useful tools available to a guitarist, or any musician for that matter. Unfortunately it’s also one of the most misunderstood devices on the planet. Perhaps it’s because the effect isn’t in-your-face obvious, like distortion, phase, or delay. It could also be the mysterious control names. Attack? Release? Is there a crazed wild animal inside the pedal?
It doesn’t have to be confusing. Once you learn how a compressor works and what the controls do, it’s easy to get yours to play nice in your rig. I’ll start by explaining the basics, then getting into what all those oddly-named knobs do.
A compressor works by adjusting the volume level of your guitar signal. Its purpose is to even out your dynamics, making loud parts quieter, and quiet parts louder. You could think of a compressor as a steam roller that squashes your bumpy signal down to a flat, even level. There’s a bit more to it than that, of course, but that’s basically what’s happening.
The notes produced by a guitar have two components to them: the initial pick attack, and the sustaining string vibration. The pick attack is the short, percussive noise of the pick or finger plucking the string, and it creates a noticeable spike in volume. The sustaining vibration isn’t as loud as the pick attack, but unless you’re doing some crazy palm muting it will last a lot longer. Quite often we wish that our pick attack wasn’t so spiky and that the vibrating string portion of the note was louder and lasted longer. A compressor can make this wish come true. It will soften the effect of the pick attack, and increase the level of the vibrating string. The result is a signal that is a lot smoother, less plucky, and more sustaining.
Compression can be used for many things in the guitar world: flattening pick attack, increasing sustain, peak limiting, boosting, or all of the above. The key to success with a comp is to understand how to dial it in.
There are many types of compressor out there with many different control layouts. I am going to cover the most common compressor controls here. If your compressor doesn’t have the control, you can assume that the circuit has it set to a specific default value. Most guitar compressor pedals tend to be pretty light on controls compared to a studio compressor, but rest assured they are performing the same function.
Level: Also might be called “Gain” or “Volume”. This, of course, adjusts the level of the signal either going into, or out of the compressor. For most guitar compressors, this will be a post-compression control, which means it is increasing or decreasing the volume of the compressed signal. Use it to set the level however you like.
Threshold: You probably won’t see this on many guitar compressors (or it might be called something else), but it definitely exists behind the scenes. The threshold is the decibel level at which the compressor kicks in. If a sound exceeds that level, the compressor will compress it. Sounds below the threshold will be left intact, with a few exceptions (see “Release” below).
Ratio: Also might be called “Compression.” The compression ratio determines how much compression is applied. Higher ratios make for stronger compression, while lower ratios are more subtle and “natural” sounding.
Attack: Don’t worry, nobody is going to get hurt! The attack control, if you have one, sets how quickly the compressor works. A fast attack means that the compressor will kick in as soon as the signal exceeds the threshold. Slower attack means that there will be a bit of a lag before compression happens. If you want the pick attack to be smashed flat, use a fast attack. If you want a more natural sound with some pick attack sneaking through, use a slow attack setting.
Release: This control is the opposite of Attack: it sets how long it takes the compressor to “let go” of the signal after it goes below the threshold. This control is often called “Sustain” on a guitar compressor because it has the nice side effect of increasing sustain when it’s set high. If you want your notes to ring out longer, turn this up.
Tone: This is sometimes a knob, sometimes a switch, and quite often completely absent. It allows you to adjust the frequency range that the compressor works with. This can be handy if you don’t want the compressor to touch the highs or the lows.
Blend: Some comps allow you to blend a bit (or a lot) of the dry signal back in. This is a nice way to make your compressed tone sound a bit more subtle or natural. You won’t find this on many compressors, but it can be a very cool feature if you have it. The Seymour Duncan Double Back Compressor accomplishes this via the “Double Back” knob. It even allows you to taylor the frequency response of the dry blended signal. Check it out in action in this video demo:
Hopefully you got through this with a better understanding of these very cool and very helpful effects. If you have a compressor, please let me know in the comments which one it is, and how you have it dialed in. Is your comp lovingly hugging your signal, or is it squeezing the life out of your tone?