What is a Compressor in Music?

What is Compression?

Compression can be very confusing, but in its most basic sense, it makes loud noises quieter and quiet noises louder. By squashing the very loudest signals down, we’re able to bring up the level of the quieter noises to match. It’s what our ears do naturally, otherwise we wouldn’t be able to hear whispering and our eardrums would burst every time a noisy motorcycle rode past.

Compression is crucial in music, so you can clearly hear every part of the mix and don’t get deafened by any volume spikes. Without compression, you wouldn’t be able to mix music because the volume fluctuations of different instruments would make it impossible to get a good balance.

Studio Compressors

Alongside EQ, compression is the most important part of mixing and mastering music — it’s what allows each instrument to find its place in a balanced mix. But studio compressors can be very complicated, so we’re here to demystify some of the most common terms you’ll see.

Threshold

Threshold is simply the level at which your signal will start to compress. Everything below the threshold will remain uncompressed, and everything above it will have the compression applied.

Level/Gain

Sometimes referred to as “makeup gain”, this controls your overall volume. When a compressor is applied, it makes the loudest parts of the signal quieter, so to compensate, you add makeup gain to bring the volume back up, as well as making the quiet parts louder and more audible than before

Attack

This is the amount of time it takes for the compression to apply. A slow attack will allow your signal to pass uncompressed for a moment, allowing the initial transient through. Something like an MXR Dyna Comp pedal has a slow attack, making it great for guitarist who want to retain their dynamics while adding some extra sustain to their notes. While the 1176 Studio Compressor is known for its fast attack that will compress the front end of every note, which has the highest volume peak already.

Release

As you might have guessed, this is the opposite of attack. It determines how long a note is compressed for before it lets go — basically controlling the amount of sustain. A fast release will allow the signal to naturally decay quickly. This is especially important for drums, which are very percussive, so you don’t want to add unnatural amounts of sustain. Whereas, a guitarist might want a slow release for a solo, to hold long sustaining notes (think David Gilmour).

Ratio

This refers to the amount of compression that is applied to your signal. For example, a fairly subtle 2:1 ratio simply means that for every 2dB your signal goes over the threshold, it will only add 1dB of volume after compression. So 3:1 compression would mean you would need to go 3dB over the threshold to add 1dB of volume. You might even see ∞:1, which will limit your signal — meaning that once your volume reaches the threshold it won’t get any louder at all.

Blend

This is an especially useful feature if you just want to add subtle compression without losing the attack of your note. Blend will combine your uncompressed (or dry) signal with your compressed signal. This way, you can add your compression to taste without compromising your dry signal. In recent years, this has become especially popular on guitar compressor pedals, and is extremely hand to have!

Knee

You won’t see this on many studio compressors, but it’s worth knowing about anyway. While most compressors will apply compression immediately to when the attack time is set, some will ramp up their compression. The knee controls this ramp up. So, if you set a 5:1 ratio, instead of it instantly compressing at 5:1, you could slow the knee, which would control the amount of time it reaches 5:1 — it might start at 2:1, then 3:1 etc. until it reaches 5:1.

Do I Need a Compressor Pedal?

Compressors are great tools for guitarists, but they’re not right for everyone. So if you’re wondering whether you should add a compressor to your rig, we’ve got you covered.

I Only Play at Home

If you’ve ever had the luxury of being able to play through a loud valve amp that’s really cooking, there’s a unique feel you get from the amp. As a valve amp is pushed close to its limit it will naturally compress, making the guitar feel easier under the fingers. It’s not necessarily a huge audible effect, but it’s like the amp is encouraging you to play — as you dig in, the amp squashes and rounds off the top-end, and each note sustains longer.

If you’re just playing at home, you’ll never get your amp loud enough to experience this, but with a compressor you can simulate that exact same feeling. When you need to be conscious of your volume, you can get into the habit of being afraid to dig in. But with a compressor on, you won’t get a huge volume spike — you’ll just get a thicker, warmer attack. So, if you have to play at low volumes, you should definitely try out a compressor pedal!

I  Mostly Play Clean

If you predominantly play with a clean tone, then a compressor is a life-saver! When you play with overdrive, your signal is already compressing, which is how the distortion is created. But if you’re playing completely clean there is almost no compression at all, meaning that it’s very difficult to control the dynamic range.

Without any compression you also won’t get much sustain, so you will get a big transient peak that will die out very quickly. Adding a compressor will control those peaks, allowing you to still play dynamically, but helping fill your sound with more sustain between each note — allowing for tight rhythm playing and seamless solos.

I Mostly Play with Overdrive

If you generally play with overdrive then you will already be compressing your signal, but adding a compressor to your signal chain can add more texture to your sound. Certain famous guitar tones such as overdriven Fender or Dumble amps are sometimes described as “chewy” — this comes from a thick, compressed mid-range. This can be replicated with a compressor. They’re also great to use for solos to boost your signal and add sustain for big bends, or to even out your dynamics when playing fast legato passages.

There are multiple ways you can stack compression with overdrive. It is most common to place a compressor in front of your overdrive, which acts as an overall tone fattener, as the added sustain will also overdrive. It is also a practical solution because, by their nature, compressors raise the noise floor — so going after your overdrives could amplify the noise floor.

Another option is to place your compressor after your overdrive, that way you retain the dynamics and attack of your guitar going into the overdrive, but it just adds some sustain and level control. Having it this way round gives the compressor a subtler effect that retains more dynamic range.

I Play Slide

Compression is very common in slide playing, and it’s often not a subtle effect. Slide guitar can be challenging and unforgiving, but compression helps alleviate that. By softening your attack and adding sustain, it’s easier to slide smoothly up and down the fretboard without sharp dynamic spikes.

A common trick among slide players is to use 2 compressors, that way the effect is even more exaggerated as the second compressor will grab the transients that the first one misses. In fact, the Origin Effects SlideRig uses this exact trick — with a knob that allows you to blend in a second layer of compression to the first. An alternative for slide guitar is to use a fuzz, which does a similar job of limiting your attack and adding sustain. Why not try a combination of compressor and fuzz to see what suits you best?

I’m a Bassist

For a bass player, compression is your most important effect and is a must-have! A bassist’s main role in most musical contexts is to lay the foundation of the groove, and for that you need to keep a steady volume. A compressor will ensure that each note has a similar volume, so when you adjust your playing dynamics, you affect the timbre of your attack without completely jumping out of the mix. A compressor will also round out the attack of the notes, ensuring a thick and rich bass sound with that classic “thump” that stays present in the mix.

Can I use a Guitar Compressor for Bass?

In short, yes. In long — a guitar compressor will work, but a bass compressor will probably work better. Compression works the same on basses and guitars, but bass compressors focus on a different frequency spectrum. Bass and electric guitars fill different areas of the frequency spectrum, and that’s partly why they sound so damn good together. A bass compressor will focus more on compressing bass and lower mid-range, much like a dedicated bass amp. While a guitar compressor is optimised for a wider spectrum, with more upper mids and treble.

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Studio-Style Compressor Pedals

Most compressor pedals will only have 2 or 3 controls, often for level, attack and amount of compression (or maybe even 4 controls if you’re lucky enough to have a blend control as well). But some pedal manufacturers such as DSM & Humboldt and Origin Effects are building a whole new breed of compressors. These are compressor pedals for guitarists that give you the control and precision of the big, expensive studio compressors — often based on legendary studio compressors like the 1176.

So if you’re looking for something super easy to work with, then a classic 2-knob compressor is perfect. But if you want to have total mastery of your tone and you’re not afraid to tweak, then check these out…

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