This is the first in a series on common guitar tones that you ought to be able to identify by ear. The guide is roughly organized into chronological order—the order in which these sounds were introduced into the world. Each week from now until ~December, I’ll post a new one. This is a living guide, so let me know what was wrong and/or unclear by commenting or emailing me at josh@guitaros.com.
Compression
The key thing to know here is that there are three slightly different things we call compression.
The first is the natural byproduct of amplifying things. The second is a studio effect used to create cohesive mixes. The third is a guitar effect, used to create a specific sound.
Conceptually, they’re all the same idea: make the loud bits quieter and the quiet bits louder.
We’re squashing the dynamic range on both sides to create a more uniform volume throughout.
Compression #1: Natural Compression
When we plug our guitar into a tube amp and crank it up real loud, we get the first kind of compression. Just by virtue of amplifying it, we’ve made even the quietest notes louder. But not just louder than they are acoustically—louder in relation to the louder bits. We’ve raised the floor, making the minimum volume louder.
We’ve also lowered the ceiling for how loud we can get. This is because no amp has unlimited headroom—at some point we exceed the capacity of the amp’s power section and/or speaker.
To recap: playing into a cranked amp doesn’t just shift the available spectrum of loudness upward. It also squashes the available dynamic range, making the quieter parts louder and the louder parts quieter.
This is natural compression from amplification. We haven’t talked about this yet, but anything that has a “gain stage”—like a preamp, boost, compressor pedal, overdrive, distortion, or fuzz—is also compressing your sound.
One last item of note here. For early amplified performances, there was no conventional PA. No one was micing the guitar amp and running it through the mains. If it needed to be loud at the back of the room, it needed to be (literally) deafening onstage. It was also normal to run the guitar, bass, & vocals into the same guitar amp.
I mention this only because it shaped what we feel guitar ought to sound like—the visceral sensation of having a ripping loud speaker shake your body, a power amp & speaker that are running at the extreme edge of their capabilities, and the natural compression that goes hand in hand with that.
It also explains so much of the tone chasing that we guitarists do:
- Every boutique overdrive pedal is just an attempt to get the tone of an insanely loud amp… at a more reasonable volume.
- Compressor pedals—which were completely unheard of for the first half of pop music’s history—are now standard issue on even modest pedalboards.
- Every time you hear someone complain that modelers like Helix & Kemper can’t compare to the real thing, the thing they’re actually missing is having their bodies shaken by an amp in the room.
Compression #2: Studio Compression
The second form of compression we’re used to hearing is studio compression. Just like in our examples from Compression #1, a studio compressor reduces the overall dynamic range of the music, making the loud parts quieter and the quiet parts louder.
Why would we want to do this? The first reason is to make produced music sound ok in the environments in which it’ll be listened to. Sure, if you’re wearing headphones in a quiet room, you’ll be able to hear the quietest quiet bits just fine. (And hopefully the loudest bits won’t blow your eardrums out.) But take that same recording into your car, and (without compression) you’ll miss half of what’s in the song—road & engine noise will eat it up.
The second reason is one of the great contradictions of producing music—in order to make something sound natural, usually you have to process it. In this case, we need to compress each individual element of the recording so that the mix sounds like a band playing together in a room.
(And again: our cultural experience of listening to recorded music has informed our perception of what “a band playing together in a room” sounds like, more so than being in the room with a band playing.)
We won’t go crazy deep into how to set compressors for each instrument. But we will talk about the most common knobs on a studio compressor so you can wrap your head around what they’re doing and how they do it.
Threshold – This sets the lowest level at which the compressor will start working.
If you set it at 70 dB, then run a 69 dB signal through it… nothing will happen—it will only affect signal that’s louder than the 70 dB threshold.
Ratio – This controls how much squashing will take place, and it’s expressed as a ratio—2:1, 3:1, 4:1 etc.
For the sake of easy-to-understand math, let’s say we set the threshold at 70 db and the ratio at 2:1.
If we run a 100 db signal into the input, the output will give us 85db.
Why? The 30 db difference gets compressed at a ratio of 2:1.
Every 2 db of input signal above the threshold exits the compressor as 1 additional db of output.
30 db at 2:1 = 15db of additional output. {(100 – 70)/2)} + 70 = 85
If this…
{(Input level – threshold)/ratio)} + threshold = output level
…is more confusing than it is illuminating, go make a copy of this Sheet and play with the numbers for a minute until it makes sense.
Attack – This is measured in milliseconds, and it controls how long the compressor waits before kicking in. We use this to retain the crack of a snare drum or the percussive attack of the pick, which would otherwise be neutered by the compressor.
Release – This controls how long the compression lasts after the input signal falls back down below the threshold. If we set it too short, the decay of notes will sound unnaturally abrupt. If we set it too long, the compressor will “pump,” momentarily boosting a decaying signal louder than it ought to be. We’ll encounter this again when we look at Compression #3—it’s what we use to give clean guitar signals added sustain.
Gain – Because adding a compressor to the signal chain usually makes it sound quieter (because we tamed the peaks), it’s often accompanied by a bit of “makeup gain.” This feeds directly into raising the level of the quietest signal. We’ll see this in Compression #3 too.
To sum up this section:
- recorded music depends heavily on compression to make the mix listenable
- and counterintuitively, making music sound natural usually requires some processing
- each instrument will be compressed differently, even (especially) the different components of a drum kit
- much like bassists, lighting guys, & sound techs, a casual observer will only notice compression when somebody messes up
I want to tie back into my earlier comment about how tube amp players dislike modelers mostly because there’s nothing moving air in the room. On the other end of the spectrum, your sound guy LOVES your modeler precisely because it sounds like a recorded guitar—complete with micing and studio compression.
It’s not an exaggeration to say that we’ve never truly heard most of our favorite guitar sounds. We’re super familiar with how Hendrix’s guitar sounds on the records, but if we were to somehow plug into his rig, it wouldn’t sound like we expect—we’re used to hearing the mic, the preamp, the studio compression, etc.
Compression #3: Compressor Pedals
Starting in the 70s, we began seeing pedal-based compressors from MXR and Ross. They were simple machines with two knobs—one for output (roughly akin to the gain knob on a studio compressor), and one knob to control both threshold & ratio. They were limited & noisy, but simple to use. They quickly found favor among Nashville session guys, who used them to fatten up their Teles while also taming the high end.
In the 80s, we saw Boss introduce pedal compressors that had attack knobs, allowing us to slightly delay the onset of compression, thereby retaining the pick attack. The 00s brought the Keeley 4-knob compressor, which added a knob for threshold.
Those were followed by comps from Wampler, Keeley, & others that include a “mix” or “blend” knob, which allowed us to run our dry unaffected signal alongside the compressed signal. More recently, we began seeing pedal compressors with all the controls of a studio comp—threshold, output, dry blend, attack, release, and ratio.
Unlike studio compression, you can definitely hear a guitar compressor in action. A prime example is Cory Wong’s rhythm-as-lead guitar playing. I’m using Takeoff as an example, but almost anything from his catalog will showcase his Strat-into-a-Wampler-Ego-Compressor sound.
Another great example of compressed guitar tone in action is from heavy-hitting country session ace Brent Mason. He recorded hundreds (if not thousands!) of songs with a Tele into a Boss compressor. He was also a big chorus user, so I made it a point to grab a tune without it: Alan Jackson’s Don’t Rock The Jukebox.
Check out the solo at 1:31, then hear it in isolation here:
