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March 2024
Vol. 23, No. 6

Zen of Recording

Why Do I Have So Many Compressors?

by Sven-Erik SeaholmMay 2021

Having first beheld, awe-stricken by the majestic splendor of an actual shoe closet filled with entries from Prada to Puma, stilettos to flats, and Ugg boots to sassy boots, I believe my verbal reaction lay somewhere betwixt “Wow” and “Whoa.”
I currently have five sets of footwear (not including socks and barefoot, my preferred indoor selections): work shoes, walking shoes, indoor/outdoor slippers, flip-flops, and fancy shoes “for special.” That’s all my current lifestyle requires. I haven’t happened upon any situation where I regretted this, but then again…I don’t wear brown.
In my audio work, however, I have tons of options when it comes to microphones, preamps, guitars, keyboards, virtual instruments, and of course, foot pedals and VST effects plugins. Sometimes I suspect it’s a sickness, lustfully poring through the internet (“Ooh…look at the stats on that one!”) in a ravenous search for just the right tools and toys to aid in making music more quickly, easily, and better (cooler) sounding.
Oddly, I find myself passing over flashy impulse buys like reverbs, synths, and special effects in favor of more seemingly mundane fare, like audio compressors.
Some people go to Home Depot and check out all the barbeque grills.
I stare at the shovels.
Compressors and compression may well have been the very first subject I covered as a music tech writer, mostly because it’s been one of the most misused and misunderstood tools in the pro and home recordists’ arsenal. The weak, “plinky” sound of an over-compressed snare in a mix was an early pet peeve, so I set about to master its use as best I could.
Essentially, compressors turn down sound that exceeds a certain threshold level, so, for example, an uneven bassline that has some notes that are too loud and others that are too soft can be smoothly evened out by bringing the louder notes down, resulting in a closer dynamic relation the soft ones. Another example would be a lead vocal that tends to jump out at you at various points in a song, resulting in it being turned down to avoid that from happening. This often results in a “buried” vocal in the mix. By generously compressing it, it can subsequently raised up louder in the mix without worry of it randomly jumping out at the listener.
These are over-simplifications of compression’s theoretical uses though. There are a great many sonic variables between different compressor models, in addition to the fact that each recording situation is innately unique. These factors are exponentially multiplied by the presence of parameters common amongst most compressors: Attack Time, which determines how much of a drum hit for instance, might be left untouched before the compressor clamps down on it. This is often referred to as “punch”; Release Time dictates how long it takes for the signal to turn itself back up to its pre-compressed level. Ratio refers to how much the signal gets turned down and the resulting dynamic relationships, i.e. a compression ratio of 3:1 means that every 3dB of volume increase above the threshold will only be output at a newly reduced level of 1dB. This means that if your threshold is set at -10db and you have a note at -11dB followed by another at -7db, the note at -11dB will be unaffected, as it is 1dB below the threshold, while the note at -7dB will now be at -10dB; still slightly louder, but not as drastically. Many compressors have an Output or Makeup Gain parameter to make up for all of this volume reduction that happens above the threshold.
Some compressors offer a variation on this basic setup, known as “Soft Knee” or “Over-Easy” compression. This type starts very subtly compressing below the threshold level and gradually compresses harder and harder the further the signal exceeds the threshold setting. This makes it a bit more natural sounding and harder to detect as an effected signal.
There are also four different flavors (and I purposely use that word) of compressors: FET, VCA, Optical, and Variable-Mu.
FET (Field Effect Transistor) compressors have a very quick response time and the transistors give you the most accurate performance, meaning when you set its attack and release times, it precisely accomplishes the task without lagging. This manifests itself as a punchy, in-your-face sound. There’s also a bit of aggressive distortion that brings things forward in the mix. The Universal Audio 1176 is the best known example of this type.
VCA (Voltage Controlled Amplifier) models are even more aggressive and really tamp down hard on anything you need to surgically address. A cleaner, less distorted sound.
Optical or “Opto” compressors work with resistors that are light dependent. The audio signal illuminates a little lightbulb or an LED, which the resistor reacts to. Electronically speaking, it’s not as efficient as the previous two types described, resulting in a comparatively sluggish performance. This is exactly why they sound so good, as their smoother reaction creates a much more pleasant and less detectable sound.
Vari-Mu is the least aggressive of the four and as such, it is your best choice for gluing all of a mix’s elements together. They also impart color, warmth and overall fatness to bass, guitars, vocals and drums. The multi-tubed Fairchild 670 is an excellent example of this type and the Beatles loved them!
We’re really just skimming the surface of this topic. Next month, I’ll select some my favorite go-to’s from the 82 different hardware and software versions that I personally choose from in the studio and dive a little deeper into why.
Sven-Erik Seaholm is an award-winning producer, recordist, singer and songwriter. He is currently barefoot.

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