Author Eric Von takes us through compression and how to get the most out of your compressors below.

First off, what is compression?

In the simplest terms, compression is the act of reducing dynamic range, or, the area between the softest and loudest part of an audio signal. There are multiple ways to achieve a reduction of dynamic range, such as limiting and distortion/saturation, but the most popular way might be achieved by using a compressor.  

What is a compressor, you ask?

Classically, a compressor is a big piece of hardware, filled with transistors, tubes, and various electrical components that will ultimately reduce the dynamic range of the audio signal that passes through it. In the digital world, plugin companies have sought to create emulations of these classic compressors.

If all of this sounds like gibberish to you, I suggest checking out Fabfilter’s two-part YouTube series: Beginner’s Guide To Compression.

Now that you’ve brushed up on the basic terminology and functions of compression and compressors, let’s explore the four main types of analog compression and when you might use them.

 FET COMPRESSION

FET stands for “Field Effect Transistor” and is the circuitry behind one of the most famous and widely used compressors of all time – the UREI 1176 – a true peak compressor with all transistor circuitry. Odds are if you’ve ever visited a studio you’ve seen one of these in the gear rack. 

Without digging us too deep into an electrical rabbit-hole, a transistor is a semiconductor that allows for both the amplification and attenuation of a signal. For example, a transmitter and a resistor make up a transistor. FET compressors generally use transistors to emulate the behavior of tube-style compression with optimal versatility.

A hallmark of FET compressors is how quickly they act upon signal that has passed through it. For example, the famous 1176 compressor mentioned above can detect signal down to a whopping 20 microseconds, or, in technical terms, fast as f***. 

Not only is it extremely fast, but FET compression is also famous for imparting some pleasing harmonic saturation. People generally describe these compressors as colorful, bright, and punchy, making them a go-to on drums, percussion, guitars and vocals. 

VCA COMPRESSION

VCA stands for “Voltage Controlled Amplifier” and it uses a control signal – movement of the threshold knob – to dictate whether or not gain reduction is applied to an incoming signal. VCA compression is probably the most widely used form of compression, and is characterized as clean, quick, and transparent compression. 

Providing a wide array of control, VCA compressors often include all the bells and whistles you’re used to seeing in compressor plugins, such as attack, release, threshold, ratio, and knee. 

Due to their transparent nature, VCA compressors are popular on master busses, sub groups, and just about everything in-between. If you’ve ever reached for a plugin emulation of the coveted SSL Bus Compressor or the API 2500 compressor, then you’re familiar with VCA compression. 

OPTICAL COMPRESSION

Often called “Opto Compressors”, these devices rely on a light source and a light-dependent resistor as their means of achieving gain reduction. Basically, the incoming audio signal is converted into light, a sensor detects the light, and then regulates the amount of reduction – the louder the signal, the brighter the light, and more gain is reduced. 

Logically, you could assume that since light is fast then an opto compressor must be fast too, right? Well that isn’t the case, when compared to FET and VCA compressors at least. This is because the components that make up the gain reduction circuit – the light source and sensor – aren’t particularly fast. 

Different light sources and sensors make these compressors less predictable and linear than their VCA and FET counter parts, and often the user doesn’t have as much control over attack and release times. 

Since these compressors tend to be slower acting with more gentle release times they are favored on less transient-heavy sources like vocals, strings and synths, or anything that needs a slight rounding-out. 

DELTA-MU COMPRESSION

Delta-MU, or Variable-MU, compressors get their name from the Greek words, Delta meaning change, and Mu, which, in electronics, means gain. You might also hear this class of compression referred to as tube-compression.

 Where these “gain-changers” are a real “game-changer” is in the fact that the gain reduction is handled directly by the tubes in their circuitry. Other types of compressors may utilize tubes to add coloration to the signal or to boost output gain but only Delta-Mu compressor use tubes in the actual gain reduction stage. 

Characterized by being smooth, rich, and fat, these compressors generally have a slower style of compression–similar to an optical compressor. They often handle transients in a very musical way and tend to impart loads of harmonic saturation making them a favorite on vocals, drums, and basses.

COMPRESSION’S GOLDEN RULE

Hopefully you now know a little bit more about the tools that are available for you, but the most important thing to remember is … If it sounds good, it is good. There are no rules – and if there are – try and break them as often as possible. Every article you read, tutorial you watch, or bit of advice you seek should serve as a starting point. This industry was built by individuals who broke rules and pushed the tools available to them to the limit. That’s what moves the needle forward.

That’s where greatness happens!