Compression is a topic that's been covered so many times - however, I’ve always approached production more as a science than as an art, and with this in mind, I think you’ll find this quick guide more helpful than you’d first have thought!
Let's dive in.
Types of Compression
Compression really comes in 3 major formats - VCA, FET and Opto. Now there are of course off shoots, but I’ll focus on these for the purpose of correlating well through both software and hardware.
VCA - Voltage Controlled Amplifier - What is it?
The interesting part about this is that it’s not actually amplifying the signal but rather attenuating it. Simply put, the input signal of your sound is fed in, and you control the main front controls (Attack, Threshold, Release) to tell the compressor at what level the signal voltage (loudness) has to be in order for it to start compressing.
Well know VCA compressors from Plugin Allience recreating the SSL Bus Glue in the for of the bx_Townhouse compressor (Bottom), and the Shadow Hills Mastering Compressor Class A (Top).
Using VCA Compression
VCA Compression is pretty transparent in terms of color so you find this in a lot of mastering grade, or stereo bus compressors like the Shadow Hills Class A compressor, or the SSL Bus Compressor heard on countless records. But you can also find this very helpful on things like Vocals for a clean vocalist you’re trying to bring to life in a more ambient track, like a live acoustic recording. It’s also well suited for both acoustic and (especially) distorted electric guitars to keep the dynamics consistent across the board. Some good examples of settings I use on the same mastering and bus examples are below that I use regularly on my mixes.
- Easily Transparent, or can add crushing distortion through compression
- Great all round Compressor, but stands out best used on Guitars, Bass, and Bus compression (as well as Mastering)
FET - Field Effect Transistor - What is it?
FET Compressors came about when small transistors started to replace large tubes that made up some of the earlier models of compression. They also found that with this, FET Compressors preserved the transients (the initial hit/attack of a sound source) much better than the VCA or Vari-Mu counterparts, and in turn, were able to help deliver far more punch to a sound than the predecessors. Because the FET compressor is signal dependent, it relies on the input signal for the compression to start. In this sense, the more signal is pushed into the unit, the more intense the compression.
Arturia's faithful recreation of the Urei 1176 FET compressor, used here in a recent session of mine on a Kick drum to add some extra punch and depth.
Using FET Compression
Possible the most well known in this area is the Urei 1176 compressor, known best due to its appearance any pretty much 90% of any mainstream record produced. Because its so well known for it’s punch and ability to preserve the transients, it’s main use has been on drums as vocals. On drums, any shells you put through this will come to life, and have some harmonic distortion added to build a warm and dense sound giving you insane sounding drums without trying too hard! With vocals, the same applies, but as it has the ability to have a much slower attach as well, you can level vocals and create radio ready vocals with just a few ‘cheat’ settings I’ve screenshotted from my sessions below.
- Natural Distortion Characteristics make this a great compresor to use to add body, and warmth to your mixes, as well as punch
- Best used on Bass, Vocals, and especially Drums!
Opto Compression - Optical Compression
Opto-compression or Optical Compression, is a dynamic range attenuator. The core of this unit relies on a photo light sensitive transducer that transforms energy from one means to another in that, the sound signal is transformed into a light via the voltage it creates in this unit. The more voltage that is given to the transducer, the brighter the LED inside the unit emites, and therefore, the more intense the compression is (also dependent on the threshold if built in). The reason this came into such popularity is that the non-linearities created in the sound when extremely pleasing to the ear.
Cakewalk's CA-2A is a great recreaton of the well known Teletronix LA-2A. I'm using it on my vocal bus to level the layers and glue them cohiesively together to form a layer of beautiful harmonies!
Using Optical Compression
Optical compression is a gentle and very transparent compression type that can be used to bring flavor into a record without being the main focus of the sound. For example, the Teletronix LA-2A is revered for its sound, not just because its optical, but because of the transparency of optical compression meant the design was able to include several valves that gave the compressor an incredible warmth, depth and character that's been the mainstay of vocal recording for generations. The same can be said for the Optical Section of the Shadow Hills mastering compressor that gently levels the sound given to it, allowing it to feed to the VCA Compression panel next in the chain to best bring the glue that Mastering engineers love.
- Transparent, nonlinear compression that's extremely pleasing to the ear and can ride more dynamic instruments with ease
- Famed as one of the best Vocal Compression types, but great on drums for a different flavor, Guitars to ride the poky transients (this shines most on acoustic guitars!), and I've even used it on a few Masters, as it can open up the stereo image and add texture to a track very easily!
Conclusion
With all of the main bases covered, keep in mind that compression can be the most surprising when you experiment with it. I love using VCA compression on Snare drums for example as I love the ‘snap’ that I can accomplish. I also regularly use a plugin version of the LA-2A as a bus compression to glue vocals together when there are several layers and harmonies that need that ‘leveling’ glue that only optical compression will give the transparency and soft style compression that isn’t too obvious to the end listener.
Try them all out on the source you’re working on, and remember that no recording is the same - so there’s not specific rules to what can and can’t be used. Use your ears and if it sounds good, it's good!