Compressors – All you need to know!
by Slade Templeton
Whether we are recording, producing, mixing or mastering, compression has its finger print somewhere in the pie. Today we will go over what types of compressors there are, what they are best used for, and some neat tips and tricks of how to use them to take your productions next level.
So let’s start by talking about the different types of compressors. Here is a handy list, and a little definition for each, along with what they are good for and ‘better known as’.
Vari-Mu Compressor
Vari-Mu stands for “Variable Mu (gain), and is made up with tubes. It uses High Gain, but low distortion tubes, and relies on a softer knee. 
This makes it best suited for Mix-Bus applications, or for when you need that “glue”.
- Whats it good for? Mixing, Mastering
- What Instruments? Overall Mixes, Drum Groups, Mix Groups
- Known Names? Vari-Mu by Manley (plus many tube style compressors from others)
FET style Compressor
FET (aka Field Effect Transistor), are typically a solid-state emulation of Tubes. Its about color. And compared to its brother the VCA 
compressor, its going to give you more ‘edge’ than the clean VCA. If color is what you are after, the FET can be your friend.
- Whats it good for? Production, Mixing, Mastering, Recording
- What Instruments? Overheads, Drums, Bass, Vocals
- Known names? 1176, 1178
Opti Compressor
Opti (Optical) Compressors are pretty terrific, even for the nerdiest of nerds. It uses a light source that gets brighter as the signal gets louder, and the light-sensitive resistor reacts to the brightness by decreasing resistance. You’re now probably saying “whoa, far out man!”, I know, 
pretty freaking cool. But don’t let this high tech explanation make you think it will color the signal heavy. It typically wont. In fact, it is made to be very organic, neutral, and even invisible in a lot of ways. Think of the Optical Compressor as Smooth, slow attack, and slow releasing. It can be a bit on the squishy vibe if pushed, and a bit loose if being used timidly. It is also known for its use as a Leveling Amp.
- Whats it good for? Recording, Mixing, (rarely but sometimes; Mastering)
- What Instruments? Guitar (acoustic), Vocals (for leveling), Overall mix (sometimes)
- Known names? LA2A
VCA Compressor
VCA (aka Voltage Controlled Amplifier) is clean. Its brutal. And it can go as hard or light as needed. 
Technically most any compressor is a “VCA” in a sense, due to the way the type of circuits, but when someone talks about a VCA compressor, they are likely talking about IC Chips being inside that have transistors following your signal coming in (voltage), to determine how much negative gain should be applied. They are fast acting, precise and clean.
- Whats it good for? Recording, Production, Mixing, Mastering
- What Instruments? Everything
- Known names? API2500, DBX160
Difference between a Compressor and Limiter?
Nothing except ratio!
In fact, a Limiter IS a Compressor, and vice-versa. Only difference is a compressor turns into a limiter once it hits a 10:1 Ratio or higher (typically). So when should you limit? Honestly, I am a firm believer that a brick wall heavy limiting should not be touched until final stages in Mastering. However, there is others that believe it is great on Vocals or Drums (kicks) in a mix too. So I say whatever works best for your workflow and style! But be weary of over-limiting things just as well as over-compressing. I feel there is already enough compression going on in a mix, that hitting a high ratio brick wall may do more harm than good once you get to the final mastering Limiters. However, high ratio limiting compression can do wonders if used in a Parallel or getting creative with compression.
Enough of the nerdy stuff! What about this getting ‘Creative with Compression’ thing?
OK, yes, we know that a compressor isn’t quite an instrument, but that doesn’t mean we can’t use it like one! One of my favorite mixing techniques is to over compress certain elements in a mix (tastefully), to add nice character when it’s appropriate. A good example of this is using an 1178 on drum overheads, and really hitting it hard, to give it overly compressed saturation. This works wonders on drums overheads and also things like percussion elements. After using the overly compressed settings, then you will want to work with a transient shaper to bring in some of the articulation of transients back from the grave. This followed by a little boost on the top or bottom end, can add some nice harmonic character. Blend into the mix of the dry and not-so-processed drums, and you will see how it gives a nice ‘bed’ of sound to the rest of the drums elements. Another technique is running a Vari-Mu on the mix bus or first stage in your mastering chain. This can add nice glue and character to the mix, in a ‘tube’ like fashion that is usually sought after. This paired with a VCA (faster acting, more precise) compressor, makes for a magic recipe for reaction and sluggish reaction, that can retain the transients while gluing the mix.
Quick tips with Parallel Compression (AKA New York Compression):
A quick run down on what Parallel Compression is; you want to essentially Compress one signal, while leaving another signal dry or uncompressed. This works wonders on Drums. You send all the drums to one aux/channel of compression (high settings * see below * ) and the same exact drum signals to a dry (uncompressed) signal, then blend to taste. Always be sure to run an EQ on the blended signal, to boost the top and bottom as it will lose some from the over compression, and to retain the punch and transients of the drum.
Now that we know more about compressors and some cool tips and tricks, I will sign off with giving you some basic (and starting point) settings for your mixes and productions on some instruments and styles.
Hope these will help you in your epic compression journey; now go make those chart topping hits!
Compression Settings
VOCALS
Type of Compressor: Any (recommend Opti for Leveling, VCA for fast acting)
Basic Settings to try: Medium to Fast Attack, Medium to Slow release (Depending on the tempo and vibe),
Ratio: 2:1 and not higher than 4:1
Reduction: 2 to 3 dB at higher ratio or 3 to 6dB at lower. Listen for fluidity and keeping it working for the style and sibilance.
BASS OR BASS SYNTH
Type of Compressor: VCA or FET
Basic Settings to try: With higher transient style bass, then medium attack and medium release. With smoother (lower sub) style bass’s, and depending on Tempo and Style, slow attack and slower release (to increase sustain) with higher ratios.
Ratio: for more tightness, use higher 4:1 to higher, for a more organic fluid approach, 2:1 to 4:1
Reduction: 2 to 3dB reduction or sometimes higher depending on the compressor and how much you want it to “sound like its working”
SYNTHS
Type of Compressor: VCA, Vari-Mu or FET
Basic Settings to try: Depends on the synth presented. For more jagged leads, Fast Attack with Fast Release for Punch. For slow pads and slower synth styles, then fast attack with slow release or slow attack with slow release will work.
Ratio: for heavier leads; 4:1 and up. For slower pads, 2:1 or 4:1
Reduction: depends on the style and what you want. 2dB to 3dB for looser and mellow gluing (works on the synth bus this way better), or for a snappy lead, higher 4dB to 6dB can work.
DRUMS
Type of Compressor: VCA
Basic Settings to try: Fast attack and fast release typically. (When using as parallel (see above article), then you can get VERY aggressive with it as it’s a purely compressed signal mixed with a dry signal. )
Ratio: 2:1 or 4:1 if on its own, 10:1 limiting for Parallel
Reduction: If by itself on a kit, then 2 to 3dB, if in Parallel mode, depending on the compressor used, you can hit upwards of 10dB or more! Really slam it for Parallel.
GUITAR
Type of Compressor: VCA (electric), Optical (Acoustic)
Basic Settings to try: Electric: Fast Attack and Slow Release / For Acoustic : medium attack and release
Ratio: 4:1 for Electric Guitar (or higher for more sustain) / 2:1 for Acoustic or use the Opti style
Reduction: For a really ‘brickwalled wall of noise’ guitar style, then 10dB is fine for Electric. For acoustic, 2 to 3dB is nice, depending how much you want to bring it into that ‘compressed’ sound and character.
PIANO
Type of Compressor: VCA (rockier styles), Optical (acoustic styles), Vari Mu (for either)
Basic Settings to try: for more transient, heavier top end focused piano, then use a medium attack and let the top end transients through to give it ‘bite’, if you want smooth and ballad style, then use a bit faster attack with slow release, or medium attack with slower release to give bite while retaining the sustain.
Ratio: 2:1 to 4:1
Reduction: 3 to 4dB for heavier piano styles, and 2 to 3dB for smoother.
Don’t forget! We also have a Compression Wizardry course from Steve Roland and Ahee at the Black Octopus Sound home page!