Analog Obsession has been making great free plugins for a while now, and one of the latest makes for a fantastic mastering compressor. SPECOMP can be used for mixing but has particular functionality that makes it a great option for subtle but powerful mastering compression.
The low ratio, soft-knee, and comprehensive attack and release times make it easy to dial in the right amount of compression. The release starts at 50 milliseconds which is perfect for making a loud master but goes higher for smoother, glued-together sounds.
The dial-in middle under the gain reduction meter lets you blend the effect in, meaning this is also a great plugin for parallel compression.
Kolin is an easy-to-use but incredibly colorful and useful mastering or bus compressor. The sound is distinct, but the mix dial, as well as variable attack and release times, make it a good option for subtle and nuanced mix bus compression and mild distortion.
Using the plugin is simple, just increase the input until attenuation begins. To the top left, we have our attack and release times which range from 1-50ms and 100-3000ms respectively.
One unique use for this plugin would be to drive the input to achieve aggressive compression, reduce the output to create some drive, and then reduce the mix dial to blend the heavy compression and mild distortion in with your mix.
Rough Rider 3 has a distinctive sound and a clean and easy-to-understand design - it can be used for both mix bus compression and parallel compression. Furthermore, the plugin makes controlling your compression much easier with a dedicated internal side-chain high-pass filter.
Use this high-pass filter to cause less compression and create a perceived louder kick and bass.
You can create some drive with the input and output and then blend this in with the mix dial. Or, stick to subtle compression by fine-tuning your threshold, ratio, attack, and release.
Compressor by Tone Boosters isn’t entirely free - however, the demo of the plugin is the full plugin without any limitations, meaning you can use it as you would the full plugin. Although not an exact replica, Compressor by Tone Boosters shares a lot in common with the FabFilter Compressor.
The designs and functionality both hold a lot of similarities to the FabFilter Compressor. What’s unique about this plugin though is the assist option , which alters the internal side-chain, and other functions, making them program dependent.
Additionally, you get an adaptive release, lookahead, range, hold, and a zone analyzer which isn’t too common.
Melda Audio often gets overlooked, but they create some of the most versatile and comprehensively designed plugins available. Included in a huge bundle of free plugins is the Mcompressor, a compressor that offers both traditional and completely unique compression functionality, in addition to advanced monitoring.
The compressor gives you the traditional functionality with ratio, threshold, attack, release, and so on, but gets interesting when you come across the Custom Shape option - with which you can create unique non-linear distortion and expansion.
By double-clicking you can add more points you can control, then drag them to cause compression that wouldn’t be possible with just about any other plugin.
Kotelnikov by Tokyo Dawn Labs has been a go-to free mastering compressor for a while now - in fact, for the longest time, it was just about the only free mastering compressor available. With that in mind, the functionality this plugin offers is tailored toward mastering.
For example, the stereo sensitivity section gives you control over your stereo image. By prioritizing the mid over the side, you can cause more compression to the mid-channel, in turn making the side louder and expanding the stereo image.
Additionally, you can set release times for both the RMS and peak value of the signal, giving you greater control over the timbre of your master.
This compressor gives you the controls you need for both mixing and mastering compression, making it easy to dial in very specific values for your compression. In addition to this, pajSoil offers advanced functionality you don’t see too often in a free-to-use compressor.
Personally, I like how specific each value can be, from the ratio to the threshold, knee, and more.
Furthermore, we get an internal high pass filter, variable lookahead, and control to alter the linearity of the compression.
Like some of the other plugins on this list, a mix dial makes parallel compression an option, if you want to add that into your signal chain.