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Best Free Compressor VST Plugins for Mixing & Mastering

Compressor plugins are an essential tool for any music producer or engineer interested in creating quality mixes and masters. If you're already fairly experienced, you'll know just how often they're used to thicken up tracks, smooth out dynamic ranges and add character to audio.

In this article, we're going to cover the best free compressor plugins available for beginners all the way to advanced producers.

What Is A Compressor VST?

Compressor VSTs squash the loudest and softest parts of an audio signal, pushing them closer together, and reducing the dynamic range of your audio. This can smooth out large volume changes, add thickness and also add a certain character, depending on the circuit style of the compressor.

Most compressor plugins are emulations of their hardware counterparts and reproduce certain circuit types to produce a particular sound or characteristic. Digital VCA, FET, Tube etc. will all emulate those hardware circuit types, for example.

However, although many plugins emulate the hardware, you can also get extremely clean compression plugins, such as FabFilter Pro C, which serve as helpful, transparent mixing tools.

What Do All These Knobs On The Compressor Do?

Here's a brief overview of what the controls on a compressor plugin do:

  • Threshold – controls where the compressor begins to add gain reduction. Once it passes the dB level set, your compressor will begin to react to the audio you feed it. Beginners can get their hands dirty by moving the large ‘Threshold' dial on the Eareckon FR-Comp 87 with analogue-sounding results. Slam Pup's ‘Bite' knob is by far the easiest way to understand this function.
  • Ratio – controls the intensity of the compression applied. A 2:1 ratio has to cross the threshold by 2dB to be attenuated by 1dB. If it crosses more, it will be attenuated on the same ratio. E.g. 10dB crossing the threshold will attenuate 5dB.
  • Attack & Release: The ‘Attack' dictates how quickly the compressor kicks in, while the ‘Release' shows how it fades out.
  • Knee: The ‘Knee' knob marks the point at which the compressor begins to function – it's the transition curve from pre-compression, to compressed audio.
  • Make-Up Gain: The ‘Make-Up Gain' compensates for gain reduction during compression. The free compressors: Kotelnikov, Comp87 and RR3 have a dedicated ‘Make-Up Gain' knob.

Do I Need A Compressor Plugin?

Yes. Compressors are important to control the dynamic range of all the instruments in your track. This is useful when you want to thicken up your sound, add warmth or just control the transients of your tracks.

They work great on vocals, drums and pretty much anything. You can also use compression plugins to smooth out audio that has a big volume range (lots of high and low volume points).

Though all DAWs come with in-built compressors, however, paid 3rd party plugins are often a much better choice than stock compression plugins as they add certain character and warmth to tracks that your DAW's built-in one, might not.

We recommend learning on a stock compressor plugin or free compressor first before you buy anything.

Compression Styles – What Should I Have in My Collection & What Do I Use Them For?

There are 5 kinds of compression, and they have different uses:

  1. VCA Compression Fast, transparent, clean compression, with minimal distortion. Use for transient heavy signals to smooth out, and add punch.
  2. FET Compression – Fast, colourful, aggressive compression. Use for adding aggression, warmth, colour and drive to any signal. Great for parallel compression.
  3. Tube Compression – Slow, warm, smooth compression. Perfect for vocals, or anything that needs thickness, warmth or drive.
  4. Optical Compression – Fast, smooth, transparent compression. Applies a glossy sound. Use to add warmth, & thicken up sounds cleanly. Great for vocals especially. Not for transient control.
  5. Digital Compression – Precise, clean, transparent compression. Use for anything you want to keep transparent but thick.

What Are The Best Free Compressor Plugins?

Here's the complete list of the best free compressor VST plugins:

  1. OTT
  2. Rough Rider 3
  3. DC1A
  4. Mcompressor
  5. Comp87
  6. Slam Pup
  7. Kotelnikov

1. Xfer Records' OTT:

Compatibility: Version 1.3.5 is compatible with Windows & macOS(Intel + M1). VST, VST3, AU & AAX. 64-bit.

Xfer Records' OTT Multiband Upward/Downward Compressor.

Pros

✅Modelled on the OTT in Ableton.

✅ Extreme upwards and downwards compression.

✅ A staple in Dubstep, Trap and Electro production

✅ Highly potent ‘Depth' control. Carefully tweak it to taste.

✅ Visual ‘Multi-Band Compressor' for higher precision.

Cons

❌ The attack and release can't be independently controlled. RR3, MComp, Comp87 & Kotelnikov are better suited at it.

❌ Suited for users with prior knowledge.

OTT, which does both upwards and downward compression, is Xfer's answer to Ableton's hugely successful native OTT unit. Being a multi-band compressor, it squeezes the frequency bands into a tight space. Within this band, softer signals are boosted and louder signals are quietened.

Adding smooth distortion to a particular band of frequencies is incredibly simple and you can get some very interesting, harsh, EDM-style results that bring sounds to life.

When used correctly, the deadly two-way compression can make any instrument cut through the mix like a knife. This becomes a lethal weapon in Dubstep, Electro and Trap where the bass needs to showcase its sonic range and be penetrative at the same time.

While the single ‘Time' knob might seem inconvenient, the ‘Depth' knob makes up for it. From smooth distortion at moderate rates to cartoon-like squeakiness at higher rates, the ‘Depth' control is this plugin's unique selling point.

What's Downward & Upward Compression?

  • Downward Compression attenuates the audio signal above a set threshold by a set ratio.
  • Upward Compression amplifies the audio signal below a set threshold by a set ratio.

How Does It Sound?

Before

‘Dry' Drums before enabling OTT.

After

Notice how OTT adds crispness and enhances the nuances in the cymbals.

2. Audio Damage's Rough Rider 3:

Compatibility: Windows, Linux and macOS. VST, VST3, AU & AAX. 64-bit.

Pros

✅Highly successful. More than half a million downloads over 10 years.

✅ Extreme compression with ratios of 1000:1. Beats MComp, Comp87, DC1A by a mile.

✅ 100ms Attack & 1000ms Release.

✅ User-friendly UI.

Cons

❌ Non-transparent.

❌ RR3 isn't as comprehensive as Kotelnikov for mastering.

Not a good advocate for transparent compression, Rough Rider 3 has a mind of its own when it comes to adding colour. With ratio levels that go up to 1000:1 that signal doom, the compressor comes of age when you oversaturate it.

Moving on from the successful Rough Rider 2, Audio Damage has included an external sidechain input and provided an option to turn off the ‘Full Bandwidth' button. This allows us to bypass the ‘warming' filter if necessary. Rough Rider 3 also comes with upgraded, more accurate metering.

As the name suggests, Rough Rider 3 is made to be pushed to its extremes. The highly responsive Attack, which gets aggressive fairly quickly, ranges from 0 to 100ms and the Release goes from 0 to 1000ms.

RR3 could easily scrunch up your snare or make your guitar riffs roar. Slap it on your drum buss or add it to your vocals in parallel. Rough Rider 3 could be your go-to compressor for years to come.

How Does It Sound?

Before

‘Dry' Drums before Rough Rider 3.

After

Notice how RR3 saturates the drums to make them sound more dominating. With the Ratio at 15:1, the ‘Attitude' is un-missable.

3. Klanghelm's DC1A:

Compatibility: Windows and macOS. VST, VST3, AU & AAX.

Klanghelm's DC1A.

Pros

✅ Free version of DC8C in a compact 2-control format.

✅ Great for adding some analogue mojo.

✅ Unique Negative compression.

Cons

❌ Doesn't match up to MCompressor or Kotelnikov for heavier tasks.

✅ Unique Negative compression.

Sounding similar to the ‘Punch' mode on the DC8C, this humble younger brother offers gentle, smooth levelling compression.

The four modes are listed below:

  • Deep: The deep mode enables the high pass filter, keeping the track devoid of booming or muddiness in the low end. Technically, it is processing more incoming volume information. This means the envelope follower can send more CV to control the VCA which in turn controls the gain of the output signal. This is especially useful in electronic genres like techno or dubstep.
  • Relaxed: By reducing the responsiveness of the compressor, ‘relaxed' offers us a slower rate with less saturation. An ideal fit for string sections or long ambient vocal drones which would otherwise be spoilt by more aggressive compression.
  • Dual Mono: By disabling the stereo link of the side-chain, we can compress the left and right channels separately. This allows space for tracks with wide stereo images to exist in a wholesome way within the mix.
  • Negative: The most interesting of the lot, it allows us to dial in negative compression ratios. This can lead to louder transients being bought down below the level of the original signal.
    Its use in side-chaining the kick in electronic music would be the most obvious. But it could also give excellent results on metal guitars and drum busses which carry high transient information.

How Does It Sound?

Before

The first 12 seconds are ‘Dry' followed by the Klanghelm DC1A.

After

Notice the transparency in the ‘Relaxed' mode. Unassuming but effective compression.

4. Melda Production's MCompressor:

Compatibility: Linux(via wine), Windows 8 onwards(32 & 64-bit) and macOS 10.14 onwards(64-bit). VST, VST3, AU & AAX.

Melda Production's MCompressor.

Pros

✅ Based on Melda Production's powerful MDynamics engine.

✅ Refined compression with volume maximization.

✅ Adjustable compression shape is its USP.

✅Up-Sampling can be adjusted from 1x-16x, enhancing clarity.

✅ Up to 7.1 or 8 channels of processing.

✅ Can be automated via MIDI.

✅ Super-fast processing for SSE & SSE2 processors.

Cons

❌ Can't think of any!

The adjustable compression shape on the MCompressor makes it the most surgical compressor on our list. From smoothing out distortion to unique sound design possibilities, the adjustable compression shape can handle it all!

The metering displays output peak level, gain reduction, ITU-R BS.1770-1 and EBU 3341 compliant loudness. A loudness distribution graph for surgical analysis of dynamic range allows the compressor to work automatically if needed.

The adjustable up-sampling from 1x-16x lends pristine clarity to the sound. Being MIDI-friendly makes all the parameters automatable.

With hard, linear and soft knee options with adjustable sizes, this free compressor vst plugin is your go-to engineer in a box!

How Does It Sound?

Before

First 12 secs. are ‘Dry' followed by the wet signal.

After

74% custom ‘Soft Knee' activated. Notice the definition in the double-bass and clarity in the brass and violins.

5. Eareckon's FR-Comp 87:

Compatibility: Windows(XP to 10) and macOS 10.6-10.14. VST, AU. 64-bit.

Eareckon's FR-Comp 87.

Pros

✅ Free user-friendly Analogue sounding compressor.

✅ Based on the Analog87 series' engine.

✅ Integrated 0dB brick wall limiter.

✅ Dedicated slow, medium and fast speed options for attack & release.

Cons

❌ Quite restrictive. No Input, Output & Wet-Dry knobs.

❌ Doesn't match up to MCompressor or Kotelnikov for heavier tasks.

Comp87 is based on Eareckon's Analog87 series which is a bundle of 5 analogue-style VST effects.

With two large knobs controlling the threshold and the make-up gain, FR-Comp87 is the easiest compressor to use on our list after Slam Pup. Three options to change the speed of attack and release times are provided. A switchable 0dB brick wall limiter lights up when activated.

Though some of the functions from the original Analog87 paid versions might be missing, this bad boy sure packs a punch!

How Does It Sound?

Before

‘Dry' Drums + Bassline before Comp87.

After

Notice the Fast Attack and Limiter tightening the kick. It clears out space for vocals on top.

6. Beatskillz Slam Pup:

Compatibility: Windows 10 & macOS 10.13.6 or later. VST, AU, AAX. 64-bit.

Beatskillz's Slam Pup.

Pros

✅ Younger brother of ‘Slam Dawg'

✅ Pure tube compression.

✅ Innovative ‘Bark' and ‘Bite' knobs.

✅ Beginner-friendly.

Cons

❌ The distortion isn't as musical as
Rough Rider 3.

❌ Doesn't match up to MCompressor or Kotelnikov for heavier tasks.

❌ Knobs aren't tight enough.

Bark: The ‘Bark' knob mimics the tube drive of the API 2520 op-amp's preamp circuit. Following the design of their multi-stage British saturators, Beatskillz does a good job at analogue emulation.

When driven, the signal breaks beautifully, lending the track a vivid harmonic distortion, rich in overtones. If you're using soft synths or have some clean vocals which could use some ‘doggie bark', all you need to do is to set the ‘Bark' knob to around 8 O'clock.

To make things quirky, the dog's face goes from innocent-looking to angry to full-on rage as we increase the ‘Bark' value. You can operate the ‘Bark' by changing the dog's facial expression which showcases the intuitive nature of the design.

Bite: The ‘Bite' knob is based on the American design used in Beatskillz's line of products. Increase the ‘Bite' to have the Slam Pup bite more of your signal and vice versa. You could alternatively increase the size of the bone to increase the threshold.

Bone: Along with an input and output gain knob, we have a bone in the centre of the plugin. You can slide the bone to dial in your desired dry/wet ratio.

All in all, a simple and quirky compressor for beginners to get their paws dirty!

How Does It Sound?

Before

‘Dry' Drums before SlamPup.

After

Tube compression via ‘Bark' completely destroys the sound. Distortion could've been more musical.

7. TDR Kotelnikov:

Compatibility: Win XP & macOS 10.9. VST, VST3, AU, AAX. 32, 64-bit.

Beatskillz's Slam Pup.

Pros

✅ Free Mastering compressor.

✅ 64-bit floating-point precision for all calculations.

✅ Latency compensated parallel bypass (i.e. processing not interrupted)

✅ Super fast, yet natural-sounding compression.

Cons

❌ CPU-heavy.

The most sophisticated compressor on our list is also the most comprehensive.

This high fidelity dynamic range compressor can use peak and RMS separately or in tandem.
Crest Factor, sometimes called the peak-to-average ratio is the difference in decibels between the peak and average levels of a signal. You can dial in a peak crest rather than just a peak vs RMS found in traditional compressors.

The ‘Low-Frequency Relax' with variable slopes of 0/3/6/9/12dB per octave can be side-chained for shaving off your bass-heavy tracks.

The innovative amongst us might use this as a De-Esser for vocals.

With dialable ‘Stereo Sensitivity', you're no longer restricted to stereo/mono. With resampling done with very high-quality linear-phase time-domain convolution, this beast is by no means CPU-friendly!

Before Compression:

‘Dry' track before Kotelnikov.

After Compression:

Around 1dB Peak Crest, 30ms Release Peak, 10dB Soft Knee is the secret sauce for sophisticated results on transient-heavy material.

FAQ:

With so many knobs, where do I even start with compression?

Scrolling through the in-built presets is a good place to start if you don't know what you're doing.

The compressor's best qualities are enhanced in their presets. Choose a preset you like. Then, slowly start moving the knobs to taste. Knowing that you can always return to the preset values, helps you to experiment more freely.

When is it the right time to stop compressing a track?

It's common to get carried away while compressing.

To understand when to stop compressing, bypass your compressor while listening. If your track feels like it can't live without the compressor, you've hit the sweet spot. If it doesn't make a difference, you don't need compression.

Another good tip is to check the next morning with a fresh pair of ears, or check on multiple systems/get another engineer's feedback. Repeat until you get the right sound.

Music production is all about making mistakes and finding out what sounds best. Do not be afraid to crank your compressor and find to what it's doing to the sound.

What Free Compressor is Best for Vocals?

The best combination of free compression for vocals is a mixture of OTT and TDR Kotelnikov set up in a series. This gives the vocals a distinct presence (OTT), followed by a thickness and increase in output volume (Kotelnikov).

There isn't a definitive answer to which is the best for vocals, but there are certain styles that can be more useful than others. The best answer is to try out different compressors and see what difference they make. Many engineers love the LA2A mixed with the 1176 in series.

You can listen to an example we made below after testing all the compressors on this list.

In the example below, we have some female vocals with a drum track.

OTT on vocals.
Dry vocals, devoid of Compression.
Vocals with OTT Compression. (Settings as per the Image above)
Vocals with OTT + Kotelnikov in Series. (Settings as per the Image)
TDR Kotelnikov on vocals after OTT in 'Series'.


By setting up the OTT followed by the Kotelnikov in ‘series', we can achieve a distinct presence.

Starting with the OTT, the depth and time are set to 38% and 66% respectively. This allows us to achieve a moderate degree of penetration without being too aggressive. By shaving the low and high end to 1.5 and 20.9 respectively, we can have the vocals sitting in a pocket in the mid-range. This is the perfect time to boost the mids to taste.

We can now soften the vocals in Kotelnikov. Relax the soft knee by around 4dB, release peak by 80ms and release RMS by 325ms.

Notice how the vocals sound louder with no output gain on the OTT and just a 0.8dB make-up gain on the Kotelnikov.

Do I Need A Vocal Compressor?

Yes. Vocal compressors are essential in many situations. You won't need to reach for one all the time, but compression on vocals can make a huge difference in how professional they sound. They help to add thickness and smooth out takes. Much of the processing done on vocals is a form of compressor.

For instance a vocal chain might look like this:

  • Pre-Amp Gain: Aim for optimum Gain Staging of -18dBFS.
  • Tuner: Melodyne/ Wave's Tune for correcting pitch.
  • Saturation: Adds harmonic overtones.
  • Parametric EQ(Subtractive): Cleaning unwanted frequencies before compressing.
  • Compression(Cohesive tone shaping): For character, add Rough Rider3, SlamPup, API2500, Manley Vari Mu, UA1176, SSL-G, Dangerous, etc.
    For transparency, add MCompressor, Comp87, Klanghelm DC1A, Kotelnikov, FabFilter Pro C2, etc.
  • DeEsser: Compress the sibilance in letters S, F ,X, Shh and soft Cs.
  • Musical EQ(Additive): Boost using analog EQ plugins like Pulteq EQP-1a, API 550, SSL-G, Manley Massive Passive,etc. for musical results. Or use your DAW's in-built Multiband EQ.
  • Modulation Effects: Insert chorus, flanger, tremolo, stereo width, auto-pan, etc. according to the vocal style, if necessary.
    Upward/Downward Compression: Can use OTT to enhance details of the vocal effects.
    Delay + Reverb: Feed Delay into Reverb to envelope it and make it cohesive. Or send desired amounts to 2 separate Delay & Reverb Bus tracks.
    Limiter: Only if necessary. To limit excessive transients. Or use it to glue the vocal effects together.

While a metal vocalist might need a faster attack and a higher ratio, a jazz scat singer might need a lower threshold and longer release to catch the nuances.

The main aspect of a rap vocal is that it be heard clearly and blends with the instrumental in a balanced way. This is primarily achieved by having compression followed by some EQ and saturation.

Different styles of vocals may require a different bag of tricks. But a compressor is a key linchpin in almost all of them.

Hardware Compressor Emulations Better Than Digital?

The answer to the question depends on whether you're going for ‘character' or for ‘transparency'. While the digital ones might lack that analogue ‘character', some of them provide such surgical compression options which leave their analogue counterparts far behind.

Companies like Universal Audio painstakingly recreate the transistors, harmonic distortion and the 50-60hz hum in their sought-after 1176 analogue emulation plugin. While others compute equations derived from the hardware unit to simulate the output response as opposed to the input. In other designs, the code is made to directly copy the original circuits.

The more ‘transparent' digital plugins generally host a simpler code. This might cause issues like ‘Aliasing'.

The MCompressor on our list doesn't suffer from this problem due to its 1x-16x up-sampling capabilities.

Free or Paid Compressor Plugins – What's Best?

Paid compression plugins are better than free compression plugins. However, it's important to understand that buying a compressor plugin will not automatically make you better at mixing or mastering. You should know how to use a free or stock compressor before considering purchasing a paid one.

We've listed below a few things to consider before buying your first paid compressor plugin:

  1. Free compressor plugins can go a long way for most producers who don't always need the full-blown channel strip of an SSL or API console each time they work.
  2. Free plugins can be a great way to get your feet wet in the world of compression as a newbie producer.
  3. It's sometimes better to stick to the ‘free' realm till your ears develop to a point where they could acutely monitor a 0.5dB change in level on a track. That's probably the time when you're ready to appreciate the analogue mojo when you slap an expensive SSL or UA compressor on your channel.
  4. It's also worth noting that free compressor plugins like the Kotelnikov or the MCompressor can give some paid plugins a run for their money.
    So don't discard it just because it's free. The world of free compressor plugins is full of pleasant surprises

Summary

To round up, here is our list of the 7 Best Free Compressor VST Plugins for Mixing & Mastering:

  1. OTT
  2. Rough Rider 3
  3. DC1A
  4. Mcompressor
  5. Comp87
  6. Slam Pup
  7. Kotelnikov

Whether you're a beginner who wants to start noodling with Slam Pup or you're a professional who can comprehend the vastness of Kotelnikov, everyone can have a slice of the pie with this free compressor plugin article.

For more cool music production-related articles like these, check out our article on the best compressor plugins.

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