FabFilter Pro-L2 is a limiter plugin, the revised and improved version of its Pro-L predecessor. FabFilter has gone from strength to strength over recent years, becoming a household name in the world of music production.

I have previously reviewed Pro-R and Pro-G, respectively a reverb and gate plugin. Take a look at those two articles as both plugins are well worth checking out.

A Few Words About Limiting

Limiting is a difficult subject to have a balanced conversation around. The technique itself is an essential skill for a music producer. However, it is the use, or perhaps overuse, of limiters in the digital age that has led to the loudness wars. Simply put, the race to make mixes seem louder and hence instantly more desirable to the listener resulted in a widespread loss of quality and clarity. The challenge then, for plugin companies, is to produce limiters that can compete with the modern standards for perceived loudness while making sure not to crush the audio into oblivion.

See also: FabFilter Pro-R Review

Using a limiter on the master channel is something most aspiring producers will tackle early on, but like compression, it does help to at least have a basic understanding of what is happening. Limiters are very similar to compressors but with a few fundamental differences which make them more suited to a specific task. Whereas a compressor will have an adjustable threshold, above which the audio will begin to compress at a ratio set by the user, a limiter will have a fixed threshold at the target volume level. Very often, the compression above this threshold will be very extreme, hence the term limiter. I like to think of the limiting threshold as a ceiling, and my audio as a blob of plasticine. The more I push the sound up towards the ceiling, the more squished it’s going to end up.

User Interface

FabFilter has an instantly recognizable aesthetic to their plugins, somewhere between science fiction and science lab, and Pro-L2 is no exception. As I’ve said in previous reviews, their GUIs are a pleasure to use. The graphics are modern, if not futuristic and sleek, and the layout and visual metering make the plugin so easy to work with that I find myself preferring them over their contemporaries just because they are so ergonomic. Pro-L2 will have a sense of familiarity to users of other FabFilter plugins, and newcomers will find their way around Pro-L2 very quickly indeed.

Most of the plugin’s real estate is given over to a visual meter, showing the audio coming into the Limiter in real time. Like several other FabFilter plugins, the input and output audio levels are superimposed over each other, the input being in light blue and the output in dark blue. This gives you a very quick and simple visual representation of where your audio is sitting as it enters and leaves the plugin. It also shows the level of gain reduction in a thin red line and labels the more significant reductions for you. Additionally, there is also a loudness curve, a thin line which measures the perceived loudness of the audio.

Controls And Workflow

A quick aside on loudness. Although whether something is loud or not seems like it should be a painfully simple matter, it, unfortunately, isn’t. There is a tremendous amount of research and scientific advancement taking place into the way humans perceive loudness, and various standards have cropped up to try and deal with loudness as an issue, and an accurate understanding of it requires a bigger brain than mine. Fortunately, FabFilter has your back. By selecting the ‘Loudness’ option on the bottom-right metering tab, a loudness meter appears and is linked to the loudness level on the primary display interface. This can be set to various accepted standards, for all sorts of applications, such as television, CD, broadcast, and even social media. Additional, a True Peak Limiting mode is an addition that helps prevent distortion caused by peaks between samples read by sample-peak meters. While testing I treated this option as a set-and-forget button, I couldn’t see a good reason not to have it on.

The gain control on the left raises the level of the audio and pushes it into the limiter threshold. This is relatively common to all limiters. However, Pro-L2 has some added features that make this better than a shot in the dark. The 1:1 mode allows you to hear exactly what the limiting is doing to your sound, without hearing the volume increase (there is a tendency to prefer a signal that is louder, therefore removing the volume increase gives you a clear and unbiased look at what Pro-L2 is doing). Also, Audition mode allows you to hear just the gain reduction itself, the ‘delta’ signal. Here, you can listen to exactly what is being removed during the limiting, for instance, if too much of your transient material is being chopped off, or if unwanted distortion is occurring. I can’t think that I’ve ever seen this feature on a limiter before, and although unusual to listen to, it does make perfect sense. Both of these controls are accessed on the in/out options tab.

FabFilter Pro-L2 features a redesigned user interface.

FabFilter Pro-L2 features a redesigned user interface.

The advanced controls add a new layer to Pro-L2 that users of the previous version may enjoy. Four new modes have been added. Modern is an all-round setting that is the new default algorithm. The Aggressive mode works well with EDM music. Bus mode is meant for individual channels and groups and adds more distortion than the other options. Finally, Safe mode goes to all lengths to avoid distortion wherever possible. Pro-L had a reputation as being a fantastic transparent limiter, but these new options expand its palette. It can now be as transparent or as colored as you wish.

The Lookahead control should be a familiar sight to most. At the expense of a bit of additional CPU processing, Lookahead instructs the plugin to examine the audio slightly prior to it hitting the limiter, therefore giving the limiter more time to react to upcoming peaks. As the speed at which a compressor kicks in is part and parcel of its sound and character, dialing this correctly is part of the challenge. More lookahead time results in a smoother sound and preserved transients, but also risk distortion as the limiter is kicking in over a shorter period.

Pro-L2 is a two-stage limiter, with a high-speed ‘transient stage’ and a slower ‘release stage’ envelope. The attack and release dials control the release stage, which is slightly different to a typical compressor. The channel linking controls allow further control over how both of these stages are linked across the stereo channels.

The Sound

FabFilter has set out with Pro-L2 to make a limiter plugin that covers all the bases. It doesn’t matter if you need the plugin to be transparent and get your music up to a level where it can be listened to alongside its contemporaries, or whether you want to pin a bass track in place in the mix with a little additional grit, you can reach for Pro-L2. Before Pro-L2’s release, I don’t remember users clamoring for extra features on its predecessor. In fact, it was widely regarded as one of, if not the best software limiters available. Kudos then, to FabFilter, for taking a product that was already working well and taking it to another level.

When I’m using a limiter, what I want is for my mix to be preserved. I’m a big fan of top-down mixing, so most of my master bus processing is dialed in from the start. When I was testing Pro-L2, every mode and every preset sounded pleasant to my ears, but most importantly, my mix was preserved beautifully. I could raise the gain without feeling the dynamics get squashed, but equally, I could use it on an individual track to control an overly-dynamic instrument, and in both very different applications, I liked the results. Also importantly, the excellent metering and intuitive functionality gave me a better sense of control over what was happening to my music.

The Verdict

I feel that FabFilter have a good grasp on getting the science to support the art. When asking for help, we’ve all heard that beautiful piece of audio advice: “Use your ears.” While undoubtedly true, it’s not actionable advice and therefore not always helpful. The person asking for help is in no better position for that particular piece of information. All this does is cause them to question whether they were somehow bestowed with faulty ears.

With Pro-L2, however, I can, of course, listen to the results, and judge whether I like what I am hearing, but crucially I can also use the meters to check visually that nothing untoward is happening. I can use the audition mode to check for distortion, and the loudness meter to make sure I’m not going to lose the energy of my song when it’s uploaded to Youtube. A great interface is not only a tool for production, but it also helps you learn and gain confidence in your audio decision making.

Pro-L2 sounds excellent. It’s flexible and diverse, easy to use and easy to learn. FabFilter maintains their excellent reputation with another great plugin.

More info: FabFilter Pro-L2 ($199)

FabFilter Pro L2 Limiter Review


Pro-L2 sounds excellent. It's flexible and diverse, easy to use and easy to learn. FabFilter maintains their excellent reputation with another great plugin.

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  1. Your Verdict section – especially the first paragraph of your Verdict, re. “use your ears” – well said! I tire so easily of people who think that that is a worthwhile thing to post in a forum thread, in response to someone validly asking a community their individual opinion on some tool or plugin or other. It’s just a lazy, unhelpful, condescending thing to post.
    Any plugin that assists visually with some act of mixing (eq, dynamics) is always more useful in my book.. Skeuomorphic interfaces just look lazy to me these days – especially in a world with plenty of FFT visualisation tooling, and any amount of unused GPU power ready to do some work in a modern computer, when our CPUs are busy crunching the plugin algorithms. Wish more plugins (delays, reverbs, modulation) tried out similar visualisation techniques as part of their interfaces, so we could see what its doing to the audio passing thru them. Why not?

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