FabFilter Software Instruments
There are plenty of paid and free audio plug-ins on the market. They all fit into the good, the bad, or the ugly categories – some great, some not so much. One of the better developers of modern audio plug-in effects is FabFilter Software Instruments in the Netherlands. While FabFilter products are known and respected in the music recording industry, they are not as well known among video editors. Any of their plug-ins would provide you with a great software tool, but the plug-in that I felt was the best fit for a video editor was their Pro-L 2 limiter plug-in.
An audio limiter, just like a broadcast safe video limiter, is typically used as a mastering tool applied to the last stage of the audio chain. You can certainly use a limiter on an individual track, like drums in a recording session or a voice-over in a video mix. However, limiting is most often applied to the final output – the master or mix output bus. While a limiter is really just a variant of a regular compressor, it is optimized to catch and restrict all peak levels and transients in order to make sure that your mix is compliant with a given loudness target.
FabFilter Pro-L 2 Limiter
Like most third-party plug-ins, the Pro-L 2 limiter installs as an AAX, AU, and/or VST/VST3 plug-in and so is compatible with most DAWs and NLEs. FabFilter plug-ins use a license key activation code after installation, so no need to mess with separate license management applications or a physical iLok hardware key. I tested the Pro-L 2 limiter in various applications and performance and behavior was great, even in Final Cut Pro, which has lately been touchy for me when using some third-party audio effects.
At first glance, the Pro-L 2 limiter might seem like most other limiter filters, but looks can be deceiving. This plug-in is rather deep with many nuanced adjustments that are easy to overlook. The good news is that FabFilter has done a good job with video tutorials and both an online and PDF user guide.
There are three big selling points for me. First, Pro-L 2 supports various mix configurations – not just mono and stereo, but also surround, including Dolby Atmos. Second, there’s built-in loudness metering. This includes an earlier K-system metering method (developed in the late 90s by noted mastering engineer Bob Katz), as well as current ATSC and EBU loudness scales. Finally, it’s the sound. You can drive the input truly hard into gain reduction and the audio stays extremely smooth-sounding without coming across as heavily compressed or distorted.
The Pro-L2 user interface is well-designed with several size options, including full screen, as well as a compact mode that hides the audio waveform graph. Metering can be changed from standard (input, output, gain reduction meters) to full loudness. Several of the components, like the advanced control panel and output gain knob are fly-out panels that might not be readily obvious until you get used to the plug-in. As this is a minimalist UI design, there are other controls, like oversampling and true peak limiting, which are enabled by small control buttons along the bottom.
One UI tool that I really liked was the lock icon. When this is unlocked (disabled) then every time you switch between limiter algorithms or presets the input and output gain levels reset, which makes it harder to compare settings. However, when it’s enabled, the gain levels are “locked” as you toggle through the options.
One final UI feature to note is that you have control over the waveform scrolling method. The display represents audio levels, gain reduction, and peaks. There are four scrolling modes depending on how you prefer to see the waveform being drawn onto the screen.
The key to the FabFilter Pro-L limiter is how it handles sound. There are numerous presets and eight limiter algorithms designed with distinct character depending on the type of audio you are processing. The last four (Aggressive, Modern, Bus, and Safe) were newly added in version two of the limiter. So whether you want something with a little crunch or totally transparent, this limiter offers you choices.
The general operating controls are similar to other compressors and limiters. There are input and output gain controls – the combination of which determines the amount of gain reduction (limiting). Attack and release controls affect how quickly and how long afterwards limiting is taking place. In addition to lookahead (how far ahead the software is looking for predicted peaks), there is also an oversampling control, which may be CPU intensive. Sound is analog, so fast peaks can occur between the regular digital sampling intervals. These peaks can, therefore, be missed by a limiter. Oversampling is a technique to catch and process any inter-sample peaks.
Channel linking is another powerful tool. Generally, a plug-in is going to process the left and right sides of a stereo signal equally. But what if your track has harder peaks on one side or the other? That’s where the channel linking controls come into play. The Transient control knob alters the amount of linking on short transients. 100% is equal on both sides, but then you can dial down the percentage of linking from there. When working with surround, these control knobs change to add functionality for the C (center) and LFE (subwoofer) channels. When these buttons are engaged, the C and LFE channels are integrated into the linking process.
One feature that is supported by most DAWs, but not by most NLEs, is side-chaining. This is a method by which the dynamics of one track control the compression/limiting being applied to a different track. For example, you could apply the limiter to a music track, but use a voice-over track as the side-chain input. This technique can be used to duck the music under the voice every time the person speaks.
Honestly, I’m not a huge fan of music ducking in the first place, because I don’t think it sounds good compared to riding the levels manually. However, it is available. I tested this with the Pro-L 2 in Logic Pro. Quite frankly, using the same process and the native Logic Pro compressor yielded more pleasing results. That’s not surprising. Although compressors and limiters are audio cousins, they do process audio a bit differently. Since it’s not a method I use anyway, it wasn’t a big deal, but still worth noting.
FabFilter Pro-L 2 offers a lot of depth and you really need to go through the user guide to fully appreciate its intricacies. That being said, it’s super easy to use. But for me, the quality of the sound is the key. I was impressed with how hard I could drive it when I needed to and still maintain good sound and proper loudness levels. That makes it worth the price of admission.
As a developer, FabFilter Software Instruments seems to be on top of things. If you are a Mac user, these plug-ins are already Apple Silicon-compatible. That not true of every audio plug-in maker. If, like me, you work across multiple NLEs, then it’s nice to have a consistent set of plug-ins that work and sound the same regardless of which NLE I’m working in. FabFilter Pro-L 2 definitely fits that bill.
In Part 4 of this series, I’ll take a look at some of the free filter options on the market.
©2021 Oliver Peters