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electronic MUSICIAN

FabFilter Pro-C 1.12 (Mac/Win) Review

By Michael Cooper | April 9, 2010

FIG. 1: At the bottom of Pro-C''s GUI, animated displays dynamically show the value of several I/O and compression parameters.

FIG. 1: At the bottom of Pro-C''s GUI, animated displays dynamically show the value of several I/O and compression parameters.

Does the world need another compressor plug-in? In the case of the FabFilter Pro-C, the answer is a resounding, “Yes.” Outstanding sound quality, parallel compression, and unmatched sidechaining capabilities are enough to raise mix engineers'' eyebrows. But mastering engineers should also take note: Pro-C is one of only a few plug-ins that offers high-quality mid-side (M-S) compression.

Pro-C''s 64-bit internal processing promises virtually unlimited headroom. The cross-platform plug-in comes in AU, RTAS, and VST formats. I tested the AU version in MOTU Digital Performer 6.02 using an 8-core 2.8GHz Mac Pro running Mac OS X 10.5.4.

That''s So Classic
Pro-C offers three modes of compression: Opto, Clean, and Classic (in ascending order of inherent knee hardness). You can also choose a relatively softer or harder knee for each mode, as well as tweak the input gain, input pan (for the 2-channel version), threshold, ratio (from 1:1 to infinity:1), and attack and release controls for each mode. The time constants for the three compression modes are program-dependent to varying degrees, but are also influenced by your manual settings. (Opto mode is the least program-dependent and Classic is the most.) A defeatable Auto-Release function tracks the amount of gain reduction to further adjust the release time.

Separate output-level and pan controls are provided for compressed and unprocessed signal paths, empowering you to fashion 
parallel-compression effects. Activate the Auto-Gain switch to have makeup gain automatically applied to the compressed signal. In M-S mode, the two output-pan controls become balance controls for mid and side channels'' levels. One pan control adjusts levels for compressed mid and side channels, while the other pan control sets levels for the unprocessed M-S signals. For the uninitiated, M-S processing separates a stereo input signal into center-panned components (audio common to both left and right channels, called the mid channel) and difference signals exclusive to each stereo channel (called the side channel).

FIG. 2: When you click on the Expert mode button, Pro-C minimizes its animated displays and shows controls for sidechaining and M-S operation.

FIG. 2: When you click on the Expert mode button, Pro-C minimizes its animated displays and shows controls for sidechaining and M-S operation.

Beginning engineers will love Pro-C''s insightful animated displays, which dynamically update I/O and gain-reduction levels and show the relationships between input levels and current control settings for knee, threshold, and ratio (see Fig. 1). Seasoned engineers may elect to disable these displays and halve their GUI footprint to focus their attention on Pro-C''s LED-style I/O and gain-reduction meters.

On the Side
When you enable Expert mode, controls for sidechaining and M-S operation appear in the GUI (see Fig. 2). The detectors can receive input filtered by Pro-C''s adjustable internal HPF and LPF sidechain filters, or they can be keyed from any external source (for example, another track) bused in to the plug-in by way of a dropdown menu.

Pro-C''s internal sidechaining capabilities are as flexible and powerful as those for any hardware or software dynamics processor I''ve seen. Four continuously variable gain and pan controls feed the detector inputs for left and right (or in M-S mode, mid and side) channels. The pan controls determine where each channel''s detector derives its signal, while the gain controls adjust the level of signal received by its recipient detector. For example, to compress only the side channel with only that channel feeding its own detector input, I first turned the gain for the mid channel''s detector all the way down so it virtually wouldn''t receive any input. Then I turned the side channel''s detector-pan control fully right to the side-channel position, limiting the detector''s input to receiving side-channel signal only.

Sound complicated? It is, but having so many controls allows you to set up any sidechain configuration imaginable. Examples include cross-channel compression (for example, the left or mid channel triggering compression in the right or side channel, and vice versa), channel linking (each channel''s detector input receives signal from both channels at once), fully unlinked channels, and even somewhat-linked channels (each channel feeding one or both detectors to the degree its gain control is turned up in the sidechain section). If all this sounds too confusing to hassle with, simply turn off Expert mode and operate Pro-C in its default stereo-linked mode.

Facilities for storing and recalling control setups in A and B workspaces—or alternatively, as permanent presets—are provided. Pro-C also allows you to control its parameters using a MIDI controller; MIDI-learn functionality aids setup.

I''m Crushed
Opto mode, with a soft knee, generally sounded the most transparent on lead vocals. Classic mode, with a hard knee and the internal HPF raised to 5kHz, provided world-class de-essing that was ultratransparent and effective.

Classic mode and parallel compression beautifully enhanced the crunch of 
double-tracked, hard-panned electric guitars while adding density. The hard-knee setting created a wonderful wall-of-sound effect without thinning the sound too much. A similar setup made drum-room mics sound positively explosive.

Clean mode, with a soft knee, sounded the most pleasing for stereo mastering, providing transparent yet effective control. Rolling off the bottom end in Pro-C''s sidechain made bass transients trigger the compressor less, resulting in a punchier sound.

Activating M-S mode, I could widen or narrow the mix and compress only the mid or side channel (or both). That said, using Pro-C''s pan controls to adjust the balance between mid and side levels seemed counterintuitive to me and caused unintended results when switching between M-S and stereo modes. For example, in M-S mode, turning the output-pan control clockwise from the noon position increased the side channel''s level relative to that for the mid channel. But when I switched to stereo mode to try something different, the retained (skewed) pan-control setting threw the mix''s imaging off to the right. I could work around this workflow snafu by storing my current stereo setup into Pro-C''s A workspace and my M-S setup 
into Pro-C''s B workspace (always using the workspaces to switch modes).

For M-S mastering applications, a better and more intuitive design for Pro-C would be to use the output-level controls for M-S level balancing. You could then use the output-pan controls to adjust imaging for the side channel. You can use the input-pan control as is to center the mid channel.

In addition, Pro-C arbitrarily retains sidechain control settings when switching between stereo and M-S modes. As these modes often require different setups, this is not optimal. Again, the A and B workspaces provide a workaround.

Something for Everyone
Pro-C sounds outstanding on a wide variety of individual tracks and full mixes. Innovative displays aid the beginner in understanding basic compression setups. A boon to professional mastering engineers, Pro-C is one of the few plug-ins that currently offers M-S compression, and its sidechaining capabilities for both stereo and M-S processing are unequaled.

That said, Pro-C''s Expert mode would be much more user-friendly if it had independent sidechain, level, and pan controls for stereo and M-S modes. The GUI''s implementation of M-S balance control is particularly flawed. Mix engineers who never touch M-S processing, however, will find Pro-C''s GUI to be nearly faultless.

Despite its interface shortcomings, I''ll continue to use Pro-C (including its M-S processing) in my professional work—the tradeoffs are worth it. Pro-C is a versatile and wonderful-sounding plug-in that, most notably, fills an important gap in current mastering offerings. And at $199, the price is right. 

EM contributing editor Michael Cooper is the owner of Michael Cooper Recording in Sisters, Ore. Visit him at

Click on the Product Summary box to visit the FabFilter Pro-C product page

Click on the Product Summary box to visit the FabFilter Pro-C product page

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