One of the joys of vintage studio hardware is its potential for revision and customisation by both its own manufacturers and 'modders' brave enough to reach for the screwdriver, and Positive Grid's drably titled new series of plugins goes some way towards emulating this.
To some, the idea will be incredibly exciting; to others it will be a level too deep; and the rest of us can just pretend to hear the difference!
The three-strong Pro Series bundle (AU/VST/ AAX) comprises FET, Tube and Optical compressors, with all but the FET looking similar to the classic hardware they're emulating. For the last two, the dynamic responses of several hardware units was measured before and after their individual elements (filters, transformers, attack, release and ratio curves), allowing you to mix and match components for - in theory - a much wider sonic range than a single model.
At the time of review, the AAX version was very unstable in Pro Tools, opening with blank GUIs and crashing the program, but the AU and VST versions worked fine, and the AAX bugs should be ironed out by the time you read this.
Optical Compressor models the Teletronix LA-2A with its big Gain and Peak Reduction knobs, and four drop-down menus along the top let you switch out various elements.
The Input Stage features a choice of three valve types (12AX7, 12AT7 and 12AU7); the two Capacitor stages can be made of Ceramic, Aluminium or Mica; and the Light Sources on offer comprise Bulb, LED and Panel, with Age and Sensitivity knobs subtly affecting the amount of compression and attack times respectively.
Below the fascia are the customisation options: Attack and Release controls (two of the latter for the two distinct release stages of an optical compressor), a Mix knob, an Input level knob, a Curve knob (soft to hard knee), and, most interestingly, a valve Bias control for subtly varying the tone, dirtying the sound and adding crunch.
The 12AU7 valve is particularly filthy, with deliciously gritty distortion. The industry favourite 12AX7 is tough and warm, and, with additional biasing, can give that classic valve thickness we know and love.
The two capacitor stages, on the other hand, don't really have much impact on the sound - they're supposed to affect tone and attack/release characteristics, but it's hard to discern the difference.
The Light Source options cause vaguely perceptible changes in peak detection - subtle in the grand scheme of things. We're a bit surprised at the lack of high-pass Filter in the detection circuitry.
Tube Compressor looks just like the Fairchild 660 on which it's modelled, and as well as the controls you'd expect (Input Gain, Threshold, Output Gain and Sensitivity, the last the equivalent of the Fairchild's Time Constant release control), it boasts the same selection of Input Stage Tubes (12AX7, 12AT7 and 12AU7) and Capacitors (Ceramic, Aluminium and Mica) as Optical Compressor, plus a choice of two Output Stage Tubes (6L6GB and EL34) and three output Transformers (American Style, British Style and Fat Style).
The output tubes open up a range of saturation colours and distortions, while the transformers subtly vary in terms of warmth, fullness and bottom-end 'glue'.
The lower panel hosts Bias knobs for each tube stage, essentially adjusting the drive or 'valve effect'; an automatic gain Make-up switch; a wet/dry Mix knob; and a Curve Knob to shape the knee from hard to soft.
The compression is gentle and almost perfectly transparent, as you'd expect, but it's the range of subtle tonal shaping on tap that make Tube Compressor a winner. Basses, acoustic instruments and vocals can all be delicately pushed so that they blend with each other into a coherent mix. Again, though, no high-pass filter is included.
FET Compressor is the only one of the three that isn't a direct emulation, although it does bear a passing resemblance to the Softube FET compressor plugin, which is a model of the Urei 1176.
It's also the only one that doesn't let you change its components. Input, Output, Threshold, Ratio, Attack and Release controls make up the main panel knobs, sitting alongside an In/Out/Gain Reduction meter select switch. Below the main panel sit the sidechain parameters - Peak/RMS detection, Low and High Cut, and Look Ahead - as well as Knee Width and Mix (for parallel compression) controls.
In use, FET Compressor is unconventional: the Threshold lowers as its knob is turned clockwise, which takes a bit of familiarisation if you're used to the more orthodox arrangement. It sounds pretty good, though, with that classic FET bite lending attitude and energy to drums, and the quick release pumping up their tails.
With so many compressors on the market, coming up with a new angle on them isn't easy.
The variable components of Optical and Tube Compressor do achieve that goal, though, being more than just a novelty.
The Capacitor options are perhaps too subtle for all but the bat-eared, but the valves and accompanying biasing possibilities, as well as the Transformer options, give an impressively broad palette from which to get interesting saturations as well as some punchy compression.