QES Labs Variable Gm

The Variable Gm is a true analog tube stereo compressor, a serious piece of gear with a lot of option to choose from, since it's built on order. The available options are: mastering version, NOS tube set, custom wound transformer set, Mid/Side Matrix, Wet/Dry control, suitable for 'parallel compression'. A piece of gear like this is what makes the difference in a studio, and is really what sets professionals from amateur.
It comes in a 3U high, 16.5 inch deep rackmount steel alloy chassis, and an external PSU, the total weight is about 53 lbs! (24 Kg).
Tubes are used throughout the audio path, while huge coils and big capacitors are used to filter the supply.
The controls are: Input, Output, Attack, Release, Threshold, Stereo link, Side-chain HPF, and hard-wired bypass. The (really nice looking) analog panel meter reads: Input, Gain Reduction, Output, via 3-step selector.
The mastering version comes with gold-laminated 24-step Elma attenuators, which track perfectly together.

UTILIZATION

Using a piece of gear like this definitely requires some practice. While most of the parameters are self explanatory, some will require some time to play around with. Reading the well written manual is of much help.
Anyway this amount of controls is what makes this a sublime compressor.

SOUND QUALITY

I have used this compressor on voices, bass, drum buss with great results, it is very easy to shape the sound you're looking for in many different ways, anyway it really excels on the mixing and/or mastering duties. It can be smooth and soft, or have a lot of character when pushed hard, still retaining transparency and being unobtrusive.
The sound can be incredibly warm, punchy when set properly.
The stereo three-dimensional image is astounding, huge, really interesting the color it imparts.
The overall sound quality of the Variable Gm is nothing less than outstanding, a rare gem with musical qualities.

OVERALL OPINION

If you're looking for a serious compressor as a top of the line gear for your professional studio, the Variable Gm is absolutely one worth considering.