The White 2A Leveling Amplifier is based on a legendary vintage unit that is entirely tube-based. It's a totally different device in terms of construction where all the compression magic happens inside an optically coupled element formed by a fluorescent panel and some photocells: the famed T4A element. There is no electronic circuitry involved with the compression itself. It's just a tube amp with photo-resistors, lighted by a fluorescent panel driven by the output signal.
At the time of this invention, there were not many ways of making an audio compressor: only variable-mu and optical. Optical was the simplest one, and if proper elements for both the light emitting panel and the photocells were matched, magic happened.
On par with the other great classic compressor, the 1176, the White 2A is so simple to use, yet very effective: just set the peak reduction knob to achieve the desired limiting effect, and adjust the gain knob to set the output level. The result is a gentle, warm and fat compression is just magic at evening out dynamic tracks where a smooth and consistent compression is needed.
Probably the most used compressor/limiter on vocals in music history it makes them stand out in a mix giving them consistent level and less need for fader rides. When driven harder it gets personality out of them, also thanks to the tube output stage and its harmonic enriching effect.
As for other compressors in the T-RackS series this module has the advantage of the digital only features allowed by the DAW format. So instead of having the need to purchase two, you can simply insert one across the stereo bus of your DAW of choice and enjoy the incredible and even leveling effect its capable of.
Bass looks like another good candidate for this module, where wide dynamics are gently kept under control with the subtle yet very pleasing harmonic saturation courtesy of the tube electronics.