Provoc Grader VX is a vocal compressor built to be fast and precise. What's unique about Grader VX is that you can choose to apply compression to a range of frequencies and leave the rest of the spectrum untouched. This feature is best used on signals with high dynamic range (such as vocals), where you may want to preserve a lot of natural dynamics and still achieve a steady overall volume.
Grader VX is not limited to vocals. When 'Resonance' is set to max (10), Grader functions as a normal compressor and can be used on a wide variety of instruments.