I'm always skeptical whenever the vendor is deliberately obtuse about what the product actually does.
Here's the vendor's summary:
Harshness control allows you to eliminate unpleasant high frequencies from complex signals and mixes. The intuitive controls of bx_refinement let you adjust various aspects of the sound with ease. Based on M/S (Mid/Side) processing, it imparts a tube-like analog smoothness and is a boon for mix engineers looking to tame unpleasant digital hardness on individual tracks.
I have questions.
1. What frequencies, exactly, are the "unpleasant" ones? It would appear that they've determined 3.3 KHz to be the center of unpleasantness. Sure, that's smack in the middle of where our ears are most sensitive, so excessive amplitude in the band might very well be judged as "harsh". But can you assume every mix needs a reduction at that frequency?
2. What is "digital hardness"? This strikes me as total marketing B.S. There simply is no such thing.
3. What is "tube-like smoothness"? Tubes do distort differently from transistors, and in a more pleasant way. But tubes by themselves don't encourage "smoothness", whatever that word means. They are more likely to add harmonic distortion, noise and hum. These are not characteristics I associate with "smooth". They can be overdriven for effect, but this is promoted as a mastering tool.
Reading further in the product description, they seem to be describing a fixed-frequency dynamic filter with a harmonic exciter. I'm a big fan of dynamic equalization. But my dynamic EQs are fully parametric, not hard-wired, and if I add distortion I want full control over it, too.
So I'm skeptical. However, all reviews I've seen have been either positive or at worst, neutral. Nothing bad. I'd love to try it out, if only to figure out what it really does. Eddie, how about running white noise through it and see what a spectrum analyzer shows on the other side of bx_refinement? Then run a sine wave through it and see what kind and how much harmonic distortion is being added (and check for aliasing while you're at it).