I tried the black filters just now. The difference is immediately apparent. However, it is a mixed blessing, along the lines discussed regarding where the boundary is between "midrange" vs "treble."
I think previous descriptions comparing black to gray filters are valid, and it meets what I interpret to be Audéo's intent - to bring up the bass and treble relatively but in a natural way. The upper bass was fuller, sometimes causing bass guitar fundamentals to mask their harmonics too much. The treble seemed flatter and smoother. But a broad, smooth decrease in mid-midrange through the lower treble was apparent.
Jennifer Warne's voice (The Well) was warm still, maybe warmer, but seemed mixed much lower and sounded further away. The treble seemed very obvious, but actually more graceful... it seemed the lower treble was attenuated a bit and upper treble was just as present. The middle and upper partials of voice were set back (but still quite audible). The sibilance range was diminished, and integration around the midrange-treble seemed smoother but tipped up, relative to the gray filters. Percussion instruments on Dave Grusin's One of a Kind had plenty of presence in the mix, and sounded natural, perhaps a bit moreso. But they seemed mixed to high compared to the midrange.
My preference would be to (magically) lower the lower treble (sibilance is evident at times, now that I have the grays back in). But I'd like the middle midrange to be brought up a bit.
So, to see if this makes any sense in terms of the FR charts:
What I would like is for the "bright" range from 3 to 5kHz to be brought down from the gray filter line, closer to the black line. But I'd want the midrange from 500 to 2500Hz to level off, joining the gray curve on the low end to the black curve on the upper end of that range. Of course, who wouldn't want "flatter?"
So, since I prefer midrange that is not recessed, I returned to the gray filters. But the smoother lower treble of the black filters would be nice as well.
