To me is like a sort of brigthness or mid to high frequency distortion. In this case, the "Wanna Be Startin' Somethin'" song starts with some "tss tss" stuff. It comes across gentler with the HD600s and more agressive with the AZ PM2s. This "tss tss" stuff is not way up high in frequency though, but it's not narrow band tones either. It's is probably not comming from an instrument, but some electronic gadget, so it may have sounded that way originally, and the 600s are mitigating the effect, but I doubt it.

I use the word glare because it feels to me as if that part of the song gets sharpen.

I don't have an ODAC, so using a Focusrite 2i2.

It could still be the 2i2, but I doubt it. This is where measurements might provide some clues. The PM's are not particularly well behaved in the mids the way the HD600s are.

LOL, actually I have a set of cheap computer speakers that measure relativley flat, but had some problems in the mids. I did a sine sweep back then, and at the 400 Hz trouble spot, it got something similar to what I describe as glear here... When similar problems happen in the bass area I usually hear farts.

   Honestly very puzzled about those measurements. On my own rig original PM-2 and my modded sets don't measure similar at all, please see the image attached (sorry about the size of the image, will do better next time;-). Well they don't sound similar at all to me neither so maybe my ears are strongly influenced by the aforementioned rig but really, put them side by side and there will be no resemblance of one with another pretty much at all. And about the low frequency extension on your measurements, to me there is just another puzzle.



 

 As for your own measurements of HD-600 vs other headsets, notice how all of your measurements display a dip starting around 1,5Khz and centering around 2,5Khz while HD-600 is just the opposite looking nice and fairly smooth in that area. Well, on my rig that's precisely where the well known HD-600s midrange peak is centered: 2,5Khz. After that there is a fairly smooth and deep roll off which in my opinion will surely mask glare present on some recordings. 

FWIW, the Oppo PM-1 and the PM-2s modded by AZ were measured using the same rig and exact same method. I also have a set of PM-1 measurements as well... and they measure relatively close as well!

I also saw Alex measurements, which came included with the cans Alex sent. Did not get that at all. Did you position the cans the same way stock vs moddified? I can say that the Oppo based cans tend to show little variability in measurements unless one goes way overboard with how one positions them.

I did have an odd ball modified Oppo by Alex before that did not measured at all like the current production. An earlier generation which could have had broken drivers. Those didn't do very well...

Dunno mang. Maybe is the ODAC

Hans, what are you using as a coupler to the mic? (note these didn't measure exactly like HD600s BTW, they seem to have retained some of the Oppo characteristics though)