-30db for me on my Senn HD497.
Weird thing is that if I play the whole track its hard to decern in my ears the distortion. If I only play the first 3 second of the guiter string I can easily identify it when I quickly switch A-B.
Also everytime I hear the distortion I say to myself thats how my tube amp sounds...lush and more grainy.
So in all my tests I say to myself what sounds like my tube amp and I get it right all the time up to -30db.
ps: I have a pretty high noise level on my computer fan beside me that I can still hear with my headphones on. I do not know if I would have scored higher if that sound was totally isolated.
Plus I got tinitis which doesnt help.
