21kHz,dang you must hang upside down and Schiit on the floor of caves. A little Bat humor. I used to be able to make it to 20 kHz when I was young, nowadays I can still hear just over 17 kHz which is probably much more than I should at my age. IMO to a large extent, there's a lot of imaginative claims about what they can discern about sample rates and resolutions best fitted for lab equipment. For now, I'll leave it alone. Till someone starts up again.