I cut off at 17khz according to this thing.
However I am not entirely sure whether it's me or maybe my earphones just don't play these extreme frequencies, or maybe the sound drivers ignore them somehow.
Just because you can't hear it doesn't mean it's your fault. Maybe your headphones can't play it.
And according to this thing I heard some minimal but present hiss all the way to 20KHz
My 50 cent earbuds are playing to at least 18kHz.
Similar result as for me, from 2hz to 16.3k or so.
Interdasting - I couldn't hear the 15k on that video, but when I used the Expression Evaluator in GoldWave to generate a 15.5k sine wave, I could hear it - and even 16k (barely).