According to master audio designer Rupert Neve though we do not "hear" the frequencies above 20KHz we can tell when they are missing!
I believe we've been through this before. I run a simple test using two audio oscillators, an amplifier and a guinea pig (human) or two with which the need for higher frequencies than the subject "can hear" is obvious. The discussion was some time back but if anyone wants to hear about it again, I'll re-create it. (Easier than chasing it down in the archives.)
Mike -- mrichter@xxxxxxx http://www.mrichter.com/