I have heard that most people over 30 do not hear frequencies up around 20kHz. So I wanted to know if there are frequency sweeps or some type of .wav files somewhere to download from 15kHz and above. I have some up to 20 hz, but not above that. I am curious what I can hear. Anyone else curious about this or have done some experimentation in this regard? I took a hearing check a few years ago and passed, but have no idea what the specifically checked and what passing means.