Ears and Eyes
Apparently “kids these days” are using ring tones that adults generally can’t hear while in school for their text messaging alerts.
Which, naturally, I care not a whit about.
I do find the biology aspect rather interesting though, and I’m not alone. There’s a blogger that has put up a series of test audio files for you to check your own hearing.
With headphones on, AIWA brand, I was able to hear up to 22,000 Hz. I picked that particular set of headphones out because they had such a wide range of frequency, and since I listen to a fair amount of classical music, I figured that was a pretty important thing to have.