The beats we hear on 50 Cents’ “In da Club” or N.W.A.’s “Express Yourself” are near the low end of our range of hearing; the ending of “A Day in Life” on the CD of the Beatles’ Sgt. Pepper’s Lonely Hearts Club Band has a few seconds of sound at 15 KHz, inaudible to most adults over 40! (If the Beatles believed to never trust anyone over 40, this may have been their test, but Lennon reportedly just wanted something to make people’s dogs perk up.)
