Paul McCartney says The Beatles put a frequency on “Sgt. Pepper” that only dogs could hear. “I asked my engineers why vinyl sounds good and they explained that there are frequencies above and below that you can’t hear… We put a sound on “Sgt. Pepper” that only dogs could hear. If you ever play “Sgt. Pepper” watch your dog.” The sound in question is a dog whistle on “A Day in the Life” that cannot be detected by the human ear.
Ironically, “Sgt. Pepper” was the Beatles’ reaction to “Pet Sounds” by The Beach Boys, which also features a dog whistle. And it was during the making of that album that singer Mike Love joked that Brian Wilson had dog ears due to some of the sound effects he used on it.
Paul McCartney on vinyl and some of the frequencies you can put on a vinyl record:
Brian Wilson on Mike Love saying he had dog ears during the making of “Pet Sounds”: