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Sean Cook
On the Beatles Sgt. Peppers album, on the song "A Day in the Life," a strange thing might occur....your Dog might start to howl. What? Huh?
Humans can hear frequencies up to 20kHz, but Dogs can detect sounds well above our capacity (as high as 45kHz) But "silent" dog whistles don't even exceed 13kHz, which should be well within our audible range. The reason for this lies in sound pressure. Any sound above 10kHz must basically be "blasted" at a high decibel(dB) level for humans to hear, but a dog can hear the sound at even a low dB level. Therefore, a dog whistle, at 13kHz and 80dB may not be audible to a human, but your dog might flip out. Sir George Martin was (and still is) a musical genious, he is considered one of the greatest record producers of all time, and also known as "The Fifth Beatle". Inputting frequencies such as these would have been no problem for him, even in the sixties with only analog technology. Paul Mcartney and John Lennon used to talk about these frequencies and decided to play a joke by adding it to the album. Paul admitted this and said ....“We’d talk for hours about these frequencies below the sub that you couldn’t really hear and the high frequencies that only dogs could hear, we put a sound on Sgt. Pepper that only dogs could hear,” he said. “If you ever play Sgt. Pepper watch your dog,” he added.
The whistle is actually audible on the CD, but not on vinyl. The reason you can hear it on the CD and not on vinyl is because of the Sampling Theorom. When CD's are sampled, an analog signal is turned into a digital signal, and then obviously back to analog again when you hear it. In order for waveforms to be converted without a loss of information (aliasing) the sample rate must be GREATER THAN double the frequency. Because a dog whistle has such a high tone, it would be extremely difficult to sample at a rate high enough to keep it the same, because the sample rate is lower than double that frequency, so it is pitched down, thus making it audible to the human ear much more clearly on cd than on the vinyl record, which obviously does not need to be sampled.
Very rarely some humans can hear this high frequency range because they have above average hearing, mostly young children who exquisitely still have all the tiny little hair folicles inside their cochlea. These people often complain about hearing the driver circuitry inside of an old CTR based TV, or failing hard drives,ect... but on average, as these little hairs die over time, we lose the ability to hear in this range. If you find all this hard to believe, slap on Sgt. Peppers and go get your dog.
