‘Silent Night’, as you might already know, is a beautiful Christmas carol which is sung in every Christian home especially in the month of December.

But, what is “A very Silent Night”? This too is music. But no one can tell if it is as beautiful because no one has ever heard it!

The CD ‘A Very Silent Night’ is exclusively for dogs! Produced to raise funds for the New Zealand SPCA, the song has been recorded at a high frequency that dogs can hear, but humans can’t.
Nevertheless, it was so popular among New Zealand dog owners that it hit No.1 there at last Christmas, raising $17,000!

The song has received mixed responses from the canine listeners. One dog was reported to have gone crazy and physically attacked the radio, totally destroying it!

You can "listen" to the music video version on the youtube.com (Beware if there is a dog in the room!)
Is a high frequency sound, very loud? There is no answer to this question because the question has an error. Frequency has nothing to do with loudness!

Sound is a form of energy. When an object moves back and forth, or vibrates, it pushes the air molecules next to it. As air molecules get compressed into waves, the energy is transferred from molecule to molecule.

Sounds can be soft or loud. This characteristic of sound is called amplitude and it measures the amount of energy in sound waves. More energy will move more air molecules and will sound louder. The amount of energy in a sound wave is measured in decibels (dB). Jet engine sound is 150dB while breathing is 10dB. The loudest sound recorded in human history is the Indonesian Krakatoa volcano eruption of 1883. The sound was heard 3,000 miles away (Bangalore to Delhi is approx 1100 miles)!

Sounds can be low like a growling of a tiger or high like a chirping of a bird. This characteristic of sound is called pitch or frequency. Objects which vibrate faster produce a higher frequency, and objects which vibrate more slowly produce a lower frequency. The frequency of a sound is equal to how many times it vibrates each second and is measured in Hertz (Hz).

Humans can hear sounds between 20 Hz - 20,000 Hz. Sounds that are lower than human hearing are called Infrasound. Those higher are called Ultrasound.

Pigeons can hear infrasound frequencies as low as 0.1 Hz, or one vibration every ten seconds! Noctuid Moths can hear up to 240,000 Hz! Elephants hear between 5 and 12,000HZ; Dogs between 50 and 45,000HZ.

When humans get older, the detection range diminishes and they have trouble hearing the high pitched sounds. I knew an old man who could hear his son’s voice well, but had trouble hearing his wife, because her voice was at a higher pitch. The wife of course insisted that he was just ignoring her!

But it isn’t only the old people who have hearing loss. The loss of sensory cells begins from as early as age 18! And this fact has been used in a novel device called 'Mosquito'. This gadget works by emitting an annoying but harmless ultra sonic tone that generally can only be heard by people aged 25 and under. This was installed by a Theatre in South West England to stop groups of youngsters from gathering around Theatre Square.

The company is now marketing a ring tone called Mosquitotone. This is a 'teen-only' ring tone for mobile phones that the young can hear, but their teachers and parents cannot!

To hear it, go to http://www.bbc.co.uk/ wiltshire/content/articles/2006/04/04/mosquito_sound_wave_feature.shtml