As sound waves travel through the inner ear in the cochlia, tiny hairlike nerve receptors called celia, percieve the soundwave vibrations and convert them into electical impulses that travel through the chochlear nerve to the brain where we percieve it as sound.

Sound volume is measured in Decibels. The chart below shows the decibel range of some common sounds.

Sound is a vibration created as a mechanical wave of pressure and displacement, through some medium, such as air or water. The speed of sound depends on the medium the waves pass through and is a fundamental property of the material. For example the speed of sound through air (at sea level) is approximately 767 mph. The speed of sound through water is much faster at approximately 3315 mph. Sir Isaac Newton was the first to theorize an equation to deduce the speed of sound.

A sonic boom is created when objects pass the sound barrier.

Sound Frequency is measured by Hertz. Different animals are able to hear within different frequency ranges. Above is a chart showing the frequency hearing range of different animals. Elephants can hear well into the Infrasonic range. With their large ears and specialized sensors in their feet they can hear a thunderstorm from 70 miles away. They use their trunks to emit very low frequency sounds that can be heard only by other elephants and from great distances. Bats and whales use echolocation in ways that can only be described as seeing with sound. They can sound out very high frequency sounds and using special receptors can essentially visualize an image in their brain by the sound that is reverberated back to them. 

An audio frequency or audible frequency is characterized as a periodic vibration and It is the property of sound that most determines pitch.