What is sound? How can we determine the pitch in a sound?

A sound is a form of energy produced by vibrating bodies. Sound is produced when something vibrates. The vibrating body causes the medium (water, air, etc.) around it to vibrate. Vibrations in the air are called travelling longitudinal waves, which we can hear. At 20 °C, the speed of sound in air is about 343 m/s. 

Pitch is based on the frequencies of the sound wave. Therefore, the pitch can be determined only in sounds that have a frequency that is clear and stable enough to distinguish from noise.

When the frequency is high the ear interprets the sound as a higher pitch or it is said that the sound is shrilling, and when the frequency is low, the ear interprets the sound as a low pitch or lower shrill.