Sound is known is known as 'nada' in Sanskrit. There are two types of sound. One type is created or caused sound. It is caused by friction, by two things rubbing together or dashing against each other. The second type is 'anahat' or uncaused sound. When sound is caused, there are two principles which create a third. This is the theory of creation. At least two things are needed to create something. Sounds is the first manifestation of divine energy. How did the cosmos come into existence? There must have been one force which split into which then created a third. From these three forces everything both seen and unseen was created.