Dhwani (Sanskrit) means sound of any kind. Out of all the Dhwanis created in the world, sounds that are ‘musical’—give an experience or perception of a ‘musical’ sound—are called Nadas. The sound of a ‘clap’ is a dhwani, but that of a bell is a nada. […]
In this way, sounds (dhwanis) are progressively classified as:
– All sounds in the world are dhwanis.
– Selected dhwanis become nadas, (innumerable), which provide a musical experience.
– Selected nadas become shrutis, (22), which create a change in the perception of 12 swaraprakaras (universal chromatic pitch classes) as we play them from one end of the string. This change happens only at 22 points as placed by nature.
– Selected (12 or fewer) shrutis become swaras —used in a particular raga.
Source: Shruti (music) – Wikipedia