Any audible sound or any sound-producing object can be defined as a Ṥrutī.

In the context of Indian classical music, the term Ṥrutī defines a unit of measurement for the frequency of a note. This concept does not derive from any scientific measurement but from the perception of sages who lived in the past. In particular, the experiment described by Bharat in the Natya Sastra demonstrates the presence of 22 microtones that divide an octave.

Although auditory perception varies from individual to individual, there are infinite frequencies within an octave. However, only twenty-two are identified.

An explanation is provided in the Saṁgītaratnākara through the theories of Indian philosophy on the subtle body, which identifies two energy channels, Iḍā and Piṅgalā, that rise, twisting around the spine, and create twenty-two secondary channels allowing us to perceive these microtones. From a Western perspective, this may appear as philosophical speculation, but it is the system on which the music of Raga is still based today—a topic useful for musicological discussion.

The Ṥrutīs in the Śāstra are classified into five different classes or Jāti.

The number of vibrations for each microtone can be measured, but since the reference tonic is movable, these are not absolute values but relative. Therefore, considering the sum of the frequencies of an entire octave and dividing it by twenty-two yields the value of a relative Ṥrutī. However, this is considered an unnecessary operation, as according to a part of Indian musicology, the Ṥrutī as a unit does not exist. There are theories admitting inequality between various microtones.