Shruti or śruti is a Sanskrit word, found in the Vedic texts of Hinduism where it means lyrics and "what is heard" in general. It is also an important concept in Indian music, where it means the smallest interval of pitch that the human ear can detect and a singer or musical instrument can produce. The musical "shruti" concept is found in ancient and medieval Sanskrit texts such as the "Natya Shastra", the "Dattilam", the "Brihaddeshi", and the "Sangita Ratnakara". "Chandogya Upanishad" speaks of the division of the octave in 22 parts.