Nada

A Sanskrit term used in Hindu musical theory to denote subtle aspects of musical sound. There are two kinds of nada: anahata is the mystical essence of sound; ahata is the conscious realization of musical sound by human beings. Anahata is heard by yogis in meditation and is related to different chakras (psychic centers) in the human body. Nada upasana is the yoga of music, which brings God-realization through pure forms of music and meditation.

Sources:

Rogo, D. Scott. Nada: A Study of Some Unusual "Other World" Experiences. 2 vols. New Hyde Park, N.Y.: University Books, 1970, 1972.

Sivananda, Swami. Music as Yoga. Rishikesh, India, 1956.