Guy Beck, Sonic Theology : Hinduism and Sacred Sound  (Columbia, South Carolina, University of South Carolina Press, 1993). [Google Books]

Guy Beck, Sacred Sound: Experiencing Music in World Religions (Waterloo, Canada, Wilfrid Laurier University Press, 2005). [Google Books]

Hazrat Inayat Khan, The Mysticism of Sound, Vol. 2, (Richmond, Virginia, Suluk Press, 2017). [Google Books]

Joachim-Ernst Berendt, The World is Sound: Nada Brahma (Rochester, Vermont, Destiny Books, 1991). [Google Books]