Significance of AUM:
AUM or OM is of paramount importance in Hinduism. This symbol is a sacred syllable representing Brahman, the impersonal Absolute of Hinduism — omnipotent, omnipresent, and the source of all manifest existence. Brahman, in itself, is incomprehensible; so a symbol becomes mandatory to help us realize the Unknowable. AUM, therefore, represents both the unmanifest (nirguna) and the manifest (saguna) aspects of God. That is why it is called pranava, to mean that it pervades life and runs through our prana or breath.
On Sitar Played by Shri. Siva Ramakrishna Rao - Sitarist and Composer