Pranava is the sole subject matter of the Mandukya Upanishad and there is a commentary on it in verse (karika) by Sri Gaudapada, the Guru of Govinda Bhagavatpada, himself the guru of Sankara Bhagavatpada. The three matras of Pranava are A, U and M, representing the witnessing awareness behind the three states of waking, dreaming and deep sleep. And the silence following it is known as Amatra and it represents absolute Pure Awareness, the One and only Reality. With such understanding one is advised to meditate on Aum. The following is the substance of the relevant verses of the Gaudapada Karika dealing with meditation on Aum: Weaning the mind from all other thought one should attune it to Pranava. Pranava is indeed Brahman, beyond all fear. Hence one perfectly attuned to it can have no fear whatever. Pranava is Brahman, both Saguna (with attributes) and Nirguna (without attributes). It is uncaused. There is no differentiation in it — it is immutable; nothing exists besi