“The Hamsa Upanishad teaches an ascent through six mystical circles [chakras, lotuses, vortexes] on to the Brahmarandhra at the top of the head. This ascent is had by meditation of the syllable Om as it becomes audible within. Hamsa repetition may help that “thunder”, the medley sound called OM, to come to the fore. Then it is fit to keep it audible as long and often as you can.

OM

This mantra-king (hamsa) has a symbolical interpretation – the individual Atman (soul) is conceived in the form of a bird, a Hamsa (goose, duck, swan).

It is told that the Hamsa and the Paramahamsa (Supreme Swan) are one – that is, the individual and the highest Atman (Spirit) are one and the same in essence.”

-Source

*Many thanks to nvg.org and freesound.org