It is also one of the 5 Bindu Upanishads (Tejo-Bindu, Amrita-Bindu, Dhyana-Bindu, Brahma-Bindu) attached to the Atharvaveda.
The Nada-Yoga practices meditations on the Nada or Shabda or on the highest Pranava, eventually with a mantra like OM or Aum as in Yoganandas Kriya Yoga.
The teaching goes beyond the Brahman : What is beyond that is the Para-Brahman, the pure all-penetrating, beyond the Kalas, the ever-shining and the source of all the Jyotis (light), should be known.
== Weblinks ==
* Aiyar, K. Narayanasvami (trans.), NĀḌABINḌU-UPANISHAḌ OF ṚGVEḌA in Thirty Minor Upanishads, 1914 -online