From Hindupedia, the Hindu Encyclopedia
By Swami Harshananda
Nādānusandhāna literally means ‘meditation on the sound’.
This is one of the methods described by the works on Haṭhayoga for the laya or dissolution of the mind. Sitting in the muktāsana and practicing the śāmbhavīmudrā the yogi should hear the nāda or sound produced by saiyama. on the suṣumnā. This nādānusandhāna has four stages which have to be learnt from competent teachers of Haṭhayoga. It leads to complete control over the mind and the senses.
- The Concise Encyclopedia of Hinduism, Swami Harshananda, Ram Krishna Math, Bangalore