Nādānusandhāna — Listening for the Unstruck Soundhatha yoga classicalYou sit in a quiet place, close the ears, and listen — not for anything in particular, but for whatever sound is already there when the outside is shut out. The instruction is to follow the subtler sound whenever two are present, and to keep following as it thins. The Haṭha Yoga Pradīpikā devotes the end of its fourth chapter to this (roughly 4.65–4.102), and is precise about the mechanism it claims: the mind is held by the sound the way a bird is held when its wings are stilled — attention bound, not entertained. Worth naming plainly what the tradition does not say: nothing here is about particular frequencies or their effects on the body. The claim is about attention.What it's for

Background Anxiety — A hum of anxiety that never quite resolves is read here as attention with no object of its own, so it takes whatever the day offers. Giving it one deliberately — and one that is always available — is the classical remedy.

Can't Fall Asleep — Not being able to drop off is read as the mind still holding objects it has not agreed to put down. Sound is offered as the last object — one that asks nothing and grows quieter as you follow it.

Tired but Wired — Exhausted and still switched on is read as attention that cannot find a place to settle, so it keeps moving out of habit rather than need. Listening asks for no effort in the direction the body has none left.