Can't seem to find anything online about practical nada yoga exercises. Just a lot of drum-beating. (Ha.)

But here's something I've done since I was little:
Listen to the highest pitch you can generate in your mind. Listen until it amplifies. It will then give way to another, higher pitch. This just keeps going, with concentration. I found out the hard way that one should be lying down; the really high pitches can knock you right over.

I was reading a book by Ram Dass when I was stunned to see that exact process described as a form of nada yoga. He said there were different states of mind associated with each pitch.

Enjoy.
-- Yeshod