So-Hum Mantra
This is the mantra of the breath; if you observe your breathing you'll hear "so-hum" as air moves in and out of your lungs. As you inhale, the sound of the vibration is "so". And as you exhale, the sound becomes "hum". If you want, you can experiment with this. Inhale deeply, close your eyes and your mouth, and exhale forcefully through your nose. If you concentrate, you'll hear the "hum" sound quite clearly.
One of the techniques of meditation is, in fact, simply focusing on where your breath comes from. With your eyes closed, inhale and think the words "so"; and on the exhale think "hum". Gradually both breath and the sound will become quieter and quieter and quieter, and the breath becomes so quiet that is almost seems to stop. When you transcend, the mantra "so-hum" entirely disappears, and your breath pauses momentarily. Time itself seems to stop and you're in a field of pure consciousness, the non local domain, spirit the ground of being.
Mantra sponsored by Deepak Chopra
From his book,