The Nadabrahma is a meditation designed by Osho which starts with humming for half an hour on the sounds of Tibetan singing bowls, then certain arm movements are made and it ends with sitting for fifteen minutes without being active – see for full instructions and for accompanying music osho.com.
It is a gentle and beneficial meditation that helps you to balance and become centered, i.e. the center of your energy shifts from your head to your belly in the middle of the body, a few centimeters below the navel, where your center is.
By humming your body and mind become attuned to each other which makes it easier to be just aware of whatever is, without any judgments, just like a mirror. All meditation techniques are aimed at loosening our identification with the body and the mind, so that we can be back in our essence: the witness, our inner ‘Buddha’. This process is described in more detail in my blog posts on “The Psychology of the Buddhas”.