Yoga and many other spiritual traditions have recognized the inborn power of sound in transforming consciousness. Nada Yoga, the yoga of sound, has developed a wide variety of techniques to expand consciousness through the medium of sound. Mantras, chanting and deep-listening help to create a ritualistic container to evoke the sacred.  According to Nada Yoga there are four essential layers to the evolutionary sound current:

Vaikhari:

Gross audible sound.
Pashyanti: Subtle sound-current heard inside the mind body organism. Examples include audible hearing the nervous system, the sound of crickets, kettle drums, a waterfall and many other subtle sounds.

Madhyama:

Sound as light.

Paranada:

Beyond all sound.

In many traditions throughout the world, sound is considered one of the first evolute of creation.  In other words, certain vibrational frequencies precede and inform the manifest realm that most of us inhabit.  As such, sound holds the potential to influence our being on multiple layers.  Sound is unique to our sensory experience in that it is very tangible and readily experienced (through language, nature and song) and at the same time its form is invisible, bridging into unseen dimensions.