The Vedas form the sound-manifestation of Ishvara. That sound has four divisions,— Para which finds manifestation only in Prana, Pasyanti which finds manifestation in the mind, Madhyama which finds manifestation in the Indriyas, and Vaikhari which finds manifestation in articulate expression.
Articulation is the last and grossest expression of divine sound-energy. The highest manifestation of sound-energy, the primal voice, the divine voice is Para. The Para voice becomes the root-ideas or germ-thoughts. It is the first manifestation of voice. In Para the sound remains in an undifferentiated form. Para, Pasyanti, Madhyama and Vaikhari are the various gradations of sound. Madhyama is the intermediate unexpressed state of sound. Its seat is the heart.
The seat of Pasyanti is the navel or the Manipura Chakra. Yogins who have subtle inner vision can experience the Pasyanti state of a word which has colour and form, which is common for all languages and which has the vibrating homogeneity of sound. Indians, Europeans, Americans, Africans, Japanese, birds, beasts—all experience the same Bhavana of a thing in the Pasyanti state of voice or sound. Gesture is a sort of mute subtle language. It is one and the same for all persons. Any individual of any country will make the same gesture by holding his hand to his mouth in a particular manner, when he is thirsty. As one and the same power or Shakti working through the ears becomes hearing, through the eyes becomes seeing and so forth, the same Pasyanti assumes different forms of sound when materialised. The Lord manifests Himself through his Mayaic power first as Para Vani in the Muladhara Chakra at the navel, then as Madhyama in the heart and then eventually as Vaikhari in the throat and mouth. This is the divine descent of His voice. All the Vaikhari is His voice only. It is the voice of the Virat Purusha. -- SRI SWAMI SIVANANDA A DIVINE LIFE SOCIETY