It is impossible to specify the nature of the nada as it extends into more subtle regions of being. They have to be personally experienced. However, as an indication of the direction that nada will lead to, the following fourfold classification has been given in the ancient texts:
- Vaikhari: This is the grossest form of sound that we hear in the world around us. It is produced by striking two objects together and is the type discussed in physics. This is the plane of the spoken word. This is the starting point of nada yoga practice from which one must retread the path through the more subtle realms of nada.
- Madhyarna: This form of nada is more subtle than vaikhari. The word madhyama means ‘in the middle’, so called because it is midway between the grossest nada and the more subtle nada. It is at this stage that nada begins to assume form and to crystallize from the formless subtle layers of nada. In nada yoga sadhana the aim is to hear sounds associated with this level.
- Pasyanti: This nada can be seen but not heard. The sound has different specific colours which can be seen by inner vision. It exists in the deeper layers of the mind beyond the range of audible nada.
- Para: This is transcendental sound. This is the point of origin of nada. It is the nada that is heard in states of super consciousness. It is way beyond normal levels of perception. It is nada that has such a high rate of vibration that it is beyond the classification of vibration. It is silent sound. It is associated with the state of samadhi. It is called the anahata nada – the unstruck sound and is beyond all conceptualization.
Many ancient texts also give a guidance to the actual sounds that can be heard during the practice of nada yoga. In the Hamsa Upanishad it gives the following list:
1. Chini nada – the sound is like the sound of the word ‘chini’.
2. Chini-chini nada – the sound is like the word ‘chini-chini’.
3. Ghanta nada – the sound of bells ringing.
4. Shankha nada – sound of a conch being blown.
5. Tantri nada – sound of a lute (tantri) or vina.
6. Tala nada – sound of cymbals.
7. Bansuri nada – sound of a flute.
8. Bheri nada – the echoing sound of a drum.
9. Mridanga nada – the sound of a double drum.
10. Megna nada – the roar of thunder, the ultimate sound. Remember that the sounds are psychic, therefore, you should not take this list too seriously – it is merely an indication. You must perceive the sounds for yourself. The sound that you hear will depend on the depth to which your awareness has penetrated the ocean of your being.