The water, fire and air tatwas keep on colliding with each other and producing different sounds which appear and disappear, the intensity of which is directly proportionate to the force of collision. According to the laws of Nature, these sound keep on emanating and disappearing. In the gross body also, these sounds can similarly be produced. The audibility of Nada depends upon the maturity of meditation process as it is a part of meditation yoga.
Nada is of two types :-
1) Natural
2) The one created by the being
1) Natural Nada
It is listened in the thousand petalled lotus by the yogins where the vedic couplets and Mantras are sung and the sounds of the seed alphabets keep on originating from time to time. In the external form these are audible in the flow of water, in the movement of air, and in the kindling of fire.
2) Nada produced by the Being (By aspirant)
1. Sounds produced during various practices.
2. Sounds originating in ignorance i. e. during worldly behaviour.
3. Sounds produced by the throat.
The following practices should be performed to realise the Nada :-
1. Sit in the Lotus posture or the posture of adepts in a lonely quiet place. If one has not the practice of these postures, one can sit in easy posture facing East. The neck should be kept straight. On closing the orifices of the ears, one will hear the sound. If one is not able to discern it, the mouth cavity should be closed and pressure should be applied with closed jaws on teeth and the sound will then become clear.
2. Close the orifices of the ear with the help of fingers or thumbs or cotton or any delicate mould, so that the air inside may not go out and air outside may not enter in. The sound will be clearly discerned. The breathing should be normal but noise-less.
3. Sit in an easy posture, keeping neck straight and drink nectar with the tongue. Apply pressure on Shushamna Nadi, the Nada will be heard.
4. Sit in an easy posture, drink Nectar, apply pressure on the navel and establish the prana in the Agnya chakra and flex chin so that it touches chest. Close the ear orifices and perform Kumbhak, gradually apply pressure on the closed eyes one will clearly hear the 'Anhad Nada'. This is a complete process. First of all Jhankar will be heard, then the sound of 'Tan-Tan' or 'Shim-Shim' then one hears the sound of 'Aarti', where in the sound of drum, trumpet, flute, Mridangum, Counch, Bell-sounds and sound of veena etc. can be heard. These sounds have no limits, hence are called 'Anahad'. After this the chirping sound of birds as on dawn is heard, and then the subtle sound of Aum. It is heard at the most subtle state of meditation and manifests clearly after the sound of veena is heard. There are other sounds also apart from AUM-these are the seed sounds, mantras sounds and sounds of vedic couplets, Master's specch and the sound of other spheres of existence.
These natural divine sound are heard in the right ear only for the subtle body rests on the right side of Agnya Chakra. It moves from here to listen to these divine sounds and obtains divine bliss. The yogins can spend years in this state of bliss. When this divine Nada results in the merger of subtle body, then this practice bestows the bliss of Samadhi and unites the soul with the Almighty.
The genesis of Anhad Nada is natural both in Universe and in body. The practices are helpful only in hearing them. The apana of the body is not considered useful in Yoga and is passed out and the Udana and Prana are made to collide. The prana generating out of this collision moves through-out the body and activates many sounds. These sounds are naturally produced by the collision of prana at various places. It proceeds towards AUM from various places in the body and through the Sushumna, nadi, pierces the Aum and disappears in the Sun and Moon points of the Brahmanda. This is how the Nada travels. The Sun, therefore is the point of origin and merger for Nada and it is the radiant Brahmpoint.
5. The process of realizing the 'Seven Notes' of Music-first carry out the practices of clarifying of sound of Aum., activate the subtle body and enter Aum and then one will realise the universal, uniform divine light and at one spot one will find the shape of a leaf on which the subtle body is lying and sucking its own thumb. As soon as the vision of Sadhaka strikes the eyes of the subtle body, shining rays like electricity develop and establish relationship between the eyes of Sadhaka and the subtle body. In the state by listening with deep meditation, the sounds of the seven notes (Sang, Rang, Gang, Mang, Pang, Dhang, Nang) can be heard and seen coiling all round the subtle body. It means that in great annihilation, these sounds protect the subtle body and help in its dissolution into the formless God.
6. The sound of the Seed Alphabets.
Relax the body completely, keep the body straight and sit in an easy posture facing north. Listen to the sound of Aum for 3 minutes and repeat it 3 times and then listen to the sound of seed Alphabets in an orderly way. Keep on drinking nectar. If you want to discern the sound of 'Aarti' from the sound of counch, the Saadhaka listens to the mix sound and catches the sound of counch, It is by this process that from the sound of Aum, the sound of all the seed alphabets can be appreciated individually. Some times it appears in the following order. Ang, Aang, Eang, Uang, Ang, Ah and Shang. These seven sounds also appear some-times as Shang., Landg, Hang, Kang, Ang or Kang, Lang, Rang-Vang. This 'Kalarava' sound indicates the attainment of Shiva Sphere.
7. The Realisation of 'So-ham' sound.
Throw out the apana air from the body completely. Sit in Lotus posture or Veera-Asana facing North. Breathe in and out seven times with full force and finally fill the breath in the body with one jerk, contract the abdominal wall, so that it touches the vertebral column. Now flex the head so that the chin is at a distance of 4 fingers from the chest Drink nectar, meditate at the center of the eye-brow. Do not allow the air to get out of the ear, so keep the ears closed with fingers.
When the light dawns, it is yellow in colour, then becomes red, later, on blue and finally it is converted into white. Similarly first we hear the cochroach's sound, chirping of birds, followed by the sounds of snakes, then tin-tin, toon-toon and then the sound of 'Aarti'. When the Dham-Dham sound merges with the thunder of clouds, the sound of 'So-ham' is clearly heard. It is an automatic sound here. The Sadhaka derives benefits by performing jap of 'So-ham' along with this sound. When the sound becomes clear, the fingers can be taken away from ears and the breathing should be normal/regular and noise-less, Enjoy, this practice the Sushumna nadi can be pierced and the sound of Shiva can be visualized.

Aum Shantih Aum Shantih Aum Shantih
Yogi Raj The Master Bharatari Hari.