Nada is the primal sound or first vibration from which all creation has emanated. During deep concentration yogis hear anahata nada, the sweet, ever-musical manifestation of nada within their own bodies. It has been said: Hearing my sound, as a deer is entrapped into a net, similarly the mind gets attached to the anahata sound, forgets everything else, and leaves all roaming about here and there.
The Hamsa Upanishad speaks of the same experience. It states that when the hamsa mantra (hamsa means I am He) is repeated ten million times with faith and feeling, varieties of nada are heard. Practice of ajapa japa (japa of the mantra Soham with the breath) and pranayama also help to hear the nada. Absorbed in this music of the soul, the mind does not run after sensual objects; it makes one deaf to all external sounds.
To practise nada upasana, sit in padmasana, siddhasana or sukhasana. Close your eyes. Close the ears with the thumb. This is shanmukhi or vaishnavi mudra. Withdraw the senses and concentrate. Abandon all worldly thoughts. Subdue your passions. Become indifferent to all sensual objects. Concentrate on the sound which annihilates the mind. Hear the sound through the right ear. After long and constant practice, it will become audible to you. You will hear the ten anahata sounds clearly.
The first sound is chini, the second is chin-chini, the third is the sound of a bell, the fourth is like that of a conch. The fifth is like that of a lute. The sixth is like that of a cymbal. The seventh is like that of a flute. The eighth is like that of a drum. The ninth is like that of a tabor or mridanga. The tenth is like that of thunder.
Change your concentration from gross sound to the subtle. The mind will soon be absorbed in the sound. You will get knowledge of hidden things when you hear the seventh sound. You will hear para-vak, divine voice, when you hear the eighth sound. You will develop the divine eye when you hear the ninth. You will attain Para Brahman when you hear the tenth.
To practise nada upasana, first retire into perfect seclusion and silence. Try to hear the sounds alone on a sea beach, on the high peak of a mountain, in the dead silence of dark starry nights, in a dense forest or a lonely cave, and then try to hear it within yourself when you command good concentration. Retain this experience and try to hear the sound in the busy hours of your daily life as well.
The imperative quality to hear anahata nada is purity of heart. The heart is naturally pure; it is made up of the sattwic portion of the five elements, but like the pure waters of a lake, its purity and transparency are ruffled and muddled with our crude and earthly attractions and repulsions. Thus the free passage through which the vibrations of His voice are streaming forth is blocked, and like the clogged and roughly handled reeds of a harmonium, it begins to emit discordant notes of envy and anger, hatred and censure. Then it is said that we do not allow the inner Krishna to blow the flute of our hearts.
Therefore, keep your heart ever unalloyed and pure and the Lord within will be highly pleased to manifest His voice through you. Then your talk will mesmerize and magnetize people. Your word will not go unheard. Nobody will have the strength to contradict your opinion. Your speech will be like Krishnas flute. Your word will soothe thousands of wounded and bleeding hearts, and radiate joy and peace.