A common misconception is the hearing of Nada. The truest of true nada occurs when the prana actually ascends in the sushumna. These nadas have the following characteristics
1) Extremely soft, no longer heard by the physical body
2) Extremely pleasing and one truly just wants to hear it again and again
3) On hearing these nada 2 things emerge. Samadhi and different kinds of Siddhis
4) Yogananda Maharaja has had a detailed description of the nadas. I would strongly urge all disciples of any form of Yoga to read his book God talks with Arjuna, a 1500 page long explanation of Bhagvada Gita. In my opinion, there never was and perhaps never will be a better explanation of Gita than this book. In short, right before the war, in the first chapter, Arujuna decides not to fight. At that time, on the battlefield, Bhisma, Dronacharya, Duryodhana all sound their conch (shankh) ! These sounds refer to the gross sounds of the physical universe, the first encounter and obstacle when one is trying to meditate. The sound of the breathing, blood circulation etc.
Later as one progresses deeper in meditation, one hears the sounds of the five conchs (shankh) of the 5 pandavas and then finally of Lord Krishna – called the Panchanjaya. The five sounds (and each conch was very aptly named by Vyasa bhagwana in Gita) produce a different sound at the 5 different chakras.
a) At Muladhar, the sound heard is of that of the Bumble bee. This produces Savitarka Sampragnata Samadhi. Here there is some doubt that is my prana really going up? Am I making the progress? This is a reflection of the mind.
b) Swadhisthana the sound is of the Flute. This produces Suvichar Sampragnata Samadhi. Here the doubts are removed and this is a reflection of the Intelligence or Buddhi
c) At manipur the sound is that of the Vina or harp. This produces Sananda Sampragnata Samadhi. The word Devadatta, the name of the conch means deva meaning joy and datta means giving. This produces a lot of happiness and there is control over the chitta
d) At anahata the sound is that of the gong bell. (Paundra). The word Paundra means to disintegrate. Here the ego begins to disintegrate. The samadhi that is produced is Sasmita sampragnata Samadhi
e) At the Vishudha chakra, one becomes totally oblivious of the physical universe and is totally within. The samadhi is called Asampragnata samadhi and the sound is the roar of the ocean
f) At the Agna chakra the sound is a very pleasing co mingling of the all the sounds and is called Panchanjaya (mixture of 5 sounds).
Finally all these steps are repeated between Agna chakra and the Sahastrar in the ultimate sublime fashion, something which cannot be reproduced in words.
I remain eternally in debt to the great saints, Gurudev, Vishnutirthji Maharaj, and Paramhansa Yogananda maharaja for blessing me with an experience to all of these steps.
However, an occasional experience is NOT satisfactory. I have to go much further to get these experiences all the time.
In Muktashastra, Yogamruta and in Mayayoga Vigyana more nada are described. In Muktashastra, Gurudev described the nada as Loud, soft and extremely soft. The true nadas are extremely soft!
The other nadas esp. those that are described as the sound of crickets etc are sounds still pertaining to the physical universe and bodily sounds. Please DO NOT dwell on them, move ahead. Much more is to be travelled than those sounds.
Since we are on the subject of Nada, I will elaborate a little further. Nadas can be Vyakta and Avyakta. Vyakta meaning that which has a comparision and Avyakta – those that cannot be compared with.