Omkara, the Symbol
Pranava, the Sound (Nada)
This entry is from Kripalu’s book on the Hatha Yoga Pradipika, Reveling the Secret. Anything in [brackets] is my own insertion.
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“The sacred syllable OM (pranava) is the bow, the soul (atman) is the arrow, and God (brahman) is the target (goal). Without any indolence and mistake, one should strike the target and should be just like the spirit of the arrow. Making his body as the wood below the the sacred syllable (OM) as the stick of wood above, he should routinely practice the churning of meditation. Thus, he will see God, the unperceived.”
In the three verses (shloka) mentioned above (2-4, 5, 6), there is only some difference in the use of words.
1. paravani — Sound in the most pure subjective idealized form; beyond speech; when one step down form god is made.
Meditation on the muladhara [root chakra] — impelling, automatic force of expression. [Meditation “on” something suggests that there is a concentration of prana in that place.]
Nada — Divine Sound.
2. pasyanti — Another step down toward the gross [away from the subtle] so that sound is perceivable and perceived.
Meditation on the manipura [navel chakra] — pure sound is heard indistinctly.
Ahamkara — Ego (the sense of self as perceiver).
3. madyamavani — Mind (thought, words and their meanings).
Meditation on the anahata [heart chakra] — madyamavani (middle heart words) heard distinctly.
Manas — Mind.
4. vaisvarivani — Gross organs (tongue, mouth, brain).
Meditation on the vishuddha [throat chakra] — gross speech begins to be expressed through the tongue.
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[Notice that the root chakra (muladhara), the first and lowest chakra, is associated with Divine Sound. This first chakra is eagerly abandoned in the minds of many Western seekers as lowly (pun intended), but here we see its importance in the journey to union with God. I have therefore included Kripalu’s writings on that chakra below.]
(Root holding energy channel focus)
Four petals (nadis): ida, pingala, sushumna, kuhu.
Mouth (face) downward.
Letters vam, sham, san, sam.
Two kinds of sounds (nada):  ahata (made by striking an object),  anahata (spontaneously generated as in speaking in tongues).
In the muladhara chakra, at the end of sabija samadhi, there is union (yoga) of prana (the up and in flowing energy) and the apana (the down and out flowing energy). This union generates the anahata (spontaneous) nada. As a result of that up going anahata nada, there descend three levels of sound:
1. Subjective perception of sound
2. Mental forming up of sound into language patterns
3. Universal speech.
So it is said that from anahata nada (spontaneous heart forced divine sound) are born the imperishable phoneme (aksara, sound which is represented by a letter of the [Sanskrit] alphabet). Then from these phonemes, a complete word is formed. From words is born speech that is filled with rhythm and rhyme. So in every chakra, letters of the Sanskrit alphabet are noted to represent these phonemes.
According to the number of aksara (the indestructible phonemes), are the letters of the Sanskrit alphabet. The seven chakras (muladhara, svadhisthana, manipura, anahata, vishuddhakhya, ajna and sahasrara) have been called respectively, dhaturdala padma (four petalled lotus), satadala padma (six petalled lotus), dasadala padma (ten petalled lotus), dvadasadala padma (twelve petalled lotus), ([missing]) (sixteen petalled lotus), dvidala padma (two petalled lotus), and sahasradala padma (thousand petalled lotus).
When the Divine Sound (anahata nada), having risen up from the muladhara, reaches the ajna chakra [sixth chakra], then there is a merging (union, absorption) of both the perishable (nature, prakriti) and the imperishable into the Being (dweller in the soul or heart, purusha). However, when the imperishable (aksara) is separate from the perishable (ksara) and stands on its own, then neither words nor Divine Sound (nada) remain (exist). We may call it (the Divine Sound, nada) the Word of God, or Beyond the Beyond God Sound (paratpara nada braman, the divine attractant).