We accrue knowledge in 2 ways. Ordinarily, through thoughts in the making of which we use our prior knowledge; so this becomes incremental knowledge. Very rarely, one comes along with direct knowledge, which is whole, total and devoid of ususl emotional baggage. Incremental knowledge is subjective and hence, deficient. But it creates a great comfort zone. From such a comfort zone to direct knowledge is a huge leap. It is traumatic, and not easy at all. That’s my take on the duel above (for those who care to know!)
The range of sound vibtrations we can ordinarily sustain in the physical world is called “vaikheri naad”. This has range and depth of vibrations of only 25% of “madhyama naad” in the astral world, which again is only 25% of “pashyanti naad” of the causal world.
AUM is the word/ sound of Ishvara, transcending the causal world which has only 25% vibrations of this fourth state, called “para naad”. At that level, the vibrations are extremely intense, appearing to be still but humongously potent. Sound is then a sparsh (touch). It is for this reason that the true AUM is heard in the meditation and any rendering on lower scales may neither bring its full vitality nor it is desired. That is also the reason why true AUM is taught only by our inner teacher.