"It seems pretty clear that the pranava is the symbol of the divine creator. "
That is fine, but I do not really care for such scriptures. But since you have mentioned it, most of the scriptures as the Upanishads and the Vedas are largely a by product of several rishis, yogis, and sages. And what they have said is not simply something philosophical, it is an expression of a certain direct experience. When the sages speak of something like the so called “Atman”, it is not simply an idea in the mind, but a certain direct realization of yoga, of seeing directly into one’s true nature. How this experience is interpreted is another matter entirely, that is why many of the scriptures differ in their different angles and perspectives. And as far as mantras are concerned, the single syllable mantras are also a by product of certain direct experience. There are two different approaches in using sound as a method for the expansion of consciousness. One is mantra yoga, using the energy of the mantra as an object of concentration, or nada yoga, developing a subtle awareness of the different levels of sound through one’s “inner ear”.
Every mantra has many different aspects to it. What you are familiar with as Om is just a gross expression of something which is much more subtle. You can pronounce Om, but you cannot pronounce the source of it’s vibration, but you can use “Om” as a gateway to the gateless, a method to the methodless. Just as atoms are made of subatomic particles, those subtomic particles made of subtler particles, and so on. Similarly, every mantra consists of a whole spectrum of energies ranging from the gross to the subtle.
Sound in general is not only audible vibration through the ears. That is what people usually think, just out of the force of habit. But there is also another dimension which is inaudible vibration, which cannot be heard through your ears. In yoga, the first is called dhawani. The second is anahata, the same word which is used for the anahata chakra at the heart, which literally means “unstruck sound”, because concentration upon anahata can be used as a method for exploring different dimensions of sound.
There are four different states of sound, ranging from the gross to the subtle. The grossest aspect is called vaikhari. Subtler than this is madhyama, subtler than this is pashyanti, and the subtlest dimension is para. Para refers to the “transcendental sound”. And the method of nada yoga is to expand one’s consciousness as to every dimension of sound from the grossest to the subtlest, the para, which is the source of all vibration itself. That is why each of mantras corresponding to the chakras have no meaning whatsoever, they are simply certain frequencies of energy in a gross form. Om is known as the “soundless sound”, because it describes a certain sound that can be heard once you come to the very source of existence itself and yet one’s “inner ear” remains active. It is still a far cry away from the sound that is heard in meditation, dimensions apart, but perhaps the best that can be done is “Om”, it is not something that can be pronounced with the human voice, or heard through the ears.
