The Four levels of Sound

Extract from David Frawley's book:

These Yogas of sound are not concerned merely with the gross articulated sounds. Four levels of sound are recognized in Vedic and Puranic literature. The Rig Veda (I.164.45.) states, "Four are the levels of sound. Three hidden in secrecy cannot be manipulated. Mortals speak only with the fourth". These four are called Vaikhari, Madhyama, Pashyanti and Para. Vaikhari dwells in the throat and is our gross, articulated sound. Madhyama dwells in the heart and is our mental pattern or idea behind the sound. Pashyanti means seeing. It dwells in the solar plexus.
It is the essential meaning behind the sound, its archetypal content. Para means the transcendent. It is the essence of all sounds. It dwells in the root chakra. (Note that the powers of sound dwell in progressively lower Chakras. This is not because they are progressively lower powers but because they have the power over progressively deeper and more difficult parts of our nature.)
Hence the Yoga of sound is meant to take us back from our gross sounds to their idea content to the perception they represent and ultimately to the pure being behind that perception. It is not a process of merely saying sounds or thinking about words but tracing the origin of sound and meaning back to awareness itself by the power of meditation.
Sanskrit is the language of mantra, of spiritually empowered sounds. Its usage is to bring our minds back to the consciousness and power of mantra. Mantra is not just concerned with sound but with meaning. According to the view of the Yoga of sound, there is only one meaning in life, which is the Divine or our own Self. Each thing ultimately means all things. Each object is a symbol for the universe itself. Words represent this universal meaning broken down, fragmented and compartmentalized. To cognize any individual object we must first recognize its ground of being, which is the Divine. Yet we fail to notice this as it is immediate and before the activity of our thought and choice. If we hold to this primacy of being as the meaning of all objects, all things become doorways to the infinite.
While ordinary language seeks more precise and differentiated meanings, spiritual languages seek an expanded and integrated comprehension until one is all and all is one. They aim to free meaning from its imprisonment in words and their arbitrary conventions. In reality, all things are meaningless in themselves, or each thing means the entire universe. It is only the universality of meaning which allows for specific meanings to occur. This inquiry into meaning is the essence of the Yoga of sound. It involves freeing our mind from its attachment to particular sounds and to the tyranny of names.
All learning involves the energization of the mind. It is by the power of attention, the concentration of the mind that one comes to know anything. As long as we are distracted or our minds are wandering, we cannot come to really see anything. Hence the real object of learning is not to learn anything in particular but to gain the mastery of the mind through the power of attention. Then we can find truth in all things.
This energization of the mind is the true purpose and meaning of mantra. Whenever we have a deep insight or profound realization in life that thought has a special power. The empowered thought is mantra. Hence the more deeply we can think and inquire into things the more our thoughts become mantra, the greater our power of observation, the more mantric force enters into our minds.