Q. How for levels of sound vaikhar• v•k, madhyam• v•k , paœiant• v•k and p•r•vak relate to the progressive chanting towards to the pure Name of Krishna?

A. Generally, the scriptures declare that upamsu-japa (chanting softly, inaudible to others) is one thousand times better vaikhari-japa (verbal chanting, audible to others, not shouting). However, manasic-japa (silent mental chanting) is ten million times better than loud chanting.

Although Srila Prabhupada did not disagree with the scriptures, he explained that the Hare Krishna maha-mantra can be chanted either loudly or silently:
“Every mantra is recommended to be uttered silently, but specifically this Hare Krishna maha-mantra can be chanted both ways—loudly and silently.”
(Letter to Mandali Bhadra, November 2, 1969)

By chanting loudly, one benefits not only oneself but also other living entities like birds, beasts, insects, trees and plants. Lord Chaitanya Himself used to chant loudly, and also all other great acaryas such as the six gosvamis of Vrindavan.