"The chanting should be heard, however, from the lips of a pure devotee of the Lord."
"Hare Krishna Hare Krishna Krishna Krishna Hare Hare/ Hare Rama Hare Rama, Rama Rama, Hare Hare is a sound that is non-different from Krishna. The sound Krishna and the original Krishna are the same. There are things that we hear but do not see -- the wind may be whistling past our ears, and we can hear it, but there is no possibility of seeing the wind. Since hearing is no less an important experience or valid one than seeing, we can hear Krishna and realize His presence through sound. Sri Krishna Himself says, 'I am not there in My abode, or in the heart of a meditating yogi, but where My pure devotees are singing.' We can feel the presence of Krishna as we actually make progress."
(Raja-Vidya: The King of Knowledge, Chapter 2)
Video produced by Caitanya dasa.
All glories to Srila Prabhupada.