Shrila Bhaktisiddhanta on mechanical chanting
"The holy name of Krishna means divine sound. It can be compared to a capsule of medicine. The capsule is not the medicine. Externally one capsule may look like another, but within one capsule maybe medicine and within another may be cyanide. The capsule itself is not the medicine. It is not the sound of Krishna’s name that is Krishna. Krishna is within the sound. The holy name must be be surcharged with the proper spirit not any mundane sentiment.
“The divine sound of the holy name must have it’s origin beyond the area of misconception or maya. Sound must have it’s origin in Goloka Vrindavana. The mere physical sound is not the holy name of Krishna. Repeating only the syllables of the holy name is called mayic sound. It has no spiritual essence. The life of the name is absent in offensive chanting.
“The most important thing in chanting the holy name is the spiritual realization backing the name which is the real name. A tape recorder can pronounce the holy name of Krishna, just like a parrot. But the physical sound is not Krishna. In the background there must be spiritual truth which is conscious. You cannot capture the holy name of Krishna simply by vibrating the syllables of the holy name with your tongue. Ravana wanted to capture Sita and he thought he did. But factually he did not even touch Her divine body. Ravana caught only a mundane replica of Sitadevi, an imitation which was like a statue of Sita.
“You cannot vibrate the holy name simply by moving the lips and tongue. The pure name of Krishna is not lip-deep but heart-deep. Ultimately, it goes beyond the heart and reaches the land of Krishna. When Krishna comes down, the name comes through the heart and moves the lips and tongue. That vibration is the holy name of Krishna. When Krishna in the form of sound descends from the transcendental world into the heart, and from the heart controlling every aspect of the nervous system comes to the lips and tongue dancing there, that is Krishna Nama.
“That sound is not produced from the material plane.The spiritual sound has come down into this plane. He can come down, but we cannot so easily go up there. The holy name is only realized when we approach Him with a very intense serving attitude. At that time Krishna Himself may come down by His grace being attracted by our pure serving nature.
“Then Krishna can influence this element and produce transcendental sound and dance within the mundane plane. That is the holy name of Krishna, Vaikuntha Nama, the real name of Krishna. We cannot produce it with our lips. The sound we create with our physical or mental production is not Krishna. He is indifferent to whatever sound we may produce. yet because He controls everything, He can appear anywhere, in any form, in any place, in any sound.”