a) By holy song one raises and builds up the Kingdom of Holiness and one merits to be raised up. So also, the opposite, the cantors and singers of the Other Side blemish the holiness and lengthen the exile. Through them people stumble and can't move, like birds caught in a trap. Therefore each person must be very careful not to hear songs from an unholy singer who doesn't intend to sing from the sake of Heaven at all but rather only for money, honour and fame. Hearing him sing causes damage to the service of G-d. So also the opposite, to hear songs from a kosher, worthy singer is beneficial for the service of G-d.
b) The rectification so that one won't be damaged by the voice of an unholy singer is by learning Talmud at night (after midnight).
c) By holy song a person can merit to an aspect of prophecy for the main way to attach yourself to G-d is by song, as will be explained.
d) By learning Torah after midnight, a thread of loving kindness is drawn upon you so you can be protected from thoughts of learning for ulterior motives. You also rectify the sound of unholy song so it won't hurt you, for it is very harmful for the service of G-d, and you merit to raise holy song so you can attach yourself to the Holy One by songs and tunes. Through this a person builds and raises the Kingdom of holiness, thus meriting to importance so that he can control anything he wants, even achieving a degree of prophecy.
e) When a person rectifies the voice of song and merits to a degree of kingship and rulership, then he can rule anything he wants; he can bring death to this one or give life to that one. However he has to be very careful to judge each person on the side of merit so he won't destroy the world, for the Holy One desires loving kindness and desires the continuance of the world.
f) When you hear the sound of joyful song and attach yourself by this to the Holy One with a broken heart, through this the sound of song is elevated even though the singer isn't worthy and, as a result, the Kingdom of holiness is raised. To merit to this completely, the rectification is by learning after midnight the Oral Torah which is the Gemorra.