What you would most likely have to do is find some instrumentals... and various accapellas and see what syncs up- mess with the tempo of the instrumental or vocal as separate tracks and do it that way- its basically what a dj would do only instead of having the two separate tracks play on tables you have to use an audio program- as far as taking vocals out of a song you would be hard pressed to be able to get it right, most of the programs and machines I've seen that say they can do it just numb out a couple frequencies but the vocal track is still there-
you would need somethin like cakewalk or cool edit or another audio studio program where you can sync up multiple tracks and just find some instrumentals and accapellas from kazaa or soundclick. 1

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