. It's a great little mixing app. It even has instructions for doing what you want. Basically, you'll want to split the song into right and left channels, then invert one of the channels, then mix them into one track. This won't work for all songs, but most songs have identical vocal tracks on the rt. and lt. channels, while the instruments have different levels to produce stereo separation. So after inverting, the vocals will cancel out, leaving only the instruments.