Music isolation/compiler?

Does anyone know of any computer software that will isolate different instruments in a song or that will compile files of different instruments together to make a song?

track separation like that depends on the nature of the original mix. Use a program like audacity to open the files. Very often if you invert the channels you will move the center panned sounds to the ouside where they can be filtered out. In pop music, the center is where the voice and lead instruments are usually placed. Once moved to the extreme left and right of the pan, they can often be filtered out, at least enough to be able to minimize them and replace them with other instruments or a new vocal track.

However there are lots of other considerations. If a vocal has a special effect, such as a ping pong delay, attached to it, then it will be all over the stereo range and you will not be able to separate it out.

Get a copy of audacity (download free from soundforge.com) open up the file you are interested in. Turn the two stereo tracks to mono and invert them (all under effects and track mixing options)... now try various filters, and see what you can do to minimize the sounds you want to get rid of.

I'd say, given all the possible ways a mix can be done, you stand about a 1 in 3 chance of being able to do what you are after.

For more information about this, check out the nyquist boards and discussion groups at soundforge.com. There's a lot of valuable mixing information there.