Check this out – this video demonstrates how you can extract one instrument from a mix, using Photosounder.

Photosounder is an image-sound editing program that it opens images and sounds indiscriminately, treats and processes them as images, and synthesizes them as sounds.

Sounds, once turned into images, can be modified to achieve effects and results that couldn’t be obtained in any other way, while images of all sorts reveal the infinite kinds of otherworldly sounds they contain.

via Photosounder:

Using the new “road roller” (smart erase) tool combined with the harmonics modifier and the magnet modifier, I was able to isolate the 24 second long synth line at the end of Ohio Player’s Funky Worm in about one minute. Back in March 2009 I tried the same thing in Photoshop and it took me about ten hours!

The result isn’t completely clean but what is shown here is the bulk of the work, for a better result only a bit more cleaning would be necessary. All the work done in this video is shown in real time, only the synthesis parts were shortened.