On FDiamondEngine (SVN repository), was implemented audio processing functions. One synthesizes a sound, with the notes sung. So you can sing a song (using your own voice), and then listen it being played by an instrument (for example, the synthesized sound of a piano).
This is not the only function implemented in FDiamondEngine, you can also obtain the approximate frequency of a wave, obtain the frequency of the closest musical note and more. Check yourself!