Today I was asked to remove the voice from a song (for a kid's Christmas event). I already knew that it is simply impossible to achieve in a general-purpose tool - it depends on the frequency arrangements of the voice parts of the song. However, I found a little program (I've used before) called Audacity that is able to help us with this task. the authors have even written a small page with the necessary steps for a specific (albeit common) case:
- Import your stereo file into Audacity.
- Open the track menu (click the arrow next to the track title), and choose “Split Stereo Track.”
- Select the lower track (the right channel) by clicking it in the area around the mute/solo buttons.
- Choose “Invert” from the Effects menu. 5. Using the track menus, change each track to “Mono.”
[See the full article in Audacity: Can I remove the vocals from a recording to make a Karaoke track?]