"Many low-end entertainment systems (boom boxes etc) have a karaoke mode that attempts to remove the vocal track from general (non-karaoke) audio CDs. This is done by
center removal which exploits the fact that in most music the vocals are in the center. This means that the voice, as part of the music, has equal volume on both stereo channels and no phase difference. To get the quasi-karaoke (mono) track the left channel of the original audio is subtracted from the right channel. The crudeness of that approach is reflected in the often poor performance of voice removal. Common effects are hearing the echo of the voice track (due to stereo echo being put on the vocals), and also other instruments that happen to be mixed into the center get removed (snare/bass drum, solo instruments), degrading this approach to hardly more than a gimmick in those devices."
good luck playing with audacity. i dunno how to subtract sia.
.. would be perfect..