"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.
