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There are a number of hardware and software products to do this, none are 100% effective. They use a combination of center-cancelling (reverse the phase of one stereo channel, combine the 2 into mono, and whatever was panned dead center should cancel out - that's often the vocals, but also any other instrument in the center of the soundstage) - and EQ to try and cut out the common vocal frequencies.
Results are variable. IF the recording had the vocals dead center, it can work well, at the expense of some damage to the instrumentaiton. If there is a lot of vocal reverb spread L and R, or the vocals are panned, or its a multi-voice recording, then all bets are off.