[LAU] Filtering out everything but the centre position in stereo

Hey hey, is there an effect or a method to filter out everything from a stereo file but the "centre"? A sort of reverse karaoke effect. In theory I'd know what to do, just not how to achieve it. i.e. find all the differences between the channels and subtract the respective difference from each channel. Any good tool/plugin or method to implement in something like Csound is appreciated. Best wishes and thanks, jeanette -- * Website: http://juliencoder.de - for summer is a state of sound * Youtube: https://www.youtube.com/channel/UCMS4rfGrTwz8W7jhC1Jnv7g * SoundCloud: https://soundcloud.com/jeanette_c * Twitter: https://twitter.com/jeanette_c_s * Audiobombs: https://www.audiobombs.com/users/jeanette_c * GitHub: https://github.com/jeanette-c She's so lucky, she's a star But she cry, cry, cries in her lonely heart... <3 (Britney Spears)