Almost certainly something like "Real-time Sound Source Separation: Azimuth Discrimination and Resynthesis" (Barry et al, https://arrow.dit.ie/argcon/35/ https:

Almost certainly something like "Real-time Sound Source Separation: Azimuth Discrimination and Resynthesis" (Barry et al, https://arrow.dit.ie/argcon/35/ https://arrow.dit.ie/argcon/35/) This is a more sophisticated generalisation of the idea of inverting one channel and averaging in order to isolate the centre-panned vocal (or remove it for karaoke purposes). It works well with mixes in which stereo placement is entirely by pan pot, adjusting the left/right volume levels of each instrument individually in order to place it on the stereo image. It doesn't work so well with real room recordings, where stereo placement is determined also by timing information (read e.g. https://www.audiocheck.net/audiotests_stereophonicsound.php https://www.audiocheck.net/audiotests_stereophonicsound.php) This is a better-specified problem than monoaural source separation, which I think is what the original article here is about.