Source separation (music)
Splitting a finished stereo mix back into vocals, drums, bass and everything else, without access to the original tracks.
A mix is a sum, and sums don't run backwards. For decades the only trick available was to invert one channel and cancel whatever sat dead centre, which removed the vocal along with half the bass. The modern approach computes a spectrogram and has a neural network estimate, bin by bin, how much of the energy belongs to which instrument. That mask is multiplied with the original and turned back into audio.
The MUSDB18 dataset of 2017 gave the field a common benchmark. Deezer's Spleeter and Meta's Demucs, both released in 2019, turned it into a free download. The best-known application is Peter Jackson's Get Back in 2021, followed by the Beatles' "Now and Then" in 2023, where John Lennon's voice was lifted off a cassette demo with a piano sitting on top of it.