Sometimes tracks with vocals are distracting, or, you want to explore the stems for fun (eg: listen to bass or drums).
2022 way: use spleeter
I used to use spleeter (made by Deezer) pretty often, and it's decent
spleeter separate -o separated_audio/ -c mp3 -b 320k -f "{filename}-{instrument}.{codec}" --verbose *.mp3
2024 way: use demucs
Made by meta (previously) and sounds a little better, smoother/less bleed vs spleeter.
If you just want instrumentals:
demucs -v -d cpu --two-stems vocals -o demucs --filename '{track}_{stem}.{ext}' -j 1 /data/Music/to_convert/
then delete all the _vocals files. Don't put –two-stems to get the vocal, piano, bass and drum stems.
oh yeah, don't bother installing them. I said screw it and caved into making a venv