Music Minus One.
Practice-with-the-band recordings since 1950. Founded in New York by Irv Kratka, Music Minus One pioneered the play-along recording format — a professionally recorded ensemble track with one part removed, so the student can play that part along with the recording. Used by every conservatory, jazz program and home practice room.
Play-along practice — what jazz musicians call "tracking" — was pioneered as a commercial format by Irv Kratka in 1950. The original Music Minus One recordings let a student play through standard concertos, sonatas and jazz tunes against a professional accompaniment, removing the single instrument the student is learning. The original LPs are now CD/digital, the catalogue covers every classical solo instrument and the entire jazz fakebook.
Below: the Music Minus One departmental catalogue. Instrument-first for the major solo instruments, format for the classical concerto and jazz play-along sub-libraries, plus the chamber music play-along and vocal play-along sub-catalogues.