Current Beatles engineer Allan Rouse explains the difference between remixing and remastering:
The “Yellow Submarine Song Songtrack” was a ‘remix’ which required going back to the original multi-track tapes and recreating a new stereo (and 5.1 surround for the film soundtrack). In the same way as the “Anthology” and “Help!” DVDs were created, along with “Let It Be… Naked” and “LOVE.” The re-masters are made from the original Sixties mono and stereo master tapes, and because of this, do not allow for the changes that can be made when mixing. Therefore, the improvements that occur with the re-masters are: vastly improved digital technology (since their first release on CD in the eighties); in addition, new technology has allowed us to remove or improve technical faults with the recordings, for example bad edits, tape drop outs, sibilance etc. Noises that were part of The Beatles’ performances such as breaths, lip noises and squeaky bass drum pedal were left alone. Finally, EQ has been used where appropriate to enhance the sound.
Master tapes = mixed recordings from which albums are sourced. Multi-track tapes = the original recordings of the separate instrumental and vocal tracks. The master tapes were created by George Martin, Norman Smith, Geoff Emerick, Ken Scott, Phil McDonald, Glyn Johns and The Beatles from the multi-track tapes, and now remastered by Allan Rouse and his team.