I'm a Berlin-based music producer and engineer with a strong backround in analog electronica & Techno.
Mixing A B tests, level-matched:
Comparing the rough mix with the finished mix before the mastering stage at a matched level. The goal of a good mixing job is to embellish the producer's vision and if necessary rebalance and clean up less optimal recorded/produced material with high end equipment.
Pop- and acoustic music first, electronic music genres in 2nd example.
Mastering A B tests, level-matched:
Comparing the sonics of the non-limited premaster file with the master with applied limiting at a reduced volume. The goal is to get a loud master with improved sonic qualities instead of a crushed audio file with worse sonics than the premaster and create a recording that transmits well on multiple playback systems.
Pop- and acoustic music first, electronic music genres in 2nd example.