What you are training
Level balance is the first pass of every mix and the one most people rush. A mix with the right faders and no processing sounds better than a mix with wrong faders and perfect plugins, yet most beginners reach for EQ before the balance is right. This drill plays two sources, moves one by a hidden amount, and asks you to match them. You learn what 1 dB, 3 dB, and 6 dB actually sound like, which is the vocabulary you need to make small, confident fader moves instead of large, nervous ones. It also trains the honesty that reference-track work depends on: you cannot judge a comparison until the levels match, because louder always sounds better. Six rounds, with the answer shown in dB after each one.
After this drill, the plan: The daily plan runs level matching before any tonal drill, so every later comparison you make is at matched loudness.