Mixing vs. mastering
Mixing balances the parts against each other. Mastering is the one final pass that makes the finished whole loud, even, and publishable.
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What it is
Mixing is where you balance the pieces against each other while every track is still separate: voice level against the music bed, EQ per track, compression on the vocal, panning, ducking, fades. Every decision is relative to another element in the session.
Mastering happens after the mix is bounced to one stereo file. It is a short, conservative pass on the whole program: broad gentle EQ, glue compression, a limiter, and a loudness target (roughly -14 LUFS for YouTube and Spotify, -16 LUFS for most podcasts, -1 dBTP true peak ceiling). Nothing is separable anymore, so nothing can be rebalanced.
Gotcha: 'mastering' does not mean 'make it louder'. If the voice is buried under the music, that is a mix problem, and cranking the limiter just gives you a loud buried voice plus pumping. Fix the balance first, then master once.
Ask AI for it
Master this bounced stereo mix for streaming: apply broad gentle EQ (moves of 2 dB or less, no surgical cuts), light glue compression at about 2:1 with slow attack and 1 to 2 dB of gain reduction, then a brickwall limiter with a -1 dBTP ceiling, targeting -14 LUFS integrated. Do not rebalance individual elements and do not squash the transients; keep the mix's dynamics recognizable.