A lot of mastering orders arrive with a folder of stems attached, usually with a note that says something like "in case it helps." I get why. More files feels like more control. For a mastering order, though, I work from the stereo mix, and the stems sit in the folder unopened.
That isn't me being lazy. It's what the job is.
What mastering works on
Mastering takes one finished stereo mix and gets it ready to release: loudness, peak safety, the overall tone, how it holds up on a phone versus a car. Every move I make touches the whole song at once. If the vocal needs to come up two dB against the guitars, that's a mix decision, and mastering can only nudge it from the outside with EQ and dynamics.
Once I open the stems and start rebalancing parts, I'm mixing. That's a different job with different decisions, more time, and a different price. It also means I'm deciding how your song should be balanced, and you didn't ask me to do that.
Why AI stems are a special case
Stems from a generator aren't the original tracks. Suno and the other tools build the song as one piece of audio, then split it into vocal, drums, bass and the rest after the fact. The split leaves bleed and artifacts: a ghost of the hi-hat in the vocal stem, a smeared reverb tail in the instrument stem. When the stems are summed back together, most of those artifacts cancel out and you hear the song you picked. Solo them and rebalance them, and the artifacts start to show.
So the stereo mix you liked is usually a cleaner starting point than the stems that came out of it. If the stereo mix is the version you chose, send that.
When stems are the right call
Send stems, and ask about mixing instead of mastering, when the balance itself is the problem. A vocal that disappears in the chorus. A kick and bass fighting so hard that nothing below 100 Hz reads. A synth that's simply too loud everywhere. Those are mix problems, and fixing them inside a master means EQ moves that change everything else in the same frequency range.
If you're on the fence, send the stereo mix and tell me what bothers you about it. If I think it's a mastering fix, I'll master it. If I think it needs a mix, I'll tell you before I start rather than after.
What to send for a mastering order
One stereo WAV, straight from the generator's desktop download or your DAW's final render, with nothing on the master bus. If you made changes in a DAW, render the mix with your effects on the tracks but no limiter or loudness plugin on the output. My note on sending the right file covers how to check it.
A folder of stems tells me you're not sure the mix is done. A single stereo file tells me it is. Know which one you're sending.
Josh, Founder, JG BeatsLab
Want this handled on your track? I master AI-generated music by hand, one song at a time, and every master comes with a Mastering Dossier that shows what I did and why. Book mastering or take the 3-minute scorecard to see where your workflow stands.
