Mixing vs mastering: what a stereo master can't fix
Mixing works on every track of your project: levels, EQ, compression, panning. Mastering works on one stereo file: final loudness, overall tone, peak level. That's the whole of mixing vs mastering, and it's why AI mastering can polish a balanced mix but can't pull a buried vocal out from under the guitars. Here's what each stage fixes, and how to check your mix before you send it off.
What is the difference between mixing and mastering?
Mixing balances the separate tracks of a song (vocals, drums, bass, synths) against each other, one track at a time. Mastering comes after: it takes the exported stereo mix and sets its final loudness, peak level and overall tone so it's ready for release. Mixing decides how the parts fit together; mastering can only treat them as one file.
Mixing and mastering side by side
| Stage | What it processes | What you adjust | When | Typical tools |
|---|---|---|---|---|
| Mixing | every track, separately | level, EQ, compression, panning and effects on each track | while producing, in your DAW | the mixer and plugins in FL Studio |
| Mastering | one stereo file | final loudness, peak level, overall tone, overall stereo width | after you export the mix | a mastering engineer, a mastering plugin, or an online AI mastering service |
Anything that means changing one track without touching the others belongs to mixing.
Can AI mastering fix a bad mix?
No, not when the problem lives inside the mix: a buried vocal, kick and bass masking each other, one track out of phase. Yes for final level and overall tone, as long as the mix is already balanced. A mastering engine, AI or human, only receives the sum of your tracks.
RoEx, a company that sells both AI mixing and AI mastering, lists the problems that survive mastering: "muddy low-mids, buried vocals, clashing frequencies, no stereo width" ("AI Mixing vs AI Mastering," February 24, 2026). Violet Recording reaches a similar conclusion in "Is AI Mastering Any Good?": results hold up on a balanced mix, and problems tend to come from the mix rather than the master.
What mastering can't fix, problem by problem
Each row starts from a common mix problem. The last column gives the per-track measurement that reveals it before you export.
| Problem | Audible in the stereo file? | Fixable in mastering? | How to measure it first |
|---|---|---|---|
| Vocal buried under the guitars (masking around 2–4 kHz) | Yes, but blended with everything else | No: boosting that range boosts the guitars too | Vocal and guitar spectra overlaid |
| Kick and bass masking each other | Yes, in the low end, with no way to separate them | No: mastering compression makes the clash worse (RoEx) | Overlaid spectra, level of each track |
| One track carrying the Master | No | No: you can't turn one track down in a stereo file | Short-term LUFS of the track within 1 LU of the Master |
| Phase problem on one track | Partly, diluted in the Master | No: any global fix affects every track | Track correlation below -0.3 |
| A track peaking above 0 dBTP before the Master | Only if it got clipped along the way | No, once the clipping is in the file | True peak of the track |
| Everything stacked in the center | Yes: a narrow image | Partly: you can widen the whole mix, not place one track | Width and pan of each track |
These thresholds (0 dBTP, -0.3, 1 LU) are the ones Fern uses to flag a problem once it lasts at least three consecutive readings, at one reading per second. They're checkpoints, not standards.
Why a limiter makes some mix problems louder
Raising a mix to release loudness means running it through a compressor or a limiter. The processor reacts to whatever is loudest at that moment and turns the whole mix down whenever that signal crosses the threshold. If a single track carries the Master, that track triggers the gain reduction, and the rest of the mix ducks with it on every hit.
The low end works the same way. RoEx puts it plainly for kick and bass: "If your kick and bass are fighting in the low end, mastering compression will make that fight worse, not better." The problem was already in the mix. Mastering makes it easier to hear, because it raises the level without being able to pull the tracks apart.
Check your mix before mastering
Four checks cover the problems in the table above:
- Measure every track while the song plays: LUFS, true peak, correlation. A track within 1 LU of the Master, or below -0.3 correlation, is worth soloing.
- Compare tracks that share a frequency range: vocal and guitars, kick and bass, with their spectra overlaid.
- Check the Master: peak below 0 dBTP, integrated loudness in line with your target. See how loud your mix should be before mastering.
- Compare against a reference track in the same style: loudness, peak, width and tonal balance.
Fern runs these checks inside FL Studio from one instance on the Master. It can measure every track from the Master, up to 125 tracks, each with a 31-band third-octave spectrum. It can also compare your mix to a reference track in WAV, MP3, AIFF or FLAC; the file is measured inside the plugin and never uploaded. Fern reads those numbers, explains what they show, and proposes settings you audition before you apply them. It's an assistant that works on every track, before the file goes out for mastering.
Does Fern master your track?
No. Fern measures and adjusts the mix in FL Studio; mastering is still yours to do, with whatever tool or engineer you prefer. Fern can read the Master's true peak and integrated LUFS to check an export.
If you're weighing AI mixing and mastering tools, compare AI mixing tools: some work on your tracks, others only receive the final file.
FAQ
Is AI mastering any good?
On a balanced mix, often yes. Violet Recording ("Is AI Mastering Any Good?") finds AI mastering produces clean, release-ready results from a balanced mix at a sensible loudness target, and struggles with problem mixes. It can't reach anything inside the mix, so the result depends on the mix you send.