What Does Mastering Actually Do? (And What It Can't Fix)

Oct 7

5 min read

Mastering is the last step between a finished mix and a release, and it's also the step people understand least. I hear the same two ideas all the time: that mastering is a magic button that makes everything sound "pro," or that it just makes the song louder. Neither one is quite right.

Here's what mastering really does, what it can't do, and how to send a mix that gives it the best possible shot.

Mixing vs mastering, in one sentence each

Mixing is balancing the individual parts of a song (vocals, drums, bass, guitars, keys) so they work together. Mastering is treating the finished stereo mix as one piece and getting it ready for the world.

In a mix, you can turn the snare down. In mastering, you mostly can't, because the snare, the vocal, and the bass are all baked into the same stereo file. That one fact explains almost everything about what mastering can and can't do.

What mastering actually does

A good mastering pass usually involves some combination of these:

Tonal balance. Broad, gentle EQ so the song isn't dull, harsh, boomy, or thin on the systems people actually listen on: earbuds, car speakers, laptops, a big PA.
Dynamics control. Careful compression and limiting to keep the level steady and controlled without flattening the life out of the performance.
Loudness. Setting the final level so the song sits comfortably next to other releases, with the peaks kept in check so it doesn't distort when it's converted for streaming.
Translation checks. Making sure the song holds together in mono, the low end is centered and solid, and nothing falls apart on a small speaker.
Cleanup. Clean fades in and out, no clicks at the top or the tail, and no stray noise before the downbeat.
Consistency across a release. On an EP or album, matching tone and level from song to song and setting the spacing between tracks, so it plays like one record instead of a pile of separate files.
Delivery. Final files in the formats your distributor asks for, with any codes or metadata the release needs.

There's one more thing mastering gives you that doesn't show up on that list: a fresh set of ears. By the time you finish a mix, you've heard it hundreds of times. Mastering is a chance for someone to hear it new and catch the things familiarity hides.

What mastering can't fix

This is the part that saves people money and frustration. Because mastering works on the whole stereo mix, it can't reach inside and fix one instrument without affecting everything else. Mastering won't fix:

A vocal that's too loud or too quiet. You can nudge the midrange a little, but that moves the guitars and the snare along with it.
Kick and bass fighting each other. Mastering can shape the overall low end, but the separation between those two parts happens in the mix.
Harsh or distorted recordings. If a track was clipped on the way in, or a cymbal is piercing, mastering can soften it a little but can't undo it.
Timing and tuning problems. Those are performance and editing issues, and they need to be handled long before mastering.
A crowded arrangement. If eight parts are fighting for the same space, no EQ on the stereo file will untangle them.

My rule of thumb: if the mix doesn't excite you at a normal listening level, mastering won't change that. Mastering takes a mix that's already working and gets it ready for release. It doesn't turn a mix that isn't working into one that is.

Loudness: louder isn't the win it used to be

For years, the goal was to make every master as loud as possible. Streaming changed the math. Spotify, for example, uses loudness normalization: by default it adjusts playback to -14 dB LUFS, measured to the ITU 1770 standard. If your master is much louder than that, Spotify simply turns it down on playback. You don't keep the extra volume, but you do keep whatever punch you gave up to get it.

Spotify's own mastering tips suggest aiming for about -14 dB integrated LUFS and keeping the true peak below -1 dB, or below -2 dB if your master is louder than -14 LUFS, so the file doesn't pick up extra distortion when it's encoded for streaming.

That doesn't mean every master has to sit exactly at -14. The genre, the song, and the artist's taste all matter, and plenty of records are mastered louder on purpose. But loudness should be a choice, not a reflex. A master that keeps its punch often sounds better on a streaming service than one that's been squeezed flat to win a volume war that normalization cancels out anyway.

How to send a mix that's ready for mastering

A lot of mastering problems start as delivery problems. Before you send a mix off, check these:

Take the limiter off the master bus. Or at least ask your mastering engineer first. Let the final loudness decisions happen in mastering.
Leave some headroom. Your loudest peaks shouldn't be slamming the top of the meter. Make sure nothing is clipping anywhere in the song.
Export at full quality. Send a WAV or AIFF at the session's sample rate and bit depth, not an MP3.
Don't trim the start and end too tight. Leave a little space before the first note, and let the last note ring out completely so the fades can be set cleanly.
Send a reference or two. Pick a couple of released songs you'd like yours to sit next to, and add a note about anything you're unsure of.
Fix it in the mix first. If something is bugging you, like a vocal sitting low or a harsh hi-hat, fix it now. It's far easier there than in mastering.

If you're sending separate tracks to be mixed rather than a finished mix to be mastered, my stem prep checklist covers that side of things.

Should the same engineer mix and master?

There's no single right answer. A separate mastering engineer gives you another set of ears in another room. Having one engineer handle both means the person mastering knows exactly what the mix was going for, and if mastering exposes a problem, they can go back and fix the mix itself instead of patching the stereo file. Either way, what matters most is that whoever masters your song listens carefully and tells you honestly when something should be fixed in the mix instead.

Getting your song finished

If you have a song that's close but not quite there, or a finished mix that needs mastering before release, take a look at my online mixing and mastering page. Send over what you've got, and I'm happy to tell you honestly whether it needs mastering, a mix touch-up, or both.

— Jim

If you'd like one-on-one help with your own mix, vocals or audiobook, you can book an online session with me.