Mixing vs mastering: the differences

"Mixing and mastering" is usually said in one breath, as if it were a single thing. They're two different processes with different goals, and understanding the difference saves you money, time and the occasional disappointment. Let's take it step by step.

What mixing is

Mixing works with every track of your song separately: lead vocals, backing vocals, ad-libs, drums, bass, melodies, effects… The goal is for all of it to sound like one piece, with every element in its place.

In the mix, among other things, you decide:

The level of each element and how it changes throughout the song (automation).
The panning: what sits in the centre and what goes to the sides.
The EQ of each track, so they don't step on each other.
The dynamics: compression to control and add punch.
The space: reverbs, delays and effects that create depth and atmosphere.

If I think of a film, mixing is shooting and editing the scene: where each character stands, what gets the light, what stays in the background.

What mastering is

Mastering comes afterwards and works with the finished mix, as a single stereo file. It can't touch the vocal without touching everything else, because it's all already combined. Its job is the final overall adjustment:

Balancing the overall tonal balance (lows, mids, highs).
Setting dynamics and loudness so the track competes without losing life.
Creating cohesion between songs on an EP or album.
Preparing the delivery files in the right format and doing a final quality check.

Sticking with film: mastering is the colour grade and the final print. The scene is already shot and edited; now the colour is unified and it's prepared for every screen.

Why mastering can't fix a bad mix

This is the most common confusion. If the vocal is buried, the bass booms or the snare can't be heard, mastering can only act on the whole. Boosting the mids to bring out the vocal also boosts the guitars, pads and everything else living in that range. It may help a little, but the problem is still there.

A good master makes a good mix sound like a record. It doesn't turn a problematic mix into a good one.

When you need mixing

You've recorded vocals over a beat and have the tracks separately.
Your track sounds unbalanced: something covers the vocal, the low end is muddy or it lacks clarity.
It sounds very different every time you play it on a different system.
You're releasing and want the track to sound professional from the ground up.

A very common case: you have the beat as a single stereo file and your vocals separately. That gets mixed too. Still, if you can get the beat as separate tracks (some licences include them), there's far more room to fit it around your voice.

When you only need mastering

Your mix is already balanced and you've checked it on several systems.
You like how it sounds, but it needs the last step of polish, loudness and cohesion.
You have several mixed songs that need to sound like one project.

Before sending it, go through what to prepare before ordering a master: headroom, format and notes.

When you need both

For most serious releases. If you're recording a new song and want to release it in good quality, the usual path is to mix first and master afterwards. Some people prefer the same person to do both, for continuity; others prefer different ears for each stage, for a fresh perspective. Both are valid.

Habits I apply in every mix

A few ideas I've repeated for years, because they make a difference:

Think in three dimensions. Every sound has a level (how loud it is), a depth (how near or far it feels) and a place in the stereo field (left, centre or right). Mixing is placing each element in those three dimensions. I go deeper into it in the stereo field.
Mix at a moderate level. At high volume the ear protects itself and stops perceiving lows and highs the same way. A good reference is a level where you can talk without raising your voice. And look after your ears: long exposure to high levels damages hearing.
Short sessions, fresh ears. After a couple of hours your ears tire and you start making bad decisions. I'd rather spread a mix over several one‑to‑two‑hour sessions on different days than do it all in one go.
Clear priorities in urban music. In rap, trap and drill: the vocal first; then percussion and bass (kick and 808); then the melody. If those pillars work, the track works.
A good mix starts at the recording. Record in the most treated, quiet room you can, leave some distance between mouth and microphone, respect the beat's tempo and key, and keep your dynamics consistent. Mixing can polish a lot, but it doesn't work miracles.

For the basic tools, start with EQ and compressor types.

What if you don't know where your track stands?

It's more common than you'd think. After listening to a mix a hundred times, your ears get used to it and it's hard to tell if it's ready. That's what a technical diagnosis is for: a critical listen with concrete notes on balance, dynamics, frequencies and space, so you know what to adjust and which step to take next.

In short

Mixing: works track by track; builds the song.
Mastering: works on the final mix; polishes it and prepares it for release.
Mastering doesn't replace mixing.
If in doubt, start by finding out where your song stands.