What does a limiter do in mastering?

It stops the signal going over a ceiling you set by turning the level down for a moment when a peak is about to get through, so you can raise the overall level without chopping the peaks off.

Is clipping always bad?

No. Careless hard clipping sounds bad, but a small amount used deliberately can shave off the tallest peaks and give you headroom before the limiter.

What is gain reduction?

How much the limiter is turning the level down at a given moment. A little, only on the odd peak, is healthy. If it is pressing down all the time, the track sounds squashed.

What is the release on a limiter?

How quickly the limiter lets the level come back up after it has turned it down. Too fast can sound gritty, too slow can mean it never recovers before the next kick.

Why should I match levels when comparing masters?

Because louder sounds better to our ears. Unless the levels match, you are mostly hearing which one is louder, not which one is better.

What a limiter actually does

Every master I send out for the clubs is loud. The thing that gets it there is the limiter. The easiest way I've found to explain what it does is a glass of water. Watch the film, or read it step by step below.

Prefer to read? The whole thing is below, step by step.

The short version

Your track is a glass. The top of the glass is the ceiling: the loudest it is ever allowed to get.
Every instrument you add is more water and less headroom.
Clipping chops off what spills over. Done carefully, you can go further than you would think before you hear distortion.
A limiter sees the splash coming and turns the whole glass down for a moment, so nothing spills. That dip is the gain reduction.
Push it too hard and it presses down all the time: loud, but squashed.

The glass

Think of your track as a glass. The top of the glass is the ceiling, the loudest your track is ever allowed to get. Nothing gets past it, everything has to fit inside it.

Headroom

Start with just the kick. It has loads of room to move, so it can be really loud and really punchy. All that space above it is your headroom.

Then you pour in the bass. In dance music that is the biggest pour, because the low end takes up more room than anything else. Then the drums, the synths and pads, and the vocal on top. The pads fill the gaps between the kicks, so the water never gets the chance to drop back.

Every instrument you add is more water and less headroom. Less room, less movement.

Clipping

So what happens if you just keep pushing it louder? It spills over the top. That is called clipping. Anything past the top just gets chopped off, and if you push far enough you hear it as distortion.

Everyone has been told that clipping is bad. But you would be surprised how far you can clip something before you hear any distortion. It is one of the biggest things I do: clip it as far as I can take it and find all the headroom I can.

The limiter

I keep the clipper on, and right after it is where the limiter comes in. It sits right at the top, and it is clever. It sees a splash coming before it gets there. That is the look-ahead.

Instead of chopping it off, it turns the whole glass down, just for a moment, just enough to fit. Then it lets it back up. That dip is the gain reduction. Because nothing spills any more, you can pour more in. That is how a master gets loud.

When it is too much

Push it too hard and it is pressing down all the time. The water cannot move and your kick has lost its punch. Every time it hits, it shoves everything else down with it, and it starts to pump. That is what people mean by squashed: loud, but nothing is moving.

Release

How quickly the limiter lets the water back up matters too. That is the release. Too fast and it wobbles about; you get grit on the bass. Too slow and it never comes back up before the next kick. Get it right and it breathes with the track.

The honest test

Louder sounds better, almost every time. Your ears are wired that way, so the louder version nearly always wins, even when it is worse.

That is why I never judge a master like that. I match the levels first, same loudness. Now you can actually hear which one is still moving.

How I do it

The job is not to avoid the limiter. Club tracks should be loud. The job is to make room in the glass before it gets there:

Keep the low end under control. It is the biggest pour.
Stop things fighting for the same space.
Clip the tallest splashes off first, further than you would think.
Then the limiter only catches the odd splash and does not have to work hard.

That is a glass that is full and still moving. Loud and moving. That is what we call dynamic. Loud and dynamic. That is the game.

Questions people ask

What does a limiter do in mastering?: It stops the signal going over a ceiling you set by turning the level down for a moment when a peak is about to get through, so you can raise the overall level without chopping the peaks off.
Is clipping always bad?: No. Careless hard clipping sounds bad, but a small amount used deliberately can shave off the tallest peaks and give you headroom before the limiter.
What is gain reduction?: How much the limiter is turning the level down at a given moment. A little, only on the odd peak, is healthy. If it is pressing down all the time, the track sounds squashed.
What is the release on a limiter?: How quickly the limiter lets the level come back up after it has turned it down. Too fast can sound gritty, too slow can mean it never recovers before the next kick.
Why should I match levels when comparing masters?: Because louder sounds better to our ears. Unless the levels match, you are mostly hearing which one is louder, not which one is better.