Limiting and loudness

Two versions of the same track. Listen to both and pick the one you prefer. The names are hidden until you answer.

If you picked the louder one, you're in good company. Nothing else changed, yet louder sounds fuller, brighter and more exciting to almost everyone. That one quirk of hearing drove the loudness war: for about twenty years, records were mastered louder and louder so they'd jump out on the radio and in the shop, at the cost of their dynamics. Metallica's Death Magnetic (2008) became the famous casualty, with fans complaining that it sounded squashed and distorted.

A limiter lets you raise the level of a master by holding back its peaks. How far you push it changes the sound, and some peaks can hide between the samples.

A limiter is a ceiling

A limiter is a compressor taken to the extreme: anything that tries to go above a set level, the ceiling, is turned down instantly so it can't get past. Because the loudest peaks are held back, you can turn the whole track up until those peaks touch the ceiling. Everything quieter comes up with it. The track gets louder and denser.

Push the track into the limiter below. Raise Gain to drive the music up against the Ceiling, then press Match so you're hearing what it does to the sound, not the volume boost.

A mastering limiter does one more thing: it looks ahead. It delays the audio by a few milliseconds so it can see each peak coming and start turning down before it arrives. That's how it holds a hard ceiling without bending the front of a sharp hit.

What pushing harder costs

Raise the gain a few dB at a time and listen to one thing: the kick.

At first the mix gets denser and more solid. Then the front of the kick and snare starts to flatten. They stop hitting and start pushing. Keep going and the whole mix dips on each beat and swells back (the release at work), the bass grows a fuzzy edge, and the loud chorus doesn't feel any bigger than the verse. The loudness number keeps rising. The excitement doesn't.

Release decides how the mix recovers. Very short and it starts to distort the low end, because it follows the bass waveform itself. Long, and one loud hit pulls the next beat down with it. There's no single right value; there's the one where this song still grooves.

Louder doesn't win any more

Today most of the big streaming services normalize playback: they measure each track's loudness and turn the loud ones down so everything plays at a similar level. A master pushed to the limit doesn't arrive louder. It arrives at the same level as everyone else, only flatter, with less punch than a track that kept its dynamics.

That changes the question. It's no longer "how loud can I get it?" but "how much density does this music want?" A club track might want a lot. A folk song or a jazz trio, very little.

Peak, true peak and loudness are different things

Three readings get confused all the time:

• Sample peak is the biggest number stored in the file, measured against full scale (dBFS). 0 dBFS is the top.
• Loudness, measured in LUFS, is how loud the track feels over time, weighted to match human hearing. Two tracks can share a peak and differ hugely in loudness. Normalization uses this number.
• True peak (in dBTP) is the highest point of the actual sound wave, which can be higher than any stored sample.

That last one sounds impossible. It isn't.

Can the sound go higher than every sample?

A digital file stores snapshots of a wave, many thousands per second. When you play it, your converter draws a smooth wave through those points. And a smooth wave can rise between the snapshots.

This is an extreme case, chosen to make the point, but milder versions happen all the time in loud masters. A limiter that only watches the samples can keep every one of them under the ceiling while the real wave pokes above it. These are intersample peaks. They're harmless in the file, then clip later: in a cheap converter, or when the track is turned into an MP3 or AAC for streaming.

That's why good limiters measure true peak, checking extra points between the samples, and why mastering engineers often leave a ceiling of −1 dBTP instead of 0. Always measure the file you actually deliver.

Same idea, different place: Digital audio explains how a smooth wave is rebuilt from samples at all. Intersample peaks aren't a defect of mastering. They're the same reconstruction that makes digital audio work.

Where the master gets hurt

Most limiting trouble starts earlier in the mix. A boomy kick tail or a huge sub bass makes the limiter clamp down on every beat, and the whole song pays for it. Taming the low end first often buys you more clean loudness than any limiter setting.

And if something already clipped before the limiter, lowering the ceiling won't bring its shape back. Find where it overloaded.

Make it yours

Take one section of your own mix: a transition into a chorus with a strong drum hit. Make two limited versions, one light and one heavy. Turn the heavy one down until both feel equally loud, then compare. Follow the kick. Which one still has the hit you wanted?

Pick the one that suits the music, then measure its true peak and loudness on the exported file. Save it alongside a single sentence about the tradeoff: "Denser chorus, a little less kick." That reason will help you decide again when the destination changes.

Quick check

1. Every sample in your file is below 0 dBFS. Can the sound still go over? Yes. The reconstructed wave can peak between the samples. A true-peak meter checks for that; a sample-peak meter can't.
2. You push a master 4 dB harder and it wins your quick A/B. After matching levels, the drums sound flatter. Which do you keep? Whichever serves the song after matching. Many streaming services turn loud tracks down anyway, so the 4 dB may never reach the listener, while the flattened drums will.
3. A compressor at infinite ratio with no lookahead. Is it a perfect ceiling? No. Without lookahead it can't react before a peak arrives, so the very start of a sharp hit can get past. Real limiters look ahead and measure true peak for that reason.

Next steps

• Go deeper: Distortion and saturation. A limiter with no attack and no release clips the wave. What does clipping add to a sound?
• Use it: Finishing and references. Loudness targets, reference tracks and knowing when to stop.