Limiting and true peak explained: what your limiter actually does, and where to set the ceiling

The limiter is the last plugin on most masters and the one people understand least. It is often treated as a loudness knob: drag the threshold down until the track sounds as loud as the reference, then export. That works, until a listener's phone turns your clean master into a crackle on the snare, or a streaming service turns it down so far that all the squashing bought you nothing.

This guide explains what a limiter does, what "true peak" means and why your DAW's peak meter can miss it, and how to set a limiter so your master survives encoding. It assumes you know what a compressor is; if not, start with our compression basics.

What a limiter is

A limiter is a compressor taken to the extreme. A normal compressor turns the signal down by a ratio, say 4:1, once it passes a threshold. A limiter uses a ratio so high it acts as a wall: nothing gets above the level you set, called the ceiling or output.

Three things make modern mastering limiters behave well:

• Fast attack. The limiter reacts quickly enough to catch drum transients.
• Lookahead. It delays the audio by a few milliseconds so it can "see" a peak coming and start turning down before it arrives. That avoids the harsh clipping of a limiter that reacts too late.
• Release. After a peak, the gain comes back up. Too fast and you hear distortion and pumping on bass; too slow and the track sounds flat and choked after every kick.

Most limiters give you two main controls: a threshold or input gain (how hard you push into it) and a ceiling (the maximum output level). Push harder and the track gets louder, because the quiet parts come up while the peaks stay pinned to the ceiling.

Sample peak vs true peak

Digital audio is a series of samples. A standard peak meter reports the highest sample value, measured in dBFS (decibels relative to full scale, where 0 dBFS is the maximum).

The catch is that the sound you hear is not the samples. When audio is converted back to an analogue waveform, or decoded from a lossy format, the converter draws a smooth curve through the samples, and that curve can rise above the highest sample. These are called inter-sample peaks. A master whose samples all sit at -0.1 dBFS can produce a waveform that goes over 0 dBFS between them, which some converters and encoders will clip.

True peak is the measurement that catches this. The ITU's BS.1770 recommendation, the same document that defines the loudness measure behind LUFS, specifies a true-peak meter that estimates the level between samples by oversampling the signal (computing extra in-between points) before measuring. The unit is dBTP, decibels true peak. A true-peak reading is always the same as or higher than the sample-peak reading of the same audio.

Why it matters more for releases than it used to: almost every listener hears your music through a lossy codec such as AAC or Ogg Vorbis. Encoding changes the waveform slightly, and those changes can push peaks higher still. Spotify's loudness page says it recommends keeping true peak at or below -1 dBTP to suit lossy formats, and below -2 dBTP if the master is louder than -14 LUFS integrated, because louder tracks are more prone to extra distortion when they are transcoded.

Broadcast reached the same number years ago. EBU R128, the European broadcast loudness standard, sets a maximum permitted true-peak level of -1 dBTP.

How to set a limiter, step by step

1. Finish the mix first. A limiter cannot fix a muddy low end or a buried vocal. If the mix needs work, our list of common bedroom mix mistakes is a good check.
2. Put the limiter last on the master bus, after any EQ, compression and saturation. Anything after it (a meter is fine, a dither plugin is fine) must not add gain.
3. Turn on true-peak mode if the limiter has one. Many current limiters offer an "ISP", "true peak" or oversampling option. With it on, the limiter controls inter-sample peaks, not just sample values.
4. Set the ceiling to -1.0 dBTP. If your limiter has no true-peak mode, set a lower sample-peak ceiling, such as -1.5 or -2.0 dBFS, and check the result on a true-peak meter.
5. Raise the input gain slowly while watching the gain-reduction meter. Start with nothing happening, then push until the limiter is only catching the loudest hits.
6. Listen at matched loudness. Toggle the limiter on and off with its output turned down so both versions play at the same perceived level. Louder always sounds better at first; matching levels removes that trick.
7. Back off at the first sign of damage: a softer kick, a snare that loses its snap, bass that crackles, cymbals that turn to hash, or a vocal that "breathes" in level.
8. Measure the whole track on a meter that shows integrated LUFS and true peak, and check the true-peak maximum is at or below your ceiling. Then export at your project's bit depth, adding dither if you reduce to 16-bit; our guide to dithering covers when that matters.

A rough guide to what you are seeing on the gain-reduction meter: a couple of dB on the loudest peaks is usually inaudible on most material. Several dB of constant reduction is where the damage starts on most genres. That is a rule of thumb, not a spec, so trust your ears and a reference track over any number.

Common mistakes

• Ceiling at 0.0 dBFS. The samples never clip, but the decoded waveform and the encoded file can. There is no benefit to the last 1 dB of peak level on a normalised platform.
• Trusting the DAW's master meter. Many stock meters show sample peak only. Check with a meter that explicitly says dBTP.
• Limiting to hit a LUFS number. Loudness targets describe what platforms do on playback, not how loud you must master. Our streaming loudness guide sorts out which targets are actually documented.
• Stacking limiters. A limiter on the drum bus, another on the mix bus and a third in mastering each take a little punch. Use one, at the end, unless you have a specific reason.
• Fixing the mix with the limiter. If one element sets off the limiter every time, such as a kick or a vocal "s", fix that element in the mix.

What we think

The usual advice frames true peak as a technical box to tick before upload. We think it is better understood as the cheapest piece of insurance in music production. Moving your ceiling from -0.1 to -1 dBTP costs nothing you can hear on a normalised service, because Spotify turns loud masters down anyway, and it protects you against the one failure you cannot fix after release: distortion baked in by a codec on a listener's device.

The less obvious point is that the ceiling is not where the loudness war is fought. It is fought on the input gain, the knob that decides how much of the song's movement you trade away. Artists who set the ceiling carefully and then push the input until the meter looks like a reference often end up with a safe master that has no life in it. Set the ceiling once, to -1 dBTP, and forget it. Spend your attention on the input, and stop at the point where the chorus still hits harder than the verse. That contrast is what listeners feel; the last decibel of loudness is something only a meter can see.