Glossary

The loudness words, each with the standard that defines it.

LUFS, dBTP, LRA, PLR, K-weighting, true peak, the gates, the penalty. Twenty-six terms, each one a short definition and a link to the document that defines it, so a number on this site can be traced to where it came from.

LUFS

Loudness Units relative to Full Scale. One number for how loud a signal is, measured the way ITU-R BS.1770 describes: the signal is K-weighted, split into blocks, the quiet blocks are gated out, and the rest is averaged. Every published streaming target is written in LUFS. Every value is negative, and −9 is louder than −14.

Defined by ITU-R BS.1770

LU

Loudness Unit. A difference between two loudness readings; 1 LU is the same size as 1 dB. A track at −9.4 LUFS is 4.6 LU louder than a −14 target. LUFS is a level, LU is a distance.

Defined by ITU-R BS.1770

LKFS

Loudness, K-weighted, relative to Full Scale. The same measurement as LUFS under the name the ITU and the US broadcast standard ATSC A/85 use; the EBU chose LUFS. A reading in LKFS and a reading in LUFS are directly comparable.

Defined by ITU-R BS.1770

Integrated loudness

The loudness of the whole programme, from start to finish, with the gates applied. When a platform or a delivery spec says LUFS with no qualifier, it means integrated. The other two windows exist for watching a meter while you work.

Defined by ITU-R BS.1770

Momentary and short-term loudness

Momentary loudness is measured over a 400 ms window and short-term over 3 s, both K-weighted and both ungated. EBU Tech 3341 defines the two windows and how a compliant meter displays them.

Defined by EBU Tech 3341

K-weighting

The two-stage filter applied before loudness is summed: a high-frequency shelf that lifts the treble, then a high-pass that reduces the lowest bass. It exists because a peak meter counts a sub-bass note and a hi-hat equally and a listener does not. It is why a bass-heavy mix and a bright one can peak at the same level and read differently.

Defined by ITU-R BS.1770

Gating

Two thresholds that decide which 400 ms blocks count toward the integrated reading. The absolute gate discards blocks below −70 LUFS, so silence is ignored. The relative gate then discards blocks more than 10 LU below the ungated average, so a long quiet intro does not drag a song’s number down.

Defined by ITU-R BS.1770

Loudness range (LRA)

How far the loud parts of a track sit from the quiet parts, in LU. EBU Tech 3342 defines it from the distribution of short-term loudness: a relative gate 20 LU below the mean removes fades and silence, then the range is the distance between the 10th and 95th percentiles. Heavy limiting produces low numbers; there is no correct value.

Defined by EBU Tech 3342

dBFS

Decibels relative to full scale, the largest value a digital file can hold. 0 dBFS is the ceiling of the format, and every sample sits at or below it. A peak meter reads dBFS. It says nothing about loudness: two files can peak at the same dBFS and be 6 dB apart in how loud they sound.

Defined by ITU-R BS.1770

Sample peak

The highest single sample value in a file, in dBFS. It is what a peak meter in a DAW shows and what most clip indicators watch. It misses the level the waveform reaches between samples, which is why true peak exists.

Defined by ITU-R BS.1770, Annex 2

True peak (dBTP)

The highest level the reconstructed waveform reaches, including the points between samples. A converter or a lossy encoder rebuilds a continuous signal from the samples, and that signal can rise above every sample in the file. BS.1770 measures it by oversampling four times and reading the peak of the result. A file can read 0.0 dBFS at every sample and +0.8 dBTP.

Defined by ITU-R BS.1770, Annex 2

Inter-sample peak

The part of the true peak that a sample-peak meter cannot see: the level between two adjacent samples when the waveform curves above both. Lossy encoders add more of it on decode. It is the reason delivery specs pair a loudness target with a true-peak ceiling below zero.

Defined by ITU-R BS.1770, Annex 2

True-peak ceiling

The highest true peak a limiter is allowed to let through. This site’s presets offer three: −1.0 dBTP, the general recommendation; −2.0 dBTP, what Spotify asks for above −14 LUFS; and −0.1 dBTP for a file nobody re-encodes. The ceiling is never traded for loudness: when a target is out of reach under it, the master is delivered short and the shortfall is stated.

Defined by AES TD1008

Headroom

The distance between a signal’s peak and a limit, usually 0 dBFS or a delivery ceiling. A mix bounced with a few dB of headroom gives a mastering chain room to work; a mix already peaking at 0 has spent it.

Defined by AES TD1008

Crest factor

The ratio of a signal’s peak level to its average level, in dB. Drums have a high crest factor, a sustained pad a low one, and limiting lowers it. It is the property a limiter spends to buy loudness.

Defined by ITU-R BS.1770

Peak-to-loudness ratio (PLR)

True peak minus integrated loudness. A master at −1 dBTP and −14 LUFS has a PLR of 13 dB; the same peak at −8 LUFS has 7. It states how much of the available range the master kept, and it is the number that changes when a platform turns a track down: the level drops, the ratio stays.

Defined by ITU-R BS.1770

Limiter

A gain reducer that holds peaks under a ceiling, working fast enough to catch every one. A true-peak limiter watches the oversampled signal so the ceiling holds after reconstruction. In this chain it sits behind a clipper and is the only limiting a master goes through; the loudest compliant gain is found by search rather than guessed.

Defined by How it works

Clipper

A stage that shaves the top off a peak instead of turning the whole signal down around it. A soft clipper rounds the cut rather than squaring it. Ahead of a limiter it buys back the headroom the limiter would otherwise spend on a few transients, which is why the chain reaches its targets on material a limiter alone left short.

Defined by The mastering chain

Loudness normalisation

Playback gain a platform applies so tracks sit near a target level. It changes the level a listener hears, never the file. Spotify: “We adjust tracks to −14 dB LUFS, according to the ITU 1770 standard.” It is not universal: Spotify documents it as off on its web player and third-party devices, and five of the largest platforms publish no target at all.

Defined by Spotify for Artists

Loudness penalty

How far a platform turns a track down: the track’s integrated loudness minus the platform’s published target, when the track is louder. A −9 LUFS master on a −14 platform is played 5 LU quieter. Only platforms that publish a figure have a penalty to calculate.

Defined by The loudness penalty calculator

Level-matched A/B

Two versions played at the same loudness so the comparison is tone and dynamics rather than volume. Louder sounds better on first hearing, which is why an unmatched before-and-after flatters whichever side is louder. This site’s previews are matched by pure gain before either plays.

Defined by How it works

Reference master

A finished record the chain measures your mix against to derive its tonal correction. Here each genre’s reference is one real master chosen by a mastering engineer; the match corrects spectral balance and width toward it and leaves the arrangement alone.

Defined by The mastering chain

Dither

Low-level noise added when a file’s bit depth is reduced, so that rounding errors become a steady hiss below hearing instead of distortion that follows the music. It belongs on the last step to 16-bit, once, and not before.

Defined by AES TD1008

ITU-R BS.1770

The international recommendation that defines how loudness and true peak are measured: K-weighting, the block and gate rules, and the oversampled true-peak meter. Every LUFS figure on this site is a BS.1770-4 measurement, and the checker is verified against ffmpeg’s implementation of it.

Defined by ITU-R BS.1770

EBU R 128

The European Broadcasting Union’s loudness recommendation for broadcast: programmes normalised to −23 LUFS with a maximum true peak of −1 dBTP, measured as BS.1770 describes. Its companion documents Tech 3341 and 3342 define the meter modes and loudness range. It is a broadcast standard; streaming platforms sit well above its target.

Defined by EBU R 128

AES TD1008

The Audio Engineering Society’s recommendations for loudness in streaming and on-demand delivery: −16 LUFS for a single track, −14 LUFS for an album, and a maximum true peak of −1 dBTP at the input of a lossy encoder, lower as bitrate falls. It is a recommendation from a standards body; it is often quoted as if a platform had published it.

Defined by AES TD1008