What Is K-Weighting?
Published · updated · by Loopin
K-weighting is the reason LUFS corresponds to perceived loudness at all. It is two filters, and knowing what they do explains several confusing measurements.
What it actually is
Two filters applied before the loudness is measured. A high-shelf boost of about +4 dB above roughly 2 kHz, approximating the resonance of the head and outer ear. And a high-pass around 38 Hz, removing very low frequencies that contribute little to perceived loudness.
The meter then measures the energy of that filtered signal. It is not measuring your track — it is measuring an approximation of what your track does to a listener.
Why bass-heavy tracks measure quiet
Because the low end is de-emphasised before measurement, a track with enormous sub content reads as quieter in LUFS than it feels. Producers see −13 on a track that sounds huge and add limiting to "fix" it.
This is the single most common misreading of a loudness meter. If the record sounds loud and measures quiet, trust the record — the meter is deliberately ignoring energy your ears also partly ignore.
Why bright tracks measure loud
The inverse. A mix with a lot of upper-mid and high content gets a boost before measurement, so it reads louder than a warm mix at the same subjective level.
Which means two records at identical LUFS can feel noticeably different in loudness, and that is not a fault in the standard — it is the limit of describing perception with one number.
What it means in practice
Do not chase a LUFS number in isolation. Use it to compare like with like — your track against a reference in the same genre, or your master against your own earlier version — where the weighting affects both equally.
Comparing an acoustic record and a bass-heavy electronic one at the same LUFS tells you very little about how they will sit next to each other.
The other half: gating
Integrated LUFS also ignores passages below a moving threshold, so silence and very quiet intros do not drag the average down. Together with K-weighting, that is why integrated loudness tracks perception better than a simple average.
It also means an artificially long silent tail changes your measurement less than you might expect. Measure the master you actually deliver rather than a rough bounce with a different structure.
Frequently asked questions
What does K-weighting do?
Two filters before measurement: a high-shelf boost of about +4 dB above 2 kHz approximating the ear, and a high-pass around 38 Hz. The meter measures that filtered signal rather than your raw track.
Why does my bass-heavy track measure quiet in LUFS?
K-weighting de-emphasises low frequencies before measuring, so heavy sub content reads quieter than it feels. If the record sounds loud and measures quiet, trust the record.
Can two tracks at the same LUFS sound different in loudness?
Yes. A bright mix gets boosted by the weighting and a warm one does not, so identical numbers can feel different. Compare like with like, in the same genre.