# What Is K-Weighting?

> K-weighting is the filter that makes LUFS match what people hear. What it does to the signal and why a bass-heavy track measures quieter than it sounds.

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# What Is K-Weighting?

Published 30 August 2026, 15:00 UTC · updated 12 August 2026, 22:06 UTC · 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](/mastering) 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.

## Related reads

- [Master your track free](/mastering)
- [What is LUFS?](/blog/what-is-lufs-explained)
- [What is loudness normalization?](/blog/what-is-loudness-normalization)

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Source: https://onloopin.com/blog/what-is-k-weighting