LKFS: Overview
LKFS (Loudness, K-weighted, relative to Full Scale) is the unit output by ITU-R BS.1770 loudness meters. It expresses perceived program level on a decibel-like scale referenced to digital full scale (0 dBFS). Lower numbers indicate quieter programs (e.g., −31 LKFS), higher numbers louder (e.g., −18 LKFS). Many documents use LUFS interchangeably; in practice they are equivalent measurements.
Why It Matters for Film and TV
While theatrical mixes rely on calibrated rooms rather than fixed loudness targets, downstream versions for streaming platforms and broadcasters must meet specified integrated LKFS windows. This keeps dialog intelligible without viewers riding the remote. Consistency also prevents encoders from applying aggressive normalization that can flatten dynamics or introduce pumping.
Measuring and Meeting Targets
Mixers analyze integrated (program-long) LKFS along with short-term and momentary values. They manage dialog anchor levels, use transparent dynamics control, and check true-peak limits to avoid codec clipping. When creating nearfield trims from a theatrical printmaster, engineers may reduce LFE, reshape EQ, and lower overall level to meet a target (e.g., −24 or −23 LKFS) while preserving intent. Always re-measure after deliverable encodes; some codecs shift levels subtly.
LKFS: Common Pitfalls
Meters configured with different gating or channel weightings yield mismatched readings; align tool settings and document versions. Don’t equate LKFS with “loud equals better”—audiences prefer steady dialog with natural dynamics over hot mixes that trigger normalization.
LKFS: Related Terms
- ITU-R BS.1770, LUFS, true-peak, loudness range (LRA).