LKFS

LKFS stands for Loudness, K-weighted, relative to Full Scale. It is a unit used to quantify the perceived loudness of an audio signal, defined by ITU-R BS.1770 and related standards. The measurement applies a K-weighting filter to mirror human loudness perception and yields a single integrated value over time, reported in LKFS.

The terms LKFS and LUFS describe the same quantity in different naming schemes; 1 LKFS equals 1 LUFS. Many broadcasters and platforms now use LUFS, but LKFS remains common in some regions and older documentation and equipment.

Integrated loudness is the principal metric, while additional short-term and momentary values may be provided. The measurement uses gating to exclude inaudible or very low-level content, as specified by ITU-R BS.1770.

Standards and usage: In Europe, broadcast loudness guidance is often -23 LUFS integrated; in the United States, ATSC A/85 has used -24 LKFS as a target. These targets are accompanied by allowed variations to accommodate production realities. LKFS/LUFS is used to normalize program material and advertisements to a consistent perceived loudness, reducing the need for manual volume adjustments.

Tools and implementations: Software meters and plugins implement ITU-R BS.1770 measurements, e.g., libebur128-based meters, and hardware monitoring systems; measurement data may include integrated loudness (LKFS/LUFS), momentary and short-term loudness, and true peak levels.