Loudness units relative to full scale (LUFS), also known asloudness, K-weighted, relative to full scale (LKFS), is a standardloudness measurement unit used foraudio normalization inbroadcast television systems and othervideo andmusic streaming services.^[1][2][3] LUFS is a synonym for LKFS that was introduced inEBU R 128.^[4]

LKFS is standardized inITU-R BS.1770.^[5][6] In March 2011, the International Telecommunication Union (ITU) introduced a loudness gate in the second revision of the recommendation, ITU-R BS.1770-2.^[7] In August 2012, theITU released the third revision of this recommendation ITU-R BS.1770-3.^[8] In October 2015, the ITU released the fourth revision of this recommendation ITU-R BS.1770-4.^[9] In November 2023, the ITU released the fifth revision of this recommendation ITU-R BS.1770-5.^[10]

K-weighting refers to thefrequency weighting function applied to the audio signal before measurement, and is defined in ITU-R BS.1770.^[11]

TheEuropean Broadcasting Union (EBU) has suggested that the ITU should change the unit to LUFS, as LKFS does not comply with scientific naming conventions and is not in line with the standard set out in ISO 80000-8. Furthermore, they suggest the symbol forloudness level, k-weighted should beL_k, which would make L_k and LUFS equivalent when LUFS indicates the value of L_k with reference to digital full scale.^[12]

LKFS and LUFS are identical in that they are both measured in absolute scale and both equal to onedecibel (dB).^[13]

Loudness units (LU) is an additional unit used in EBU R128. It describes L_k without direct absolute reference and therefore describes loudness level differences.

• dBFS

• Sound technology

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