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{{short description|Loudness measurement unit}}
'''Loudness, K-weighted, relative to full scale''' ('''LKFS''') is a standard [[loudness]] measurement unit used for [[audio normalization]] in [[broadcast television systems]] and other [[video streaming|video]] and [[music streaming service]]s.<ref>
{{cite tech report
| title = Towards a Recommendation for a European Standard of Peak and LKFS Loudness Levels
| author1 = E.M. Grimm
| author2 = R. van Everdingen
| author3 = M. J. L. C. Schöpping
| url = http://loudness.hku.nl/Peak_and_LKFS_-_Grimm_ea.pdf
| archive-url = https://web.archive.org/web/20140912174936/http://loudness.hku.nl/Peak_and_LKFS_-_Grimm_ea.pdf
| archive-date = 2014-09-12
}}</ref><ref>{{Cite web |url=https://artists.spotify.com/faq/mastering-and-loudness#how-does-spotify-calculate-loudness |title=Mastering & loudness – FAQ |website=Spotify for Artists |url-status=dead |archive-url=https://web.archive.org/web/20210302030525/https://artists.spotify.com/faq/mastering-and-loudness |archive-date=2021-03-02 |language=en |access-date=2020-02-13}}</ref><ref>{{Cite web|url=https://www.masteringthemix.com/blogs/learn/mixing-and-mastering-using-lufs|title=Mixing and Mastering Using LUFS|website=Mastering The Mix|language=en|access-date=2020-02-13}}</ref>
LKFS is standardized in '''ITU-R BS.1770'''.<ref>{{citation |title=ITU-R BS.1770 Algorithms to measure audio programme loudness and true-peak audio level |url=https://www.itu.int/dms_pubrec/itu-r/rec/bs/R-REC-BS.1770-5-202311-I!!PDF-E.pdf |publisher=International Telecommunication Union ([[ITU]])}}</ref><ref>{{citation |title=R 128 LOUDNESS NORMALISATION AND PERMITTED MAXIMUM LEVEL OF AUDIO SIGNALS |url=https://tech.ebu.ch/docs/r/r128.pdf |publisher=European Broadcasting Union}}</ref> {{Not in citation|date=April 2024|reason=does not mention "Loudness, K-weighted, relative to full scale" or "LKFS"; if does under different term, should be mentioned}} In March 2011, the International Telecommunication Union ([[ITU]]) introduced a loudness gate in the second revision of the recommendation, ITU-R BS.1770-2.<ref>{{citation |title=ITU-R BS.1770-2 Algorithms to measure audio programme loudness and true-peak audio level |url=http://www.itu.int/dms_pubrec/itu-r/rec/bs/R-REC-BS.1770-2-201103-S!!PDF-E.pdf |publisher=International Telecommunication Union}}</ref> In August 2012, the [[ITU]] released the third revision of this recommendation ITU-R BS.1770-3.<ref>{{citation |title=ITU-R BS.1770-3 Algorithms to measure audio programme loudness and true-peak audio level |url=http://www.itu.int/dms_pubrec/itu-r/rec/bs/R-REC-BS.1770-3-201208-S!!PDF-E.pdf |publisher=International Telecommunication Union}}</ref> In October 2015, the ITU released the fourth revision of this recommendation ITU-R BS.1770-4.<ref>{{citation |title=ITU-R BS.1770-4 Algorithms to measure audio programme loudness and true-peak audio level |url=https://www.itu.int/dms_pubrec/itu-r/rec/bs/R-REC-BS.1770-4-201510-I!!PDF-E.pdf |publisher=International Telecommunication Union}}</ref> In November 2023, the ITU released the fifth revision of this recommendation ITU-R BS.1770-5.<ref>{{citation |title=ITU-R BS.1770-5 Algorithms to measure audio programme loudness and true-peak audio level |url=https://www.itu.int/dms_pubrec/itu-r/rec/bs/R-REC-BS.1770-5-202311-I!!PDF-E.pdf |publisher=International Telecommunication Union}}</ref>
'''Loudness units relative to full scale''' ('''LUFS''') is a synonym for LKFS that was introduced in [[EBU R 128]].<ref>{{citation |title=EBU Recommendation R 128: Loudness normalisation and permitted maximum level of audio signals |url=http://tech.ebu.ch/docs/r/r128.pdf |publisher=[[European Broadcasting Union]] |date=August 2011 |page=3 |accessdate=2013-05-31}}</ref>
The 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 for ''loudness level, k-weighted'' should be '''L<sub>k</sub>''', which would make L<sub>k</sub> and LUFS equivalent when LUFS indicates the value of L<sub>k</sub> with reference to digital full scale.<ref>{{citation |title= EBU Tech 3343 - Practical guidelines for Production and Implementation in accordance with EBU R 128 |url=https://tech.ebu.ch/docs/tech/tech3343.pdf |publisher=European Broadcasting Union |accessdate=2014-03-14}}</ref>
LKFS and LUFS are identical in that they are both measured in absolute scale and both equal to one [[decibel]] (dB).<ref>{{citation |title=Loudness Explained |url=https://www.tcelectronic.com/brand/tcelectronic/loudness-explained|publisher=TC Electronics |accessdate=2018-02-19}}</ref>
'''Loudness units''' ('''LU''') is an additional unit used in EBU R128. It describes L<sub>k</sub> without direct absolute reference and therefore describes loudness level differences.
==References==
{{Reflist}}
[[Category:Sound technology]]