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{{short description|Application of gain to a recording to achieve a target level}}
{{Use American English|date=March 2021}}
{{Use dmy dates|date=March 2021}}

'''Audio normalization''' is the application of a constant amount of gain to an [[audio recording]] to bring the amplitude to a target level (the norm). Because the same amount of gain is applied across the entire recording, the [[signal-to-noise ratio]] and [[Dynamics (music)|relative dynamics]] are unchanged. Normalization is one of the functions commonly provided by a [[digital audio workstation]].

Two principal types of audio normalization exist. '''Peak normalization''' adjusts the recording based on the highest signal level present in the recording. '''Loudness normalization''' adjusts the recording based on perceived [[loudness]].

Normalization differs from [[dynamic range compression]], which applies varying levels of gain over a recording to fit the level within a minimum and maximum range. Normalization adjusts the gain by a constant value across the entire recording.

==Peak normalization==
One type of normalization is peak normalization, wherein the gain is changed to bring the highest [[pulse-code modulation|PCM]] sample value or analog signal peak to a given level{{snd}}usually 0 [[dBFS]], the loudest level allowed in a digital system.<ref name=Myths>{{cite web |author=Des |date=April 20, 2008 |url=http://www.hometracked.com/2008/04/20/10-myths-about-normalization/ |title=10 Myths About Normalization |publisher=Hometracked |access-date=2012-06-10}}</ref>

Since it searches only for the highest level, peak normalization alone does not account for the apparent loudness of the content. As such, peak normalization is generally used to change the volume in such a way to ensure optimal use of available dynamic range during the mastering stage of a [[digital recording]]. When combined with compression/limiting, however, peak normalization becomes a feature that can provide a loudness advantage over non–peak-normalized material. This feature of digital recording systems, compression and limiting followed by peak normalization, enables contemporary trends in program loudness.<ref>{{Cite book|url=http://ir.lib.uwo.ca/cgi/viewcontent.cgi?article=1709&context=etd|title=Audio Mastering as Musical Practice|last=Shelvock|first=Matt|publisher=University of Western Ontario: EDT|year=2012|location=London|pages=26}}</ref><ref>{{Cite book|title=Mastering Audio: The Art and the Science|url=https://archive.org/details/masteringaudioar00katz|url-access=limited|last=Katz|first=Bob|publisher=Focal Press|year=2007|isbn=978-0-240-80837-6|pages=[https://archive.org/details/masteringaudioar00katz/page/n159 168]}}</ref>

==Loudness normalization==
Another type of normalization is based on a measure of loudness, wherein the gain is changed to bring the average loudness to a target level. This average may be approximate, such as a simple measurement of average power (e.g. [[root mean square|RMS]]), or more accurate, such as a measure that addresses human perception e.g. that defined by [[EBU R128]] and offered by [[ReplayGain]], [[Sound Check (iTunes feature)|Sound Check]] and [[GoldWave]].

For example, [[YouTube]]'s preferred loudness level is −14 [[LKFS|LUFS]], so if an audio program is analyzed to be −10 LUFS, YouTube will lower the loudness by 4 dB to bring it to the preferred level.

Loudness normalization combats varying loudness when listening to multiple songs in a sequence. Before loudness normalization, one song in a playlist might be quieter than the rest, so the listener would have to turn a volume knob up to adjust the playback volume.<ref>{{cite web |title=What are the "loudness wars" and loudness normalization? |url=https://www.hybridstudiosca.com/mastering/ |website=Hybrid Studios |access-date=1 July 2018 |archive-date=27 June 2018 |archive-url=https://web.archive.org/web/20180627230633/https://www.hybridstudiosca.com/mastering/ |url-status=dead }}</ref>

Depending on the dynamic range of the content and the target level, loudness normalization can result in peaks that exceed the recording medium's limits, causing clipping. Software offering loudness normalization typically provides the option of [[dynamic range compression]] to prevent [[clipping (audio)|clipping]] when this happens. In this situation, signal-to-noise ratio and relative dynamics are altered.

===Loudness standards===
Standardised normalized loudness levels vary by territory and application.<ref name="pro-vid">{{cite web |last1=Tépper |first1=Allan |title=How many LUFS for ideal audio loudness? Why can't we be friends? |url=https://www.provideocoalition.com/how-many-lufs-for-ideal-audio-loudness-why-cant-we-be-friends/ |website=Pro Video Coalition |date=23 March 2018 |access-date=11 July 2019}}</ref>
* −24{{nbsp}}LUFS: [[ATSC]] [https://www.atsc.org/atsc-documents/a85-techniques-for-establishing-and-maintaining-audio-loudness-for-digital-television/ A/85] (US TV), NPRSS,{{what|date=March 2022|reason=Referent of acronym is unclear}} and [[Public Radio Exchange|PRX]] radio broadcast<ref>{{cite web |url=https://help.prx.org/hc/en-us/articles/360003516334-Formatting-Audio-Files-for-Broadcast |title=Formatting Audio Files for Broadcast |website=PRX – Help Desk |publisher=[[Public Radio Exchange|PRX]] |access-date=21 March 2022 |quote=Loudness at -24 LUFS, ± 2 LU (recommended)}}</ref><ref name="pro-vid"/>
* −23{{nbsp}}LUFS: [[EBU R 128]] broadcast<ref name="pro-vid"/>
* −19 to −16 LUFS: PRX podcasts<ref>{{cite web |url=https://help.prx.org/hc/en-us/articles/360022234293-How-should-I-format-my-audio-files-for-Publish- |title=How should I format my audio files for Publish? |website=PRX – Help Desk |publisher=[[Public Radio Exchange|PRX]] |access-date=21 March 2022 |quote=Set your loudness between -16db LUFS and -19db LUFS. There is no set industry standard, [...]}}</ref>
* −14{{nbsp}}LUFS: [[Spotify]], [[YouTube]] and other [[Streaming media|streaming]] platforms<ref name="pro-vid"/>

==See also==
* [[Alignment level]]
* [[Dialnorm]]
* [[Loudness war]]
* [[Normalization (image processing)]], image analog

==References==
{{Reflist}}

==External links==
* [http://www.hydrogenaud.io/forums/index.php?showtopic=85571 Discussion of inter-sample clipping when normalizing to 0 dBFS peaks]
* [http://transom.org/?p=16413 Detailed article about levels by Jeff Towne]

[[Category:Digital signal processing]]
[[Category:Audio engineering]]

Audio normalization - Revision history

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