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{{Short description|Nominal signal level in an audio signal chain}}
{{Use British English|date=July 2020}}
{{Multiple issues|
{{Original research|date=February 2011}}
{{No footnotes|date=February 2011}}
}}

The '''alignment level''' in an audio [[signal chain]] or on an [[audio recording]] is a defined anchor point that represents a reasonable or typical level.

== Analogue ==
In analogue systems, alignment level in [[broadcast]] chains is commonly 0 [[dBu]] (0.775 volts RMS) and in professional audio is commonly ''0 VU'' (4 dBu, 1.228 volts RMS). Under normal situations, the 0 VU reference allows for a [[headroom (audio signal processing)|headroom]] of 18 dB or more above the reference level without significant distortion. This is largely due to the use of slow-responding [[VU meter]]s in almost all analogue professional audio equipment, which, by their design and by specification, respond to an average level, not peak levels.

== Digital ==
In digital systems alignment level commonly is at −18 [[dBFS]] (18 dB below [[digital full scale]]), in accordance with [[EBU]] recommendations.<ref>{{Cite journal |year=2000 |title=EBU Technical Recommendation R68-2000 - Alignment level in digital audio production equipment and in digital audio recorders |url=https://tech.ebu.ch/docs/r/r068.pdf |journal=EBU Recommendations |publisher=[[European Broadcasting Union]] |quote=The EBU recommends that, in digital audio equipment, its Members should use coding levels for digital audio signals which correspond to an alignment level which is 18 dB below the maximum possible coding level of the digital system, irrespective of the total number of bits available.}}</ref> Digital equipment must use peak-reading metering systems to avoid severe digital distortion caused by the signal going beyond digital full scale. 24-bit original or master recordings commonly have an alignment level at −24 dBFS to allow extra headroom, which can then be reduced to match the available headroom of the final medium by [[audio level compression]]. FM broadcasts usually have only 9 dB of headroom, as recommended by the EBU, but digital broadcasts, which could operate with 18 dB of headroom, given their low noise floor even in difficult reception areas, currently operate in a state of confusion, with some transmitting at maximum level, while others operate at a much lower level, even though they carry material that has been compressed for compatibility with the lower dynamic range of FM transmissions.{{cn|date=January 2024}}

== EBU ==
In EBU documents{{specify|date=January 2023}} ''alignment level'' defines −18 dBFS as the level of the ''alignment signal'', a 1 kHz sine tone for analog applications and 997 Hz in digital applications.

== Motivation ==
Using alignment level rather than [[maximum permitted level]] as the reference point allows more sensible headroom management throughout the audio signal chain; [[audio level compression|compression]] happens only where intended.

[[Loudness war]]s have resulted in increasing playback loudness. [[Loudness normalisation]] to a fixed alignment level can improve the experience when listening to mixed material.

== See also ==
* [[Audio normalization]]
* [[Full scale]]
* [[Nominal level]]
* [[Transmission-level point]]

== External links ==
* [http://tech.ebu.ch/docs/r/r128.pdf EBU Recommendation R128 - Loudness normalisation and permitted maximum level of audio levels (2010)]
* [http://tech.ebu.ch/docs/r/r068.pdf EBU Recommendation R68-2000]
* [http://tech.ebu.ch/docs/r/r117.pdf EBU Recommendation R117-2006] (against [[loudness war]])
* [https://web.archive.org/web/20080308193128/http://www.irt.de/IRT/FuE/as/pdf/AES2002OnLevelling.pdf AES Convention Paper 5538 On Levelling and Loudness Problems at Broadcast Studios]
* [http://www.ebu.ch/CMSimages/en/tec_doc_t3282_tcm6-10542.pdf EBU Tech 3282-E on EBU RDAT Tape Levels] {{Webarchive|url=https://web.archive.org/web/20090909130542/http://www.ebu.ch/CMSimages/en/tec_doc_t3282_tcm6-10542.pdf |date=2009-09-09 }}
* [http://www.ebu.ch/CMSimages/en/tec_text_r89-1997_tcm6-4703.pdf EBU R89-1997 on CD-R levels]{{dl|fix-attempted=yes|date=May 2023}}
* [https://web.archive.org/web/20060617172836/http://www.tcelectronic.com/media/lund_2004_distortion_tmt20.pdf Distortion to the People — TC Electronics]
* [http://tech.ebu.ch/groups/ploud EBU Loudness Group]

[[Category:Audio engineering]]
[[Category:Broadcast engineering]]
[[Category:Sound production technology]]
[[Category:Sound recording]]
[[Category:Sound]]

Alignment level - Revision history

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