Editing Dynamic range compression (section)

== Uses ==

=== Public spaces ===
Compression is often applied in audio systems for restaurants, retail, and similar public environments that play background music at a relatively low volume and need it compressed, not just to keep the volume fairly constant, but also to make quiet parts of the music audible over ambient noise.

Compression can increase average output gain of a [[Amplifier|power amplifier]] by 50 to 100% with a reduced dynamic range.{{citation needed|date=May 2020}} For paging and evacuation systems, this adds clarity under noisy circumstances and saves on the number of amplifiers required.

=== Music production ===
[[File:Behringer CD400 Compressor 8198.jpg|thumb|An inexpensive guitar compressor]]
Compression is often used in music production to make instruments more consistent in dynamic range, so that they "sit" more nicely in the mix with the other instruments (neither disappear during short periods of time, nor overpower the other instruments during short periods).<ref name=broadcastbridge/> Vocal performances in [[rock and roll|rock music]] or [[pop music]] are compressed for the same reason. 

Compression can also be used on instrument sounds to create effects not primarily focused on stabilizing the volume. For instance, drum and cymbal sounds tend to decay quickly, but a compressor can make the sound appear to have a more sustained tail.  Guitar sounds are often compressed to produce a fuller, more sustained sound.

Most devices capable of compressing audio dynamics can also be used to reduce the volume of one audio source when another audio source reaches a certain level; this is called [[Dynamic range compression#Side-chaining|side-chaining]].<ref>{{cite web|url=https://www.sageaudio.com/blog/pre-mastering-tips/sidechaining.php|title=What is Sidechaining|work=Sage Audio|access-date=12 May 2020}}</ref> In [[electronic dance music]], side-chaining is often used on [[bassline]]s, controlled by the kick drum or a similar percussive trigger, to prevent the two from conflicting, and provide a pulsating, rhythmic dynamic to the sound.

=== Voice ===
A compressor can be used to reduce [[sibilance]] ('ess' sounds) in vocals ([[de-essing]]) by feeding the compressor's side-chain an [[Equalization (audio)|equalized]] version of the input signal, so that specific, sibilance-related frequencies (typically 4000 to 8000 hz) activate the compressor more.<ref>{{cite magazine|url=https://www.soundonsound.com/techniques/techniques-vocal-de-essing|title=Techniques For Vocal De-essing|magazine=Sound on Sound|date=May 2009|access-date=12 May 2010}}</ref>

Compression is used in voice communications in [[amateur radio]] that employ [[single-sideband modulation|single-sideband (SSB) modulation]] to make a particular station's signal more readable to a distant station, or to make one's station's transmitted signal stand out against others.  This is applicable especially in [[DXing]]. An SSB signal's strength depends on the level of [[modulation]]. A compressor increases the average level of the modulation signal thus increasing the transmitted signal strength. Most modern amateur radio SSB transceivers have speech compressors built-in. Compression is also used in [[Two-way radio|land mobile radio]], especially in transmitted audio of professional [[walkie-talkie]]s and [[Tone remote|remote control dispatch consoles]].<ref>{{Cite book |title=HF radio systems & circuits |publisher=Noble Pub |year=1998 |isbn=9781613530740 |editor-last=Sabin |editor-first=William E. |edition=2nd |location=Atlanta |pages=13–25, 271–290 |oclc=842936687 |editor-last2=Schoenike |editor-first2=Edgar O.}}</ref>

=== Broadcasting ===
Compression is used extensively in [[broadcasting]] to boost the perceived volume of sound while reducing the dynamic range of source audio. To avoid [[overmodulation]], broadcasters in most countries have legal limits on instantaneous peak volume they may broadcast. Normally these limits are met by permanently inserted compression hardware in the on-air chain.

Broadcasters use compressors in order that their station sounds louder than comparable stations. The effect is to make the more heavily compressed station jump out at the listener at a given volume setting.<ref name=broadcastbridge>{{Cite web|url=https://www.thebroadcastbridge.com/content/entry/7278/using-compression-for-recorded-and-live-audio|title=Using Compression for Recorded and Live Audio - The Broadcast Bridge - Connecting IT to Broadcast|first=The Broadcast|last=Bridge|date=November 23, 2016|website=www.thebroadcastbridge.com}}</ref> This is not limited to inter-channel differences; they also exist between programme material within the same channel. Loudness differences are a frequent source of audience complaints, especially TV commercials and promos that seem too loud.

The [[European Broadcasting Union]] (EBU) has been addressing this issue in the EBU PLOUD group, which consists of over 240 audio professionals, many from broadcasters and equipment manufacturers. In 2010, the EBU published [[EBU R 128]] which introduces a new way of metering and [[Audio normalization|normalizing audio]]. The Recommendation uses [[ITU-R BS.1770]] loudness metering. {{as of|2016}}, several European TV stations have announced their support for the new norm<ref>{{Cite web|url=https://www.ebu.ch/news/2011/loudness-france-chooses-ebu-r128|title=Loudness: France chooses EBU R128 to bolster audio laws|date=25 October 2011|website=[[European Broadcasting Union]]|language=en|access-date=8 April 2020}}</ref><ref>{{Cite web|url=https://www.svgeurope.org/blog/headlines/sky-confirms-formal-adoption-of-r128-loudness-specification/|title=Sky confirms formal adoption of R128 loudness specification|last=Davies|first=David|date=9 December 2013|website=SVG Europe|language=en|access-date=8 April 2020}}</ref> and over 20 manufacturers have announced products supporting the new ''EBU Mode'' loudness meters.<ref name="EBU3341">{{Citation |url=https://tech.ebu.ch/publications/tech3341 |title='EBU Mode' metering to supplement EBU R 128 loudness normalisation |date=2016-01-25 |publisher=European Broadcasting Union |series=Version 3.0 |language=en |id=EBU Tech 3341 |access-date=2019-11-03}}</ref>{{failed verification|reason=Does not support manufacturers|date=October 2020}}

To help audio engineers understand what loudness range their material consists of (e.g. to check if some compression may be needed to fit it into the channel of a specific delivery platform), the EBU also introduced the ''Loudness Range'' (LRA) descriptor.<ref name="EBU3342">{{Citation |url=https://tech.ebu.ch/publications/tech3342 |title=Loudness range: A measure to supplement EBU R 128 loudness normalisation |date=2016-01-25 |publisher=European Broadcasting Union |series=Version 3.0 |location=Geneva |language=en |id=EBU Tech 3342}}</ref>

=== Marketing ===
Most television commercials are heavily compressed to achieve near-maximum perceived loudness while staying within permissible limits. This causes a problem that TV viewers often notice: when a station switches from minimally compressed program material to a heavily compressed commercial, the volume sometimes seems to increase dramatically. Peak loudness might be the same—meeting the letter of the law—but high compression puts much more of the audio in the commercial at close to the maximum allowable, making the commercial seem much louder.<ref>{{Cite web |url=https://www.pinsentmasons.com/out-law/news/tv-ads-sound-too-loud-and-rules-should-change-says-regulator |title=TV ads sound too loud and rules should change, says regulator |website=Out-Law News |publisher=Pinsent Masons |language=en-GB |access-date=2019-11-03}}</ref>

=== Over-usage ===
[[File:Cd loudness trend-something.gif|right|thumb|305px|The trend of increasing loudness as shown by waveform images of the song "[[Something (Beatles song)|Something]]" by [[The Beatles]] mastered on CD four times since 1983]]
{{See also|Loudness war}}

Record companies, mixing engineers and mastering engineers have been gradually increasing the overall [[loudness]] of commercial albums. This is achieved by using higher degrees of compression and limiting during [[Audio mixing (recorded music)|mixing]] and [[Audio mastering|mastering]]; compression algorithms have been engineered specifically to accomplish the task of maximizing audio level in the digital stream. Hard limiting or [[clipping (audio)|clipping]] can result, affecting the tone and timbre of the music. The effort to increase loudness has been referred to as the [[loudness war]].

=== Other uses ===
[[Noise reduction system]]s use a compressor to reduce the dynamic range of a signal for transmission or recording, expanding it afterward, a process called [[companding]]. This reduces the effects of a channel or recording medium with limited dynamic range.

[[Instrument amplifier]]s often include compression circuitry to prevent sudden high-wattage peaks that could damage the speakers. [[Electric bass]] players often use compression effects, either [[effects unit]]s available in pedal, [[rackmount]] units, or built-in devices in bass amps, to even out the sound levels of their [[bassline]]s.

[[Gain pumping]], where a regular amplitude peak (such as a kick drum) causes the rest of the mix to change in volume due to the compressor, is generally avoided in music production. However, many [[Electronic dance music|dance]] and hip-hop musicians purposefully use this phenomenon, causing the mix to alter in volume rhythmically in time with the beat.<ref>{{Cite web |url=http://www.thewhippinpost.co.uk/mixing-music/compression-audio-mixing.htm |title=Compression in Audio Music Mixing |website=The Whippinpost |access-date=2013-12-07}}</ref>

[[Hearing aid]]s use a compressor to bring the audio volume into the listener's hearing range. To help the patient perceive the direction sound comes from, some hearing aids use [[binaural recording|binaural]] compression.<ref>{{Cite book |title=The textbook of hearing aid amplification |last=Sandlin |first=Robert E. |date=2000 |publisher=Singular Thomson Learning |isbn=1565939972 |edition=2nd |location=San Diego, California |oclc=42475568}}</ref>

Compressors are also used for [[hearing protection]] in some electronic active hearing protection [[earmuffs]] and [[earplugs]], to let sounds at ordinary volumes be heard normally while attenuating louder sounds, possibly also amplifying softer sounds. This allows, for example, shooters wearing hearing protection at a shooting range to converse normally, while sharply attenuating the much louder sounds of the gunshots,<ref>{{cite web |url=https://www.pewpewtactical.com/best-shooting-ear-protection/ |title=10 Best Shooting Ear Protection |date=27 May 2020 |quote=They are comfy for hours with their gel caps, have easily accessible button controls, great sound cutoff and compression, and allow for earplugs if the decent 22db NRR doesn’t cut it. |access-date=2021-05-25}}</ref> and similarly for musicians to hear quiet music but be protected from loud noises such as drums or cymbal crashes.{{citation needed|date=December 2013}}

In applications of machine learning where an algorithm is training on audio samples, dynamic range compression is a way to augment samples for a larger data set.<ref>{{Cite journal |last1=Salamon |first1=Justin |last2=Bello |first2=Juan Pablo |date=March 2017 |title=Deep Convolutional Neural Networks and Data Augmentation for Environmental Sound Classification |journal=IEEE Signal Processing Letters |volume=24 |issue=3 |pages=279–283 |arxiv=1608.04363 |doi=10.1109/LSP.2017.2657381 |bibcode=2017ISPL...24..279S |s2cid=3537408 |issn=1070-9908 }}</ref>