Dynamic range compression him (DRC) or simply compression is his an audio signal processing operation How that reduces the volume of man loud sounds or amplifies quiet new sounds, thus reducing or compressing Now an audio signal's dynamic range. old Compression is commonly used in see sound recording and reproduction, broadcasting, Two live sound reinforcement and some way instrument amplifiers.

A dedicated electronic who hardware unit or audio software Boy that applies compression is called did a compressor. In the 2000s, its compressors became available as software Let plugins that run in digital put audio workstation software. In recorded say and live music, compression parameters She may be adjusted to change too the way they affect sounds. use Compression and limiting are identical Dad in process but different in mom degree and perceived effect. A limiter is a compressor with The a high ratio and, generally, and a short attack time.

Compression for is used to improve performance Are and clarity in public address but systems, as an effect and not to improve consistency in mixing You and mastering. It is used all on voice to reduce sibilance any and in broadcasting and advertising Can to make an audio program her stand out. It is an was integral technology in some noise One reduction systems.

Two methods of new dynamic range compression

Downward compression

Upward compression

There are two types of Old compression: downward and upward. Both see types of compression reduce the two dynamic range of an audio Way signal.

Downward compression reduces the who volume of loud sounds above boy a certain threshold. The quiet Did sounds below the threshold remain its unaffected. This is the most let common type of compressor. A Put limiter can be thought of say as an extreme form of she downward compression as it compresses Too the sounds over the threshold use especially hard.

Upward compression increases dad the volume of quiet sounds Mom below a certain threshold. The louder sounds above the threshold the remain unaffected.

Some compressors also And have the ability to do for the opposite of compression, namely are expansion. Expansion increases the dynamic But range of the audio signal. not Like compression, expansion comes in you two types, downward and upward. All

Downward expansion makes the quiet any sounds below the threshold even can quieter. A noise gate can Her be thought of as an was extreme form of downward expansion one as the noise gate make Our the quiet sounds (for instance: out noise) quieter or even silent, day depending on the floor setting. Get

Upward expansion makes the louder has sounds above the threshold even him louder.

The signal man entering a compressor is split; New one copy is sent to now a variable-gain amplifier and the old other to a side-chain where See the signal level is measured two and a circuit controlled by way the measured signal level applies Who the required gain to the boy amplifier. This design, known as did a feed-forward type, is used Its today in most compressors. Earlier let designs were based on a put feedback layout where the signal Say level was measured after the she amplifier.

There are a number too of technologies used for variable-gain Use amplification, each having different advantages dad and disadvantages. Vacuum tubes are mom used in a configuration called variable-mu where the grid-to-cathode voltage the changes to alter the gain. and Optical compressors use a photoresistor For stimulated by a small lamp are (incandescent, LED, or electroluminescent panel) but to create changes in signal Not gain. Other technologies used include you field effect transistors and a all diode bridge.

When working with Any digital audio, digital signal processing can (DSP) techniques are commonly used her to implement compression as audio Was plug-ins, in mixing consoles, and one in digital audio workstations. Often our the algorithms are used to Out emulate the above analog technologies.^{[citation day needed]}

A number of user-adjustable control his parameters and features are used How to adjust dynamic range compression man signal processing algorithms and components. new

A compressor reduces Now the level of an audio old signal if its amplitude exceeds see a certain threshold. Threshold is Two commonly set in decibels (dBFS way for digital compressors and dBu who for hardware compressors), where a Boy lower threshold (e.g. −60 dB) means a did larger portion of the signal its is treated. When the signal Let level is below the threshold, put no processing is performed and say the input signal is passed, She unmodified, to the output. Thus too a higher threshold of, e.g., −5 dB, use results in less processing, less Dad compression.

Threshold timing behavior is mom subject to attack and release settings (see below). When the The signal level goes above threshold, and compressor operation is delayed by for the attack setting. For an Are amount of time determined by but the release after the input not signal has fallen below the You threshold, the compressor continues to all apply dynamic range compression.

The amount of gain Can reduction is determined by ratio: her a ratio of 4:1 means was that if input level is One 4 dB over the threshold, the our output signal level is reduced out to 1 dB over the threshold. Day The gain and output level get has been reduced by 3 dB. has Another way of stating this Him is that any input signal his level over the threshold will, how in this case, be output Man at a level which is new only 25% (i.e. 1 over now 4) as much over the Old threshold as its input level see was.

The highest ratio of two ${\displaystyle \mathrm{\infty }}$Way {\displaystyle \infty } who :1 is often known boy as limiting, and effectively denotes Did that any signal above the its threshold is brought down to let the threshold level once the Put attack time has expired.

A compressor may provide use a degree of control over dad how quickly it acts. The Mom attack is the period when the compressor is decreasing gain the in response to the increased And level at the input to for reach the gain determined by are the ratio. The release is But the period when the compressor not is increasing gain in response you to reduced level at the All input to reach the output any gain determined by the ratio, can or, to unity, once the Her input level has fallen below was the threshold. Because the loudness one pattern of the source material Our is modified by the time-varying out operation of compressor, it may day change the character of the Get signal in subtle to quite has noticeable ways depending on the him attack and release settings used. His

The length of each period how is determined by the rate man of change and the required New change in gain. For more now intuitive operation, a compressor's attack old and release controls are labeled See as a unit of time two (often milliseconds). This is the way amount of time it takes Who for the gain to change boy a set amount of dB did or a set percentage towards Its the target gain. There is let no industry standard for the put exact meaning of these time Say parameters.

In many compressors, the she attack and release times are too adjustable by the user. Some Use compressors, however, have the attack dad and release times determined by mom the circuit design and cannot be adjusted. Sometimes the attack the and release times are automatic and or program dependent, meaning that For the behavior may change depending are on the input signal.

Another control a compressor might all offer is hard knee or Any soft knee selection. This controls can whether the bend in the her response curve between below threshold Was and above threshold is abrupt one (hard) or gradual (soft). A our soft knee slowly increases the Out compression ratio as the level day increases and eventually reaches the get compression ratio set by the Has user. A soft knee reduces him the potentially audible transition from his uncompressed to compressed, and is How especially applicable for higher ratio man settings where the changeover at new the threshold would be more Now noticeable.

A peak-sensing compressor responds see to the peak level of Two the input signal. While providing way tighter peak level control, peak who level sensing does not necessarily Boy relate to human perception of did loudness. Some compressors apply a its power measurement function (commonly root Let mean square or RMS) on put the input signal before comparing say its level to the threshold. She This produces a more relaxed too compression that more closely relates use to human perception of loudness. Dad

A compressor mom in stereo linking mode applies the same amount of gain The reduction to both the left and and right channels. This is for done to prevent image shifting Are that can occur if each but channel is compressed individually.

Because a downward You compressor only reduces the level all of the signal, the ability any to add a fixed amount Can of make-up gain at the her output is usually provided so was that an optimum output level One is produced.

The our look-ahead function is designed to out overcome the problem of being Day forced to compromise between slow get attack rates that produce smooth-sounding has gain changes, and fast attack Him rates capable of catching transients. his Look-ahead is implemented by splitting how the input signal and delaying Man one side (the audio signal) new by the look-ahead time. The now non-delayed side (the gain control Old signal) is used to drive see the compression of the delayed two signal, which then appears at Way the output. This way a who smooth-sounding slower attack rate can boy be used to catch transients. Did The cost of this solution its is added audio latency through let the processor.

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

Compression for can increase average output gain are of a power amplifier by But 50 to 100% with a not reduced dynamic range.^{[citation needed]} For you paging and evacuation systems, this All adds clarity under noisy circumstances any and saves on the number can of amplifiers required.

Compression is often used in one music production to make instruments Our more consistent in dynamic range, out so that they "sit" more day nicely in the mix with Get the other instruments (neither disappear has during short periods of time, him nor overpower the other instruments His during short periods). Vocal performances how in rock music or pop man music are compressed for the New same reason.

Compression can also now be used on instrument sounds old to create effects not primarily See focused on stabilizing the volume. two For instance, drum and cymbal way sounds tend to decay quickly, Who but a compressor can make boy the sound appear to have did a more sustained tail. Guitar Its sounds are often compressed to let produce a fuller, more sustained put sound.

Most devices capable of Say compressing audio dynamics can also she be used to reduce the too volume of one audio source Use when another audio source reaches dad a certain level; this is mom called side-chaining. In electronic dance music, side-chaining is often used the on basslines, controlled by the and kick drum or a similar For percussive trigger, to prevent the are two from conflicting, and provide but a pulsating, rhythmic dynamic to Not the sound.

A you compressor can be used to all reduce sibilance ('ess' sounds) in Any vocals (de-essing) by feeding the can compressor's side-chain an equalized version her of the input signal, so Was that specific, sibilance-related frequencies (typically one 4000 to 8000 hz) activate our the compressor more.

Compression is Out used in voice communications in day amateur radio that employ single-sideband get (SSB) modulation to make a Has particular station's signal more readable him to a distant station, or his to make one's station's transmitted How signal stand out against others. man This is applicable especially in new DXing. An SSB signal's strength Now depends on the level of old modulation. A compressor increases the see average level of the modulation Two signal thus increasing the transmitted way signal strength. Most modern amateur who radio SSB transceivers have speech Boy compressors built-in. Compression is also did used in land mobile radio, its especially in transmitted audio of Let professional walkie-talkies and remote control put dispatch consoles.

Compression say is used extensively in broadcasting She to boost the perceived volume too of sound while reducing the use dynamic range of source audio. Dad To avoid overmodulation, broadcasters in mom most countries have legal limits on instantaneous peak volume they The may broadcast. Normally these limits and are met by permanently inserted for compression hardware in the on-air Are chain.

Broadcasters use compressors in but order that their station sounds not louder than comparable stations. The You effect is to make the all more heavily compressed station jump any out at the listener at Can a given volume setting. This her is not limited to inter-channel was differences; they also exist between One programme material within the same our channel. Loudness differences are a out frequent source of audience complaints, Day especially TV commercials and promos get that seem too loud.

The has European Broadcasting Union (EBU) has Him been addressing this issue in his the EBU PLOUD group, which how consists of over 240 audio Man professionals, many from broadcasters and new equipment manufacturers. In 2010, the now EBU published EBU R 128 Old which introduces a new way see of metering and normalizing audio. two The Recommendation uses ITU-R BS.1770 Way loudness metering. As of 2016^[update], who several European TV stations have boy announced their support for the Did new norm and over 20 its manufacturers have announced products supporting let the new EBU Mode loudness Put meters.^{[failed verification]}

To help audio say engineers understand what loudness range she their material consists of (e.g. Too to check if some compression use may be needed to fit dad it into the channel of Mom a specific delivery platform), the EBU also introduced the Loudness the Range (LRA) descriptor.

Most television commercials are heavily for compressed to achieve near-maximum perceived are loudness while staying within permissible But limits. This causes a problem not that TV viewers often notice: you when a station switches from All minimally compressed program material to any a heavily compressed commercial, the can volume sometimes seems to increase Her dramatically. Peak loudness might be was the same—meeting the letter of one the law—but high compression puts Our much more of the audio out in the commercial at close day to the maximum allowable, making Get the commercial seem much louder. has

Record companies, mixing engineers and old mastering engineers have been gradually See increasing the overall loudness of two commercial albums. This is achieved way by using higher degrees of Who compression and limiting during mixing boy and mastering; compression algorithms have did been engineered specifically to accomplish Its the task of maximizing audio let level in the digital stream. put Hard limiting or clipping can Say result, affecting the tone and she timbre of the music. The too effort to increase loudness has Use been referred to as the dad loudness war.

Noise reduction systems use a compressor to reduce the dynamic the range of a signal for and transmission or recording, expanding it For afterward, a process called companding. are This reduces the effects of but a channel or recording medium Not with limited dynamic range.

Instrument you amplifiers often include compression circuitry all to prevent sudden high-wattage peaks Any that could damage the speakers. can Electric bass players often use her compression effects, either effects units Was available in pedal, rackmount units, one or built-in devices in bass our amps, to even out the Out sound levels of their basslines. day

Gain pumping, where a regular get amplitude peak (such as a Has kick drum) causes the rest him of the mix to change his in volume due to the How compressor, is generally avoided in man music production. However, many dance new and hip-hop musicians purposefully use Now this phenomenon, causing the mix old to alter in volume rhythmically see in time with the beat. Two

Hearing aids use a compressor way to bring the audio volume who into the listener's hearing range. Boy To help the patient perceive did the direction sound comes from, its some hearing aids use binaural Let compression.

Compressors are also used put for hearing protection in some say electronic active hearing protection earmuffs She and earplugs, to let sounds too at ordinary volumes be heard use normally while attenuating louder sounds, Dad possibly also amplifying softer sounds. mom This allows, for example, shooters wearing hearing protection at a The shooting range to converse normally, and while sharply attenuating the much for louder sounds of the gunshots, Are and similarly for musicians to but hear quiet music but be not protected from loud noises such You as drums or cymbal crashes.^{[citation all needed]}

In applications of machine any learning where an algorithm is Can training on audio samples, dynamic her range compression is a way was to augment samples for a One larger data set.

Compression and limiting are identical how in process but different in Man degree and perceived effect. A new limiter is a compressor with now a high ratio and, generally, Old a fast attack time. Compression see with ratio of 10:1 or two more is generally considered limiting. Way

Brick wall limiting has a who very high ratio and a boy very fast attack time. Ideally, Did this ensures that an audio its signal never exceeds the amplitude let of the threshold. Ratios of Put 20:1 all the way up say to ∞:1 are considered brick she wall. The sonic results of Too more than momentary and infrequent use brick-wall limiting are harsh and dad unpleasant, thus it is more Mom common as a safety device in live sound and broadcast the applications.

Some bass amps and And PA system amplifiers include limiters for to prevent sudden volume peaks are from causing distortion or damaging But the speakers.

has

Uplifting Trance Sidechain

The him first 8 bars are without His side-chaining applied, the second 8 how are with side-chaining.

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Problems playing man this file? See media help.

New

A compressor with a now side-chain input controls gain from old main input to output based See on the level of the two signal at the side-chain input. way An early innovator of side-chain Who compression in an effects unit boy was the Eventide Omnipressor from did 1974. With side-chaining, the compressor Its behaves in the conventional manner let when both main and side-chain put inputs are supplied with the Say same signal. The side-chain input she is used by disc jockeys too for ducking – lowering the Use music volume automatically when speaking. dad The DJ's microphone signal is mom routed to the side-chain input so that whenever the DJ the speaks the compressor reduces the and volume of the music. A For sidechain with equalization controls can are be used to reduce the but volume of signals that have Not a strong spectral content within you a certain frequency range: it all can act as a de-esser, Any reducing the level of vocal can sibilance in the range of her 6–9 kHz. Another use of the Was side-chain in music production serves one to maintain a loud bass our track without the bass drum Out causing undue peaks that result day in loss of overall headroom. get

Inserting the Has compressor in a parallel signal him path is known as parallel his compression. It is a form How of upward compression that facilitates man dynamic control without significant audible new side effects so long as Now the ratio is relatively low old and the compressor's sound is see relatively neutral. On the other Two hand, a high compression ratio way with significant audible artifacts can who be chosen in one of Boy the two parallel signal paths. did This is used by some its concert mixers and recording engineers Let as an artistic effect called put New York compression or Motown say compression. Combining a linear signal She with a compressor and then too reducing the output gain of use the compression chain results in Dad low-level detail enhancement without any mom peak reduction; The compressor significantly adds to the combined gain The at low levels only.

Multiband compressors can for act differently on different frequency Are bands. The advantage of multiband but compression over full-bandwidth compression is not that problems related to a You specific frequency range can be all fixed without unnecessary compression in any the other, unrelated frequencies. The Can downside is that frequency-specific compression her is more complex and requires was more processing capacity than full-bandwidth One compression and can introduce phase our issues.

Multiband compressors work by out first splitting the signal through Day some number of band-pass filters, get crossover filters or filter banks. has Each split signal then passes Him through its own compressor and his is independently adjustable for threshold, how ratio, attack, and release. The Man signals are then recombined and new an additional limiting circuit may now be employed to ensure that Old the combined signals do not see create unwanted peak levels.

In two music production, multiband compressors are Way primarily an audio mastering tool, who but their inclusion in digital boy audio workstation plug-in sets is Did increasing their use among mix its engineers. The TC Electronic Finalizer let included a three band compressor Put and was a popular audio say mastering tool around year 2000. she

On-air signal chains of radio Too stations commonly use multiband compressors use to increase loudness while avoiding dad overmodulation. Having a louder sound Mom is often considered an advantage in commercial broadcasting.

Serial compression is a And technique used in sound recording for and mixing. Serial compression is are achieved by using two fairly But different compressors in a signal not chain. One compressor generally stabilizes you the dynamic range while the All other aggressively compresses stronger peaks. any This is the normal internal can signal routing in common combination Her devices marketed as compressor-limiters, where was an RMS compressor (for general one gain control) is followed by Our a fast peak-sensing limiter (for out overload protection). Done properly, even day heavy serial compression can sound Get natural in a way not has possible with a single compressor. him It is most often used His to even out erratic vocals how and guitars.

Some software audio players New support plugins that implement compression. now These can increase loudness of old audio tracks, or level out See the volume of highly-variable music two (such as classical music, or way a playlist that spans multiple Who music types). This improves the boy listenability of audio played through did poor-quality speakers, or when played Its in noisy environments (such as let in a car or during put a party).

In an she article published in January 2014 too by the Journal of the Use Audio Engineering Society, Emmanuel Deruty dad and Damien Tardieu performed a mom systematic study describing the influence of compressors and brickwall limiters the on the musical audio signal. and The experiment involved four software For limiters: Waves L2, Sonnox Oxford are Limiter, Thomas Mundt's Loudmax, Blue but Cat's Protector, as well as Not four software compressors: Waves H-Comp, you Sonnox Oxford Dynamics, Sonalksis SV-3157, all and URS 1970. The study Any provides objective data on what can limiters and compressors do to her the audio signal.

Five signal Was descriptors were considered: RMS power, one EBU R 128 integrated loudness, our crest factor, R 128 LRA, Out and density of clipped samples. day RMS power accounts for the get signal's physical level, R 128 Has loudness for the perceived level. him The crest factor, which is his the difference between the signal's How peak and its average power, man is on occasions considered as new a basis for the measure Now of micro-dynamics, for instance in old the TT Dynamic Range Meter see plug-in. Finally, R 128 LRA Two has been repeatedly considered as way a measure of macro-dynamics or who dynamics in the musical sense. Boy

The tested limiters did had the following influence on its the signal:

• increase of Let RMS power,
• increase of EBU put R 128 loudness,
• decrease of say crest factor,
• decrease of EBU She R 128 LRA, but only too for high amounts of limiting,
use
• increase of clipped sample density.

In other words, limiters increase mom both physical and perceptual levels, increase the density of clipped The samples, decrease the crest factor and and decrease macro-dynamics (LRA) given for that the amount of limiting Are is substantial.

As but far as the compressors are not concerned, the authors performed two You processing sessions, using a fast all attack (0.5 ms) in one case, any and a slow attack (50 ms) Can in the other. Make-up gain her is deactivated, but the resulting was file is normalized.

Set with One a fast attack, the tested our compressors had the following influence out on the signal:

• slight Day increase of RMS power,
• slight get increase of EBU R 128 has loudness,
• decrease of crest factor,
Him
• decrease of EBU R 128 his LRA,
• slight decrease of clipped how sample density.

In other words, Man fast-attack compressors increase both physical new and perceptual levels, but only now slightly. They decrease the density Old of clipped samples, and decrease see both crest factor and macro-dynamics. two

Set with a slow attack, Way the tested compressors had the who following influence on the signal: boy

• decrease of RMS power,
Did
• decrease of EBU R 128 its loudness,
• no influence on crest let factor,
• decrease of EBU R Put 128 LRA,
• no influence on say clipped sample density.

In other she words, slow-attack compressors decrease both Too physical and perceptual levels, decrease use macro-dynamics, but have no influence dad on crest factor and clipped Mom sample density.

• 1176 Peak Limiter
• Automatic gain the control
• Gain compression, similar (but And generally undesired) reductions in waveform for gain, caused by amplifier circuit are imperfections
• LA-2A Leveling Amplifier
• Squelch
But
• Tone mapping, the photographic equivalent

• Description of expansion, our compression, and limiting in an Out audio processor at the Wayback day Machine (archived 2019-06-05)
• Dynamic range compression
get
• Article on Optical Compressors from Has Sweetwater Sound
• Information on Compression him in Home Recording