Dynamic range compression

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This article is about a process that intentionally reduces the dynamic range of audio signals. Dynamic range compression_sentence_0

For similar reductions caused by circuit imperfections, see Gain compression. Dynamic range compression_sentence_1

For processes that reduce the size of digital audio files, see Audio compression (data). Dynamic range compression_sentence_2

Dynamic range compression (DRC) or simply compression is an audio signal processing operation that reduces the volume of loud sounds or amplifies quiet sounds, thus reducing or compressing an audio signal's dynamic range. Dynamic range compression_sentence_3

Compression is commonly used in sound recording and reproduction, broadcasting, live sound reinforcement and in some instrument amplifiers. Dynamic range compression_sentence_4

A dedicated electronic hardware unit or audio software that applies compression is called a compressor. Dynamic range compression_sentence_5

In the 2000s, compressors became available as software plugins that run in digital audio workstation software. Dynamic range compression_sentence_6

In recorded and live music, compression parameters may be adjusted to change the way they affect sounds. Dynamic range compression_sentence_7

Compression and limiting are identical in process but different in degree and perceived effect. Dynamic range compression_sentence_8

A limiter is a compressor with a high ratio and, generally, a short attack time. Dynamic range compression_sentence_9

Types Dynamic range compression_section_0

Downward compression reduces loud sounds over a certain threshold while quiet sounds remain unaffected. Dynamic range compression_sentence_10

A limiter is an extreme type of downward compression. Dynamic range compression_sentence_11

Upward compression increases the loudness of sounds below a certain threshold while leaving louder sounds unaffected. Dynamic range compression_sentence_12

Both downward and upward compression reduce the dynamic range of an audio signal. Dynamic range compression_sentence_13

An expander increases the dynamic range of the audio signal. Dynamic range compression_sentence_14

Expanders are generally used to make quiet sounds even quieter by reducing the level of an audio signal that falls below a set threshold level. Dynamic range compression_sentence_15

A noise gate is a type of expander. Dynamic range compression_sentence_16

Design Dynamic range compression_section_1

The signal entering a compressor is split; one copy is sent to a variable-gain amplifier and the other to a side-chain where the signal level is measured and a circuit controlled by the measured signal level applies the required gain to the amplifier. Dynamic range compression_sentence_17

This design, known as a feed-forward type, is used today in most compressors. Dynamic range compression_sentence_18

Earlier designs were based on a feedback layout where the signal level was measured after the amplifier. Dynamic range compression_sentence_19

There are a number of technologies used for variable-gain amplification, each having different advantages and disadvantages. Dynamic range compression_sentence_20

Vacuum tubes are used in a configuration called variable-mu where the grid-to-cathode voltage changes to alter the gain. Dynamic range compression_sentence_21

Optical compressors use a photoresistor and a small lamp (incandescent, LED, or electroluminescent panel) to create changes in signal gain. Dynamic range compression_sentence_22

Other technologies used include field effect transistors and a diode bridge. Dynamic range compression_sentence_23

When working with digital audio, digital signal processing techniques are commonly used to implement compression as audio plug-ins, in mixing consoles, and in digital audio workstations. Dynamic range compression_sentence_24

Often the algorithms used emulate the above analog technologies. Dynamic range compression_sentence_25

Controls and features Dynamic range compression_section_2

A number of user-adjustable control parameters and features are used to adjust dynamic range compression signal processing algorithms and components. Dynamic range compression_sentence_26

Threshold Dynamic range compression_section_3

A compressor reduces the level of an audio signal if its amplitude exceeds a certain threshold. Dynamic range compression_sentence_27

Threshold is commonly set in decibels (dBFS for digital compressors and dBu for hardware compressors), where a lower threshold (e.g. −60 dB) means a larger portion of the signal is treated. Dynamic range compression_sentence_28

When the signal level is below the threshold, no processing is performed and the input signal is passed, unmodified, to the output. Dynamic range compression_sentence_29

Thus a higher threshold of, e.g., −5 dB, results in less processing, less compression. Dynamic range compression_sentence_30

Threshold timing behavior is subject to attack and release settings (see below). Dynamic range compression_sentence_31

When the signal level goes above threshold, compressor operation is delayed by the attack setting. Dynamic range compression_sentence_32

For an amount of time determined by the release after the input signal has fallen below the threshold, the compressor continues to apply dynamic range compression. Dynamic range compression_sentence_33

Ratio Dynamic range compression_section_4

The amount of gain reduction is determined by ratio: a ratio of 4:1 means that if input level is 4 dB over the threshold, the output signal level is reduced to 1 dB over the threshold. Dynamic range compression_sentence_34

The gain and output level has been reduced by 3 dB. Dynamic range compression_sentence_35

Another way of stating this is that any input signal level over the threshold will, in this case, be output at a level which is only 25% (i.e. 1 over 4) as much over the threshold as its input level was. Dynamic range compression_sentence_36

The highest ratio of ∞ :1 is often known as limiting. Dynamic range compression_sentence_37

It is commonly achieved using a ratio of 60:1, and effectively denotes that any signal above the threshold is brought down to the threshold level once the attack time has expired. Dynamic range compression_sentence_38

Attack and release Dynamic range compression_section_5

A compressor may provide a degree of control over how quickly it acts. Dynamic range compression_sentence_39

The attack is the period when the compressor is decreasing gain in response to increased level at the input to reach the gain determined by the ratio. Dynamic range compression_sentence_40

The release is the period when the compressor is increasing gain in response to reduced level at the input to reach the output gain determined by the ratio, or, to unity, once the input level has fallen below the threshold. Dynamic range compression_sentence_41

Because the loudness pattern of the source material is modified by the time-varying operation of compressor, it may change the character of the signal in subtle to quite noticeable ways depending on the attack and release settings used. Dynamic range compression_sentence_42

The length of each period is determined by the rate of change and the required change in gain. Dynamic range compression_sentence_43

For more intuitive operation, a compressor's attack and release controls are labeled as a unit of time (often milliseconds). Dynamic range compression_sentence_44

This is the amount of time it takes for the gain to change a set amount of dB or a set percentage towards the target gain. Dynamic range compression_sentence_45

There is no industry standard for the exact meaning of these time parameters. Dynamic range compression_sentence_46

In many compressors, the attack and release times are adjustable by the user. Dynamic range compression_sentence_47

Some compressors, however, have the attack and release times determined by the circuit design and cannot be adjusted. Dynamic range compression_sentence_48

Sometimes the attack and release times are automatic or program dependent, meaning that the behavior may change depending on the input signal. Dynamic range compression_sentence_49

Soft and hard knees Dynamic range compression_section_6

Another control a compressor might offer is hard knee or soft knee selection. Dynamic range compression_sentence_50

This controls whether the bend in the response curve between below threshold and above threshold is abrupt (hard) or gradual (soft). Dynamic range compression_sentence_51

A soft knee slowly increases the compression ratio as the level increases and eventually reaches the compression ratio set by the user. Dynamic range compression_sentence_52

A soft knee reduces the potentially audible transition from uncompressed to compressed, and is especially applicable for higher ratio settings where the changeover at the threshold would be more noticeable. Dynamic range compression_sentence_53

Peak vs RMS sensing Dynamic range compression_section_7

A peak-sensing compressor responds to the peak level of the input signal. Dynamic range compression_sentence_54

While providing tighter peak level control, peak level sensing does not necessarily relate to human perception of loudness. Dynamic range compression_sentence_55

Some compressors apply a power measurement function (commonly root mean square or RMS) on the input signal before comparing its level to the threshold. Dynamic range compression_sentence_56

This produces a more relaxed compression that more closely relates to human perception of loudness. Dynamic range compression_sentence_57

Stereo linking Dynamic range compression_section_8

A compressor in stereo linking mode applies the same amount of gain reduction to both the left and right channels. Dynamic range compression_sentence_58

This is done to prevent image shifting that can occur if each channel is compressed individually. Dynamic range compression_sentence_59

This becomes particularly noticeable when a loud element that is panned to either edge of the stereo field raises the level of the program to the compressor's threshold, causing its image to shift toward the center of the stereo field. Dynamic range compression_sentence_60

Stereo linking can be achieved in two ways: The compressor uses the sum of the left and right inputs to produce a single measurement that drives the compressor; or, the compressor calculates the required amount of gain reduction independently for each channel and then applies the highest amount of gain reduction to both (in such case it could still make sense to dial different settings on left and right channels as one might wish to have less compression for left-side events). Dynamic range compression_sentence_61

Make-up gain Dynamic range compression_section_9

Because a downward compressor only reduces the level of the signal, the ability to add a fixed amount of make-up gain at the output is usually provided so that an optimum output level is produced. Dynamic range compression_sentence_62

Look-ahead Dynamic range compression_section_10

The look-ahead function is designed to overcome the problem of being forced to compromise between slow attack rates that produce smooth-sounding gain changes, and fast attack rates capable of catching transients. Dynamic range compression_sentence_63

Look-ahead is implemented by splitting the input signal and delaying one side by the look-ahead time. Dynamic range compression_sentence_64

The non-delayed side is used to drive the compression of the delayed signal, which then appears at the output. Dynamic range compression_sentence_65

This way a smooth-sounding slower attack rate can be used to catch transients. Dynamic range compression_sentence_66

The cost of this solution is added audio latency through the processor. Dynamic range compression_sentence_67

Uses Dynamic range compression_section_11

Public spaces Dynamic range compression_section_12

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. Dynamic range compression_sentence_68

Compression can increase average output gain of a power amplifier by 50 to 100% with a reduced dynamic range. Dynamic range compression_sentence_69

For paging and evacuation systems, this adds clarity under noisy circumstances and saves on the number of amplifiers required. Dynamic range compression_sentence_70

Music production Dynamic range compression_section_13

Compression is often used in music production to make performances more consistent in dynamic range so that they "sit" in the mix of other instruments. Dynamic range compression_sentence_71

Vocal performances in rock music or pop music are compressed to improve clarity and to make them stand out from the surrounding instruments. Dynamic range compression_sentence_72

Compression can also be used on instrument sounds to create effects not primarily focused on boosting loudness. Dynamic range compression_sentence_73

For instance, drum and cymbal sounds tend to decay quickly, but a compressor can make the sound appear to have a more sustained tail. Dynamic range compression_sentence_74

Guitar sounds are often compressed to produce a fuller, more sustained sound. Dynamic range compression_sentence_75

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 side-chaining. Dynamic range compression_sentence_76

In electronic dance music, side-chaining is often used on basslines, 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. Dynamic range compression_sentence_77

Voice Dynamic range compression_section_14

A compressor can be used to reduce sibilance ('ess' sounds) in vocals (de-essing) by feeding the compressor or its side-chain with an equalized version of the input signal, so that only those frequencies activate the compressor. Dynamic range compression_sentence_78

If unchecked, sibilance can cause distortion even at moderate levels. Dynamic range compression_sentence_79

Compression is used in voice communications in amateur radio that employ 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. Dynamic range compression_sentence_80

This is applicable especially in DXing. Dynamic range compression_sentence_81

An SSB signal's strength depends on the level of modulation. Dynamic range compression_sentence_82

A compressor increases the average level of the modulation signal thus increasing the transmitted signal strength. Dynamic range compression_sentence_83

Most modern amateur radio SSB transceivers have speech compressors built-in. Dynamic range compression_sentence_84

Compression is also used in land mobile radio, especially in transmitted audio of professional walkie-talkies and remote control dispatch consoles. Dynamic range compression_sentence_85

Broadcasting Dynamic range compression_section_15

Compression is used extensively in broadcasting to boost the perceived volume of sound while reducing the dynamic range of source audio. Dynamic range compression_sentence_86

To avoid overmodulation, broadcasters in most countries have legal limits on instantaneous peak volume they may broadcast. Dynamic range compression_sentence_87

Normally these limits are met by permanently inserted compression hardware in the on-air chain. Dynamic range compression_sentence_88

Broadcasters use compressors in order that their station sounds louder than comparable stations. Dynamic range compression_sentence_89

The effect is to make the more heavily compressed station jump out at the listener at a given volume setting. Dynamic range compression_sentence_90

This is not limited to inter-channel differences; they also exist between programme material within the same channel. Dynamic range compression_sentence_91

Loudness differences are a frequent source of audience complaints, especially TV commercials and promos that seem too loud. Dynamic range compression_sentence_92

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. Dynamic range compression_sentence_93

In 2010, the EBU published EBU R 128 which introduces a new way of metering and normalizing audio. Dynamic range compression_sentence_94

The Recommendation uses ITU-R BS.1770 loudness metering. Dynamic range compression_sentence_95

As of 2016, several European TV stations have announced their support for the new norm and over 20 manufacturers have announced products supporting the new EBU Mode loudness meters. Dynamic range compression_sentence_96

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. Dynamic range compression_sentence_97

Marketing Dynamic range compression_section_16

Most television commercials are heavily compressed to achieve near-maximum perceived loudness while staying within permissible limits. Dynamic range compression_sentence_98

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. Dynamic range compression_sentence_99

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. Dynamic range compression_sentence_100

Over-usage Dynamic range compression_section_17

See also: Loudness war Dynamic range compression_sentence_101

Record companies, mixing engineers and mastering engineers have been gradually increasing the overall volume of commercial albums. Dynamic range compression_sentence_102

The greater loudness is achieved by using higher degrees of compression and limiting during mixing and mastering; compression algorithms have been engineered specifically to accomplish the task of maximizing audio level in the digital stream. Dynamic range compression_sentence_103

Hard limiting or clipping can result, affecting the tone and timbre of the music. Dynamic range compression_sentence_104

The effort to increase loudness has been referred to as the loudness war. Dynamic range compression_sentence_105

Other uses Dynamic range compression_section_18

Some applications use a compressor to reduce the dynamic range of a signal for transmission, expanding it afterward. Dynamic range compression_sentence_106

This reduces the effects of a channel with limited dynamic range. Dynamic range compression_sentence_107

See Companding and Noise reduction system. Dynamic range compression_sentence_108

Bass amplifiers and keyboard amplifiers often include compression circuitry to prevent sudden high-wattage peaks that could damage the speakers. Dynamic range compression_sentence_109

Electric bass players often use compression effects, either effects units available in pedal, rackmount units, or built-in devices in bass amps, to even out the sound levels of their basslines. Dynamic range compression_sentence_110

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. Dynamic range compression_sentence_111

However, many dance and hip-hop musicians purposefully use this phenomenon, causing the mix to alter in volume rhythmically in time with the beat. Dynamic range compression_sentence_112

Hearing aids use a compressor to bring the audio volume into the listener's hearing range. Dynamic range compression_sentence_113

To help the patient perceive the direction sound comes from, some hearing aids use binaural compression. Dynamic range compression_sentence_114

Compressors are also used for hearing protection in some electronic "active sound protection" earmuffs and earplugs, to let sounds at ordinary volumes be heard normally while attenuating louder sounds, possibly also amplifying softer sounds. Dynamic range compression_sentence_115

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, and similarly for musicians to hear quiet music but be protected from loud noises such as drums or cymbal crashes. Dynamic range compression_sentence_116

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. Dynamic range compression_sentence_117

Limiting Dynamic range compression_section_19

Main article: Limiter Dynamic range compression_sentence_118

Compression and limiting are identical in process but different in degree and perceived effect. Dynamic range compression_sentence_119

A limiter is a compressor with a high ratio and, generally, a fast attack time. Dynamic range compression_sentence_120

Compression with ratio of 10:1 or more is generally considered limiting. Dynamic range compression_sentence_121

Brick wall limiting has a very high ratio and a very fast attack time. Dynamic range compression_sentence_122

Ideally, this ensures that an audio signal never exceeds the amplitude of the threshold. Dynamic range compression_sentence_123

Ratios of 20:1 all the way up to ∞:1 are considered 'brick wall'. Dynamic range compression_sentence_124

The sonic results of more than momentary and infrequent hard/brick-wall limiting are harsh and unpleasant, thus it is more common as a safety device in live sound and broadcast applications. Dynamic range compression_sentence_125

Some bass amps and PA system amplifiers include limiters to prevent sudden volume peaks from causing distortion and/or damaging the speakers. Dynamic range compression_sentence_126

Some modern consumer electronics devices incorporate limiters. Dynamic range compression_sentence_127

Sony uses the automatic volume limiter system (AVLS), on some audio products and the PlayStation Portable. Dynamic range compression_sentence_128

Side-chaining Dynamic range compression_section_20

A compressor with a side-chain input controls gain from main input to output based on the level of the signal at the side-chain input. Dynamic range compression_sentence_129

The compressor behaves in the conventional manner when both inputs are supplied with the same signal. Dynamic range compression_sentence_130

The side-chain input is used by disc jockeys for ducking – lowering the music volume automatically when speaking. Dynamic range compression_sentence_131

The DJ's microphone signal is routed to the side-chain input so that whenever the DJ speaks the compressor reduces the volume of the music. Dynamic range compression_sentence_132

A sidechain with equalization controls can be used to reduce the volume of signals that have a strong spectral content within a certain frequency range: it can act as a de-esser, reducing the level of vocal sibilance in the range of 6–9 kHz. Dynamic range compression_sentence_133

A de-esser helps reduce high frequencies that tend to overdrive preemphasized media (such as phonograph records and FM radio). Dynamic range compression_sentence_134

Another use of the side-chain in music production serves to maintain a loud bass track without the bass drum causing undue peaks that result in loss of overall headroom. Dynamic range compression_sentence_135

Parallel compression Dynamic range compression_section_21

One technique is to insert the compressor in a parallel signal path. Dynamic range compression_sentence_136

This is known as parallel compression, a form of upward compression that facilitates dynamic control without significant audible side effects, if the ratio is relatively low and the compressor's sound is relatively neutral. Dynamic range compression_sentence_137

On the other hand, a high compression ratio with significant audible artifacts can be chosen in one of the two parallel signal paths—this is used by some concert mixers and recording engineers as an artistic effect called New York compression or Motown compression. Dynamic range compression_sentence_138

Combining a linear signal with a compressor and then reducing the output gain of the compression chain results in low-level detail enhancement without any peak reduction (since the compressor significantly adds to the combined gain at low levels only). Dynamic range compression_sentence_139

This is often beneficial when compressing transient content, since it maintains high-level dynamic liveliness, despite reducing the overall dynamic range. Dynamic range compression_sentence_140

Multiband compression Dynamic range compression_section_22

Multiband compressors can act differently on different frequency bands. Dynamic range compression_sentence_141

The advantage of multiband compression over full-bandwidth compression is that unneeded audible gain changes or "pumping" in other frequency bands is not caused by changing signal levels in a single frequency band. Dynamic range compression_sentence_142

Multiband compressors work by first splitting the signal through some number of band-pass filters or crossover filters. Dynamic range compression_sentence_143

The frequency ranges or crossover frequencies may be adjustable. Dynamic range compression_sentence_144

Each split signal then passes through its own compressor and is independently adjustable for threshold, ratio, attack, and release. Dynamic range compression_sentence_145

The signals are then recombined and an additional limiting circuit may be employed to ensure that the combined effects do not create unwanted peak levels. Dynamic range compression_sentence_146

Software plug-ins or DSP emulations of multiband compressors can be complex, with many bands, and require corresponding computing power. Dynamic range compression_sentence_147

Multiband compressors are primarily an audio mastering tool, but their inclusion in digital audio workstation plug-in sets is increasing their use among mix engineers. Dynamic range compression_sentence_148

On-air signal chains of radio stations commonly use hardware multiband compressors to increase apparent loudness without fear of overmodulation. Dynamic range compression_sentence_149

Having a louder sound is often considered an advantage in commercial competition. Dynamic range compression_sentence_150

However, adjusting a radio station's multiband output compressor requires some artistic sense of style, plenty of time, and good ears. Dynamic range compression_sentence_151

This is because the constantly changing spectral balance between audio bands may have an equalizing effect on the output, by dynamically modifying the on-air frequency response. Dynamic range compression_sentence_152

A further development of this approach is programmable radio output processing, where the parameters of the multiband compressor automatically change between different settings according to the current program block style or the time of day. Dynamic range compression_sentence_153

Serial compression Dynamic range compression_section_23

Serial compression is a used in sound recording and mixing. Dynamic range compression_sentence_154

Serial compression is achieved by using two fairly different compressors in a signal chain. Dynamic range compression_sentence_155

One compressor generally stabilizes the dynamic range while the other aggressively compresses stronger peaks. Dynamic range compression_sentence_156

This is the normal internal signal routing in common combination devices marketed as compressor-limiters, where an RMS compressor (for general gain control) is followed by a fast peak sensing limiter (for overload protection). Dynamic range compression_sentence_157

Done properly, even heavy serial compression can sound natural in a way not possible with a single compressor. Dynamic range compression_sentence_158

It is most often used to even out erratic vocals and guitars. Dynamic range compression_sentence_159

Software audio players Dynamic range compression_section_24

Some software audio players support plugins that implement compression. Dynamic range compression_sentence_160

These can increase perceived volume of audio tracks, or even out the volume of highly-variable music (such as classical music, or a playlist that spans multiple music types). Dynamic range compression_sentence_161

This improves listenability of audio played through poor-quality speakers, or when played in noisy environments (such as in a car or during a party). Dynamic range compression_sentence_162

Such software may also be used in micro-broadcasting or home-based audio mastering. Dynamic range compression_sentence_163

Objective influence on the signal Dynamic range compression_section_25

In an article released in January 2014 by the Journal of the Audio Engineering Society, Emmanuel Deruty and Damien Tardieu performed a systematic study describing the influence of compressors and brickwall limiters on the musical audio signal. Dynamic range compression_sentence_164

The experiment involved four software limiters: Waves L2, Sonnox Oxford Limiter, Thomas Mundt’s Loudmax, Blue Cat’s Protector,as well as four software compressors: Waves H-Comp, Sonnox Oxford Dynamics, Sonalksis SV-3157, and URS 1970. Dynamic range compression_sentence_165

The study provides objective data on what limiters and compressors do to the audio signal. Dynamic range compression_sentence_166

Five signal descriptors were considered: RMS power, EBU3341/R128 integrated loudness, crest factor, EBU3342 LRA, and density of clipped samples. Dynamic range compression_sentence_167

RMS power accounts for the signal's physical level, EBU3341 loudness for the perceived level. Dynamic range compression_sentence_168

The crest factor, which is the difference between the signal's peak and its average power, is on occasions considered as a basis for the measure of micro-dynamics, for instance in the TT Dynamic Range Meter plug-in. Dynamic range compression_sentence_169

Finally, EBU3342 LRA has been repeatedly considered as a measure of macro-dynamics or dynamics in the musical sense. Dynamic range compression_sentence_170

Limiters Dynamic range compression_section_26

The tested limiters had the following influence on the signal: Dynamic range compression_sentence_171

Dynamic range compression_unordered_list_0

  • increase of RMS power,Dynamic range compression_item_0_0
  • increase of EBU3341 loudness,Dynamic range compression_item_0_1
  • decrease of crest factor,Dynamic range compression_item_0_2
  • decrease of EBU3342 LRA, but only for high amounts of limiting,Dynamic range compression_item_0_3
  • increase of clipped sample density.Dynamic range compression_item_0_4

In other words, limiters increase both physical and perceptual levels, increase the density of clipped samples, decrease the crest factor and decrease macro-dynamics (LRA) given that the amount of limiting is substantial. Dynamic range compression_sentence_172

Compressors Dynamic range compression_section_27

As far as the compressors are concerned, the authors performed two processing sessions, using a fast attack (0.5 ms) in one case, and a slow attack (50 ms) in the other. Dynamic range compression_sentence_173

Make-up gain is deactivated, but the resulting file is normalized. Dynamic range compression_sentence_174

Set with a fast attack, the tested compressors had the following influence on the signal: Dynamic range compression_sentence_175

Dynamic range compression_unordered_list_1

  • slight increase of RMS power,Dynamic range compression_item_1_5
  • slight increase of EBU3341 loudness,Dynamic range compression_item_1_6
  • decrease of crest factor,Dynamic range compression_item_1_7
  • decrease of EBU3342 LRA,Dynamic range compression_item_1_8
  • slight decrease of clipped sample density.Dynamic range compression_item_1_9

In other words, fast-attack compressors increase both physical and perceptual levels, but only slightly. Dynamic range compression_sentence_176

They decrease the density of clipped samples, and decrease both crest factor and macro-dynamics. Dynamic range compression_sentence_177

Set with a slow attack, the tested compressors had the following influence on the signal: Dynamic range compression_sentence_178

Dynamic range compression_unordered_list_2

  • decrease of RMS power,Dynamic range compression_item_2_10
  • decrease of EBU3341 loudness,Dynamic range compression_item_2_11
  • no influence on crest factor,Dynamic range compression_item_2_12
  • decrease of EBU3342 LRA,Dynamic range compression_item_2_13
  • no influence on clipped sample density.Dynamic range compression_item_2_14

In other words, slow-attack compressors decrease both physical and perceptual levels, decrease macro-dynamics, but have no influence on crest factor and clipped sample density. Dynamic range compression_sentence_179

See also Dynamic range compression_section_28

Dynamic range compression_unordered_list_3

Credits to the contents of this page go to the authors of the corresponding Wikipedia page: en.wikipedia.org/wiki/Dynamic range compression.