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Audio level compression, also called dynamic range compression, volume compression, compression, limiting, or DRC (often seen in DVD player settings) is a process that manipulates the dynamic range of an audio signal. Compression is used during sound recording, live sound reinforcement, and broadcasting to improve the perceived volume of audio. A compressor is the device used to create compression. The inside of a DVD player A DVD player is a device for playing discs produced under the DVD Video standard. ...
Dynamic range is a term used frequently in numerous fields to describe the ratio between the smallest and largest possible values of a changeable quantity. ...
Methods and media for sound recording are varied and have undergone significant changes between the first time sound was actually recorded for later playback until now. ...
A sound reinforcement system is an electromechanical system for accurately amplifying, reproducing, and sometimes recording audio, so that persons not near the original source may experience the sound as if they were. ...
Broadcasting is the distribution of audio and/or video signals (programs) to a number of recipients (listeners or viewers) that belong to a large group. ...
Explanation
 The relationship between input level, output level, and gain reduction in a compressor A compressor reduces the dynamic range of an audio signal if its amplitude exceeds a threshold. The amount of gain reduction is determined by a ratio control. For example, with a ratio of 4:1, an increase of 4 dB will be needed to increase the output signal level by 1 dB over the threshold. Contrast this with the complementary process of an expander, which increases the dynamic range of a signal if its amplitude falls below a threshold. [1] Image File history File links Audio-level-compresion-diagram-01. ...
Image File history File links Audio-level-compresion-diagram-01. ...
The decibel (dB) is a measure of the ratio between two quantities, and is used in a wide variety of measurements in acoustics, physics and electronics. ...
A compressor accomplishes its task of reducing dynamic range by using a variable-gain amplifier to reduce the gain of the signal. This is typically carried out in analog systems by using a voltage controlled amplifier which has its gain reduced as the power of the input signal increases. Optical compressors use a light sensitive diode (an optocoupler) to detect changes in signal gain. This vintage technique is believed by some to add smoother characteristics to the signal, because the response times of the light and the diode soften the attack and release. In electronics, gain is usually taken as the mean ratio of the signal output of a system to the signal input of the system. ...
Generally, an amplifier is any device that uses a small amount of energy to control a larger amount of energy. ...
In electronics, gain is usually taken as the mean ratio of the signal output of a system to the signal input of the system. ...
A voltage-controlled amplifier is an electronic amplifier that varies its gain depending on a control voltage (often abbreviated CV). ...
Opto-isolator An opto-isolator is a device that uses optical techniques to electrically isolate two related circuits, typically a transmitter and a receiver. ...
Currently, digital signal processing techniques are commonly used to implement compression via digital audio editors, or dedicated workstations. Digital signal processing (DSP) is the study of signals in a digital representation and the processing methods of these signals. ...
This article should be merged with Digital Audio Workstation. ...
A Digital Audio Workstation (DAW) is a system designed to record, edit and play back digital audio. ...
Limiting A limiter is a compressor with a higher ratio, and generally a faster attack time. There is no absolute consensus on what ratio constitutes limiting as compared with compression, but most engineers would consider anything with a ratio greater than 10:1 as limiting. Compression and limiting are no different in process, just in degree and in the perceived effect. Engineers sometimes refer to soft and hard limiting which are differences of degree. The "harder" a limiter, the lower its threshold and the higher its ratio.
Brick wall limiting effectively ensures that an audio signal never exceeds the amplitude threshold that is set. In practice, this is a ratio of 50:1 or greater. The sonic results of more than momentary and infrequent hard limiting are usually characterized as harsh and unpleasant; thus it is more appropriate as a safety device in live and broadcast applications than as a sound-sculpting tool.
Some modern consumer electronics devices incorporate limiters, such as AVLS (Automatic Volume Limiter System), found on certain Sony audio products and the PlayStation Portable. To meet Wikipedias quality standards, this article or section may require cleanup. ...
The PlayStation Portable (officially abbreviated as PSP) is a handheld game console released and manufactured by Sony Computer Entertainment. ...
- See also: Clipping (audio)
Clipping is one form of distortion that occurs when an amplifier is overdriven, which happens when it attempts to increase voltage or current beyond its limits. ...
Side-chaining This feature uses the dynamic level of another input to control the compression level of the signal. This is used by disc jockeys to lower the music volume automatically when speaking, for example (known as ducking). A frequency-specific compressor (often used for de-essing) may be constructed by feeding a high-pass filtered copy of the original signal into the side-chain input of the compressor so that volume reduction on the original signal only takes place when a specific frequency is present in large amounts (such as sibilant sounds that tend to overdrive preemphasized media such as phonograph records and FM radio). Another use of the side-chain in music production serves to maintain a loud bass track, while still keeping the bass out of the way of the drum when the drum hits. For other meanings of DJ, see DJ (disambiguation). ...
Ducking is an effect commonly used in pop music and espicially dance music. ...
A high-pass filter is a filter that passes high frequencies well, but attenuates (or reduces) frequencies lower than the cutoff frequency. ...
A sibilant is a type of fricative, made by speeding up air through a narrow channel and directing it over the sharp edge of the teeth. ...
In processing electronic audio signals preemphasis refers to a system process designed to increase, within a band of frequencies, the magnitude of some (usually higher) frequencies with respect to the magnitude of other (usually lower) frequencies in order to improve the overall signal-to-noise ratio by minimizing the adverse...
Multiband compression Multiband compressors are compressors that can act differently on different frequency bands. It is as if each band has its own compressor with its own threshold, ratio, attack, and release. They are primarily an audio mastering tool, but their inclusion in digital audio workstation plug-in sets is increasing their use among mix engineers. Hardware multiband compressors are also commonly used in the on-air signal chain of a radio station, either AM or FM, in order to increase the station's apparent loudness without fear of overmodulation. Having a louder sound is often considered an advantage in commercial competition. However, adjusting a multiband output compressor of a radio station also requires some sense of style and a good pair of ears. 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. This article or section does not cite its references or sources. ...
A Digital Audio Workstation (DAW) is a system designed to record, edit and play back digital audio. ...
To meet Wikipedias quality standards and appeal to a wider international audience, this article may require cleanup. ...
Loudness is the quality of a sound which is high in volume (amplitude, or sound pressure). ...
Overmodulation is the condition that prevails in telecommunication when the instantaneous level of the modulating signal exceeds the value necessary to produce 100% modulation of the carrier. ...
Compressor features and usage Compressors usually have controls to set how fast the compressor responds to changes in input level, known as attack, and how quickly the compressor returns to no gain reduction once the input level falls below the threshold, known as release. Because the loudness pattern of the source material is modified by the compressor it may change the character of the signal in subtle to quite noticeable ways depending on the settings used.
A second control on a compressor is hard/soft knee. This controls whether the bend in the response curve is a sharp angle or has a rounded edge. A soft knee reduces the audible change from uncompressed to compressed, especially for higher ratios where the changeover is more noticeable. [2]
An audio engineer might use a compressor in a subtle way in order to reduce the dynamic range of source material in order to allow it to be recorded optimally on a medium with a more limited dynamic range than the source signal, or they might use a compressor in order to deliberately change the character of an instrument being processed.
Engineers wishing to achieve dynamic range reduction with few obvious effects might choose a relatively low threshold and low compression ratio so that the source material is being compressed very slightly most of the time. To deliberately soften the attack of a snare drum, they might choose a fast attack time and a moderately fast release time combined with a higher threshold. To accentuate the attack of the snare, they might choose a slower attack time to avoid affecting the initial transient. It is easier to successfully apply these controls if the user has a basic knowledge of musical instrument acoustics.
Because the compressor is reducing the gain (or level) of the signal, the ability to add a fixed amount of make-up gain at the output is provided so that an optimum level can be used.
Common uses Compression is often used to make music sound louder without increasing its peak amplitude. By compressing the peak (or loudest) signals, it becomes possible to increase the overall gain (or volume) of a signal without exceeding the dynamic limits of a reproduction device or medium. The net effect when compression is applied along with a gain boost, is that relatively quiet sounds become louder, while louder sounds remain unchanged.
Compression is used extensively in this manner in broadcasting to boost the perceived volume of the sound track while keeping it within strict limits (broadcasters in most countries have legal limits on instantaneous peak volume they may broadcast). Normally these limits are met by permanently inserted hardware in the on-air chain (see multiband compression above). Broadcasting is the distribution of audio and/or video signals (programs) to a number of recipients (listeners or viewers) that belong to a large group. ...
Also, for on-air broadcasts, a compressor can be used to reduce the volume of one audio source when another audio source reaches a certain level. This allows the DJ to talk over the music and still be clearly audible. This usage is called 'ducking'. [3]
Compression is also required to reduce the dynamic range of source audio (typically CDs) to a range that can be accommodated by the narrower-range broadcast signal. The same recording can have very different dynamics when heard via AM, FM, CD, or other media (although frequency response and noise are large factors as well). AM broadcasting is radio broadcasting using Amplitude Modulation. ...
FM broadcasting is a broadcast technology invented by Edwin Howard Armstrong that uses frequency modulation (FM) to provide high-fidelity sound over broadcast radio. ...
CD may stand for: Compact Disc Canadian Forces Decoration Cash Dispenser (at least used in Japan) CD LPMud Driver Centrum-Demokraterne (Centre Democrats of Denmark) Certificate of Deposit České Dráhy (Czech Railways) Chad (NATO country code) Chalmers Datorförening (computer club of the Chalmers University of Technology) a 1960s...
Frequency response is the measure of any systems response to frequency, but is usually used in connection with electronic amplifiers and similar systems, particularly in relation to audio signals. ...
Noise in audio, recording, and broadcast sytems refers to the residual low level sound (usually hiss and hum) that is heard in quiet periods of programme. ...
Most television commercials are compressed heavily in order to achieve near-maximum perceived loudness while staying within permissible limits.
Compression is also applied in audio systems for restaurants, retail, and similar public environments, where background music is played at a relatively low volume and needs to be compressed not just to keep the volume fairly constant, but also in order for relatively quiet parts of the music to be audible over ambient noise, or audible at all.
In recent years (as of 2006), record companies have been increasing the overall volume of commercial albums (particularly rock music and pop music) by using higher and higher degrees of compression during mastering, sometimes impacting sound quality. [4]. This phenomenon has been referred to as the "loudness war". 2006 is a common year starting on Sunday of the Gregorian calendar. ...
Rock and roll (also spelled Rock n Roll, especially in its first decade), also called rock, is a form of popular music, usually featuring vocals (often with vocal harmony), electric guitars and a strong back beat; other instruments, such as the saxophone, are common in some styles. ...
For popular music (music produced commercially rather than art or folk music), see Popular music. ...
Audio mastering is the process of preparing and transfering recorded audio to a medium for future duplication. ...
This article or section is in need of attention from an expert on the subject. ...
When recording vocals, a compressor can be used to reduce sibilance ('ess' sounds) by feeding the compressor with an EQ set to the relevant frequencies, so that only those frequencies activate the compressor. If unchecked, sibilance could cause distortion even if sound levels are not very high. This usage is called 'de-essing'. [5]
Compression can also be used on instrument sounds to create effects not-primarily-focused on boosting loudness. 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 in order to obtain a fuller, more sustained sound. Loudness is the quality of a sound which is high in volume (amplitude, or sound pressure). ...
Compression is also often used in music production to make performances more consistent in dynamic range so that they "sit" in the mix of other instruments better and maintain consistent attention from the listener. Vocal performances in rock music or pop music are usually compressed in order to make them stand out from the surrounding instruments and to add to the clarity of the vocal performance. Rock and roll (also spelled Rock n Roll, especially in its first decade), also called rock, is a form of popular music, usually featuring vocals (often with vocal harmony), electric guitars and a strong back beat; other instruments, such as the saxophone, are common in some styles. ...
For popular music (music produced commercially rather than art or folk music), see Popular music. ...
Compression is used in voice communications in amateur radio that employ SSB modulation. Often it is used 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 occurs especially in pileups where amateur radio stations are competing for the opportunity to talk to a DX station. Since an SSB signal's amplitude depends on the level of modulation, the net result is that the average amplitude of the signal and hence average transmitted power would be stronger than it would be had compression not been used.[1] Most modern amateur radio SSB transceivers have speech compressors built in. Ham radio station with separate transmitter, receiver and power supply. ...
SSB might be an acronym or abbreviation for: SSB - diesel propelled ballistic missile submarine Schulich School of Business Single-sideband modulation strategic system builder Single-strand binding protein. ...
In telecommunications, modulation is the process of varying a periodic waveform, i. ...
DX communication is communication over great distances using the ionosphere to refract the transmitted radio beam. ...
Amplitude is a nonnegative scalar measure of a waves magnitude of oscillation, that is, magnitude of the maximum disturbance in the medium during one wave cycle. ...
In telecommunications, modulation is the process of varying a periodic waveform, i. ...
Other uses A compressor is sometimes used to reduce the dynamic range of a signal for transmission, to be expanded afterwards. This reduces the effects of a channel with limited dynamic range. See Companding. A waveform before and after the compression stage of non-linear companding In telecommunication, signal processing, and thermodynamics, companding (occasionally called compansion) is a method of reducing the effects of a channel with limited dynamic range. ...
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 dance musicians use this phenomenon in a creative way, causing the mix to alter in volume rhythmically in time with the beat.
Compressors for software audio players Some software audio players support plugins which implement compression. These can be used to increase the perceived volume of audio tracks, or to even out the volume of highly-variable music (such as classical music, or a playlist spanning many music types). This improves the listenability of audio when played through poor-quality speakers, or when played in noisy environments (such as in a car or during a party). Such software may also be used in micro-broadcasting or home-based audio mastering. An audio player is a kind of media player for playing back digital audio, including optical discs such as CDs, SACDs, DVD-Audio, HDCD, and audio files. ...
A plugin (or plug-in) is a computer program that interacts with a main application (a web browser or an email program, for example) to provide a certain, usually very specific, function. ...
Classical music is a broad, somewhat imprecise term, referring to music produced in, or rooted in the traditions of, European art, ecclesiastical and concert music, encompassing a broad period from roughly 1000 to the present day. ...
Low-power broadcasting is the concept of broadcasting at very low power and low cost, to a small community area. ...
Available software includes:
The Winamp plugins can also be enabled for Windows Media Player and other players via ffdshow. Winamp is a multimedia player made by Nullsoft. ...
A command line interface or CLI is a method of interacting with a computer by giving it lines of textual commands (that is, a sequence of characters) either from keyboard input or from a script. ...
WAV (or WAVE), short for Waveform audio format, is a Microsoft and IBM audio file format standard for storing audio on PCs. ...
Windows Media Player (WMP) is a digital media player and media library application developed by Microsoft that is used for playing audio, video and images on personal computers running the Microsoft Windows operating system, as well as on Pocket PC and Windows Mobile-based devices. ...
iTunes is a digital media player application, introduced by Apple Computer on January 10, 2001 at MacWorld Expo in San Francisco,[1] for playing and organizing digital music and video files. ...
RealPlayer is a media player, created by RealNetworks, that plays a number of multimedia formats including MP3, MPEG-4, QuickTime, and Windows Media formats as well as multiple versions of proprietary RealAudio and RealVideo codecs. ...
ffdshow video decoder configuration ffdshow is an open source DirectShow and VfW codec for decoding/encoding many video and audio formats, including DivX and XviD movies using libavcodec, XviD and other open source libraries with a rich set of postprocessing filters. ...
To achieve volume-compressed playback on devices other than computer-based audio players, files may need to be processed via the above software then output as wavs, mp3s, or other audio formats. WAV (or WAVE), short for Waveform audio format, is a Microsoft and IBM audio file format standard for storing audio on PCs. ...
MPEG-1 Audio Layer 3, more commonly referred to as MP3, is a popular digital audio encoding and lossy compression format, designed to greatly reduce the amount of data required to represent audio, yet still sound like a faithful reproduction of the original uncompressed audio to most listeners. ...
See also In telecommunications, squelch is a circuit function that acts to suppress the audio (or video) output of a receiver in the absence of a sufficiently strong desired input signal. ...
Automatic gain control (AGC) is an electronic system found in many types of devices. ...
Gain compression in an electronic amplifier circuit, is a reduction in differential or slope gain caused by nonlinearity of the transfer characteristic of the amplifier. ...
External links
References - ^ "HF Radio Systems & Circuits", Sabin & Schoenike, editors. Noble, 1998, pp. 13-25, 271-290
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