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Generation loss is the loss of quality between subsequent copies or transcodes of data. Anything that reduces the quality of the representation when copying, and would cause further reduction in quality on making a copy of the copy, can be considered a form of generation loss. File size increases are a common result of generation loss, as the introduction of artifacts may actually increase the entropy of the data through each generation.


Analog generation loss

In
analog
analog
systems (including systems that use digital recording but make the copy over an analog connection), generation loss is mostly due to
noise Noise is unwanted sound In physics, sound is a vibration that propagates as an acoustic wave, through a transmission medium such as a gas, liquid or solid. In human physiology and psychology, sound is the ''reception'' of such waves and t ...
and
bandwidth Bandwidth commonly refers to: * Bandwidth (signal processing) or ''analog bandwidth'', ''frequency bandwidth'', or ''radio bandwidth'', a measure of the width of a frequency range * Bandwidth (computing), the rate of data transfer, bit rate or thr ...
issues in
cables Cable may refer to: Mechanical * Nautical cable A nautical cable is a band of tightly woven and clamped ropes, of a defined cable length, used during the age of sail for deep water anchoring, heavy lifting, ship to ship transfers and towing durin ...
,
amplifier An amplifier, electronic amplifier or (informally) amp is an electronic device that can increase the power Power typically refers to: * Power (physics) In physics, power is the amount of energy transferred or converted per unit time. In ...

amplifier
s, mixers, recording equipment and anything else between the source and the destination. Poorly adjusted
distribution amplifier In electronics, a distribution amplifier, or simply distribution amp or DA, is a device that accepts a single input signal and provides this same signal to multiple Electrical isolation, isolated outputs. These devices allow a signal to be distr ...
s and mismatched impedances can make these problems even worse. Repeated conversion between analog and digital can also cause loss. Generation loss was a major consideration in complex analog audio and
video editing Video editing is the manipulation and arrangement of video Video is an electronic Electronic may refer to: *Electronics Electronics comprises the physics, engineering, technology and applications that deal with the emission, flow and ...
, where multi-layered edits were often created by making intermediate mixes which were then "bounced down" back onto tape. Careful planning was required to minimize generation loss, and the resulting noise and poor frequency response. One way of minimizing the number of generations needed was to use an audio mixing or video editing suite capable of mixing a large number of channels at once; in the extreme case, for example with a 48-track recording studio, an entire complex mixdown could be done in a single generation, although this was prohibitively expensive for all but the best-funded projects. The introduction of professional analog noise reduction systems such as
Dolby A A Dolby noise-reduction system, or Dolby NR, is one of a series of noise reduction Noise reduction is the process of removing noise from a signal In signal processing Signal processing is an electrical engineering subfield tha ...
helped reduce the amount of audible generation loss, but were eventually superseded by digital systems which vastly reduced generation loss. According to ATIS, "Generation loss is limited to analog recording because digital recording and reproduction may be performed in a manner that is essentially free from generation loss."


Digital generation loss

Used correctly, digital technology can eliminate generation loss. This implies the exclusive use of lossless compression codecs or uncompressed data from recording or creation until the final lossy encode for distribution through internet streaming or optical discs. Copying a digital file gives an exact copy if the equipment is operating properly. This trait of digital technology has given rise to awareness of the risk of unauthorized copying. Before digital technology was widespread, a
record label A record label, or record company, is a brand A brand is a name, term, design, symbol or any other feature that identifies one seller's good or service as distinct from those of other sellers. Brands are used in business, marketing, and ad ...
, for example, could be confident knowing that unauthorized copies of their music tracks were never as good as the originals. Generation loss can still occur when using lossy video or audio compression codecs as these introduce artifacts into the source material with each encode or reencode. Lossy compression codecs such as
Apple ProRes Apple ProRes is a high quality, lossy In information technology, lossy compression or irreversible compression is the class of data compression, data encoding methods that uses inexact approximations and partial data discarding to represent the con ...
,
Advanced Video Coding Advanced Video Coding (AVC), also referred to as H.264 or MPEG-4 MPEG-4 is a method of defining compression Compression may refer to: Physical science *Compression (physics), size reduction due to forces *Compression member, a structural ele ...
and
mp3 MP3 (formally MPEG-1 Audio Layer III or MPEG-2 Audio Layer III) is a coding format for digital audio Digital audio is a representation of sound recorded in, or converted into, Digital signal (signal processing), digital form. In digital a ...

mp3
are very widely used as they allow for dramatic reductions on file size while being indistinguishable from the uncompressed or losslessly compressed original for viewing purposes. The only way to avoid generation loss is by using uncompressed or losslessly compressed files; which may be expensive from a storage standpoint as they require larger amounts of storage space in flash memory or hard drives per second of runtime. Uncompressed video requires a high data rate; for example, a 1080p video at 30 frames per second can require up to 370 megabytes per second. Lossy codecs make Blu-rays and streaming video over the internet feasible since neither can deliver the amounts of data needed for uncompressed or losslessly compressed video at acceptable frame rates and resolutions. Images can suffer from generation loss in the same way video and audio can. Processing a lossily compressed file rather than an original usually results in more loss of quality than generating the same output from an uncompressed original. For example, a low-resolution digital image for a web page is better if generated from an uncompressed raw image than from an already-compressed
JPEG JPEG ( ) is a commonly used method of lossy compression In information technology, lossy compression or irreversible compression is the class of data encoding methods that uses inexact approximations and partial data discarding to represe ...

JPEG
file of higher quality.


Techniques that cause generation loss in digital systems

In
digital systems Digital electronics is a field of electronics Electronics comprises the physics, engineering, technology and applications that deal with the emission, flow and control of electrons in vacuum and matter. It uses active devices to control elect ...
, several techniques, used because of other advantages, may introduce generation loss and must be used with caution. However, copying a digital file itself incurs no generation loss—the copied file is identical to the original, provided a perfect copying
channel Channel, channels, channeling, etc., may refer to: Geography * Channel (geography), in physical geography, a landform consisting of the outline (banks) of the path of a narrow body of water. Australia * Channel Country, region of outback Austr ...
is used. Some digital transforms are reversible, while some are not.
Lossless compression Lossless compression is a class of data compression In signal processing Signal processing is an electrical engineering subfield that focuses on analysing, modifying, and synthesizing signals such as audio signal processing, sound, image ...
is, by definition, fully reversible, while
lossy compression In information technology, lossy compression or irreversible compression is the class of data compression, data encoding methods that uses inexact approximations and partial data discarding to represent the content. These techniques are used to r ...
throws away some data which cannot be restored. Similarly, many DSP processes are not reversible. Thus careful planning of an
audio Audio most commonly refers to sound In physics Physics (from grc, φυσική (ἐπιστήμη), physikḗ (epistḗmē), knowledge of nature, from ''phýsis'' 'nature'), , is the natural science that studies matter, its Motion ( ...

audio
or
video Video is an electronic Electronic may refer to: *Electronics Electronics comprises the physics, engineering, technology and applications that deal with the emission, flow and control of electrons in vacuum and matter. It uses active d ...

video
signal chain from beginning to end and rearranging to minimize multiple conversions is important to avoid generation loss when using lossy compression codecs. Often, arbitrary choices of numbers of pixels and sampling rates for source, destination, and intermediates can seriously degrade digital signals in spite of the potential of digital technology for eliminating generation loss completely. Similarly, when using lossy compression, it will ideally only be done once, at the end of the workflow involving the file, after all required changes have been made.


Transcoding

Converting between lossy formats – be it decoding and re-encoding to the same format, between different formats, or between different bitrates or parameters of the same format – causes generation loss. Repeated applications of
lossy compression In information technology, lossy compression or irreversible compression is the class of data compression, data encoding methods that uses inexact approximations and partial data discarding to represent the content. These techniques are used to r ...
and decompression can cause generation loss, particularly if the parameters used are not consistent across generations. Ideally an algorithm will be both ''
idempotent Idempotence (, ) is the property of certain operations in mathematics Mathematics (from Ancient Greek, Greek: ) includes the study of such topics as quantity (number theory), mathematical structure, structure (algebra), space (geometry), an ...
,'' meaning that if the signal is decoded and then re-encoded with identical settings, there is no loss, and ''scalable,'' meaning that if it is re-encoded with lower quality settings, the result will be the same as if it had been encoded from the original signal – see Scalable Video Coding. More generally, transcoding between different parameters of a particular encoding will ideally yield the greatest common shared quality – for instance, converting from an image with 4 bits of red and 8 bits of green to one with 8 bits of red and 4 bits of green would ideally yield simply an image with 4 bits of red color depth and 4 bits of green color depth without further degradation. Some lossy compression
algorithm In and , an algorithm () is a finite sequence of , computer-implementable instructions, typically to solve a class of problems or to perform a computation. Algorithms are always and are used as specifications for performing s, , , and other ...

algorithm
s are much worse than others in this regard, being neither idempotent nor scalable, and introducing further degradation if parameters are changed. For example, with
JPEG JPEG ( ) is a commonly used method of lossy compression In information technology, lossy compression or irreversible compression is the class of data encoding methods that uses inexact approximations and partial data discarding to represe ...

JPEG
, changing the quality setting will cause different quantization constants to be used, causing additional loss. Further, as JPEG is divided into 16×16 blocks (or 16×8, or 8×8, depending on
chroma subsampling Chroma subsampling is the practice of encoding images by implementing less resolution for chroma information Information is processed, organised and structured data. It provides context for data and enables decision making process. For examp ...
), cropping that does not fall on an 8×8 boundary shifts the encoding blocks, causing substantial degradation – similar problems happen on rotation. This can be avoided by the use of or similar tools for cropping. Similar degradation occurs if video keyframes do not line up from generation to generation.


Editing

Digital resampling such as
image scaling In computer graphics and digital imaging, image scaling refers to the resizing of a digital image. In video technology, the magnification of digital material is known as upscaling or resolution enhancement. When scaling a vector graphic imag ...
, and other DSP techniques can also introduce artifacts or degrade
signal-to-noise ratio Signal-to-noise ratio (SNR or S/N) is a measure used in science and engineering Engineering is the use of scientific principles to design and build machines, structures, and other items, including bridges, tunnels, roads, vehicles, and ...
(S/N ratio) each time they are used, even if the underlying storage is lossless. Resampling causes
aliasing In signal processing Signal processing is an electrical engineering subfield that focuses on analysing, modifying, and synthesizing signals such as audio signal processing, sound, image processing, images, and scientific measurements. Sig ...

aliasing
, both blurring low-frequency components and adding high-frequency noise, causing
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, while rounding off computations to fit in finite precision introduces quantization, causing banding; if fixed by
dither Dither is an intentionally applied form of noise Noise is unwanted sound In physics, sound is a vibration that propagates as an acoustic wave, through a transmission medium such as a gas, liquid or solid. In human physiology and psyc ...

dither
, this instead becomes noise. In both cases, these at best degrade the signal's S/N ratio, and may cause artifacts. Quantization can be reduced by using high precision while editing (notably floating point numbers), only reducing back to fixed precision at the end. Often, particular implementations fall short of theoretical ideals.


Photocopying, photography, video, and miscellaneous postings

Successive generations of photocopies result in image distortion and degradation. It has been documented that successive repostings on
Instagram Instagram is an American photo 396x396px, '' View from the Window at Le Gras'' (1826 or 1827), by Nicéphore Niépce, the earliest known surviving photograph of a real-world scene, made with a camera obscura. Original (left) & Film coloriz ...

Instagram
results in noticeable changes. Likewise, repeated postings on
YouTube YouTube is an American online video sharing and social media platform Social media are interactive technologies that allow the Content creation, creation or information sharing, sharing/exchange of information, ideas, career interests, an ...

YouTube
degraded the work. Similar effects have been documented in copying of
VHS VHS (Video Home System) is a for consumer-level on tape . From the 1950s, video recording became a major contributor to the television industry, via the first commercialized s (VTRs). At that time, the expensive devices were used only i ...

VHS
tapes. This is because both services use lossy codecs on all data that is uploaded to them, even if the data being uploaded is a duplicate of data already hosted on the service, while VHS is an analog medium, where effects such as noise from interference can have a much more noticeable impact on recordings.


Popular culture

Generation loss has been the subject of artistic works that exposed the phenomenon. The Generation Loss project was inspired, at least in part, by an earlier effort"
I Am Sitting in a Room ''I am sitting in a room'' is a sound art piece composed in 1969 and one of composer Alvin Lucier's best known works. The piece features Lucier recording himself narrating a text, and then playing the magnetic tape, tape recording back into the ro ...
" (1969) by
Alvin Lucier Alvin Lucier (born May 14, 1931) is an American composer of experimental music and sound installations that explore acoustic phenomena and auditory perception. A long-time music professor at Wesleyan University, Lucier was a member of the influent ...
.


See also

*
Signal-to-noise ratio Signal-to-noise ratio (SNR or S/N) is a measure used in science and engineering Engineering is the use of scientific principles to design and build machines, structures, and other items, including bridges, tunnels, roads, vehicles, and ...
* Editing digital images *
Lossless data compression Lossless compression is a class of data compression In signal processing Signal processing is an electrical engineering Electrical engineering is an engineering discipline concerned with the study, design, and application of equipme ...


Notes


External links

* {{DEFAULTSORT:Generation Loss Data compression Copying