Analog recording A recording in which continuous magnetic signals are written to the tape that are representations of the voltage signals coming from the recording of the video camera or microphone. Analog signals stored on tape deteriorate with each copy or generation; in contrast see digital.
Analog-to-digital The process in which a continuous analog signal is quantized and converted to a series of binary integers.
ANSI See standards.
Archival format A video format that provides reliable playback, without information loss. The format should be a current (as opposed to obsolescent) professional one supported by the industry. At present archival video material is typically stored on magnetic tape however in the near future computer-based storage is likely to become an option for archives. The advantage of uncompressed digital formats over analog formats is that they can be copied without generational loss. For this reason many archives are using digital formats for creating their archival masters. Ideally these formats should be uncompressed, component formats; however, for practical and cost reasons for Suitable archival formats will change as older formats become obsolete and are no longer supported. Ideally, archival master material is transferred onto new stock every 5-7 years and at this point a decision should be made about whether it is necessary to move to a new format as well. An archival format is therefore one that can be migrated onto new stock and new formats without the loss or distortion of information.
Artifact An undesirable picture element in a video image, which may naturally occur in the recording process and must be eliminated in order to achieve a high quality image. Most common artifacts are cross-color and cross-luminance. Not to be confused with artifact as a cultural product.
Back coat Optional layer applied to backside of tape substrate layer, useful in reducing tape friction and distortion, as well as dissipating static charge in playback. See image.
Baking A process of gently heating damaged videotape in an oven with controlled relative humidity in order to enable playback. As magnetic tape deteriorates the polymer of the binder deteriorates by hydrolysis, resulting in what is typically called sticky shed. Archivists have reported success in baking tapes that are suffering severe sticky shed; however, to date the scientific research has not been done to explain this. The temperature and humidity of the oven must be tightly controlled, as does the time for which a tape is baked. This process is not recommended except in extreme circumstances, as there is a suggestion that it will ultimately speed up the deterioration of the tape, although it might enable playback for remastering. There is unfortunately very little research in this area.
Bearding A type of video distortion that appears as black lines extending to the right of bright objects.
Bit Shorthand for binary digit, which has two optional values “0” or “1.” Eight bits means 8 binary digits. There are 256 possible combinations for 8 binary digits and therefore color depth of 8 bits represents 256 (2x2x2x2x2x2x2x2) possible colors. Because each pixel of a video picture contains 3 samples Y’, R-Y’, B-Y’, the possible colors of an 8-bit system would be 16.7 million (256 x 256 x 256). Nowadays archives will be receiving digital material into their collections or will be generating it as part of their preservation program. It is therefore necessary that we understand digital and analog technology.
Bit rate The amount of data transported in a given amount of time, usually defined in Mega (Million) bits per second (Mbps). Bit rate is one way to define the amount of compression used on a video signal.
Bit error rate (BER) The percentage of bits that have errors in playback. One possible indicator for the deteriorationPlayback is never perfect and there are many possible causes of error such as noise, dirt and dust, and drop out. In the binary world of digital data a bit is either correct or incorrect. Since it only has two states, the challenge is to correctly identify whether a bit is correct or not. To enable this the data is therefore coded by adding redundant bits. All systems build in redundancy and error correction mechanisms. Information about bit error rates can refer to the bit error rate prior to error correction or the residual errors after error correction.
Black, or Color Black, Blackburst A composite color video signal comprised of composite sync, reference burst and a black video signal which is usually at a level of 7.5 IRE (0.05V) above the blanking level. Also refers to fade-to-black between scenes.
Blocking The sticking together or adhesion of successive windings in a tape pack. Blocking can result from deterioration of the binder, storage of tape reels at high temperatures, and/or excessive tape pack stresses.
Blooming The defocusing of regions of a picture where brightness is excessive. Also refers to adjusting the white levels, on video monitors, to the point of leaving gray and becoming white.
BNC A connector used with coaxial cable, common in radio-frequency electronic systems. For more information about cables and connectors, check out The Cable Bible
Burst (or Color Burst) The reference for establishing the picture color, burst is seven to nine cycles (NTSC) or ten cycles (PAL) of subcarrier placed near the end of horizontal blanking to serve as the phase (color) reference for the modulated color subcarrier.
Burst vector composite video signals, the amplitude and angle of the color reference signal.
Byte A multi-digit binary number is called a word. A word of 8 binary digits or bits is called a byte. The amount of data that can be moved over time is expressed as MBps (Megabytes per second) or KBps (Kilobytes per second). A kilobyte of memory contains 1024 bytes, one megabyte contains 1024 kilobytes and a gigabyte contains 1024 megabytes. These concepts are essential to understanding issues relating to the storage and format choices of digital materials as well as the terminology surrounding the measurement of errors.
Capstan crease Wrinkles or creases pressed into the tape by the capstan/pinch roller assembly.
Carbon black An anti-static agent added to tape binder, which also attracts debris to tape.
Chroma crawl An artifact of encoded video also known as dot crawl or cross-luminance. Occurs in the video picture around the edges of highly saturated colors as a continuous series of crawling dots and is a result of color information being confused as luminance information by the decoder circuits.
Chroma level A reference to amount of color saturation; high level chroma that produces pastel, washed out color; low level chroma produceces heavy, saturated colors. The absence of chroma would result in black and white.
Chroma noise A condition in which colors appear to be moving on screen. In color areas of picture, chroma noise is usually most noticeable in highly saturated reds.
Chrominance The color part of a signal relating to the hue and saturation, but not to the brightness or luminance of the signal. E.g., black, gray and white have no chrominance, but any colored signal has both chrominance and luminance. U,V; Cr,Cb; I,Q: (R-Y, B-Y) represent the chrominance information of a signal.
Cinch Interlayer slippage or magnetic tape in roll form, resulting in buckling of some strands of tape. The tape will in many cases fold over itself causing permanent vertical creases in the tape. Also, if not fixed, will cause increased dropout. See windowing.
Cinching The wrinkling, or folding over, of tape on itself in a loose tape pack. Normally occurs when a loose tape pack is stopped suddenly, causing outer tape layers to slip past inner layers, which in turn causes buckling of tape in the region of the slip. Results in large dropout or higher error rates.
Clipping level An electronic limit to avoid overdriving the video or audio portion of the television signal.
Cleaning Debris between the head and the surface of a tape will cause errors in playback. However, the term “cleaning” is sometimes used in a general way to refer to more than the removal of debris from the surface of a tape, but to the removal of products of deterioration and other actions of the “cleaning” machines. For example, it may be that one of the important functions of “cleaning” systems is to smooth deformations in the surface of the tape and this function could not correctly be described as cleaning but may be one of the actions being carried out by machines. These cleaning systems have a number of elements - contact with Pellon cloth, a vacuum chamber and a polishing stone. Research could valuably be conducted to establish what the effect of these cleaning systems are, what is being removed, the effect of the different elements and whether modifications could usefully be made. In addition to the systems described on the BAVC DVD Playback: Preserving Analog Video, there are also professionals who have skills and experience to hand clean videotape.
Component video An unencoded video signal in which luminance (black and white) and chrominance (color) are transmitted as separate components, as such requires greater bandwidth than composite video. Component analog video consists of three primary color signals (RGB) that together convey all necessary picture information.
Composite video A mixed encoded signal combining luminance (black and white), chrominance (color), blankingsyncNTSC, PAL, subcarrier to the luminance signal of approximately 3.58MHz in NTSC and 4.43 MHz in PAL. pulses and color burst, that includes horizontal or vertical synchronizing information, using one of the coding standards:
Compression A process employed to reduce the bit rate of digital video. Compression algorithms aim to do this in ways that minimize the visible effects. For example, most images contain large amounts of identical or similar pixels that are repeated within a frame or a sequence of frames. Intra-coded compression will identify such redundancy within each frame whereas Inter-coded compression takes into account redundancy from one picture to the next. An intra-coded compression system therefore uses a time delay to calculate the pixel differences between pictures. The first picture is an absolute picture known as an Intra-coded or “I” picture. “I” pictures are sent periodically and require a large amount of data, this is then used as the reference in order to calculate the picture differences between successive pictures known as the differentially coded picture. Essentially this form of compression takes advantage of the similarities between successive pictures sending only the differences between pictures to cut down on the amount of data transmitted. Other techniques are based on the human ability to perceive picture detail and the predictability of the signal.
Compression, lossless Coding essentially expands to provide identical data, bit compression factor of such a system is usually around 2:1. Digital Betacam is a format that employs “lossless” intra-coded compression.
Compression, lossy Coding does not expand to produce identical data to the source material and differences are detectable. MPEG 2 is an example of a lossy inter-coded compression standard. MPEG-2 is the compression system used for DVD.
Conservation The action taken to identify and assess the risks to a work of art, or artifact, from agents of deterioration, format or technology. It is part of the role of a conservator to identify and, where possible, to mitigate such risks. Where undesirable change has occurred a conservator may explore ways of intervening and treating the work of art or artifact. Decision-making is based on information about the effects of deterioration or change, an understanding of the historical and aesthetic value of that artifact and of the likely effects of any proposed action. Appropriate conservation techniques and treatments are developed in accordance with an agreed professional code of ethics. Conservators have a responsibility to future generations in preserving the historical and aesthetic value of a work. There is much debate around what constitutes “undesirable change.” For example, in the case of a video installation, debates around the parameters of acceptable change will focus on whether it is appropriate to substitute different equipment or display technologies as older formats and technologies become obsolete or difficult to maintain. Artists have an important role to play in deciding what is essential to preserve, however conservators also have a responsibility to the historical integrity of the work. Conservation decisions are complex judgements made in consultation with other relevant parties such as the artist, where possible, and the curator or historian. The professional body for conservation in the USA is the American Institute for Conservation (AIC) http://aic.stanford.edu/. In for bit, with the original source data, although the processing does introduce the possibility of errors.
A starting point for a conservator is therefore to provide a full description of the work of art or artifact being considered. Conservators are responsible for documenting changes that occur, decisions made about treatment or care and subsequent evaluation of such decisions. The relevant agents of change are dependant on the nature of the work of art or artifact being considered. Different types of artifacts will have different vulnerabilities to change and therefore different vocabularies of risk. For example, in the case of videotape we may be concerned about the impact of environmental factors such as temperature and humidity that increase the rate of deterioration or the obsolescence of a particular
The worldwide body for conservation is the International Institute of Conservation (IIC) http://www.iiconservation.org/
Conservation report A detailed description of the work of art or artifact, its condition, an analysis of the risks to that object and a description of how those risks might be mitigated. If treatment is proposed the report should document each stage of any action taken, the decision making process involved and a description and assessment of the outcome. Reports should be signed and dated.
Control track A synchronizing signal on the edge of the videotape, which provides a reference for tracking control and tape speed. Control tracks which have heavy dropout
Cross-color A picture defect that appears as spurious rainbow patterns on highly textured objects, such as a striped shirt or a tweed jacket, attributed to the make-up of the NTSC signal, whcih mixes high luminance and chrominancecomposite baseband spectrum.
Crosslinking A chemical reaction of polymers. Crosslinking will lead to embrittlement when the binder is no longer flexible and the chemical makeup of the binder has changed and tightened. A reaction happens when chemicals within the binder crosslink. Mechanical action of the tape is difficult due to the tightened tape structure.
Crosstalk An undesired signal interfering with the desired signal, and usually caused by unintentional capacitive (AC) coupling. Can result in several types of picture distortion, mistracking, and/or noisy picture. Also refers to signal interference from one part of videotape to another.
Curvature error A change in track shape that results in a bowed or S-shaped track. This becomes a problem if the playback head is not able to follow the track closely enough to capture the information.
Data Information transmitted as binary code. In the case of component video each pixel is a vector quantity and includes information for all color components Y’, R-Y’ and B-Y.’ High quality standard definition for a moving color picture requires a data rate of 200 million bits per second.
Data Compression A techique that provides for the transmission or storage, without noticeable information loss, of fewer data bits than were originally used when the data was created.
Decoder A device used to recover the component signals from a composite (encoded) source. Decoders are used in displays and in various processing hardware where component signals are required from a composite source, such as composite chromakeying of color correction equipment, etc.
Deterioration The degradation of videotape, most typically with the binder, which is responsible for holding the magnetic particles on the tape and facilitating tape transport. If the binder loses integrity - through softening, embrittlement, loss of cohesiveness, or loss of lubrication - the tape may become unplayable. Sticky tape and sticky shed are commonly used terms to describe the phenomenon associated with deterioration of the magnetic tape binder. See image.
Drop-frame time code SMPTE time code format that continuously counts 30 frames per second, but drops 2 frames from the count every minute, except in every tenth minute (drops a total of 108 frames every hour) to maintain synchronization to clock time.
Dropout Momentary signal loss of video or audio during playback on a tape machine, and caused by momentary loss of tape contact with the playback head, tape head clog, flaws in the tape or other features that cause an increase in the head-to-tape spacing. Dropout can also be cause by missing magnetic material. Video dropout generally appears as a white spot or streak on the video monitor. When several video dropouts occur per frame, the TV monitor will appear snowy. The frequent appearance of dropout on playback is an indication that the tape or recorder is contaminated with debris and /or that tape binder is deteriorating.
Dubmaster The copy of a master used for making additional copies.
DVD Abbreviation for Digital Versatile Disc. There are a number of different types of DVD. At the time of writing these include DVD-R, DVD-Rom, DVD-RAM, DVD+RW, DVD-R/W. DVD is not a suitable archival format for video mainly because it uses a lossy form of compression - MPEG2. It is also a format that is likely to see rapid changes in technology and therefore the risk of speedy obsolescence is high. DVDs are made up of a reflective aluminium layer, a polycarbonate substrate, a dye layer and a clear lacquer. The aluminium layer is highly susceptible to pollution and the lacquer layer does not sufficiently protect the aluminium layer to prevent oxidation. Where the DVD is double-sided the two sides are bonded using an adhesive. The adhesive have not been subjected to accelerated aging tests by the manufacturers and there is little data on their life expectancy. A DVD is the same diameter as a CD (120cm) but cannot be read by the same equipment. DVD and CD both record data by encoding it as tiny pits in tracks that correspond to the zeros and ones of binary digits. The pits are read by laser and played back. DVD is able to store more data by making the pits smaller and the tracks closer together and employing the compression system MPEG II. Many artists use DVD-R as an exhibition format and this has replaced laser disc as a popular display format for many museums and galleries. However, because of the way the data is encoded frame-accurate control cannot be achieved by referencing the picture content as it can with laser disc. Where external control is needed for display it is important to be clear of any specific requirements of the control system before having the disc(s) made.
DVD-R discs were introduced in 1997 with the capacity of 3.95 GB and a track pitch of 0.8 microns that later, by reducing the track pitch to 0.74 microns, this was increased to 4.7GB.
There are two types of DVD-R discs; “General” and “Authoring”. This has caused some compatibility issues as the lasers in the players for these discs need to be angled differently. Professional DVD players will have both lasers, however if you are using a domestic model it is important to check which discs your player is compatible with. This is also true for all other types of disc as there is unfortunately a lack of compatibility between playback equipment at this time. DVD is a rapidly developing technology and there is a continued push to increase the amount of data that can be stored on a disc.
Echo A wave which has been reflected at one or more points in the transmission medium. Echoes may be leading or lagging the primary signal, and appear in the picture monitor as reflections or double images commonly known as ghosts.
Edge curl Usually occurs on the outside one-sixteenth inch of the videotape. If the tape is sufficiently deformed it will not make proper contact with the playback heads. An upper curl (audio edge) crease may affect sound quality. A lower curl (control track) may result in poor picture quality
Edge damage Physical distortion of the top or bottom edge of the magnetic tape, usually caused by pack problems such as popped strands or stepping. Edge damage effects audio and control track, sometimes preventing playback.
EDL (edit decision list) An EDL can be a handwritten list or computerized set of instructions used to direct the final outline editing assembly of the video programs.
EIAJ Standard tape format for 1/2” VTRs after 1969.
Erasure Loss of signal on the tape, resulting from extreme temperatures defined as above 275 F/175 C.
Error correction The data in magnetic recordings can be corrupted due to dropout, poor tracking, poor headnoise in the replay circuits and heads. In optical recordings the light beam might be interrupted by scratches or dirt or the disc might be warped. Whatever the causes there are two types of error - large isolated corruptions where a clump of bits are in error or random errors effecting single bits. Error correction is entirely necessary in order to maximize the efficiency of recorders. In the binary world of digital media a bit can only be right or wrong. Therefore if you know which bits need correcting, all that needs to be done is for the value of the bit to be inverted. However, the difficulty is in predicting which bits are in error. This is done by adding what is known as redundancy. Redundancy is information added to the data about the data, the resulting unit is called a code word. Code words are more robust than data alone and enable the error correction mechanism to detect errors and correct them. If it is not possible to correct all the errors then the uncorrected errors are concealed. Concealment may be detectable as it is only the approximation of the information in error whereas corrected data is not detectable and perfectly accurate.
Exhibition format Tape or disc copies that are used expressly for frequent playback, as opposed to master tapes should only be played as part of the archival process. The criteria for a good exhibition format are different from that of an archival format. For example hard disc, DVD and laser disc are all good exhibition formats for video as they are reliable and because playback is made possible without mechanical deterioration to the media as a result of being played. This is important where a video is on display all day every day. Although in the near future it is likely that we will see uncompressed digital video being streamed from hard discs for display, it is more common that the video is compressed. Such compression would not be acceptable for the master copy but may be a compromise that is acceptable for display. Each media have different advantages and disadvantages, but the important point is to be clear that the criteria for display may be different than for archiving for example the display of a complex video work may require reliable frame-accurate synchronization.
Flagging A horizontal displacement of the upper portion of a picture. Also called skewing.
Flicker Picture distortion mainly related to vertical syncs and video fields display. Some flicker typically exists due to interlacing and is more apparent in 50HZ systems (PAL). Flicker also shows when static images are displayed on the screen, such as computer generated text transferred to video. Poor digital image treatment, found in low quality system converters (going from PAL to NTSC and vice versa) creates annoying flicker on the screen. There are several electronic methods to eliminate flicker.
Flutter Very short rapid variations in tape speed which may result in a jumpy or jittery picture.
Foldover Tape that has folded over resulting in the oxide surface facing away from the heads.
Format See videotape formats.
Frequency A measurement of an analog signal’s vibration, represented as cycles persecond or Hertz (Hz).
Gamma correction A process used with video and computer graphics images to correct brightness and internal micro-contrast within the image, allowing a change of ratio between the brightest red component of an image and the weakest red.
Gamut The range of voltages allowed from a video signal, or a component of a video signal. Signal voltages outside of the range (i.e., exceeding the gamut) may lead to clipping, crosstalk or other distortions.
Generation Copy of original video program material. The original videotaped material (source footage) is the first generation. A copy of the original is a second generation tape and so on. Generally the edited master tape is a second generation tape. In analog systems, extensive efforts are made to keep generations to a minimum, since each copy or process adds noise and other artifacts resulting in diminished quality with each generation.
Generational loss Degradation cause by tape duplication.
Ghost A shadowy or weak image in the received picture, offset either to the right or to the left of the primary image, and the result of transmission conditions where secondary signals are created and received earlier or later than the primary signal casued by a reflected RF signal.
Glitch A form of low frequency interference, appearing as a narrow horizontal bar moving vertically across the picture.
Head Magnetic pickup device in a VTR used to record, erase or reproduce video and audio signals.
Head switching There are two write heads mounted on the video head assembly. The write heads are mounted 180 degrees apart. The videotape is wound on the head drum at slightly more than 180 degrees. This allows for a slight overlap in information between the heads. The video head rotates under the tape so that the tape travels at one speed and the video head travels underneath at a much higher speed. The tracks are scanned alternately by the “A” head and the “B” head. Each track corresponds to one field of the interlaced video signal.
During the playback of the tape, the video heads are timed to avoid double playing the redundant region. The video head switching pulse falls in the “blacker than black” area below the bottom of the television. However, it can be seen by adjusting the vertical hold control so that the vertical sync pulse moves into the viewing area. Any picture disturbance during the head switch over should be hidden by the vertical over-scanning on a TV or monitor. The head drum and capston drive form a very precise control system known as a servo. Poor servo tension can cause a large switching error that is visible in the picture.
Horizontal Resolution Chrominance and luminance resolution (detail) expressed horizontally across a picture tube. This is usually expressed as a number of black to white transitions or lines that can be differentiated. Limited by bandwidth of the video signal or equipment.
Hue (Tint, Phase, Chroma Phase) One of the characteristics that distinguishes one color from another. Hue defines color on the basis of its position on the spectrum, i.e., whether red, blue, green or yellow, etc. Hue is one of the 3 characteristics of television color, along with saturation and luminance. In NTSC and PAL video signals, the hue information at any particular point in the picture is conveyed by the corresponding instantaneous phase of the active video subcarrier.
Hydrolysis The chemical process in which scission or a chemical bond occurs via reaction with water. The polyester chemical bonds in tape binder polymers are subject to hydrolysis, producing alcohol and acid end groups. Hydrolysis is a reversible reaction, meaning that the alcohol and acid group can react with each other to produce a polyester bond and was as a byproduct. In practice, however, a severely degraded tape binder layer will never fully reconstruct back to its original integrity when placed in a very low humidity environment. See image.
Interlaced (See also: noninterlaced) (Short for interlaced scanning) A system of video scanning whereby the odd- and even- numbered lines of a picture are transmitted consecutively as two separate interleaved fields. Also called line interlace.
IRE (Institute of Radio Engineers) Units of measurement dividing the area from the bottom of sync to peak white level into 140 equal units. 140 IRE equals 1V p-p. The range of active video is 100 IRE.
Laser disc A form of optical media that, unlike DVD, stores video as a composite analog signal. The laser disc was first introduced by Philips and MCA in 1972, and has been on the market since 1978. Laser discs can be glass or plastic. There are essentially two types of laser disc: those mastered for constant linear velocity (CLV) and those mastered for constant angular velocity (CAV). CAV store approximately 30 minutes of video, can be controlled in a frame-accurate way and can be still framed. CLV discs can store approximately one hour of video but cannot be controlled frame-accurately and cannot be still-framed. Once a popular display format for many artists, the laser disc has now largely been superseded by DVD. Laser discs could not handle saturated areas of color, and would produce artifacts appearing as herring bone patterns. CAV discs did, however, have the advantage of frame-accurate external control.
LTC (Longitudinal Time Code) Another expression for the SMPTE time code signal recorded onto the third audio track of a videocasstte tape.
Luminance The portion of the video signal which contains the black and white information. Luminance indicates the amount of light intensity in a picture which is perceived by the eye as brightness. The color video picture information contains two components: luminance (brightness and contrast) and chrominance (hue and saturation).
Magnetic media Tape and discs that store information on a magnetized surface such as videotape, audiotape or computer floppy discs. See image.
Magnetic remanence The ability of the pigment to retain a magnetic field.
MARC MAchine Readable Cataloging. The standard system for computerizing cataloging records. IN US, also called USMARC, and systems may vary internationally, e.g., DenMARC. See IMAP website for more information: http://www.imappreserve.org/faq.html
Mistracking The phenomenon that occurs when the path followed by the read head of the recorder does not correspond to the location of the recorded track on the magnetic tape. Mistracking can occur both longitudinal and helical scan recording systems. The read head must capture a given percentage of the track in order to produce a signal for playback.
Moire 1. A wavy or satiny effect produced by the convergence of lines. It usually appears as a curving of the lines in the horizontal wedges of a test pattern. It is a natural optical effect when converging lines in a television picture are nearly parallel to the scanning lines. 2. Optical disturbance caused by interference of similar frequencies.
Noise Any unwanted signal present in the total signal.
Nondrop Frame Time Code (NTSC) SMPTE time code format that continiously counts a full 30 frames per second. Because NTSC video does not operate at exactly 30 frames per second, nondrop frame time code will count 108 more frames in one hour than actually occur in the NTSC video in one hour. The result is incorrect synchronization of time code with clock time. Drop frame time code solves this problem by skipping or dropping 2 frame numbers per minute, except at the tens of the minute count.
Noninterlaced The process of scanning whereby every line in the picture is scanned during the vertical sweep. See interlaced.
NTSC ( National Television Systems Committee) The US standard for color television transmission, calling for 525 lines of information, scanned at a rate of 30 frames per second. NTSC standard is used mainly in North America, Japan, and part of South America. One of three international standards, including PAL and SECAM.
NTSC Color Bars A pattern generated by the NTSC Generator, consisting of eight equal width color bars. Colors are white (75%), black (7.5% setup level), 75% saturated pure colors red, green, and blue, and 75% saturated hues of yellow, cyan, and magenta (mixtures of two colors in 1:1 ratio without third color).
Off-Line Editing Editing that is done using inexpensive, nonbroadcastquality equipment to produce an edit decision list (EDL) which will be used later for assembling a broadcast quality program using more expensive, high quality equipment.
Online Editing Final editing session in which the finished program master is assembled from the original production material.
Pack slip A lateral slip of select tape windings causing high or low spots (when viewed with tape reel laying flat on one side) in an otherwise smooth tape pack. Pack slip can cause subsequent edge damage when the tape is played, as it will unwind unevenly and may make contact with the tape reel flange.
PAL (Phase Alternate Line): The European standard for color television transmission, calling for 625 lines of information, scanned at a rate of 25 frames per second. Used mainly in Europe, China, Malaysia, Australia, New Zealand, the Middle East and parts of Africa. One of three international standards, including NTSC and SECAM.
Physical damage Any distortion of the magnetic tape which prevents proper head to tape contact and is therefore detrimental to the tape playback. These distortions can include edge damage, wrinkles, cinches, and tape stretch. See image.
Pedestal 1. In the video waveform, the signal level corresponding to black. Also called setup. 2. A pulse (usually with a flat peak) that elevates the base level of another waveform.
Phase (chroma Phase, Hue, Tint) The relative timing of a signal in relation to another signal. If the time for one cycle of a signal is represented as a 360 degree along a time axis, the phase position for the second signal is called phase angle expressed in degrees. The subcarrier phase TV colors can be adjusted and this changes the huesignalhue of a color signal correct. Color phase is the timing relationship in a video that is measured in degrees and keeps the colors themselves.
Playback The viewing of recorded video footage or reproduction of recording video signal via a magnetic pickup device.
Playback demagnetization A loss of magnetization and thus a degradation of recorded information caused by repeated playing of a recorded tape.
PLUGE (Picture Line-Up Generation Equipment) Also called Black Set. Used for aligning monitors and other video devices. In some versions of color bars, PLUGE is the black set at the bottom of the red bar that contains bars that are blacker than black, black, and whiter than black. Used to adjust monitor brightness by watching the PLUGE so that the whiter than black bar is just visible and both the black and blacker than black bars are no longer distinct.
Polymer A long organic molecule made up of small, repeating units (literally, many mers). Analogous to a freight train, where each individual unit is represented by a freight car. At very high magnification, a chunk of polymer would resemble a bowl of cooked spaghetti. Plastic materials are polymers. The strength and toughness of plastics is due, in part, to the length of its polymer molecules. If the chains (links in the freight train) are broken by hydrolysis, the shorter chains will impart less strength to the plastic. If enough polymer chains are broken, the plastic will become weak, powdery, or gooey. See binder.
Preservation See Video preservation.
Print through The condition where low frequency signals on one tape winding imprint themselves on the immediate adjacent tape windings. It is most noticeable on audio recordings where a ghost of a recording can be heard slightly before playback of the actual recording.
Remastering, migration, transferring Terms used interchangably to refer to the process of copying the content of an existing videotape to new media.
Resolution A measure of the ability of a camera or television system to reproduce detail (the number of picture elements that can be produced with good definition).
Restoration The process and work of improving the degraded quality of the sound or image in terms of video and audio preservation. It is important to be clear whether a proposed restoration relates to aspects of an image that are part of the historical nature of the technology being used at the time and are part of the original work and damage which has occurred after the piece was made due to deterioration, poor handling or bad transfers. It is important to recognize that the artifacts of the original technology are of historical value and are part of the texture of the work. These should not be removed. However, where damage has occurred after the work was finished there may be a case for intervention. Dropout, for example, can be digitally “filled in” by copying information from the surrounding areas. There are also systems that detect artifacts in the image using motion compensation. A copy of the original un-restored video should always be archived alongside any restored version.
RGB (Red, Green and Blue) The basic parallel component set in which a signal is used for each primary color; or the related equipment or interconnect formats or standards. The same signals may also be called “GBR” as a reminder of the mechanical sequence of connections in the SMPTE interconnect standard.
Roll A lack of vertical synchronization which causes the video picture to move upward or downward.
Saturation (Chroma, Chroma Gain, Color): 1. The intensity of the colors in the active picture. The voltage levels of colors. The degree by which the eye perceives a color as departing from a gray or white scale of the same brightness. A 100% saturated color does not contain any white; adding white reduces saturation. In NTSC and PAL video signals, the color saturation at any particular instant in the picture is conveyed by the corresponding instantaneous amplitude of the active video subcarrier. 2. The point on the operational curve of an amplifier at which an increase an input amplitude will no longer result in an increase in amplitude at the output.
Scanning The rapid movement of the electron beam in a pickup device of a camera or in the CRT of a television receiver. It is formatted in a line-for-line manner across the photo sensitive surface which produces or reproduces the video picture. When referred to a video surveillance field, it is the panning or the horizontal camera motion.
SECAM (Sequential Couleur Avec Memoir “sequential color with memory”) A color television standard with 625 lines per frame and 50 fields per second developed by France and the U.S.S.R. Color difference information is transmitted sequentially on alternate lines as an FM signal. One of three international standards, including NTSCPAL. and
Signal to noise ratio (S/N) Expressed in decibels (dBs), this term describes a ratio or difference of wanted audible or visual information (signal) versus unwanted information experienced by distorted sounds and pictures (noise). Comparatively high decibel numbers mean better sound or visual images.
Sine wave Type of pure waveform having an equal distance from its peak to the zero or center line and from its trough to the center line and in which the positive hump and negative hump of the wave are exactly equal in length, shape and height but flipped in a mirror image about the center line.
Skew A bending of picture at top or bottom of television screen caused by the changing of the video track angles on the tape from the time of recording to the time of playback. This can occur as a result of poor tension regulation by the VCR or by ambient conditions which affect the tape.
SMPTE (Society of Motion Picture and Television Engineers) Organization dedicated to researching, proposing, and promoting video standards.
SMPTE Time Code Time code that conforms to SMPTE standards. It consists of an 8-digit number specifying hours: minutes: seconds: frames. Each number identifies one frame on a videotape. SMPTE time code may be of either the frop-frame or non-drop frame type. In GVG editors, the SMPTE time code mode enables the editor to read either drop-frame or non-drop frame code from tape and perform calculations for either type (also called mixed time code).
Squeal Undesirable audio effect that is typically caused by a build up of debris on a guide or head. Sometimes a cleaning of the offending surface will eliminate the squeal. Squeal is also caused by the tape having poor lubrication or losing its lubrication with age. A solution is to overcoat a tape with a lubricant solution, which will eliminate the squeal so a copy can be made.
RLG - Research Libraries Group
Stick slip The process in which (1) the tape sticks to the recording head because of high friction; (2) the tape tension builds because the tape is not moving at the head; (3) the tape tension level reaches a critical level, causing the tape to release from and briefly slip past the read head at high speed; (4) the tape slows to normal speed and once again sticks to the recording head; (5) this process is repeated indefinitely. Characterized by jittery movement of the tape in the transport and/or audible squealing of the tape. See image.
Sticky shed The gummy deposits left on tape path guides and heads after a sticky tape had been played. Sticky shed is also known as the phenomenon whereby a tape binder has deteriorated to such a degree that it lacks sufficient cohesive strength so that the magnetic coating sheds on playback. The shedding of particles by the tape is a result of binder deterioration that causes dropout on VHS tapes. See image.
Sticky tape Tape characterized by a soft, gummy, or tacky tape surface; tape that has experienced a significant level of hydrolysis so that the magnetic coating is softer than normal; tape characterized by resinous or oily deposits on the surface of the magnetic tape. See image.
Subcarrier The basic signal in all NTSC sync signals. It is a continous sine wave, usually generated and distributed at 2V in an amplitude, and having a frequency of 3.579545MHz. Subcarrier is usually divided down from a primary crystal running at 14.318180MHz, and that divided by 4 is 3.579545. All other synchronizing signals are directly divided down from the subcarrier. Color subcarrier is the 3.58 MHz signal that carries color information. This signal is superimposed on the luminance level. Amplitude of the color subcarrier represents saturation, and phase angle represents hue.
Sync (abbreviation for synchronous) The portion of an encoded video signal that occurs during blanking and is used to synchronize the operation of cameras, monitors and other equipment. Horizontal sync occurs within the blanking period in each horizontal scanning line and vertical sync occurs within the vertical blanking period. In video, sync is an essential element for maintaining the proper clocking of video signals. TOP
Tape clog See head clogging.
TBC (Time Base Corrector) Hardware that corrects the timing irregularities that occur during VCR playback. Time base correction is not necessary for direct playback from a VCR to a TV set.
Time code tape for logging time code. See also SMPTE time code. Electronic indexing method used for editing and timing video programs. Time code denotes hours, minutes, seconds and frames elapsed on videotape. Time code permits very time efficient and accurate editing, and is displayed in a “ window dub”
Tracking The angle and speed at which the tape passes the video heads. Loss of tracking is evidenced by picture breakup or loss of video in segments of the picture.
Transferring, migration, re-mastering
Vectorscope Oscilloscope that reads chrominance portion of a video signal. See waveform.
Videotape formats Recording formats. Current video tape formats include C, U-MAtic, Betacam, M, Betcam SP, Mll, D1, D2, video to Terms used interchangably to refer to the process of copying the content of an existing videotape to new media. Oxide-coated plastic-based magnetic tape used for recording video and audio signals. that differ in magnetic patterns of information, but rely on the same fundamental process of recording image and sound on magnetic tape. A particular format needs its own playback machine that is able that to read the magnetic pattern.There are several characteristics that distinguish one format from another, such as the type of recorded signal, tape speed, width and placement of the video tracks and audio tracks. After 1970 the EAIJ standard was accomplished. The VHS (video home system) 1/2” consumer videotape format is one example. Since 1956, approximately 50 formats have been introduced world wide. For examples, see the resources Hardware section. D3, D5, Digital Betacam, Beta, VHS, Hi-*, 8mm, S-VHS, DVC Pro and DVcam.
Video preservation An archival system that ensures the survival in perpetuity of the program content according to the highest technical standards reasonably available. There are three major facets of video preservation: (1) safeguarding the recording under secure and favorable storage conditions, (2) providing for its proper restoration and periodic transfer to modern formats before the original or next generation copy is no longer technologically supportable, and (3) continuing protective maintenance of at least a master and a copy, physically separated in storage, preferably in different geographic locations. (From the National Film Preservation Board’s Television/Video Preservation Study: Volume 1: Report 1997.
Video signal to noise ratio An indication of the amount of noise in a black and white picture.
Vinegar syndrome Characteristic of the decomposition of acetate-based magnetic tape where acetic acid is a substantial by product that gives the tape a vinegar-like odor. After the onset of vinegar syndrome, hydrolysis of the acetate backing is catalyzed further by the presence of acetate acid byproduct.
Waveform Oscilloscope that reads luminance and other parts of the compositesync, blanking, video, etc. that may need adjustment for accurate display. See vectorscope.degrade at an accelerated rate - the Abbreviation for videotape recorder. video signal, such as
White balance An electronic process used in video cameras to retain true colors.
Window dub time code.
Windowing Interlayer slippage or magnetic tape in roll form, resulting in bucking of some strands of tape. The tape will in many cases fold over itself causing permanent vertical crease in the tape. Also, if not fixed, will cause increased dropout. See cinching.
Wrinkle A physical deformity of the videotape; any or wrinkle in the videotape may produce dropout or loss of picture information upon playback. See creasing. Copies of videotape with “burnt in” time code display. Hours, minutes, seconds and frames appear on the recorded image. Window dubs are used in off-line editing. See
Glossary contributions by Rebecca Bachman; Pip Laurenson, Sculpture Conservator, Tate UK; Heather Weaver, Online Editor, BAVC; Dr. John Van Bogart; and Snader & Associates Inc.
Originally published in Playback: A Preservation Primer for Video, Copyright 1998, Bay Area Video Coalition.