Aliasing Undesirable ‘beating’ effects caused by sampling frequencies being too low to reproduce image detail faithfully.

Alpha channel Term used to describe an element of a graphics file that will create a hole cutter allowing specified elements of a graphic to be revealed over a background image.

Alpha wrap A method used to wind videotape around a helical scan drum.

Anti-aliasing The smoothing and removing of aliasing effects by filtering and other techniques. Most DVEs and character generators contain anti-aliasing circuitry.

Archive Long-term storage of information. Pictures and sound stored in digital form can be archived and recovered without loss or distortion. The storage medium must be both reliable and stable. As large quantities of information need to be stored, cost is a major consideration. Lowest cost is magnetic tape.

Artefact Particular visible effects which are direct results of some technical limitation. Artefacts are frequently judged on a subjective level. For example, the visual perception of contouring in a picture cannot be described by a signal-to-noise ratio or linearity measurement.

Aspact ratio The ratio of frame width to frame height. The standard aspect ratio for television is 4:3 which closely matches the 16 mm movie film frame. With high definition TV, 16:9 widescreen is also being used.

Assemble (1) To edit on or add material at a point determined by an edit point decision in videotape editing. (See Auto-assemble and Insert editing.) (2) The recording technique where all recording heads go into record at the same time. Video, audio, timecode and control track all go into record.

Audio and control track head Usually a stationary head on a VTR. This head performs at least two functions: the upper portion serves as the audio head, recording and playing back an audio signal (sometimes there are two or more audio tracks); the lower portion records a control track of pulsed or sinusoidal phase information, which is used to control tape/head rotation speed and phase during playback (very much like the sprocket holes in film).

Audio dub To record or re-record the audio portion of a videotape without disturbing the existing video signal or, in some cases, disturbing other audio tracks. (See Insert editing) Auto-assemble Editing handled by an edit controller. The term applies to both VTR (linear) editing and nonlinear editing.

Auto-conform Another term for auto-assemble. When auto-conforming in a linear suite it is essential that the EDL is correct and all the edits are as finally required.

Azimuth The angle of a recording head in relation to audio or videotape. The normal angle is 90 degrees to the direction of the recording track.

Azimuth recording A system of recording where the gaps of the two heads are at different angles to normal. Adjacent tracks are recorded at plus or minus an angle to the normal so that they can be run very close together without interference. It is used on both the Betamax and VHS domestic formats. It is also used in Betacam recorders.

Bandwidth Defines the amount of information that can be passed in a given time. Large bandwidth is needed to show sharp picture detail and is a factor in the quality of recorded or transmitted images. CCIR 601 and SMPTE RP 125 allow analogue luminance bandwidth of 5.5 MHz and chrominance bandwidth of 2.75 MHz, the highest quality attainable in any standard broadcast format. Digital image systems require large bandwidth, hence the reason why many storage and transmission systems use compression techniques to accommodate the signal.

Bearding Artefact associated with poor quality recordings. identified by black line ‘ragging’ on high contrast transitions. Usually due to either over-modulation on a recording or worn record/playback heads.

Betacam The trademark for a half-inch professional component videocassette format, developed by Sony.

Binder A chemical that adheres, and at the same time separates iron oxide particles, to videotape backing or base.

Black The darkest of the electronically generated steps of the grey scale. Also called TV Black or 0 V. This ‘black’ is only as dark as a screen of a television tube when switched off.

Black crushing The pushing of the black recording level so that low-light picture information in the shadows is lost.

Blacked tape A tape that is ‘black’ or ‘blacked’ with blanking level and synchronizing information but no active picture information except for control track and timecode. (See Striped tape)

Black level The bottom level of a video signal, below which are the sync, blanking and other control signals that do not appear as picture information.

Blank tape Unused audio or videotape. Also called virgin tape.

Blanking The electronic beam shut-off period on a television tube during which the line is changed (line blanking), or the next field is changed (filed blanking).

Blanking signal Part of the video signal, which is recorded to indicate the timing and length of time for line and field changes.

Break-up A momentary disruption of a television picture, caused by extraneous electronic signals, loss of primary signal or loss of head-to-tape contact in a recording system.

Burnt-in timecode Timecode that is superimposed on pictures. Useful for off-line selection of footage, or for accurate location when assessing viewing copies of edited items.

Burst The small portion of a video signal that contains approximately 10 cycles of 4.433 MHz colour sub-carrier (PAL) and is used for synchronizing colour throughout the broadcast chain from reeording/playback to transmission and reception.

Cassette A self-contained, reel-to-reel cartridge holding either audio or videotape.

CCD scanner A camera/telecine device for the transfer of light to video signal. Charge couple devices (CCD) are now almost exclusively found in TV cameras.

CCIR Comité Consultatif International de Radio-Communications) This has been absorbed into the ITU under ITU-RCCIR 601 (ITU-R 601). The international standard for digitizing component colour television video in both 525 and 625 line systems, derived from the SMPTE RP125 and the EBU Tech. 3246-E. CCIR 601 deals with both colour difference (Y, R-Y, B-Y) and RGB video, and defines sampling systems, RGB/Y, (R-Y), (B-Y) matrix values and filter characteristics. CCIR 601 is normally taken to refer to colour difference component video (rather than RGB), for which it defines 4:2:2 sampling at 13.5 MHz with 720 luminance samples per active line with 8 or 10 bit digitizing.

Chroma Colour hue and saturation.

Chroma key A method of electronically matting (inserting) an image from one video source into the picture produced by another. The effect is achieved by replacing the colour (often blue but could be any colour) in one scene with another video input. Also called colour separation overlay.

Chroma noise Unwanted random variations of chroma, a common problem with multi-generation videotape recordings.

Chroma output The level of colour output signal recorded. Normally related to the level given by a reference tape.

Chrominance channel The red, green and blue colour channels produced either by a colour camera or a telecine.

Chrominance signal The portion of the total video signal that contains the colour information (R-Y and B-Y), often just referred to as chrominance.

Colour bars An electronically generated video test pattern consisting of vertical bars used to set the chrominance and luminance of cameras and videotape recorders. Colourbars come in a number of standards: 100%, 95% and 75% bars and SMPTE bars.

Colour burst A very accurately phased burst of high frequency (4.433 MHz for PAL) at the beginning of each TV scanning line used to control the reproduced colour of the active picture.

Component (video) A video signal in which the luminance and chrominance remain as separate components, e.g. analogue components in Mil and Betacam VTRs, digital components Y, Cr, Cb in CCIR 601. Component signals retain maximum luminance and chrominance bandwidth. Component video is used in Betacam and some digital formats, e.g. D1, D5, Digi Betacam and DVC Pro.

Composite (Video) The combination of luminance and chrominance using one of the coding standards – PAL, NTSC and SECAM – to make composite video. The process, which is an analogue form of video compression, restricts the bandwidths (image detail) of components. Chrominance is added to the luminance using a visually acceptable technique but it becomes difficult, if not impossible, to reverse the process (decode) accurately into pure luminance and chrominance.

Compression Cvideo) The process of reducing the amount of bandwidth or data rate for video. The broadcast standards used today – PAL, NTSC and SECAM – are analogue video compression systems. For digital systems, pictures are analysed looking for redundancy and repetition and so discard unnecessary data. The techniques were primarily developed for digital transmission but have been adopted as a means of handling digital video in computers and reducing the storage demands for digital VTRs.

Compression ratio The ratio of the data in the uncompressed digital video signal to the compressed version. Modern compression techniques start with the CCIR 601 component digital signal so the amount of data of the uncompressed video is well defined: 75 GB/hour for 625/50 and 76 GB/hour for the 525/60 standard. The compression ratio should not be used as the only method to assess the quality of a compressed signal. For a given technique, greater compression can be expected to result in worse quality; but different techniques give widely different results for the same compression ratio. The only sure method of judgement is to make a very close inspection of the resulting pictures.

Contouring An unwanted edge or artefact. Digital systems exhibit contouring when insufficient quantizing levels are used or inaccurate processing occurs.

Control track The recorded track which controls by timed pulses the playback speed of the tape and the drum. It is essential for videotape editing.

D1 A format for digital videotape recording working to the CCIR 601 4:2:2 standard using 19 mm wide tape. As a component recording system it is ideal for studio and post-production work. Offers multi-generation capability with little or no picture degradation. Despite this it has not had a large take-up due to high cost.

D2 The standard for digital composite (coded) PAL or NTSC signals. Often used as a direct replacement for 1″ VTRs. Although offering good slo-mo modes and muiti-generation capabilities, being a coded system means coded characteristics are present, i.e. colour framing sequences.

D3 A VTR standard using ¹/₂″ tape cassettes for recording digitized composite (coded) PAL or NTSC signals sampled at 8 bits. Characteristics are generally as for D2 except that the small cassette size has allowed a full family of VTR equipment to be developed, including a camcorder.

D5 A VTR format using the same cassette as D3 but recording component signals sampled to CCIR 601 recommendations at 10 bit resolution. With internal decoding D5 VTRs can play back D3 tapes and provide component outputs. Being an uncompressed digital component recorder, D5 enjoys all the benefits of D1, and in addition has provision for HDTV recording using 5:1 compression.

DCT (Discrete Cosine Transform) compression A widely used method of data compression of digital video. Picture information is resolved in blocks (usually 8x8 pixels) into frequencies, amplitudes and colours. JPEG depends on DCT.

Digital disk recorder Disk systems that record digital video. They are typically based on parallel transfer disk drives and offer short duration, around a minute or so, of recording time. They are often used as video caches to provide extra digital video sources for less than the cost of a digital VTR.

Digitizing time Time taken to record footage into a disk-based editing system. Digitizing time is frequently regarded as dead time. With good resource management systems this need not necessarily be so. New technologies are now able to reduce this time (e.g. Panasonic DVCPro and Sony SX).

Dissolve Visual effect performed on a vision mixer. In the videotape post-production environment it requires a three-machine edit suite.

Distortion An unwanted change in an electronic signal, resulting in unfaithful reproduction of audio and/or video signals.

Dropout A loss of picture information and syncs either upon recording or playback. Usually caused by dirt or clogged heads. Identified by white lines across or partly across the television picture or can be exhibited by parts of the reproduced image being filled with noise (black and white dots). Some video players will compensate by repeating the previous line.

Dropout compensator An electronic device that replaces the lost’ picture information from the previous scanning line. Most professional VTRs are equipped with a dropout compensator.

DT (Dynamic Tracking) or DMC (Dynamic Motion Control) Term used to describe the use of the ‘piez’ quartz videotape head to produce slow-motion and still frame effects of videotape recorders.

Dub To duplicate or copy audio or videotape masters.

DVE (Digital Video Effects) unit A picture manipulation device allowing both positional and size control of the picture. Some units offer both 2 and 3 dimensional control of the image.

Editing The selection and assembly of a series of scenes to produce a coherent sequence on film or tape.

EDL (Edit Decision List) A list of the decisions, defining a series of edits. Often recorded to a floppy disk. EDLs can be produced during an off-line session and passed to the on-line suite to control the conforming of the final edit.

Electronic Field Production (EFP) The use of portable high quality video recording equipment for on-location productions other than newsgathering.

Electronic News Gathering (ENG) The use of portable video cameras and recorders of high quality to record ‘on-the-scene’ news reports for television broadcasts. Typically these are now all done with camcorders.

FDD1 (Fibre Data Distribution Interface) A high speed fibre optic data interface operating up to 100 Mbits/s.

Field One half of a complete scanning cycle for a picture frame. Two fields are interlaced to form the one frame.

Field sequenceA television frame or picture consists of two fields. Each successive frame of component 525 and 625 line television repeats a pattern and so can be edited to frame boundaries – iike film editing. Composite video, coded as PAL, NTSC or SECAM, carries colour information on a sub-carrier whose cyclic pattern repeats over a longer period – 4 frames in PAL and 2 frames in NTSC and SECAM – known respectively as the 8 and 4 field sequence. An edit should not break this sequence, by its very nature a less precise operation than with component video. The restrictions apply whether the source is analogue or digital. CCIR 601 component digital signals can edit on any frame boundary while composite digital systems (e.g. D2 or D3 VTRs) are restricted to 4 or 8 field boundaries, otherwise picture hopping or quality changes (through additional processing) will occur.

FrameA complete television picture comprising two fields or a single picture from film.

Frame frequencyThe number of television pictures per second (30 in NTSC; 25 in PAL and SECAM). Also called frame rate or picture rate. For film this is 24 frames per second.

Freeze frameMotion that is stopped by tracking one field (in some cases a single frame) of video information continuously. Some systems can generate two field freeze frames. Most digital DVEs and nonlinear systems can offer both single-field or both-field freeze frames.

GenerationA stage in the duplication of a videotape.

Generation lossThe degradation caused by successive recordings or copying of the same material. Every recording or re-recording makes another generation of material (video and/or audio). Recordings straight from the camera are first generation; one re-recording makes the second, as in the first edit of camera rushes. This is a major consideration when working in analogue suites, but less of a consideration in digital suites. The best multi-generation results are possible with disk-based systems recording the uncompressed CCIR 601 signal. With compressed systems there is every chance that digital artifices will accumulate if compressed video crosses too many analogue-to-digital or even inter-coding boundaries.

GlitchA form of low-frequency interference. On a television screen, a glitch appears as a narrow horizontal bar that moves vertically through the picture.

GPI (General Purpose Interface)Usually a switch closure, allowing remote control of external devices on an exact frame. The GPI can be triggered by timecode, giving great accuracy.

GUI (Graphical User Interface)A means of operating a system through the use of interactive graphics displayed on a screen. Examples in the computer world are Apple Mac and Microsoft Windows.

Hard disks (fixed disks)Hard disk drives comprise an assembly of up to 10 rigid platters coated with magnetic oxide, each capable of storing data on both sides. Each recording surface has a write/read head, any one of which may be activated at a given instant. Hard disks give rapid access to vast amounts of data. Hard disk technology is moving very fast with ever-higher capacities becoming available in smaller packages at lower cost per megabyte. Currently for nonlinear editing, hard disk drives are supplied in 4 GB or 9 GB units or even up to 23 GB. Data transfer rates range from 1 to 10 MB/s (SCSI 2) up to 20 MB/s (SCSI Wide).

HDTV (High Definition Television)A television format with a new widescreen aspect ratio of 16:9 (the current is 4:3) and capable of reproducing much more detail (5 to 6 times more) than existing broadcast systems. HDTV should not be confused with widescreen variants of PAL (PALplus), NTCS or SECAM where the screen shape is changed but the quality improvement is small compared with HDTV. Currently there is no agreement for a world HDTV standard. The only consensus so far is that transmission for home viewing and contribution will be digital and compressed, using MPEG 2.

HeadA small electromagnetic transducer that reads, writes or erases magnetic signals on an audio or videotape. Video heads are usually in motion, while audio heads are usually stationary.

Headroom(1) Space that should be left between the top of a person’s head and the top of frame. (2) In audio, the available gain that could be applied without introducing distortion.

Helical scanA videotape recording system that uses one or two recording heads on a drum to write video information horizontally/transversely in long parallel slants across a tape wrapped in a helix around the drum.

InsertVideotape editing in which only the picture or audio information is replaced but the control track and timecode tracks remain untouched. To insert edit on a blank tape one must first record a control track with timecode, called pre-striping or blacking a tape.

Insert editingThe best editing technique to ensure flexibility in selecting tracks to edit on. As a tape editing process, vision, audio and even timecode tracks can be selected in any combination. Requires a pre-blacked tape which has control track, colour black and usually timecode.

ISDN (Integrated Services Digital Network)Allows data to be transmitted at high speed over the public telephone network. ISDN operates from a basic rate of 64 kbits/s up to 2 MB/s. In the television and film industries audio facilities are already using it and some companies have developed systems to allow the exchange of images between machines on a global basis using ISDN. A TV frame takes 2-3 minutes to transmit at the basic rate.

ITUThe United Nations regulatory body covering all forms of communication. The ITU sets mandatory standards and regulates the radio frequency spectrum.

Jam syncMethod of retaining the synchronicity of time-code when dubbing (copying of tapes) by using a generator to regenerate an identical timecode for the recording. Also should be used with cameras to provide continuous and sequential timecode even if the camera is stopped. Greatly assists in post-production.

JitterTimebase fluctuations in playback signals due to incorrect reading (or recording) of the control track. The picture quivers horizontally. Can also occur with playback from a hard drive.

JPEG (Joint Photographic Experts Group, ISO/ITU-T)A standard for data compression of still pictures. In particular its work has been involved with pictures coded to the CCIR 601 standard. JPEG uses DCT and offers compression of between 5 and 100 times. Three levels of processing are defined: baseline, extended and ‘lossless’ encoding. In general, compression can be expected to impose some form of loss or degradation to the picture, its degree depending on the algorithm used as well as the compression ratio and the contents of the picture itself.

Level(1) In video, the signal strength (amplitude) measured in volts. (2) In audio, sound volume measured in decibels.

LineA single trace of the electron beam from left to right across the screen.

Line frequencyThe number of lines scanned in one second. For PAL, 625 lines at 25 times per second = 15.625 kHz.

LoggingMaking a list of shots. This usually applies to recorded tape or film and can be vital for speeding up the selection of material for editing. This is especially true when going to a disk-based system where digitizing time can be a minimum. The list or log can be on paper or a computer floppy disk. When on disk great savings can be made during the digitizing process. Examples are media log and Phoenix log.

LTC (Longitudinal Timecode)Timecode recorded on a linear track on tape and read by a static head. This timecode can be read when the tape is moving forwards or backwards but cannot be read when the tape is stationary.

LuminanceA component, the black and white or brightness element, of an image. It is written Y, so the Y in YUV, YIQ, (Y, R-Y, B–Y) and Y, Cr, Cb is the luminance information of the signal. In a colour TV system the luminance is usually derived from the RGB signals, originating from the camera, by a matrix or summation of approximately: Y = 0.3R + 0.6G + 0.1 B.

Luminance channelA signal that is derived from the three chrominance channels to produce the basic black and white signal.

Match frameTerm used to indicate correct matching of source material back onto itself, having already been edited. For example, a shot already used in a programme needs to be re-edited back into the programme at exactly the same place so that a name super can be added.

MonitorA high quality television set without a tuner, used to display directly composite video or R, G and B signals.

MPEG 1 and 2 (Mowing Picture Experts Group, ISO/ITU-T)MPEG is involved in defining a standard for the data compression of moving pictures. Its work follows on from that of JPEG to add interfield compression, the extra compression potentially available through similarities between successive frames of moving pictures. MPEG 1 was originally designed to work at 1.2 MB/s, the data rate of CD-ROM, so that video could be played from CDs. However, the quality is not sufficient for TV broadcast. MPEG 2 has been designed to cover a wide range of requirements from VHS quality all the way up to HDTV through a series of algorithm ‘profiles’ and image resolution ‘levels’ with data rates generally between 2 and 10 Mbits/s.

NoiseAn unwanted electrical disturbance or random signal that creates extraneous sound or picture signal interference. In video, noise shows up on the TV screen as ‘snow’. Analogous to grain in film.

Nonlinear editingMeans of off-line editing using picture and sound information digitized to a hard drive computer system, e.g. Avid, Edit, Media 100 and Lightworks. More and more these systems are being used to finish the programme for transmission.

NTSC (National Television Standards Committee)Defined the 525 line 60 fields per second standard for television used in the USA and Japan.

Off-line (editing)A decision-making process using low-cost equipment to produce an EDL or a rough cut which can then be conformed or referred to in a high quality on-line suite. This cuts down the cost of a production by removing the decision-making from the expensive post-production environment. While in the past most off-line suites would enable the selection of shots and the defining of transitions such as cuts and dissolves, very few would allow the setting of DVEs, colour correction or keyers. The modern systems now offer these facilities, e.g. Avid, Edit, Lightworks, Quantel.

Omega wrapA configuration of videotape that has been wound around a helical scan drum. (See also Alpha wrap.)

OMFI COpen Media Framework Interchange)A specification for media interchange between a range of equipment. In principle OMFI is an open, public standard file format for digital media interchange between applications which supports video, audio, graphics, animation and CG. It will also contain all descriptive data representing all editing decisions, how media is organized and how a programme is to be played. It also offers multi-platform compatibility. A powerful concept that is gaining momentum, with several manufacturers now actively involved, e.g. Avid, AMS Neve, Digidesign, Studer, Synclavir.

On-line (editing)An edit suite where the final edit is performed in full programme quality. Being higher quality than off-line, time costs more. Preparation in the off-line will save time and money in the on-line.

PAL (Phase Alternating Line)The system devised in West Germany and Britain as one standard for 625 line 50 fields per second colour television.

Parallel transfer drivesThese are a variant of Winchester disks with enhanced electronics allowing each of the read/write heads to operate simultaneously. This allows data to be transferred to or from the disk at very high speeds (approximately 10 to 20 MB/s). With careful design and special interfacing, these drives can be used for random access real-time video storage.

PersistenceThe length of time a phosphor dot glows on a television screen or flying spot telecine: longer for the former, extremely short for the latter.

PixelThe name given to one sample of picture information. A shortened version of ‘picture cell’ or ‘picture element’. Pixel can refer to an individual sample of R, G, B, luminance or chrominance, or sometimes to a collection of such samples if they are co-sited and together produce one picture element.

Play backTo operate an audio or videotape recorder in a ‘read’ mode to give sound and/or picture images.

Post-dubbingThe process of adding a sound track to a recorded – and usually edited – videotape recording.

Pre-rollThe process of running two or more tapes in synchronization in preparation for an electronic edit. The pre-roll time is usually 5 seconds in Betacam edit suites. Some nonlinear edit systems also offer this capability, but it is not really an appropriate process within the nonlinear environment and performing a basic edit. However, there are situations where pre-roll does have its place in the nonlinear environment.

PTC (Piece to Camera) or StandupperUsed to describe a sync piece of dialogue spoken direct to camera. A favourite with journalists.

Quantizing (quantization)The process of sampling an analogue waveform to provide packets of digital information representing the original signal.

RAID (Redundant Array of Industry standard (or Inexpensive)Drives)A grouping of standard disk drives together with a controller to provide performance beyond that available from individual drives. RAIDs can offer very high capacities, fast data transfer rates and much increased security of data. The latter is achieved through disk redundancy so that disk errors or failures can be corrected or masked.

Random access (editing)The ability to read any frame at any time, with instant access and no restrictions on dubbing time during the actual editing process. Random access is a completely new way of working, freeing one from the restrictions of linear working.

RasterThe pattern formed by the scanning spot on the face of a cathode ray tube. It creates the illumination area of the tube.

ResolutionA measure of the finest detail that can be seen, or resolved, in a reproduced image. Whilst it is influenced by the number of pixels in an image (e.g. HDTV approx. 2000 x 1000, broadcast TV 720 x 576 or 720 x 487), the pixel numbers do not define ultimate resolution but merely the resolution of that part of the equipment. The quality of lenses, cameras, display tubes, film scanners, etc. used to produce the image on the screen must all be taken into account.

Resolution-independentTerm used to describe the notion of equipment that can operate at any or many resolutions. Dedicated TV equipment is designed to operate at a single resolution although some modern equipment can switch between the specific formats and aspect ratio of 525/60 and 626/50. Computers by their nature can handle files of any size so, when applied to imaging, they are termed resolution-independent.

Rotary erase headAn erase head incorporated into the rotating drum of a recorder. Essential for perfect electronic editing. Also called a flying erase head.

SamplingProcess applied to convert an analogue signal into a series of digital values.

Sampling standardA standard for sampling analogue waveforms to convert them into digital data. The official sampling standard for television is CCIR 601 (now known as ITU-R 601).

ScanOne horizontal electron beam sweep across a television camera target, picture tube or flying spot scanner. A scan is accomplished in 64 microseconds (PAL).

ScanningThe continuous movement of the electron beam as it scans across a cathode ray tube from left to right and from top to bottom.

SCSI (Small Computer Systems Interface)A high data-rate general-purpose parallel interface. A maximum of 8 devices can be connected to one bus, for example a controller and up to 7 disks or devices of different sorts – Winchester disks, optical disks, tape drives, etc. – and may be shared between several computers. SCSI specifies a cabling standard (50 way), a protocol for sending and receiving commands and their format. It is intended as a device-independent interface so the host computer needs no details about the peripherals it controls. But with two versions (single-ended and differential/balanced), many connector types and numerous variations in the level of implementation of the interface, SCSI devices cannot be ‘plug and play’ on a computer with which they have not been tested. Also with total bus cabling for the popular single-ended configuration limited to 6 metres all devices must be close together. Standard SCSI has a maximum data transfer rate of nearly 5 MB/s. SCSI 2 offers faster transfer rates (up to 10 MB/s) and an extended set of commands. SCSI Wide has a 16 bit bus allowing data transfers of up to 20 MB/s.

SECAM (Séquential Couleur à Mémoire)The French colour television transmisson system using 625 lines and 50 fields per second. Also adopted in eastern Europe.

Serial controlGenerally used to describe remote control of a device via a data line. The control is transmitted down the line in serial form, i.e. one control signal after another. Frequently used in the RS 422 form for control between VTRs, vision mixers and DVEs.

Serial digital interfaee (SDI)The standard based on a 270 Mbits/s transfer rate. This is a 10 bit, scrambled, polarity independent interface, with common scrambling for both component CCIR 601 and composite digital video and four channels of (embedded) digital audio. Most new broadcast digital equipment includes SDI, which greatly simplifies the installation of equipment and signal distribution.

ServoUsed to control the tape and head speeds from the control track pulses.

Signal-to-noiseThe ratio of the strength of a video signal (S) to the accompanying electronic interference (noise, N). The higher the S/N ratio (more signal, less noise) the better the quality of the resulting sound or video. S/N ratios are expressed in dB.

Still pictureProduced when the tape is stopped and the video heads are made to play back the same tracks on the tape continuously. On most player/recorders there is a loss of resolution in the reproduced picture. Still frame should not be left on for too long or tape damage/head wear will be accelerated. Most recorders have a pre-set shut-down time at which point tape tension is reduced round the heads to prevent these problems. On digital recorders it is strongly recommended that the tape be removed from the transport when not being used. This is due to the very small size of the head gap of digital recorders, and there is a possibility on some digital machines that the video head drum will not spin down until tapes are removed.

Striped tapeA term used to describe videotape pre-recorded with colour black and burst. The tape will have a continuous control track and uninterrupted timecode recorded along its entire length. This is the tape that would be used in the recorder for insert editing.

SyncShort for synchronization. The electronic pulses (vertical and horizontal) that synchronize the scanning in a camera, VTR or flying spot telecine with the scanning in a monitor. The sync pulses can be derived internally, i.e. from the video signal, or externally from a sync generator.

Sync pulseThe electronic pulse produced by a sync generator and entered into the video signal during the blanking interval to ensure exact synchronization.

Sync signalA series of sync pulses is the composite video signal.

Talking headA single shot of someone talking. Usually used to describe interviews or PTCs (Piece to Camera).

TapeAn audio or video recording medium consisting of a polyester or mylar base, a binder, and a suspension in the binder of magnetizable particles such as ferric oxide or chromium dioxide. The tape is approximately 25 microns thick. Standard widths are ¼″, 8 mm, ½″, 3/4″ and 1″. Modern digital formats go down to 6 mm in width.

Tape speedThe rate at which tape passes over the fixed head (audio) of a recorder. The rate differs from format to format.

TerminationA load inserted to a transmission line used to keep the signal from bouncing back (reflections) along the line. In video, the terminator is a 75 ohm resister and must be inserted or switched in at the end of a video chain. Also used to end the chain of SCSI hard drives on nonlinear edit systems.

TimecodeA digital signal recorded onto tape providing a reference for all frames recorded on that tape. The reference provided is in units of hours:minutes:seconds:frames (note that in the PAL TV system there are 25 frames per second). After the invention of the videotape recorder, timecode was the next most significant development. It provides two vital elements to post-production: accuracy and repeatability.

Tracking(1) The angle and speed at which a video head passes across the tape. (2) The accuracy with which a playback head follows the correct recording path across the tape.

U-maticTrade name for the 3/4″ videocassette format developed by Sony Corporation. Available in three formats: High Band SP and High Band used for broadcast and Low Band used in educational and industrial applications. Now largely a redundant format with the arrival of low budget Beta SP and semi-pro digital formats.

VapourwareSoftware or hardware that is promised or talked about but is not yet completed – and may never be realized.

VCRVideocassette recorder or video cartridge recorder.

VectorscopoAn electronic display device, similar to an oscilloscope, used to visually measure the amplitude and phase of the R, G and B television colour signals.

VideoThe picture and sync pulse portions of a television signal. Often used to refer to the recording of television pictures.

Video headThe recording or playback head which transfers the video signal to and from the tape.

Video signalTelevision picture frequencies ranging from 0 up to 5.5 MHz. It is an amplified signal containing picture information, sync and blanking pulses.

VITC (Vertical Interval Timecode)Timecode data in digital form, integrated as part of the vision information on tape. This can be read by the video heads at any time that pictures are displayed, even during jogging and freeze but not during spooling. This complements LTC, ensuring timecode can be read at all times there is head (audio/video) to tape contact.

VTR (Videotape Recorder)The electromechanical device used to record television images, audio signals and control information on magnetically coated tape. Also used to play back for viewing or editing.

Waveform monitorAn oscilloscope used to analyse and adjust television signal characteristics visually. Usually displays the R, G and B signals separately on the same screen. Can also display full coded PAL signal sometimes useful in the editing suite for an overall picture of signals as they will be replayed.

WinchesterA particular form of hard disk which has several disk platters and their associated heads sealed in a dust-free enclosure. It offers high reliability and a high data-packing density.

WipeVisual effect performed on a vision mixer. Most mixers offer over 30 different wipe patterns, most with border or softness as additional controls.

WORM(1) Write Once/Read Many – a type of storage device on which data once written cannot be erased or rewritten. Being optical, WORMs offer very high recording densities and are removable making them in some applications useful for archiving. WORMs have not made a significant impact in the post-production world, mainly due to the slow transfer rates currently available for the optical WORMS. (2) Type of virus, found on Macintosh computers.

Writing speedThe relative speed between the heads and the tape during recording and playback. In audio where the heads are fixed the speed of the tape is the writing speed. In video the speed of the heads rotating on the periphery of the drum is virtually the writing speed. The relationship of writing speed and head gap determines the maximum frequency recordable and played back.

Y, (R-Y), (B-Y)Analogue luminance, Y, and colour difference signals (R-Y) and (B-Y) of component video. Y is pure luminance information and the two colour difference signals are the colour information. The signals are derived from the original RGB source. The Y, (R-Y), (B-Y) signals are fundamental to much of television. For example, in CCIR 601 (or more correctly ITU-R 601) it is these signals that are digitized to make 4:2:2 component digital video and in PAL and NTSC TV systems they are used to generate the final composite coded signal. When digitized, the convention is to designate the signals as Y, Cr, Cb.

Z axisThe third dimension of the three-dimensional world. The Z axis is at right angles to the Xand Y axes. A control offered on 3-D picture manipulation devices.

ZitsSlang for short-term errors in digital recordings.