A dictionary for the language of digital media production.
Alpha channel: A computer generated keying channel for 2D and 3D graphics and video applications. A keying channel implies the “clear” part in which no signal or data exists, allowing the existing signal or data to be laid over another channel.
Amplifier: An electronic device for increasing voltage and power of a video or audio signal. Types of devices include microphone preamps, mixing booster amps and distribution amplifiers.
Anti-aliasing: Smoothing of aliasing effects by filtering and other techniques in computer applications. Aliasing is an effect generated when horizontal or diagonal lines in computer and video displays have noticeable “stairstepping” or “jaggedies” by display resolution detail being too low.
Aperture: See Iris
Aspect ratio: The relationship of horizontal and vertical dimensions in image displays. Computer and video displays have an aspect ratio of 4:3; film has an aspect ratio of 16:9, which explains the technique of “letterboxing” or “pan and scan” that is necessary for film to be converted to video.
Back focus: Adjustable portion of the lens on industrial and broadcast cameras that may determine the rear of the focal depth. See focal depth.
Balanced: Circuitry that causes the audio signal to swing plus and minus of the system’s ground reference. Noise induced into both wires of a cable run will cancel at the input of a balanced device.1
BNC: A round, metal, locking cable connector found on composite, component, and YC video cables, as well as computer network cables.
Character Generator (CG): A computer system for providing electronically generated graphics and titles of various sizes and forms.
Increasingly replaced by desktop computer systems.
Chroma keying: A keying channel in which the range of signal, to be overlaid or dropped out, is defined by a specific color, usually blue or green. The color must be uniform throughout the keying range for successful overlay to occur. See alpha channel.
Clearcom: A brand name for two-way headset communication systems used in live electronic media productions. Individual units consist of headsets, belt packs, and a cable, with one central base receiver for each chain.
Clipping: A harsh form of audio distortion in which a signal’s
waveform is flattened by a system’s inability to deliver
any higher voltage.2
Color bars: Video test signal consisting of a series of vertical bars of fully saturated color: white, yellow, cyan, green, magenta, red, blue, black. Used to adjust brightness, contrast, hue, and chrominance of monitors and projection systems.
Color corrector: Circuitry that can pinpoint a small band of the color spectrum, with minimal effect on other colors in the spectrum. Will adjust the gain (amplification), black level, and gamma (tonal contrast) of the separate red, green, and blue channels in component video.
Color temperature: The temperature of light affects its color. Although the human eye compensates for this phenomenon, a camera lens does not, which dictates the need for white balancing and color filters. Typically, daylight color temperature is > 5500°K, and tungsten, or incandescent, light is 3200°K. Some newer cameras make automatic digital adjustments for changes in color temperature.
Component video: A video signal in which luminance and chrominance are separated into three colors: red, green, and blue, with the addition of a separate sync pulse.
Composite video: A video signal in which luminance, chrominance, and sync pulses are combined. Composite cable features BNC, or RCA, style connectors.
Compression: The removal of data from a signal, used primarily in computer applications, in which bandwidth considerations must be taken into account. Common compression schemes include JPEG, TIF, AIFF, WAV, MotionJPEG, H264, and MPEG 1, 2, 3 and 4. Compression removes like data based on user-defined keyframes, or snapshots taken of the signal. It works well on video signals that do not change their subject point often, such as “talking heads.”
Compressor/limiter: A device that reduces input gain on audio signals as that signal increases. Limiting is infinite compression, in which output levels remain the same regardless of the amount of gain given to an input signal. Most units may adjust the point at which audio signals become compressed or limited.3
Control track: A linear track recorded onto videotape at frame frequency as a reference for the running speed of a videotape recorder and for the positioning of video tracks. The videotape equivalent to sprocket holes in the edges of film. Not used on computer-based media files.4
Decibel: Measurement system for the loudness of an audio signal; expressed in dB. Decibels are measured exponentially, not incrementally; sustained exposure to 85db or greater may cause hearing damage.
Digitize: The encoding process that translates an analog video signal into digital form (1s and 0s), for purpose of manipulating in the digital realm.
Director: Leader of the live event crew; gives commands for operation.
DV: Digital video (DV) is a video format that records digital data onto traditional magnetic tape. Variants include DVCPro and DVCAM.
DVD: Digital Versatile Disc, a video playback format utilizing the same laser technology that compact disks employ along with MPEG compression. A popular consumer format for film rentals, and still the best low-cost optical medium for data archival.
Filter wheel: Function on some industrial and broadcast field cameras that compensates for variation in Kelvin temperature. Typically, setting one is for indoor light, two for sunny days outdoors, and three for overcast days outdoors. Newer cameras may make this adjustment automatically.
FireWire: Data transmission technology developed by Apple Computer to transfer data from digital videotape to computer hard drives. Technically known as IEEE 1394.
Focal Depth: The distance within which a frame’s subject is in focus. Varies depending on the distance of the subject from the camera, the focal length, and the aperture. The more open the iris is (smaller f/stop #) the more shallow the depth of focus.
Focal length: The relative position of the zoom (wide or telephoto).
Frame: The entire rectangular area within the eye of the camera, or what the camera sees. Aesthetically used to describe the collection and composition of all objects within the visible area of the lens. Also a single still image of video (1/30th of a second) or film (1/24th of a second), or the space within which a graphic image is produced in design.
Frequency: Expressed in Hz, the number of vibrations of a sound wave per second. The range of the human ear 20Hz to 20,000Hz is considered the standard for audio production.
Gain: Artificial supplementation of the luminosity of the video signal through the addition of decibels of video signal. Creates brighter images while forsaking quality (creating noise).
Gate: A device that turns on an audio path when a signal is present and turns it off when a signal is absent. User adjustable.
Generations: Number of times that an original video source has been copied or duplicated onto another source.
HDTV: High-definition TV. Original broadcast color television standards of 525-lines of interlaced picture resolution were fashioned largely by the need to provide systems compatible with then existing black and white services. High-definition television converts this standard from analog to digital and approximately doubles the number of real-world lines of resolution. Standards include 720 progressive, 1080 interlaced, and 1080 progressive.
Hue: The predominant sensation of color; e.g., red, green, blue. Te hue is an adjustable setting on most display units in digital media, in a scale of red to green.
Iris: The ring of a camera that determines the amount of light given to an image. The more open it is (smaller f/stop #), the more light is let into the camera.
JPEG: Common compression scheme for computer graphics; the standard for Internet use. MOTION JPEG is a standard for video, as well.
Kelvin scale: Temperature measurement system used in video for determining the color of light. The higher the Kelvin color, the hotter (more blue) the light is.
Linear Editing: A sequential style of video editing in which video is copied form one analog source to another. Results in generation loss and an inability to modify completed sequences.
Lines of resolution: Standard definition NTSC television makes video by creating 525 horizontal lines 30 times every second (frame), through a method of interlacing in which every other line of a frame is drawn in one-sixtieth of a second.
Luminance: The true measure brightness of a surface. For example, snow has high luminance, reflecting 93-97 percent of the light falling on it, but black velvet has low luminance, reflecting approximately one percent of light falling on it.
Medium: A communication form, including oral, print, or electronic, through which messages are sent and received. All communication occurs through a medium or media.
Moore’s Law: The dictum that computer memory and processing speed doubles every two years. This has basically held true since 1967, when Gordon Moore made this marketing (economic) prediction at Intel.
MPEG: Data compression scheme, with many revisions. MPEG-1 is oldest but remains a common Internet format; MPEG-2 is the standard for DVD; MPEG-3 is the common format for audio. MPEG-4 is a much-improved video format.
Multi-camera: A type of video production using multiple cameras simultaneously by composing shots with instantaneous switching between camera sources. Usually limited to studio and live event productions, including worship services and news broadcasts.
Noise: Spurious information interfering with a signal.
Noise reduction: Generally refers to a multiband gating device that attenuates an audio signal when it is below an established threshold. Used to reduce hiss and pop in a signal to a point that desired frequencies become dominant.
Non-linear editing: A non-sequential style of computer/digital video editing, where it is possible to edit out of time. Without generation loss
National Television Systems Committee (NTSC): A broadcast group that established the North American video standard of 525 horizontal lines of resolution in 1952. Concessions in quality were made at the time to accommodate existing black and white technology. Also referred to as “Never Twice Same Color.”
RGB: Acronym for red, green, and blue, the basic color scheme of television and computer displays.
Router: A device through which multiple image sources may be sent to a single output, usually a switcher. Useful with smaller switchers having limited input options.
Rule of thirds: A “tic-tac-toe” shaped grid that is a common method of determining effective frame composition
Saturation: The extent to which a color has been diluted with white. If a hue is pure and undiluted, it has 100 percent saturation.
Signal-to-Noise ratio: Abbreviated as S/N and expressed in decibels, the ratio of noise to pure signal information.
Single camera: A style of video production dependant on editing, in which one camera created all source material. Used in most films.
Switcher: Device receiving inputs from various sources and mixing to a primary output.
Sync Pulse: Timing reference in video, which keeps frames moving steadily at 30 frames per second.
Talking Head: Footage of a person creating a voiceover track during a video segment. Avoid too much of it!
Technical Director: Switcher operator. Takes commands from director.
Time Base Corrector (TBC): Circuitry used to insert accurate sync pulses when incoming sync pulses are lost or distorted. In other words, makes live video feeds smooth when they would otherwise jerk or drop out, removing jitter on videotape playback and correcting color errors. A primary difference between amateur and professional video.
Unbalanced: Audio circuitry that connects one wire of an audio path to the system ground. Cables are highly susceptible to noise pickup; unbalanced cables provide no defense against this possibility.
White balance: Mechanism/action that determines white and black points. All other colors are determined from this luminosity.
