A glossary of terms covering lighting, audio, vision and staging in the event and theatrical industry.
There can be a number of meanings for some terms which can vary from country to country and manufacturer to manufacturer. Information within this guide is indicative and every situation can require a different approach and solution. All care has been taken, however, Image Group NZ accepts no responsibility for inaccuracies. If you have any suggestions, comments or queries regarding this list please contact us.
Comparing the performance of two or more models of equipment, such as amplifiers or speaker systems, by listening and switching quickly from one to the other.
The ability of a room to take up or absorb the acoustic energy radiated within it. There are many types of absorption since it can be frequency dependent. There are certain materials such as acoustical ceilings that may absorb more high frequencies than lows. Diaphragmatic absorptions (caused by loose wall panels or cavities behind the panels) cause certain low frequencies to be absorbed.
Short for ALTERNATING CURRENT.
Relating to the production, effects and transmission of sound waves; the transmission of sound waves through various mediums. Pertaining to the act or sense of hearing, the science of sound, or the sound heard.
Sound or properties of sound; the acoustical response of a room has to do with the way that room responds to sound.
The application of acoustic or sound absorbing material to a room or enclosure to obtain the desired acoustic characteristics.
A type of electronic circuitry that can increase the gain or amplitude of a signal. Active gain controls. Active Equalization. Active Direct Boxes. Active Crossover.
ACTIVE MATRIX TFT
The most common type of LCD used in most laptops and projectors. A typical active matrix TFT display is a single panel of LCD glass that controls all three primary colours. TFT displays are noted for their quick response time and ability to display full motion video and animations without image ghosting.
A connector which allows two or more electrical devices to be connected to a single power outlet. The connection is normally parallel, that is, each device is fed the same voltage, but the current is divided between them.
ADDITIVE COLOUR MIXING
See COLOUR MIXING.
Assistive Listening System. This term refers to systems used to augment the regular sound system to allow hearing impaired persons to more clearly hear. These can be either hardwired (earphones) or wireless (inductive loop, FM, infrared). The FM and infrared wireless systems are most common and allow the user to have individual control of the listening volume.
(amp) Named after Andre Ampere (1775-1836), French scientist. A unit of measurement of electrical current (I). One amp of current represents 6.2818 x 10 electrons flowing past a given point in one second, and is equal to one coulomb.
An increase in signal magnitude from one point to another, or the process causing this increase.
A device capable of increasing the gain (magnitude) or power level of a voltage or current that is varying with time (frequency), without distorting the wave form of the signal. An amplifier is used to increase weak signals (such as those from a program source) to a level sufficient to drive loudspeakers.
A physical variable which remains similar to another variable insofar as the proportional relationships are the same over some specified range. The electrical signal produced by a microphone is an electrical analog of the acoustic sound that the microphone is reproducing. The continuous electrical signal that the microphone produces varies in voltage and frequency as a direct correlation to the nonelectrical acoustic information impressed on the transducer. The electrical signal is analogous to the acoustical sound that the microphone reproduces, i.e., the voltage that the microphone produces is the electrical analog of the acoustic sound source.
The way information is transmitted over a continuously changing electrical wave that is similar to, or analogous with, the original signal. A continuously variable signal that can have any value over a given range.
In lighting: an analogue voltage within the range 0 to 10 Volts can have values of 0, 2, 8.785 or any value between. Most dimmers require an analogue voltage in order to operate (from 0 to -10V or 0 to +10V depending on the manufacturer). Most lighting control desks produce a digital multiplexed output, which is converted by a demux box to an analogue signal for the dimmer. See also DIGITAL DIMMER.
Sound: An analogue recording will record the exact waveform of the original sound, simply converting it to an electrical signal at the microphone, and back into air movement at the speaker. See DIGITAL.
Refers to a room in which all surfaces are lined with acoustic absorption material to such an extent that the room absorbs sound energy instead of reflecting it around the room (no echo). A room that offers nearly total absorption is called an Anechoic Chamber and must be quite large in order to accommodate low frequencies.
A standard for measuring light output that is used to compare projectors. Unfortunately, there are enough variables that the eye will often disagree radically with the ANSI rating. At best, ANSI lumens do fairly well comparing "apples" to "apples". If however one projector uses Halogen lamps and another metal-halide, the halogen projector will seem noticeably dimmer even if the two units rate the same. Other variables, including type of LCD technology (active matrix TFT, Poly-Si, passive), type of overall technology (LCD vs. DLP vs. CRT), contrast ratios, etc. all effect the end result.
Originally Ante Proscenium, meaning in front of the proscenium.
See DISCHARGE LAMP.
A type of linear filament lamp with contacts at 90 degrees to the filament which can gives the appearance of a continuous line of light (similar to neon, but dimmable).
The most popular aspect ratio is 4:3 (4 by 3). Early television and computer video formats are in a 4:3 aspect ratio, which means that the width of the image is 4/3 times the height. Other formats are 5:4 used by the 1280x1024 SXGA resolution, 16:9 used by HDTV, and 3:2 for 35mm slides.
Aspect ratio of 4 units wide by 3 units high can also be described as 1.33 aspect ratio (i.e. width is 1.33 times height).
A decrease in signal magnitude from one point to another, or the process causing this decrease.
An adjustable passive network which reduces the power level of a signal without introducing any appreciable distortion.
The order of sequence for connecting audio components, i.e. microphone, preamplifier (mixer), effects device, graphic equalizer, crossover, amplifier, and speaker.
Any frequency corresponding to a normally audible sound wave.
20 Hz to 20,000 Hz. (Twenty cycles per second to twenty thousand cycles per second). The frequency response spectrum of human auditory perception.
A system for detecting errors in colour balance in white and black areas of the picture and automatically adjusting the white and black levels of both the red and blue signals as needed for correction.
AUTOMATIC GAIN CONTROL (AGC)
A process by which gain is automatically adjusted as a function of the input level or other parameter. A device used to automatically control the level of a sound system based on the input level.
See MOVING LIGHT.
AUX INPUT / AUX OUTPUT
An auxiliary input or output that is generally a direct connection to the device's internal signal bus. These are used to interconnect devices which have the same signal level. That is, where gain is not required such as when connecting a microphone to a mixer. Typical devices that operate at "aux level" are tape decks, CD players, equalizers, signal processors, etc.