Glossary of Terms - R

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.


System whereby battery-powered practicals / props on stage can be controllable from offstage with no connecting leads.

Residual Current Device. Protects the user against short circuit (earth faults) and earth leakage caused by damaged cable or faulty equipment. A RCBO is a combined MCB and RCD, protecting against earth leakage/short circuit and overload. Known as a GFI (Ground Fault Interruptor) in the USA.

Remote Device Management. New lighting control protocol (officially ANSI E1.20 standard) currently under development at ESTA, which allows two-way communication over standard DMX512 cable. See also MULTIPLEXED SIGNAL.

To change the lighting rig after the last performance of one show to the positions for the next show.

A resistive like property that offers opposition to electron flow in an alternating current (AC) circuit. There are two types of reactance; capacitive reactance (XC) and inductive reactance (XL). Reactance varies with frequency.

An electronic instrument used to measure the combined response of an audio system and the room in which the system is operating.

Using an opaque screen, the projector is placed behind the screen, invisible to the audience. The image projects onto the screen which the audience sees on the other side. Good rear projection screens actually produce brighter images than some standard screens. A projector with a short throw lens is typically used to accommodate the lack of space behind the screen. Since the projector can be placed at the ideal height, without blocking anyone's view, keystoning is not a problem. Some mid-room projectors have available 3rd party short throw lenses. Since the image is projected through the screen, the image must be reversed.


    O dB - In the measurement of SPL or Sound Pressure Level, 0 dB is referenced to the threshold of hearing or auditory perception of a tone of 1000 cycles (hertz) per second (1 kHz). 0 dB must always be referenced to some base of measurement. In gain functions 0 dB is unity gain (1).
    3 dB - The amount of SPL gained by doubling the power to a speaker. Also the amount gained by doubling the number of speakers.
    +/- 3 dB - Plus or minus 3 dB as used to express a measurement of frequency response indicates that the response will be no more than +3 dB and no less than -3 dB below a given reference. It is actually a 6 dB window. The Response of 60 Hz to 14 kHz +/-3 dB means that within the bandwidth of sixty cycles per second to fourteen thousand cycles per second, no frequency is +3 dB more nor -3 dB less than a specified reference frequency.
    3 dB DOWN (-3 dB) - The point at which a measured power level is 3 dB below the specified level. In an electronic crossover, the point (frequency) at which the high pass signal is -3 dB down in response or power level is considered the crossover point (frequency).
    -6 dB - The amount of loss in SPL as you double the distance away from a sound source.
    dBm - A decibel scale referenced to 0 dBm = 1 milliwatt of power into 600 Ohms or .775 volts RMS across 600 ohms.
    dBu - Primarily a British term for gain referenced to 0 dBu = .775 volts RMS.
    dBV - A decibel scale referenced to 1 volt RMS; 0 dBV = 1 volt.
    dBW - A term for power gain referenced to 0 dBW = 1 Watt.

The volume which yields a reading of 0 VU on a standard volume indicator.

The bouncing back or return of sound waves from walls or other obstacles which they strike.

A change in direction or bending of the propagation of a sound wave when it passes from one medium to another in which the velocity of sound is different.

An ergonomic issue that is directly related to long-term ease of use. A higher refresh rate translates to a more "flicker" free display on a CRT. Bandwidth and horizontal and vertical scanning rates depict a projector's ability to provide a higher resolution and refresh rate.

In audio, regeneration is another word for feedback; when something regenerates it continues or sustains itself as an oscillation. When an electronics engineer designs an oscillator, he takes the output of a gain stage and feeds it back into the input through a tank circuit (an RC, resistor and capacitor or an LC, inductor and capacitor combination); when the circuit is turned on it begins to regenerate or oscillate at a specific frequency determined by the value of the RC or LC combination. When the output of a loudspeaker in a sound reinforcement system is able to get back into a microphone or sound system input, at some level and resonant frequency, the system is going to go into regeneration or feedback oscillation (squeal).

Opposition to the flow of electrical current. Measured in ohms.

A now obsolete method of dimming which decreases the current available to the load by introducing a variable resistance between supply and load. The excess current is converted into heat. Based around a rheostat.

An electronic component designed to have a definite amount of resistance; used in circuits to limit current flow or to provide a voltage drop.


    The point during a drama when the plotline reaches a conclusion, and conflict is resolved.
    The quality of a sound sample is measured by the sample rate (e.g. 44.1kHz is CD quality sample rate) and the resolution (either 8 bit or 16 bit normally).
    A measure of the quality of a video display. The density of lines and dots per line, which make up a visual image. Usually, the higher the numbers, the sharper and more detailed the picture will be. In terms of DTV, maximum resolution refers to the number of horizontal scanning lines multiplied by the total number of pixels per line, called pixel density.

A tendency of mechanical parts, loudspeaker cone, enclosure panels or electrical circuits to vibrate at or emphasize one particular frequency, every time that frequency, or one near it, occurs.

The range of frequencies to which an amplifier or speaker will respond, and the relative amplitude or intensity with which these frequencies are reproduced.

A cue to resume or return to any previous state, setting or function. (e.g. "at the end of the dance number we restore to a warm general cover").

A modification that can be made to an existing piece of equipment after purchase to bring it up to date.

An input, typically found on a mixing console, used to patch a signal returning to a particular BUS after having been further processed, such as an echo or effects return.

The prolongation of sound at a given point after direct sound from the source has ceased, due to such causes as reflection from physical boundaries. (Electro-mechanical) An electro-mechanical device usually employing springs which randomly reflect as great amount of sound as possible, therefore simulating natural reverberation. (Digital Reverb) An electronic reverberation effects processor that uses digital electronics to introduce the multiple delay paths.

The sustaining of acoustical energy in a room after the reception of the direct field (the sound coming directly from the source) ceases in producing sound. Reverberation is caused by the reflections and scattering of sound energy from the boundary surfaces of the room.

Reverse image is a feature found on most projectors which flips the image horizontally. When used in a normal forward projection environment, text, graphics, etc, are backwards. Reverse image is used for rear projection.

Remote Focus Unit. Name used by ETC for a remote control for the lighting desk. Same as RIGGERS CONTROL.

Red, Green, Blue; the standard type of monitor used with computers. Examples of usage: RGB input or output often referred to as computer input or output.


    The construction or arrangement of lighting equipment for a particular production.(noun)
    Installing lighting, sound equipment and scenery etc for a particular show.(verb)

(also known as LAMP CHECK) The process of checking all lanterns in the rig are working correctly prior to each performance. Should be done daily in sufficient time to change a lamp if necessary.
Most venues do not have the electrical capacity to run all lanterns at full for a rig check, so a level of 25% is normally used.
N.B. this is NOT the same as preheating - a rig check happens before each performance and involves the whole rig, and preheating involves individual lanterns/dimmers and happens before a cue in which that lantern appears.

A remote control for a lighting desk which enables dimmer channels to be called up from the stage when rigging or focusing. Usually battery powered, sometimes with infra-red (cordless) control. A Designers Control allows whole memories to be called up and/or played back, as well as individual dimmers.

A tone or frequency sounded in a room with a live sound reinforcement system prior to the system breaking into feedback. A ring mode lies just below the threshold of feedback.

The square root of the time average of the square of a quantity; for a periodic quantity the average is taken over one complete cycle. RMS voltage is .707 times the peak voltage of a sine wave.

A signal is rolled off when it is attenuated or reduced in level above (high pass roll off) or below (low pass roll off) a certain frequency. The amount of roll off is rated at so many decibels per octave. A signal that is rolled off below 100 Hz at a rate of 18 dB/octave would be reduced in level or attenuated -18 dB at 50 Hz, -36 dB at 25 Hz, etc.

The time required for sound to drop to - 60 dB in level once the source of sound has been stopped. The -60 dB is below that of the measured level while the sound system was on and after any initial transients or fluctuations settled.

A plot giving details of the changes between cues, as distinct from a state plot which gives the whole state of the system at any time. For example, a lighting plot on a manual board is normally a running plot. It is difficult to start a running plot half way through; often the operator has to go back to the beginning and work through until the required point is reached. However, it contains the minimum information necessary to perform the cues, and is therefore more efficient on a manual lighting desk or complex sound setup.


Production & Styling Services for
events, functions and weddings

154 Fairs Road | Palmerston North
06 354 4421