Glossary
Aspect Ratio
The shape of a video frame, independent of pixel count. Mismatched ratios force a choice between stretching, letterboxing and cropping.
Clipping
Distortion caused by a signal exceeding what a stage can carry. It cannot be undone later in the chain — the detail is gone at the point it happened.
DI Box
Direct Injection box. Converts a high-impedance instrument output into a balanced signal that can run a long distance to the stage box without picking up noise.
DMX512
The control protocol most lighting fixtures speak. One universe carries 512 channels down a single cable, and each fixture listens to a run of them starting at its address.
FOH
Front of House. Both the audience area and the mix position that serves it, as distinct from the monitor position serving the performers.
Feedback
The howl produced when a microphone hears the loudspeaker reproducing that same microphone, and the signal loops and builds. Broken by distance, direction, level or EQ.
Focus
The process of aiming and shaping each fixture once it is hung. Also the sharpness of a profile fixture's projected edge.
Gain
How hard a signal is driven into the system at the preamp, before any mixing. Distinct from a fader, which sets how much of that signal reaches the mix.
Gel
A coloured polyester sheet placed in front of a fixture to filter its output. Subtractive — it removes everything except the colour that passes through.
Get-In
The load-in period before a show, when everything is unloaded, rigged and focused. Its counterpart at the end is the get-out or load-out, where fatigue-related incidents cluster.
Gobo
A cut or etched pattern placed in a profile fixture's gate so the beam carries that shape. Most often used to add texture to a flat wash rather than to project a recognisable image.
Headroom
The unused range between normal operating level and the point at which a signal clips. It exists so the loudest unplanned moment of the show still fits.
MBS
Minimum Breaking Strength. The load at which an item is expected to fail. A test figure, never an operating one; the WLL is derived from it by dividing by a safety factor.
Monitors
Loudspeakers or in-ear systems that let performers hear themselves. Mixed separately from the audience mix, because performers need a different balance.
Native Resolution
The actual physical pixel count of a display. Feeding exactly this avoids scaling, which is the sharpest a display can be.
Noise Floor
The constant low-level hiss present in any system. Setting gain too low means amplifying this along with the signal later.
Patch
The console's map of which DMX addresses belong to which fixture. An unpatched fixture responds to nothing; a mispatched one responds to the wrong instruction.
Phantom Power
48V sent up a microphone cable from the console to power condenser microphones and active DI boxes. Harmless to most gear, but switch it off before patching.
Pixel Pitch
The distance in millimetres between the centres of adjacent LEDs on a video wall. Smaller pitch means the audience can stand closer before seeing individual dots.
SDI
Serial Digital Interface. Professional video over coaxial cable with a locking BNC connector, favoured on site because it survives long runs and being walked on.
Scaler
A device or process that converts a video signal from one resolution to another. Necessary, but every scale either invents detail or discards it.
Shackle
A connector joining two pieces of rigging. Bow shackles tolerate loads from several directions; dee shackles want a straight in-line pull.
Shock Load
A sudden force from something starting, stopping or falling. Can momentarily impose several times the static weight, which is why nothing near its limit should be moving.
Universe
One complete set of 512 DMX channels. Rigs larger than 512 channels use multiple universes.
WLL
Working Load Limit. The maximum load a piece of rigging hardware may carry in service — the only figure you work to. Not to be confused with breaking strength.
Wash
A fixture, or a look, providing soft even coverage over a wide area. The opposite of a spot, which isolates.