GLOSSARY
A glossary of live show visuals: the vocabulary used on a show floor
31 terms, grouped by the department that uses them. Every group links to the page where those terms are used in context rather than defined in isolation.
How this vocabulary got its shape
borrowed first, defined later
Live visuals borrows most of its vocabulary from older trades. Rigging and lighting supplied the words first and the video department arrived into a room where the language already existed, which is why a video engineer talks about hang points and palettes.
The entries below are written the way the terms are actually used on a show floor, not the way a manufacturer defines them in a specification.
Where the same word means two things to two departments, both are given. That is not pedantry: most of the arguments documented across this site start as one, and the design and running halves of the craft frequently use the same term for different objects.
- Throw ratio
- Throw distance divided by image width. A property of the lens, not the projector body; change the lens and every position on the drawing changes. Calculator.
- Keystone
- Correction for a projector that is off-axis to a flat surface. It squares up a single trapezoid and assumes the surface is flat, which is why anything more interesting needs a mesh instead.
- Mesh warp
- Subdividing the projected image into a grid and moving each vertex independently, so the picture can be pushed onto curves, folds and compound angles.
- Edge blend
- Ramping the brightness of two overlapping projectors down through their overlap so their sum stays constant and the seam does not read as a bright band.
- Mask
- Removing the parts of a projected image that would otherwise spill onto structure, floor or audience.
- Registration
- Whether the projected image sits exactly where the geometry says it should. Registration marks left visible in a test pattern are how it is checked.
- Pixel pitch
- Centre-to-centre distance between adjacent diodes, in millimetres. Smaller pitch is more resolution, more weight, more power and more money. Calculator.
- Moire
- Interference between the regular grid of the wall and another regular grid, usually a camera sensor. It cannot be fixed at the wall; it is managed at the camera or in the content.
- Volumetric
- Distributing LED elements through depth rather than across one plane, so the picture has real parallax instead of a rendering of depth.
- Nit
- A unit of brightness. The number that decides whether a wall reads in daylight at a festival or disappears.
- Processor
- The hardware that takes a video signal and maps it onto the physical arrangement of panels. A wall is not a screen until the processor says what shape it is.
- Truss
- Modular structural steel or aluminium, assembled from short members, from which almost everything above a stage is hung.
- Load path
- The route a weight takes from the object being hung down to the ground or up to the building steel. Every element has a rating and the weakest one governs.
- Span
- The unsupported distance between two truss supports. Capacity falls off sharply with span, so wide clear spans are expensive in a way no rendering shows.
- Hang point
- A location in the venue structure rated to take a load. Their number and position constrain the design more than any aesthetic decision does.
- Load-in
- The process of getting the rig into the venue and built. The clock everything else is measured against.
- VJ
- The person playing the visual picture live: selecting, layering and cutting in response to what the musicians are actually doing.
- Clip bank
- The grid of material available during the show. Organised by energy and function rather than by name, because at showtime nobody reads.
- Tempo lock
- Tying clip playback speed to the music’s beat, so material cut at one tempo stays in time at another. Without it the picture drifts within bars.
- Layer
- One element of the composite output. A typical live picture is a bed, a mid layer carrying motion, a top layer for hits, and a global treatment.
- Media server
- The machine that stores, decodes and outputs content, usually against timecode. On large shows it is what actually plays the picture.
- Timecode
- A shared clock, usually SMPTE, distributed to lighting, video and playback so each runs its own show and everything lands on the same frame.
- Cue stack
- The ordered list of lighting states for the show, each with its own fade times and triggers. The show’s script, as far as lighting is concerned.
- Palette
- A named, reusable reference — this colour, this position, this beam shape; that cues point to instead of storing absolute values. What makes a rig tourable.
- Gobo
- A pattern placed in the beam path of a fixture to shape the light into a texture or a shape rather than a plain disc.
- Haze
- Fine atmospheric particulate that makes beams visible. Also what lifts the black level of every projected surface, which is why the amount is always a negotiation.
- FOH
- Front of house — the position in the room from which the show is operated, and the vantage point most design decisions are judged from.
- Previs
- Previsualisation: building the show in a 3D model before the rig exists, to test sightlines and pre-program cues while changes are still free.
- Sightline
- What is actually visible from a given seat. A camera placed at that seat in the model settles most design arguments without an opinion being involved.
- Virtual rig
- The modelled version of the physical rig, accurate where decisions depend on it and rough everywhere else.
- Pre-programming
- Building cues against the virtual rig so the show arrives at the venue already running, and the room is spent verifying rather than discovering.
About this glossary
the things people ask about thisWhy is this glossary grouped rather than alphabetical?
Because terms are used inside departments, and somebody arriving from a production page is usually trying to understand one part of the picture rather than the whole vocabulary. Each group links to the page where its terms are used properly, in context.
Is this vocabulary standard across the industry?
Mostly, with local variation. Rigging and lighting terminology is well settled and largely international; video and content terms are younger and vary more between vendors, territories and generations of practitioner. Where a term has competing meanings the entry says which one is used here.
Why do so many of these terms come from lighting?
Because lighting is the older discipline, and video arrived into a room where the vocabulary already existed. A great deal of how the video department talks about its work is borrowed from people who were hanging fixtures decades earlier.
Something is missing or wrong here. Can it be corrected?
Yes, and corrections are the most useful message this site receives. If an entry is inaccurate, or a term in common use is absent, let the editors know.