Glossary of Terms - T

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.


A Level 1 digital transmission system operating at 1.536 mbps. Also known as DS-1.

Lighting focused onto the front tabs to before the show starts.

Also known as BARE ENDS, TAILS refers to a cable or set of cables with a connector at only one end which is used for connecting a company's equipment directly to the mains supply in a venue. The connection should only be made by a qualified electrician with the power off!

(Trade Name) A retractable alloy vertical ladder on an adjustable wheeled base. The platform at the top is just large enough to hold one person. Used for rigging lanterns, focusing etc. Collapsible enough to fit through a standard doorway. Outriggers are used to stabilise the tower from falling sideways. Two people are used to move and steady the tallescope. Sometimes known as a "TALLEY".

Usually the first time the show is rehearsed in the venue, with lighting, scenery and sound. Costumes are sometimes used where they may cause technical problems (eg Quick changes). Often a very lengthy process. Often abbreviated to the Tech. A DRY TECH is without actors to rehearse the integration of lighting, scenic changes etc. It follows that a WET TECH is a full technical rehearsal with actors and all technical elements, although this term isn't used as often as DRY TECH.


Thin Film Transistor.

When a single frequency of specified level is applied to the input of a system, the ratio of the voltage of the fundamental frequency to the voltage of all harmonics observed at the output of the system because of the nonlinearities of the system. THD is expressed in percent.

Distance between a light source (e.g. lantern or projector) and the actor or object being lit.

Also known as an SCR (Silicon Controlled Rectifier). An electronic switch which will pass current when triggered until the current passing through it falls to zero. See also TRIAC.


  1. Up and down (vertical) movement of a lantern, camera or moving light. See also PAN.
  2. Feature on pinball machines which detects excessive movement of the case. Only related to theatre in connection with the musical "Tommy".

Timbre is a word that relates to the musical quality of sound. It is the relation of the fundamental frequency to the level and number of the associated harmonics. The human ear can perceive differences in timbre. Two different instruments, such as a saxophone and a flute playing the same note or fundamental at the same loudness, sound different to the listener due to the two instruments different number and level of related harmonics also produced at the same time as the fundamental. The two instruments are said to have a difference in timbre.

The facility on memory lighting boards for playing back timed fades at the touch of a button.

Also known as HIGH HAT or SNOOT. Cylinder of metal inserted into colour runners on the front of a parcan or other lantern to limit spill light.

Any device or element which converts an input signal into an output signal of a different form. A transducer changes energy from one form to another. A microphone is a transducer that changes acoustical energy (sound) into electrical energy (voltage). A loudspeaker is a transducer that changes electrical energy into mechanical energy, producing sound or acoustical energy.

An instant scene change, often effected by exploiting the varying transparency of gauze under different lighting conditions.

An electrical component consisting of multiple turns of wire placed in a common magnetic field (medium) which will transfer electrical energy from one electrical circuit to the next. A transformer will only pass alternating currents (AC) and will not pass direct current (DC). By adjusting turn ratios, a step up or down condition of voltage can be achieved.

An input or output that is coupled by means of a transformer in a configuration that makes it balanced or capable of being operated so that the voltages of the two conductors at any transverse plane are equal in voltage and opposite in polarity with respect to ground. A transformer balanced input or output will offer common-mode rejection, which means any common-mode interference signal will not pass through the transformer because it will be cancelled out.

Rapidly changing peaks of short duration in the level of sound such as would be produced by a cymbal crash or a rim shot on a snare drum. A wave having a very short or no sustain time.

Transient distortion interferes with the ability of an amplifier to accurately follow abrupt changes in volume, such as the sudden burst of sound when an instrument is first played. Minimum transient distortion is vital to clean and crisp overall sound.

Ability of an amplifier or loudspeaker to accurately follow abrupt changes, such as the sudden burst of sound generated by an instrument. Good transient response is vital to "clear" or "crisp" overall sound.

Separating the audio spectrum into three bands, i.e., high frequencies, mid-band frequencies and low frequencies by means of an electronic crossover and using three separate power amplifiers to amplify the three outputs of the crossover (high pass, mid pass, low pass outputs) driving three separate components of a speaker system; resulting in increased headroom and dynamic range.

(Triode Alternating Current switch) Electronic Semiconductor device which is an integral part of modern dimmers. When a current is applied to a triac, it starts conducting, and continues until the current passing through it falls to zero. Whereas a thyristor can only conduct half of the AC wave, a triac (as long as it's triggered at the appropriate point) will conduct both halves of the wave. See further explanation below.


  1. Tough Rubber Sheath. Jargon for any Rubber-sheathed mains cable.
  2.  Tip Ring Sleeve. The three contacts on a stereo jack audio connector.

Metal or plastic wall-mounted enclosure for cables. Box shaped in cross-section.

U-shaped bracket between the hook clamp and the main body of a lighting instrument, enabling it to be tilted to any angle.

A framework of alloy bars and triangular cross-bracing (usually of scaffolding diameter) providing a rigid structure, particularly useful for hanging lights where no permanent facility is available. Very often box-shaped in cross section, so known as BOX TRUSS. This type of truss is useful for touring as lanterns / speakers etc can be hung inside the truss which protects them when loading and takes up less space in the truck.

Telephony System Specification.

A standard tungsten filament lamp loses its brightness in its' lifetime. Tungsten Halogen lamps use a Quartz envelope ("bulb") filled with halogen gas to give an almost constant colour temperature. See HALOGEN CYCLE.



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