Glossary of Technical Theatre Terms – Sound

A TYPE
See JACK.

A-D CONVERTER
Short for Analogue / Analog to Digital Converter. Changes a continuously varying electrical signal into a stream of binary data. Found in computer soundcards, MiniDisc & CD Recorders etc..

A2
Assistant Sound Operator/Engineer (Audio 2)

AAC
Digital audio encoding format. The name stands for Advanced Audio Coding. The format provides slightly better audio quality than the MP3 format.
File extensions in use for AAC files include .m4a, .m4b, .m4p, .m4v, .m4r, .3gp, .mp4, .aac.
AAC is used on all Apple devices (including iTunes downloads), and was developed in 1997. Like MP3, it uses lossy compression, but provides an improvement in audio quality for the same file size. 

AB
1) A technique used to record in stereo. Two (identical) microphones are placed next to each other, parallel to each other, and pointing in the same direction. As you're looking at the action, the one on the left is panned hard left on the mixer and the one on the right is panned hard right. There are some problems with this technique, such as reflections off each microphone, leading to comb filtering and also a narrow coverage. Some sound techs try to overcome the coverage problem by spacing out the microphones, although this can lead to 'muddy' sounds due to delays. See COMB FILTERING and XY.
2) An AB System (or A and B System) is a sound design concept first implemented by Martin Levan in 1988 on the musical Carrie. It uses two sets of speakers which are used to provide two complete systems for vocal reinforcement, which improves the clarity and reduces phasing problems when multiple radio microphones are output through the same set of speakers. Some microphones go through the A system, and some through the B system. 

AB POWERING
See PHANTOM POWER.

ABO
Association of British Orchestras.
ABO website

ABSORPTION
The ability of a surface to absorp sound. The absorption coefficient of a material is a figure between 0 and 1, representing its degree of absorption.

ABTT
(UK) The Association of British Theatre Technicians, which was formed in 1961 as a charity, to provide a forum for discussion among theatre technicians, architects and managers of all disciplines, and disseminate information of a technical nature, to all its members.
ABTT Website

AC
Short for ALTERNATING CURRENT. An AC cord or cable is used to connect between a mains power socket and a piece of equipment.
A range of different connectors are used to connect to the equipment. The 3-contact IEC cable is common in Europe, and is sometimes known as a Kettle Lead. A figure 8 cable is used on smaller equipment which is double-insulated and has just two connections. Powercon is used on heavier duty equipment and locks into place to prevent accidental disconnection.

ACOUSTIC PICK-UP
See PICK UP

ACOUSTIC SHELL
(also known as BAND SHELL or CHORAL SHELL). A hard smooth curved surface which is designed to reflect the sound from the stage towards the audience. Some venues have shells which can be removed / repositioned or flown out of view to change the acoustics of the venue for different types of event. 

ACOUSTICS
The behaviour of sound and its study. The acoustic of a room depends on its size and shape and the amount and position of sound-absorbing and reflecting material. The quality of sound in a given space, measured and analyzed by its clarity, loudness, liveliness, reverberance, echoes, dynamic range, envelopment, spaciousness, warmth and silence or noise control rating.

ACTIVE
In electronics (particularly audio), an 'active' circuit operates with an external power supply and is usually low power, while a 'passive' circuit operates directly on the signal using the inherent power of the surrounding circuitry.
This is why an active crossover is usually placed before the amplifiers, with integrated circuits and line level signal processing (100 Ohms impedance or greater), while a passive crossover acts after the amplifiers where the power level is much greater (16 Ohms impedance or less). Amp to speaker level is generally between 2 and 16 Ohms, while preamplifier electronics are generally 100 to 100K Ohms.
Submitted by Bruce Trotter

ACTIVE SPEAKER
A speaker that contains a built-in amplifier, which requires a power supply and audio input signal to operate. 
Also known as a POWERED SPEAKER.
See also PASSIVE SPEAKER.

ADAM
See DIGITAL RECORDING.

ADAPTOR
1) 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. Sometimes known as a 'Twofer'. A three-way splitter is known as a 'Threefer'. A Series splitter is also available where a voltage is shared equally between two loads.
2) Also an ADAPTOR can be the same as a JUMPER.
See SERIES SPLITTER, JUMPER and GRELCO.

ADAT
See DIGITAL RECORDING.

ADDRESS
(LIghting) Each item of equipment controlled by DMX512 has an address, which is the first DMX control channel to which it will respond. A dimmer rack requires 1 DMX channel per dimmer. A moving light requires many DMX channels.
For example, in a situation where you have three 6-way dimmer racks, the first should be addressed to 1, the second to 7 and the third to 13. Moving lights requiring 16 DMX channels each might be addressed to 120, 137, 154 etc.
The address is either set via pushbuttons (up / down) to get to the correct channel, via a menu screen, via small rotary selectors where you can set each digit of the address, or via DIP switches where each switch represents a binary digit which combine to give the full address.
In larger systems, where more than 512 channels are required, each block of 512 addresses is called a Universe. By default, Universe 1 is used, so DMX address 120 on Universe 1 is known as 1/120. 
Some control desks permit the use of absolute addresses, where the first address of the 2nd Universe, normally called 2/001, is numbered 513.

ADR
Stands for Automated Dialogue Replacement. Also known as "looping" this is the post-production process on a film / TV shoot where actors re-record their lines after original filming, either because the original production sound was not up to standard or due to external factors (aircraft noise in a period piece) which weren't noticed at the time of filming.

AEOLIPHONE
More commonly known as a wind machine, this is a specialist musical instrument / sound effects generator used to produce the sound of a gusty wind.
Video

AERIAL
Cable or rod used to send and receive radio signals (connected to transmitter and receiver or tuner).

AES/EBU
Audio Engineering Society / European Broadcast Union. Digital audio transfer standard, similar to S/PDIF, first launched in 1985. Uses 3 pin XLR connectors.
See also AES67. 
AES/EBU on WikiAudio

AES67
AES67 is a standard for high-performance audio over IP interoperability, fully building on IP / Layer 3 protocols and above. AVB is a set of protocols expanding Ethernet / Layer 2 capabilities to enable the time-sensitive transport of media data including video and audio.
First published in 2013.
See also AES/EBU
AES67 FAQ on AIMS

AFILS
Audio-Frequency Induction Loop System. A way of broadcasting messages, announcements and other audio information direct to hearing aids worn by people with hearing deficiencies. 

AFM
American Federation of Musicians. See MUSICIANS UNION. 
AFM Website

AGC
Automatic Gain Control. Circuitry within recording equipment which compensates for differences in volume in the incoming sound signal by adjusting the gain automatically. Helps to reduce wild swings in volume.

AIFF
Audio Interchange File Format. Uncompressed Audio file format used on Mac systems.
Digital Audio File Formats

AMBIENCE
The character or atmosphere of a space. 
In theatrical terms, this applies to the combination of scenic & prop design along with lighting and sound, working together to create a unique atmosphere, where, particularly in immersive theatre, the space becomes one of the characters, which tells its' own story. 
The term also applies to the background sound in a space used for recording, or the soundscape used as a background sound to establish the location. 

AMBIENT NOISE
The sound heard in a given room with no sound sources. Each space has a particular sound which aids our identification of the kind of space we're in.

AMP
Abbreviation for ;
1) AMPERE
2) AMPLIFIER

AMPLIFIER
Sound equipment that amplifies/boosts the low voltage, low current audio signal from a computer, mixing desk etc. into a higher current signal suitable for driving speakers.
As a general rule, each speaker in a sound system requires a separate amplifier. Each amplifier unit usually contains two amplifiers (for the two stereo components (left and right) of the sound signal), so with a single amplifier box, you can drive two speakers.
See POWER AMPLIFIER, CROSSOVER.

AMPLITUDE
The strength of a vibrating wave; in sound, the loudness of the sound.

ANALOGUE SIGNAL
A continuously variable signal that can have any value over a given range.
1) 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.
2) 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.

ARRANGEMENT
The arrangement of a piece of music defines how it will be performed, and how it will sound. It covers which musical instruments will play each part of the melody and harmonies. The score for a piece of musical theatre may have arrangements for a small (school) band, or a large Broadway orchestra.

ARRAY
A set of loudspeakers flown in a performance space. See also CLUSTER.

ARTIC
Short for Articulated Lorry. Lorries of 40 feet length (or more) are used to transport sets, costume, props and sound & lighting equipment from venue to venue. A number of companies specialise in moving theatrical and musical tours around the country / world.
Known in the USA as a SEMI (short for Semi-Trailer, where a trailer box with a rear axle only is pulled by a tractor unit). 

ASSOCIATION OF SOUND DESIGNERS
UK & international organisation representing the interests of sound designers and technicians.
Association of Sound Designers website

ATMOSPHERE
The normal background sound at any location.

ATMOSPHERIC SOUND
Ambient or Atmospheric sound can be used to define a location or to help the audience to understand the world of the play better.
In live performance, it consists of subtle and carefully balanced audio effects which should not overshadow the performance, but set the scene. 
In film-making, atmospheric sound in a location (with no dialogue or other actor sounds) is recorded so that a consistent audio background is available, to make sound editing an easier process, to smooth-over edits. The recording of atmospheric sound is known as the 'wild track'.

ATTENUATE
To reduce the intensity of a sound signal. This is what the 'PAD' switch does on a sound desk.

AUDIO
Another name for the Sound department. 

AUTOMATIC STOP
Many reel-to-reel tape players for theatrical use have a facility that stops the tape mechanism when a piece of clear leader passes a detector adjacent to the erase head. This can be used to cue the tape up ready to start the next effect.

AUTOMATION
1) Facility available on larger sound mixing desks allowing channel muting or even fader moves to be taken under the control of a computer to ensure accurate and repeatable mixing.
2) Describes the method used instead of stage crew for moving bits of set or actors around stages on productions with sufficient budget. See MOUSE, SPADE, DOG, KNIFE.
Scenic Automation on Theatrecrafts.com

AUXILIARY INPUT or RETURN
A route back into the sound desk for a line level signal sent to a piece of outboard equipment (usually effects processor / EQ unit etc.) via an auxiliary send.

AUXILIARY OUTPUT or SEND
An additional line level output from a sound desk which can be used for foldback or monitoring without tying up the main outputs.
Analogue desk: Each input channel will have a path to the Aux buss, which will usually have a master level control, before the signal leaves the sound desk via the Auxiliary (Aux) output. A cable is then run to the outboard equipment (e.g. graphic equaliser, digital effects processor, recording device, monitor mixing desk). If the outboard equipment needs a path to return the audio to the main system after processing (e.g. Equaliser, effects processor), an Auxiliary Return is used to come back into the desk. There will be an Aux Return master level control and the option to send that signal to the main outputs or (on some desks) to sub-groups. 
Digital desk: Aux busses are used to provide additional routes around the console through the on-board effects processor or EQ unit. The resulting signal is Returned to the main outputs or groups. 

B-TYPE
See JACK.

BACKING VOCALS (B.V.s)
Additional vocals for a musical which are performed offstage, often in a specially constructed booth (or an adapted room just offstage). The BV Booth has a video feed from the musical director so the singers can keep time.

BACKLINE
Backline refers to the equipment which stands at the rear of a live band when they are performing. Guitar amps, bass amps etc. are standard backline equipment. Basically, everything a live band needs apart from the instruments the band hold (e.g. guitars), the PA (and front of house desks etc.) and the band themselves is backline.

BAFFLE
1) A sheet of material used to prevent a spill of light in a lantern or in part of a set.
2) A panel in a loudspeaker cabinet designed to reduce back interference noise by isolating the front and rear of the loudspeaker diaphragm.
3) A panel in an auditorium positioned so as to reduce sound reflections and improve the acoustics of the space.
4) What most of this jargon will do to any non-technical theatrical type.

BALANCED LINE
A method of carrying sound or data signals which reduces interference by using a third conductor, the shield. In the balanced line the shield, which is grounded, is in addition to the two signal- (or data-) carrying conductors. Balanced lines are less prone than unbalanced to interference. In balanced lines, one of the signal wires carries the audio signal, while the other carries an out-of-phase (inverted) copy. When the signal reaches the destination, the inverted copy is flipped and added to the original. Any noise added by interference is also inverted. When combined with the non-inverted noise, the two noise signals cancel each other out. See UNBALANCED LINE.

BALUN
A device which changes an audio or video signal from unbalanced wiring to balanced (or vice versa). The name is derived from BALanced / UNbalanced.
The term is commonly seen now for devices that adapt an analogue audio or video signal so that it can travel long distances over standard wiring (such as CAT5).

BANDWIDTH*
The range of a piece of sound equipment. If an equalizer has cutoff frequencies of 200 and 2000 Hz, then the bandwidth is the difference between them, in this case 1800 Hz.

BANTAM
See JACK.

BASS
Lower end of the musical scale. In acoustics, the range (below about 200Hz) in which there are difficulties, principally in the reproduction of sound, due to the large wavelengths involved.

BASS BIN
Slang for a speaker cabinet containing a Woofer designed for Bass sound reproduction (see also Subwoofer).

BEAT
1) In acoustics, a periodic variation in amplitude which results from the addition of two sound waves with nearly the same frequency. Also affects radio reception.
2) A deliberate pause for dramatic / comic effect.
3) A measure of time when cueing (e.g. "The LX cue needs to go four beats after the door is closed" or "Leave it a beat after the blackout, then play the sound cue").
4) A unit of action, as suggested by Stanislavski to help actors determine the through-line of a role.

BECTU
Broadcasting, Entertainment, Cinematograph and Theatre Union. The UK entertainment technicians union. (US equivalent is IATSE)
BECTU website

BEGINNERS
A call given by Stage Management to bring those actors who appear in the first part of a play to the stage. e.g. "Act One Beginners to the stage, please". The actors are then called by name.
A similar call is given after the interval (e.g. "Act Two Beginners to the stage please").
The call is usually given 5 minutes before the advertised performance start time, but this may vary depending on how long the actors take to get into position.
See also HALF, QUARTER.
See Calls and Cans

BELL BOARD
A live sound effects board on which are mounted a number of different types of doorbells / phone bells etc. Usually operated by stage management. The switch or bell push to operate the doorbell (or even the whole bell board) can easily be mounted on the set if the director wants the actors to operate it themselves. 

BELTPACK
Part of the communication ('cans') system in a theatre, the Beltpack contains the controls and circuitry to drive the HEADSET worn by crew members. Each beltpack connects into the headset ring and back to a PSU (Power Supply Unit) which is powered from the mains.
See also CANS.

BI-AMPLIFICATION
A way of optimising the efficiency of a speaker system by separately amplifying the High Frequency (HF) and Low Frequency (LF) portions of the sound signal (after the crossover) and sending them down two pairs of cables to the speaker. Multipin Speakon connectors have been developed to do this.

BINARY*
BIT = Binary Digit. More information coming soon.

BINAURAL
Sound reproduction using two microphones usually in a 'dummy head' (to emulate the shape and the response of the human hearing system) feeding a pair of headphones, so that the listener hears the sound they would have heard at the recording location.

BLUETOOTH
A technology enabling devices to wirelessly connect together over a short range for the purposes of playing or recording sound, or transferring data, or controlling a fixed device with a mobile device (e.g. mouse / keyboard).

BNC
Coaxial connector used for carrying a composite video signal or radio frequency signal. BNC stands for Bayonet Neill Concelman - after original inventors Carl Concelman and Paul Neill who developed the connector in the late 1940s. BNC is also thought to stand for 'Bayonet Nut Connector'.
See also TNC.

BOOM
1) Vertical scaffolding pole (usually 48mm diameter) on which horizontal boom arms (also known as sidearms or de-rig arms) can be mounted, carrying lanterns. Often used behind wings for side-lighting etc. Booms have a base plate (known as a TANK TRAP) or boom stand at the bottom and are tied off to the grid or fly floor at the top (not always necessary for short booms). Booms can also be fixed to the rear of the proscenium arch (Pros. Boom) or hanging from the ends of lighting bars. Sometimes known in the US as a LIGHT TREE. A light tree mounted upstage of a Tormentor is known as a Torm Tree. A boom used in the wings for dance lighting is sometimes known as a BALLET BOOM (which consists of 3 lanterns on each boom, at shin height, waist height, and head height, known as SHINS, MIDS and HEADS). 
2) An arm mounted on a microphone stand.
3) A long lightweight support for a directional microphone used to capture dialogue in TV/Film production. 
Boom Arms - Doughty Engineering (UK)

BOOTH
(US) Control Room.

BOUNDARY MICROPHONE
A microphone mounted on a flat plate which acts as a reflective surface directing sound into the mic capsule. Used for general pick-up over a large area. A PZM (Pressure Zone Microphone) is an omnidirectional boundary mic for picking up sound from all around. A PCC (Phase Coherent Cardoid) picks up only from in front of the microphone.
See also THREE TO ONE RULE and COMB FILTERING.

BREAKOUT
A connection at the end of a multicore cable which allows the connection of many items to it. (e.g. there is a breakout box at the end of a sound multicore cable which allows you to plug microphone cables into it).

BRIDGE
1) A walkway, giving access to technical and service areas above the stage or auditorium, or linking fly-floors.
See also CATWALK.
2) A lighting position above the auditorium, commonly with a catwalk above it to access lighting equipment and electrical systems is known in Dutch as a Zaalbrug.
3) A section within a song which provides a break from the previous verse / chorus, to prepare for the final chorus or climax, and can also provide a contrast with the previous lyrical tone or style.

BRIDGING
Technique for getting more power out of a stereo amplifier by feeding it a mono input signal and then connecting the outputs together. The amplifier is said to be 'BRIDGED'. Check the owner's manual of the amplifier before trying this. Some amplifiers have a switch which does the bridging internally.

BUSS
A signal line within a sound mixing desk that can receive its signal from a number of sources. eg the Aux 1 buss carries the signals from the input channels to the Aux 1 Send master control.

CABLE
Wiring, temporarily rigged, to carry electrical current. Depending on the size of the cable (current carrying capacity), cables are used to supply individual lanterns, whole dimmer racks, or carry signals from a microphone etc.

CABLE TESTER
A tool designed to check connections and terminations on a range of cables used in audio, lighting and audio-visual applications. 

CABLE TIE
Lockable (and sometimes releasable) plastic strap used to tie a bundle of cables together, amongst many other things.
Cable ties are absolutely not to be used to suspend anything (of any size, or at any height). Also known as Zip Ties.

CALLING THE SHOW
The process of giving verbal cues to the lighting, sound, fly operators and stage crew during the performance. Usually done from the prompt corner by the DSM on the book or Stage Manager over cans.
Being 'on the book' involves verbally giving the 'GO' cues to all technical departments (lighting, sound, flies, automation, av etc). The cues are written in the prompt script. A 'STANDBY' (UK) or 'WARN' (US) cue is given first, so that the operators are ready for the actual cue.

CANS
1) Headset earpiece, microphone and beltpack used for communication and co-ordination of technical departments during a performance. (e.g. "Electrics on cans", "Going off cans", "Quiet on cans!").
A commonly used system in the UK is produced by Canford Audio under the TecPro brand. In the USA, ClearCom is commonly used.
As many of the technical operators are tied to expensive pieces of equipment, headsets are often wired. However, stage management (and any other crew who move around) often wear wireless versions, often known as radio cans. There are interfaces between wired and wireless versions enabling both to be part of the same system.
Many headset systems have multiple channels, enabling different sub-groups to communicate separately.
[Named after the well-known usage of two tin cans connected by a piece of string being able to transmit and receive a sound mechanically].
Also called 'Comms' short for Communications - the same phrases can be used (e.g. 'LX Off Comms' when leaving the operating position).
See link below for Cans Etiquette.
2) Any headphones.
3) Short for PARCANs.
Calls and Cans

CAPACITANCE*
TO BE DEFINED

CARDOID
See PICK-UP.

CARTRIDGE or CART
(Sound) An audio tape loop in a box which can cue itself up to the beginning of the recorded track in a cartridge player. Previously used extensively for radio jingles, and sometimes for theatre sound effects, it was superceded by MiniDIsc, and now by computer-based playback. 

CASSETTE
Originally, Compact Cassette. Popular domestic 1/8' tape format. Difficult to cue up accurately, so awkward for live theatre, but cheap, so often used by small scale touring companies as sound effects source. A different cassette is used for each effect. However, Minidisk prices are coming down to the extent that cassettes are rarely used for sound effects now.

CASUALS
Part-time temporary technicians (paid by the hour).

CCTV
Closed Circuit television. A video relay system, used in the theatre to give a view of the stage to remote technical operators (especially stage managers). Also used to give musical performers a view of the conductor (and vice versa) to help in keeping time. It's called Closed Circuit because the signal is not being broadcast anywhere - there's a direct link between camera and monitor.

CD (Compact Disc)
Digital sound storage medium introduced in 1982. Provides a high quality source of music, sound effects etc. of up to 74 minutes total duration. 
Initially the technology to create CDs from recordable media did not exist, but as it was introduced, long-running shows such as the Woman In Black moved over to CD playback, from the original reel-to-reel. When Multimedia PC computers became affordable, it became possible for many productions to use CD playback.
However, due to the ease of playback control, and ability to easily (and reliably) re-record and edit the media, MiniDisk was a better replacement for reel-to-reel tape playback in many venues, although digital samplers (e.g. the Akai S1000) were used on bigger shows. 
The recordable disks were available in two types; 
CD-R - Recordable Compact Disc - Data was written to it, then it was 'Finalised' which made it playable in any standard-compliant CD player, including domestic decks. 
CD-RW - Rewritable Compact Disc - Data could be re-written many times. Not playable in domestic CD decks, so more suitable for computer-based playback. 
Wikipedia entry

CHANNEL
A complete control path for signals in lighting or sound equipment.
In a lighting desk, the channels are directly controllable by the lighting operator. Within the desk, the channels are 'patched' to a dimmer or dimmers which the desk then sends a signal to depending on the level of the channel.
On a sound desk, the channels typically refer to a particular input or output path, and on digital sound desks can be configured in whichever way is appropriate for the event being set up. 

CHECK
1) Opposite of Build; a smooth diminishment of light or sound level (e.g. Lighting: 'I think we should check this state down a touch as the song begins')
2) See Prefade Listen.

CHINAGRAPH PENCIL
Usually white, wax-based pencil used for marking magnetic tape prior to splicing. Also used for marking identifying numbers on lighting gels.

CHOIR
A group of vocal performers who perform songs, and remain relatively static whilst doing so. 
The vocal ranges of the performers are categorised in terms of the pitches of their voices: 
Soprano [high female or boys voice]
Alto [low female or boys voice]
Tenor [high adult male voice]
Bass [low adult male voice]

CHORUS
1) In Greek theatre, a character (or group) representing an element in the drama which comments on the action, and advances the plot.
2) A sound processing effect which adds 'body' to a sound by overlapping a number of slightly delayed versions of the original sound.

CITT
Canadian Institute for Theatre Technology.
CITT website

CLASSIC GEAR
Long-running column in Lighting & Sound International magazine, by Rob Halliday, discovering the history and origins of many essential technologies and bits of equipment that have made entertainment technology what it is today. 
See the Lighting & Sound International archive for many examples. 

CLICK TRACK
Technique for reinforcing the live sound of a musical or band with recorded sound from one track of a tape. The other track of the tape consists of a click used by the musical director to keep the live band and cast synchronised with the recorded band or cast.

CLICKS AND POPS
Any miscellaneous problem with a sound system (e.g. 'There are a few clicks and pops with the sound interface, but that should get sorted when we change the driver').

CLIPPING
Distortion in a sound signal caused by an amplifier or mixer being unable to handle the level of signal being fed to it.

CLUSTER
Generic name for a grouping of loudspeakers hung in a performance space. (e.g. The central cluster). Also known as ARRAY.

COAXIAL CABLE
A shielded copper cable used for satellite TV, analogue TV, video and some digital connections.
Sometimes shortened to 'Coax cable', it consists of an inner solid copper conductor surrounded by a plastic insulator, which is wrapped with a braided copper screen, with an outer protective sheath.
There are different connectors used for coaxial cable, including RF connector, threaded F type satellite TV connectors, or locking BNC connectors. There are also different types of coaxial cable, for different purposes, identified by their electrical impedance. 75 Ohm (written as 75Ω) cable is used for video, while 50 Ohm (50Ω) is used for data and radio signals.

COMB FILTERING
An effect caused by the same sound arriving at a given point at slightly different times. This could be the listening position or a microphone. Comb filtering can be reduced in the case of sound from speakers by employing delays, and in the case of microphones by following the three to one rule. See THREE TO ONE RULE and DELAY.

COMPANDER
Outboard sound equipment. Combination of a COMPRESSOR and an EXPANDER.

COMPRESSOR
A piece of sound processing equipment that ensures all wanted signals are suitably placed between the noise and distortion levels of the recording medium. It evens out the unwanted changes in volume you get with close-miking, and in doing so, adds punch to the sound mix. A Limiter is used to stop a signal from exceeding a preset limit. Beyond this limit, the signal level will not increase, no matter how loud the input becomes. A Limiter is often used to protect speaker systems (and human ears) by preventing a system from becoming too loud.

CONDENSER MIC
(Capacitor Mic) A microphone that uses the varying capacitance between two plates with a voltage applied across them to convert sound to electrical pulses. Condenser microphones need a power supply to provide the voltage across the plates, which may be provided by a battery within the case of the microphone, or it may be provided from an external phantom power supply. A condenser mic is more sensitive and has a faster reaction to percussive sounds than a Dynamic mic and produces a more even response. See Electret Mic.

CONSTANT VOLTAGE SYSTEM
See HUNDRED VOLT LINE.

CONTACT MIC
A microphone that directly picks up the sound transmitted by a solid material. See Boundary Mic, PCC, PZM.

CONTROL ROOM
Room at the rear of the auditorium (in a proscenium theatre) where lighting and sometimes sound is operated from. Known in the US as the BOOTH. The stage manager calling the cues is very often at the side of the stage (traditionally stage left) but in some venues they may be in the control room also. The control room is usually soundproofed from the auditorium so that communications between operators cannot be heard by the audience. A large viewing window is obviously essential, as is a show relay system so that the performance can be heard by the operators. Obviously if sound is being mixed, the operator should be able to hear the same as the audience, so some control rooms have sliding or removable windows, or a completely separate room for sound mixing. Where possible, the sound desk is moved into the auditorium so that the operator can hear the same as the audience.
Also known as the BOX.

CROSS FADE / CROSSFADE
Bringing a new lighting state up whilst bringing the previous one down, so that the new one completely replaces the old one. Also applies to sound effects / music. Sometimes abbreviated to Xfade or XF.
A DIPLESS CROSSFADE occurs when the lighting doesn't dip significantly between states, which results in a more subtle transition.
Some sound mixers (especially those for DJs) have a cross-fader - a single fader which can be used to fade one music source out while simultaneously fading the next one in.

CROSSOVER
1) A route leading from one side of the stage to the other, out of the audiences view.
2) An electronic filter in a sound system that routes sound of the correct frequency to the correct part of the speaker system. Different speakers handle high frequencies (tweeters) and low frequencies (woofers). Sometimes known as a crossover network.
An active crossover splits the signal from the mixing desk into high, mid and low frequencies which are then sent to three separate amplifiers.

CROSSTALK
A leakage between two audio circuits (e.g. between two channels on a sound mixer).

CROWN
Manufacturer of PA amplifiers and microphones.
Crown website

CUE
1) The command given to technical departments to carry out a particular operation. E.g. Lighting Cue, Fly Cue or Sound Cue. Normally given by stage management, but may be taken directly from the action (i.e. a Visual Cue).
Departments are often abbreviated: Lighting is LX, Sound is SD (or sometimes SX, but this is too similar to LX, so SD should be used). 
2) Any signal (spoken line, action or count) that indicates another action should follow (i.e. the actors' cue to enter is when the Maid says "I hear someone coming! Quick - Hide!" - this is known as a Cue Line. 
Cues given verbally may be known as 'audible cues', although as this is the normal type of cues, they're usually just called 'Cues'. Cues that technical operators take themselves, without an audible cue, are known as Visual Cues. 
3) A journal published between 1979 and 1988. A complete collection of CUE journals is available on the Backstage Heritage Collection website to read online.
The Prompt Book

CUE LIST
A list of sound, lighting, automation, scene change, video, followspot (etc) cues in order of their appearance in the show. Each cue is given a unique number, and the list includes a brief description of what it does (e.g. for Lighting: Blackout, Dim Downstage Wash, Red Spot Upstage; for Sound: Preshow Music, Fade Out, Snap Music to Quiet etc. )
Cue is often abbreviated to 'Q". 
Also known as a Plot Sheet. 

CUE TO CUE
(also known as 'Topping and Tailing')
Cutting out action and dialogue between cues during a technical rehearsal, to save time. (e.g. "OK, can I stop you there - we'll now jump to the end of this scene. We'll pick it up from Simon's line "And from then on it was all downhill" in a moment. OK - we're all set - when you're ready please.")

CUEING
There is a standard sequence for giving verbal cues:
Stand-by 'Sound Cue 19' (Stand-by first)
'Sound Cue 19 Go' (Go last).

DAISY-CHAINING
Connecting items of equipment together by linking from one to the next in a chain. Used for connecting demux boxes to dimmers etc.

DANTE
Audio protocol developed by Audinate, which replaces the need for multiple connections between audio devices with a single computer network. 
Audinate Website - What Is Dante

DAT (Digital Audio Tape)
See DIGITAL RECORDING.

DBX
A tape-recording noise reduction process.

DCC
(Digital Compact Cassette) Manufactured by Philips in the Netherlands, this format was supposed to be the successor to the compact cassette, but Mini Disk won the marketing war. DCC was discontinued for mass market use in 1996. See DIGITAL RECORDING.

DEAD ROOM
A room with very thick sound absorbers, causing a very dull sound with no reverberation.

DEATH BY CUES
A colloquial phrase when the speaker believes that there are a lot of unnecessary cues going on. 
It's the job of the lighting or sound designers to ensure the show can be run reliably every night, in discussion with stage management. If there are lots of cues running in a short period of time, it may be better to simplify them, or make them timed auto-follows, or run them from timecode, to avoid 'death by cues'.

DECIBEL (dB)
Relative measurement for the volume (loudness) of sound. One dB is the smallest variation in loudness that the human ear can detect. Also used to measure the difference between two voltages, or two currents. See ZERO DB.

DECK
1) Stage/Rostrum Floor (e.g. "Fly that flat in to the deck") [known in German as bühnenboden]
2) Tape deck/Record deck.
3) A steel-framed platform with a wooden top used with replaceable scaffold legs (Trade names include Steeldeck, Metrodeck (made by Maltbury), ProDeck).

DELAY
1) Outboard sound equipment that can momentarily stores a signal being sent to part of a P.A. system so that delayed reinforced sound reaches the audience at the same time (or just after) the live sound from the stage. Using the 'Haas Effect' the audience cannot detect the sound as amplified.
2) The term Delay Line refers to the equipment that is used to produce the delayed sound signal.  
3) A function in lighting control software / systems  which holds the start of a cue (or part of a cue) for a specified time. The Delay Time can be used to hold (for example) the Up Time of a cue for a few seconds while the stage is cleared during a dim state. 

DI BOX / D.I.BOX
Interface unit to convert the high impedance unbalanced output of an instrument (e.g. Electric guitar) into a low impedance balanced signal of low level suitable for connection to the microphone input of a mixing desk. Usually has an output jack socket so that the instruments unprocessed signal can be passed direct to the musicians amplifier. DI = Direct Injection.

DIAPHRAGM
1) Lighting: See IRIS.
2) Sound: The part of a microphone which responds to sound waves.
3) Human Biology: (from WIkipedia) a dome-shaped muscular partition separating the thorax from the abdomen in mammals. It plays a major role in breathing, as its contraction increases the volume of the thorax and so inflates the lungs.
4) A rare type of trapdoor. See TRAPs. 

DIEGETIC
Music or sound that is heard by the characters on stage (rather than just being for the audience to hear) is said to be DIEGETIC. (e.g. a piece of music played on a radio on the set).
The opposite (NON-DIEGETIC) sound or music is specifically NOT heard by the actors (e.g. scene change music, or an emotional underscore).
A piece of music can be both diegetic and non-diegetic, if it starts out at low-volume, coming from a radio on the set (diegetic), and then swells in volume and expands to fill the whole sound system (non-diegetic). It obviously cannot be both simultaneously, however!
The term can also be applied to lighting. A light source that is seen on stage (or on film) and is part of the world in which the characters exist, is said to be diegetic. A stylised light source, such as dramatic eye-light in an expressionist film, or a spotlight which isolates a character in a musical, is non-diegetic. 

DIGITAL
Many electronic devices use digital logic. Information is handled in separate bits (either ON or OFF) rather than continuously variable analogue signals. Most computer lighting boards give a digital multiplexed output, and more and more sound equipment is going digital.

DIGITAL EFFECTS
Reverb, Delay, Phasing, Flanging, Harmonising, Chorusing. Pitch Change.
These audio effects can be added to a sound source in a number of ways, either in software, if the track is pre-recorded, or 'live' via outboard processing equipment (e.g. Yamaha SPX90), or via the effects functions built into a digital mixing desk. 
More information coming soon !
Yamaha SPX90 in the Backstage Heritage Collection

DIGITAL RECORDING
1) ADAM : (Akai Digital Audio Multitrack). 12 track recording onto Video 8 tape. 16 bit, 44.1 or 48kHz sampling rate.
2) ADAT (Alesis Digital Audio Tape) Digital 8 track multitrack recording format introduced in 1991. There are two formats of recording: Type 1 (16 bit) Type 2 (20 bit) at two sample rates (44.1kHz and 48 kHz) onto standard SVHS video tapes.
3) DAT (Digital Audio Tape) Cassette-like system which has much higher quality than standard audio cassettes. Introduced in 1987, and widely used in gathering sound effects, for news gathering, and for playback of music.
4) DCC (Digital Compact Cassette) Rival to DAT which also plays standard audio cassettes. DCC was discontinued in 1996.
5) MiniDisc (MD) : Uses magnetic disk technology, rather than tape. A laser heats an area of magnetic disk which is then written to by a magnetic head. When cooled, the magnetic information is read from the disk by laser. Tracks can be named, and are instant start. Very theatre-friendly system.
6) Direct to Disk : Uses the hard disk present in most PCs as the recording medium.
Alesis Website

DIN
Deutscher Industrie Normen. European standard covering audio connectors and tape equalisation characteristics.

DIPOLE
Aerial used with radio microphone systems. A relatively long aerial in two parts, with an insulator at each end, connected in the middle to a coaxial cable which then connects to the receiver.

DIRECT INJECTION BOX
See DI BOX.

DISTORTION
Usually undesirable result of overloading sound equipment. Reducing the levels can remedy the situation.

DIVERSITY
A way of maximising the quality of received radio signal by using two receivers and aerials tuned to the same frequency - the circuitry automatically silently switches to the strongest signal.

DOGBOX
Channel at the rear of a mixing desk flight case used to contain cables and adaptors to enable some cabling to remain connected whilst in the case. Some cases have a hinged removable dogbox cover to hide the cables during operation where the appearance of the desk is important.

DOLBY
Trade name for a series of noise reduction systems that have become standard on many tape playback machines. Most film soundtracks are produced using this process. Different varieties are found from Dolby B on most personal cassette players, to Dolby SR and Digital, the current state of the art for cinema.
Dolby Labs Website

DOOR SLAM
A small wooden box with a heavy door and various bolts and locks used to simulate slamming and other door sound effects offstage.

DRAMATIC PAUSE
A brief pause (a few beats) in an actors' delivery of a line to emphasise a moment or to heighten anticipation. 
It's important that the DSM does not shout out the next line, while the lead actor is pausing dramatically. 

DRESS REHEARSAL
A full rehearsal, with all technical and creative elements brought together. The performance as it will be 'on the night'.
German: hauptprobe (final rehearsal)

DRUM KIT
A collection of drums, cymbals and other percussion instruments set up to be played by one person. 

DRY
1) An actor forgetting the words of his script.
2) To record a sound without using any effect or other processing is to record it 'dry'. Recording with an effect is recording 'wet'.

DUBBING
The analogue process of copying a sound or video from one source to another for backup purposes, or for mass distribution.

DYNAMIC MIC
Robust type of microphone which picks up the sound on a diaphragm connected to a coil of wire which moves within a magnet. An alternating current is induced into the wire which provides the electrical output. Most dynamic mics have low output impedances of 200 Ohms. See CONDENSER MIC and ELECTRET MIC.

DYNAMIC RANGE
A measurement between the loudest and quietest sound that can be recorded or reproduced by an audio system. 

EARTH LOOP
Normally refers to audio interference resulting from a situation where two pieces of sound equipment are connected together over a long distance. The earths of the equipment are at different potential, and this results in an audible hum or buzz. Can be cured by removing the screen connection on one end of the signal cable. Electrical earth connections must never be removed.

EARTHING
Electrical safety requirement that metal parts of electrical equipment are connected to a common earth or ground point so that in the event of a fault, excess current can be carried away, causing the fuse to blow. Known in the USA as Ground. Some sound problems (such as hums) can be cured by altering the earthing / grounding arrangements of the system, but this should never involve removing the earth connections to equipment, only by adding an earth connection where none exists, or by adjusting the way audio cables are wired. Seek professional advice to avoid safety problems.

ECHO
A repeated sound received late enough to be heard as distinct from the source.
Echo is produced digitally at the touch of a button, but was originally produced using magnetic audio tape and a pair (or more) of machines; one was used to record the audio from the stage onto the tape, which was then played back by another machine. A separate TAPE ECHO machine was also available, consisting of a loop of tape and separately controllable record and playback heads. Either the speed of the tape or the physical separation of the heads defined the time delay between the recorded and played audio. 
See REVERB.

EDM
Acronym for Electronic Dance Music. Repetitive beats and an awesome light show.

EFFECTS, SOUND
1) Recorded : Often abbreviated to FX. There are many sources for recorded sound effects, from Compact Discs, to downloading from the internet. May form an obvious part of the action (train arriving at station) or may be in the background throughout a scene (e.g. birds chirping).
2) Live : Gunshots, door slams, and offstage voices (amongst many others) are most effective when done live.
See Door slam, Thunder Sheet, Rain box.
See also Compressor, Digital Effects, Exciter, Noise Gate, Reverb.

ELECTRET MIC
A condenser microphone where the capacitor plates are given a charge during manufacture which they retain, therefore requiring no external power supply.

ENCODER WHEEL
A flat disc with an indentation used to control certain functions of (often) moving lights on a lighting control desk.

ENHANCER
Sound processing equipment which increases the presence of the vocal track in a mix by adding to the treble information in the signal. Also known as an Exciter.

ENTERTAINMENT TECHNOLOGY
Any technical or practical craft used in the creation of live events or experiences. As the definition of 'live events or experiences' includes music concerts, theatre, theme parks, visitor attractions, museums and sports events, the skills needed are very broad. It's not necessary for anyone to be highly skilled in all of the crafts, but an understanding of the whole picture is very helpful, and knowing when to call in a specialist (and where to find them) is vital.

The crafts involved in entertainment technology include, but are not limited to:
Lighting (stage lighting and architectural lighting)
Sound (live and recorded)
Video and Media (projection or display)
Scenic Construction and Automation
Show Control
Animatronics
Costume
Props and Masks
Make-Up and Prosthetics

ENVIRONMENTAL SOUND
A sound that is not specifically mentioned in the text of the play, but helps to create a feeling of reality / appearance of truth. Examples include dripping water in a cave, distant organ music heard in a church graveyard, traffic heard passing outside an office.  
See also MOTIVATED SOUND. 

EQUALISATION
The process of adjusting the tonal quality of a sound. A graphic equaliser provides adjustment for a wide range of frequency bands, and is normally inserted in the signal path after the mixing desk, before the amplifier. See FEEDBACK.
(Equalisation is the British English spelling. American English uses Equalization)

ESTA
(US) Entertainment Services and Technology Association. See PLASA for the UK equivalent.
ESTA website

EXCITER
1) See ENHANCER.
2) Exciter Lamp - the lamp in a film projector that shines through the optical soundtrack and enables it to be read by a light sensor.

EXPANDER
See Noise Gate.

FADE
A fade is an increase, diminishment or change in lighting or sound level.
A snap fade is an instant change. A slow fade could be anything from 5 seconds to a few minutes (or even more, for a naturalistic sunset lighting effect). A quick fade is a couple of seconds long.
A fade out takes the lighting state to blackout (or a particular sound to silence). A fade in does the opposite.
A crossfade smoothly transitions from one state to another, without going through darkness (or silence for sound).

FADE UP
An increase in lighting or sound level, over a given time period. An increase in level from an existing state is known as a BUILD.

FADER
A vertical slider which is used to remotely set the level of a lighting or sound channel.

FAT FINGER
A common problem among lighting & sound operators, when two buttons are accidentally pressed at the same time by a finger that's too large for the buttons. 

FEED
1) A power supply to a piece of equipment or installation is termed a 'feed'. Sound equipment and sensitive computer equipment should have a clean feed - that is, a supply that is free from interference from other equipment.
2) A signal from one system to another is also known as a feed (for example, an audio signal from the FOH desk to a TV company videoing a concert is known as a feed. A video relay of the conductor to screens in the wings is known as a Conductor Feed, etc.)

FEEDBACK / HOWLROUND
(Sound) A loud whistle or rumble heard emanating from a sound system. It is caused by a sound being amplified many times. (E.g. a sound is picked up by a microphone and amplified through the speaker. The microphone picks up this amplified sound and it is sent through the system again). Feedback can be avoided by careful microphone positioning, and can be reduced by use of Equalisation to reduce the level of the frequency band causing the feedback.

FEEDBACK DESTROYER
Outboard piece of sound equipment which can immediately block any unwanted feedback sounds, resulting from microphones being too close to speakers, or microphone being covered by a hand etc. 
The Feedback Destroyer has all of the live microphones routed through it, and can instantly filter out any narrow band of frequencies that is causing feedback. 

FEEDER
In the US, a main power cable to an installation is known as a feeder.

FEMALE / MALE CONNECTORS
This terminology is beginning to change, as it's not very subtle, and sometimes isn't as clear as it could be. 
Connector manufacturers and crew members refer to plug connectors (with pins) as MALE, and sockets (which receive the pins) as FEMALE. 
Many modern companies refer to plug and socket instead of the genderised terms, but that in itself can cause confusion. The situation remains confusing. 
Sound: Microphones have pins on them, so a XLR cable socket is used to connect to them. The other end of that cable is a plug, which connects to the mixing desk. 
Power: Sockets are used to supply power so that it's not possible to touch live connectors. Plugs are used to connect equipment to the supply. 

FIBRE OPTICS
A method of directing light down a very thin glass fibre. Fibre Optics are used mostly in communication, but find theatre applications in star cloths which are black backcloths with the ends of optical fibres poked through, to create a mass of pin pricks of light. A large bundle or harness of fibres may be fed from one light source, sometimes with a motorised colour or flicker wheel.
New technology enables digital sound signals to be sent down optical fibres, replacing heavy and expensive multicore cables.

FILLS
Term for speakers additional to the main PA to improve the sound in particular locations (e.g. 'Front fills' add sound at the front of the auditorium which might be just out of range of the main PA stacks at the sides of the stage).

FILTER
1) See Colour. 2) Electronic device to isolate and redirect specific frequencies in a speaker system.

FLIGHTCASE / FLIGHT CASE
Metal framed wooden box on wheels with a removable lid used for transporting equipment between venues. Flightcases are very strong, and have reinforced corners and edges. Care should be taken when lifting flightcases as they can be very heavy.
The term comes from their original use in protecting delicate equipment when being loaded into air transport and being both very strong and relatively lightweight.
Additional information by Chris Higgs

FLOAT MIC
See FLOATS.

FLOATS
Early form of footlights using burning wicks floating in oil across the front of the stage. Now applies to anything rigged on the front edge of the stage (eg Float microphones, Uplights / footlights etc.)

FOH
See FRONT OF HOUSE.

FOLDBACK
Means by which musicians can part of the rest of the sound mix (including voices) and how their instruments sound after being amplified. Also enables actors on stage to hear musicians or effects when they cannot hear the output of the auditorium sound system.

FOUND SOUND
Refers to an audio composition created using sounds that have been recorded for the project, sometimes all from the same location, to which the project relates.
See also MUSIQUE CONCRETE.

FREQUENCY
(measured in Hertz - Hz - cycles per second) The number of times a sound source vibrates each second. A high frequency (HF) sound has a higher pitch and is uni-directional. A low frequency (LF) sound has a lower pitch and is omnidirectional.

FX
Abbreviation for Effect, usually referring to Sound Effects, but can also mean special stage effects.

GAFFER TAPE / GAFFA TAPE
Ubiquitous sticky cloth tape. Most common widths are .5 inch for marking out areas and 2 inch (usually black) for everything else. Used for temporarily securing almost anything. Should not be used on coiled cables or equipment. Originally known as Gaffer's Tape, from the Gaffer (Master Electrician) on a film set. Also known as Duct Tape.
See also PVC Tape.

GAIN
1) The level of amplification given to a signal or of a system.
2) A control of the amount of pre-amplification given to a sound signal on its way into a mixer. Particularly important for microphone inputs - a quiet vocal will require a lot of gain, a loud singer less so.

GAIN STRUCTURE
Also known as GAIN STAGING. This is the process of setting the GAIN (audio input level) of each part of the sound system to achieve the best quality sound with the best controllability. 
Microphone Gain Structure at AudioTechnology

GENDER CHANGE
As audio connectors are usually referred to as male or female versions, a gender changer is used to change a male connector to a female etc. 

GRAMS
Refers to a Gramophone, originally the only way of playing back sound effects from vinyl or shellac record discs. A Grams cue, then, is a cue to play back recorded sound. Some TV productions (particularly shows that are shot "as live" or broadcast live) list GRAMS OPERATOR in the credits. The term is rarely used in theatre nowadays.

GRAPHIC
Short for GRAPHIC EQUALISER.

GRAPHIC EQUALISER
See EQUALISATION.

GROUP
A subdivision, permanent or optional, of a lighting board control preset, or a sound desk.

GUN MIC
See Shotgun Mic.

HAAS EFFECT
A psychoacoustic phenomenon whereby an audience will focus on an actual sound source if the reinforced sound from speakers arrives 10 - 15 milliseconds later. The setting up of delays can be time-consuming but the Haas Effect can make a vast difference to the perceived quality of the sound in a show. The delays are set up by experimentation rather than by using distance/speed/time formulae.

HEAD
See RADIO MIC.

HEAD SOUND
The head of the sound department, which deals with any recorded music, sound effects, vocal reinforcement and music amplification required in the production.
See also NO.1 SOUND.

HEADROOM
In sound mixing, this refers to the amount of additional volume you can increase before the system goes into distortion. The difference between the current sound level and the maximum. It's important to set up the system so there is sufficient headroom to allow for necessary adjustments, without the system distorting. 

HEADSET
1) General term for theatre communication equipment.
2) A headphone and microphone combination used in such communications systems with a beltpack.
See also CANS.

HORN
Part of a large speaker system designed to distribute high-frequency sound, using an acoustic horn.

HOT
One of three connections on an audio or power connector. 
Hot - the 'live' or positive or signal cable, often coloured red
Cold/Common - the 'neutral' or return cable to complete the circuit
Ground - the 'earth' or ground connection which ensures electrical safety. In an audio connector is this often connected to the metal sheath of the cable. 

HOWLROUND
See FEEDBACK.

HRTF
Head-Related Transfer Function. A way of measuring how each pair of human ears responds to sound, based on the size and shape of the head, ears, ear canal, density of the head, and the size and shape of nasal and oral cavities.

HUM HEAD
See NOISE BOY. Term popular around the Edinburgh Festival.

HUNDRED (100) VOLT LINE
Way of sending speaker signals over long distances without losing signal strength. Transformers are used in each speaker cabinet to convert the signal from 100 Volts to a more usable level. (100V is used in the UK, 70.7V in the USA)

HYDROPHONE
Transducer that captures sound waves underwater (e.g. ocean, swimming pool) so they can be recorded. 

HYPERCARDOID
See PICK-UP

IEM / I.E.M.
See IN EAR MONITORS

IMPULSE RESPONSE
(Sound) Abbreviated to IR. An Impulse Response is a digital recording of a burst of a full range of frequencies (known as an impulse) across the audible spectrum, which is used to create a digital 'acoustic autograph' of a space. The impuise response recording is analysed by software which can then be used to recreate the acoustic of the original space digitally.
This enables a precise match to how a recording sounded in the space when trying to recreate it in the studio.

IN EAR MONITORS
Small headphones worn inside the ear by members of a pop band so they can hear the monitor mix (or the backing track they're miming to) without having lots of monitor speakers onstage. The advent of in-ear monitoring has improved the sound quality of the monitoring for these band members as they no longer have to try to hear the monitors over screaming from the audience. Each member of the group can have their own monitor mix which is guaranteed to be the same in every venue on the tour. Known as I.E.M.s or IEMs for short.

INCIDENTAL MUSIC
Music heard by the audience in a non-musical performance, either as background atmosphere as underscore, or between scenes or to set the mood. Incidental music is not heard by the characters in the play, so is non-diegetic.

INDUCTION LOOP
System which amplifies audio frequency currents (from a microphone over the stage) around a large loop of cable (around the auditorium) to generate a magnetic field which can be picked up by a hearing aid switched to the 'T' position.

INFRASOUND
Very low frequency sound which is not normally audible by the human ear. Usually describes sound waves below 20Hz. At high enough volumes (sound pressure levels) sound waves as low as 12 Hz can be perceived by some ears. When they can't be perceived as sound, the waves can be felt as pressure either in the ear drums, or elsewhere on the body. Some scientists have linked the presence of infrasound in buildings (produced by air conditioning systems or large empty rooms) with feelings of unease, nervousness, or even perceptions of supernatural presences by visitors.
Infrasound cannot be reproduced by normal (or even bass) speakers, and requires large specialist speakers and tubes to enable the powerful low-frequency waves to be generated. 

INSERT
1) An additional route into a sound desk.
2) An extra lighting state added into the sequence later. See POINT CUE.

INTERCOM
Usually refers to microphone/headset communications equipment. Abbreviated to 'comms'. Also known as 'cans'.

INTERRUPTIBLE FOLDBACK (IFB)
IFB is monitoring and cueing system used in live events, television, filmmaking, video production, and radio broadcast for one-way communication from the director or assistant director to on-air talent or a remote location. It is also known as Interrupt for Broadcast. The foldback normally contains a feed of production audio, which can then be interrupted by the director microphone to give specific information or instructions.

INTERVAL MUSIC
Music played in the foyer and/or auditorium during intervals. Most usually Vivaldi's Four Seasons.

INTRO
An introduction to set the scene at the start of a performance, or a piece of music / media at the beginning of a longer piece. 
See also OUTRO. 

ISOPROPYL ALCOHOL
Also known as IPA or by the general term 'Rubbing Alcohol', Isopropyl Alcohol is a flammable solvent used to clean tape heads and other metallic parts, to clean solvent-contaiminated make-up brushes, or to clean silicone prior to painting. 
Care should be taken to store the chemical correctly, and to wear appropriate protection when using it.

JACK
1) Segmented audio connector. Mono Jacks have two connections - tip and sleeve, and are unbalanced. Stereo jacks have three connections - tip, ring and sleeve.The configuration is often abbreviated (T = Tip, R = Ring, S = Sleeve), so a strereo jack is TRS, a mono one is TS. 
B-type jacks (also known as Bantam jacks) were originally designed for use in telephone exchanges and provide a high quality (and expensive) connection in jackfields.
A-type jacks are cheaper and more common, but more fragile. A type jacks are available in 2 sizes : quarter inch and eighth inch.
2) (US) A hinged brace. In the open position, it holds up a flat or other unit of scenery. A Tip Jack is a combinaton of a jack and castors so scenery can be supported or rolled. When it is in position, it is tipped to vertical. When rolling, it leans backwards.

JACKFIELD
An array of jack sockets ('jills'), providing connections to equipment/outlets etc. A patch panel.

JUMPER
An adaptor from one type of electrical connector to another. For example, a 13 - 15A jumper has a 13A plug and a 15A socket at either end of a short cable. Also applicable to sound cables.

KEY
A section on a lighting or other technical layout plan, which denotes what the symbols on the plan refer to. 
Although many symbols are standardised, there are variations, and to avoid confusion (or errors) when rigging and laying out equipment, a key is essential to ensure the requirements of the design are correctly interpreted. 
Lighting Paperwork

KILL
To switch off (a light/sound effect); to strike/remove (a prop).
(e.g. Kill channel 6 please)

KILOWATT
1 kilowatt (1kW) is equal to 1000 Watts. The WATT is a measure of electrical power. The single letter 'k' is often used to represent 'kilowatt'. "2k fixture" means a 2000 Watt (or 2kW) lantern etc.

LADY AND THE TRAMP
A Lady and the Tramp moment occurs when two people clearing and coiling LX or sound cables end up both coiling the same one. Named after the Disney classic animation where two dogs end up eating the same piece of spaghetti.

LATENCY
In digital live sound systems there are tiny time delays due to the processing time required to convert sound from analogue to digital and back again. This time period is known as the LATENCY of the system.

LAVALIER MICROPHONE
Originally, a mic worn around the neck on a string. Now applies to a small 'tieclip' microphone. These microphones are used for TV and also in musical productions requiring the amplification to be 'invisible'. The mic is worn in clothing, in hair / wigs, over the ear or on the face (heavily made-up).

LEADER TAPE
Non-magnetic plastic tape used to begin and end sound tapes and to separate cues on tape. Clear leader tape is used to activate the automatic stop on some playback machines. Leader tape is available in a variety of colours.

LEMO
A small metal multipin connector used for connecting radio microphone heads into the transmitter pack.

LEVEL
1) The setting of a light or sound control channel. On a lighting desk, levels range from 0% to 100% (also known as FULL). On a sound desk, the bottom of the fader is ∞ (infinity) and the top may be +20. The fader is designed to be operated at it's optimal position which is labelled 0dB. The decibel (dB) scale is a measure of sound intensity. 
2) A platform used to change the height of an actor. Interesting dynamics between different characters in the play can be explored using various levels. 

LIMITER
See COMPRESSOR.

LINE ARRAY
A vertical cluster of flown speaker cabinets positioned either side of a stage to give a more controlled coverage of sound than is achievable with speakers on stage. Line Array speakers provide a more focussed beam of sound with a high loudness level without wasting energy amplifying sound which is projected towards floors / ceilings.  
Sound on Sound: Line Arrays Explained

LINE CHECK
An important part of the sound check process, the line check is a methodical test of every instrument or microphone that is connected to the sound desk. It enables the sound engineer to ensure that everything is working correctly and is connected as he expects it to be, and is in the correct place on stage.

LINE LEVEL SIGNAL
Standard' level at which the inputs and outputs of domestic and professional sound equipment operate. Slight variations are that some equipment works at +4dB, some at -10dB. See MIC LEVEL SIGNAL.

LINE-UP TONE
Signal of known frequency and level used for setting up sound recording equipment levels accurately.

LOOM
A neatly-organised bunch of cables. A wiring loom is used to avoid messy runs of cables by keeping the cables going in the same direction (to the same piece of equipment) tied together. This saves time when installing and packing-down equipment, and ensures that a piece of cable can't be mislaid or left behind. 
The cables can be taped together (using PVC tape, never Gaffer Tape) or, for more long-lasting arrangements, with cable ties. More environmentally-friendly companies use short lengths of rope for the same purpose, which are re-used over and over again. Strips of rubber can be used for the same purpose. 
The looms are named according to their purpose (e.g. the Control Loom goes from the control desk to associated equipment, and may contain a power cable, a communication cable and a DMX512 cable for the control signals). 
Known as a 'hod' in the USA (apparently from old French term for intestines).
Also known as a TRIPE. 

LOUDSPEAKER
Device for converting the electrical signal from an amplifier back into sound waves, most commonly by vibrating a paper cone. Most speaker systems are composed of a number of sources - each designed to handle a specific range of frequencies. See Tweeters and Woofers, Bi-Amplification.

MADI
Acronym for Multichannel Digital Audio Interface, this is a standard way of sending digital audio signals over distances over 100m. Developed by AMS Neve, Mitsubishi, Solid State Logic and Sony, it is defined and monitored by the Audio Engineering Society. The standard is also known as AES10. MADI supports serial digital transmission over coaxial cable or fibre-optic lines of 28, 56, or 64 channels; and sampling rates of up to 96 kHz with resolution of up to 24 bits per channel.

MASTER
1) An overall control fader or lever on a lighting or sound control board. The Grand Master takes precedence over all other controls and allows the operator to fade out the entire output of the lighting desk.
On a lighting desk the PRESET MASTER allows the control of a section of the desk independently from the rest.
See also SUBMASTER.
2) An original (e.g. Master tape, master plan) which should be used only to make a copy from which to work.
3) A Department Head (e.g. Master Carpenter, Master Electrician).

MATRIX OUTPUT
Set of outputs on a mixing desk which allows the user to preset a number of output configurations. eg on a 8 x 8 matrix, each of the 8 group outputs from the channels can be routed to any or all of the matrix outputs.

MD
1) See MUSICAL DIRECTOR.
2) Mini Disc. See DIGITAL RECORDING.

MIC
(pronounced 'Mike') Abbreviation for microphone.

MIC CHECK
Process of testing the functionality and audio quality of the microphones used in each performance. It's particularly important when using radio mics, to check for any crackles or loss of signal. 
One by one, the mics are tested, ideally with no other noise or activity taking place on stage. The sound team can listen for unusual noises and can confirm that each mic is connected correctly (ie that it appears in the correct channel on the sound desk) and that it works. 
It's a different process from the sound check, which takes place with the performers, to check for the correct placement of the mics, and to enable the sound team to balance / adjust the mics for best quality. 

MIC LEVEL SIGNAL
Low level audio signal produced by circuitry in microphone. Needs boosting either by a pre-amp or a mixing desk before it can be amplified. Susceptible to interference over long cable runs.

MIC PLOT
A chart showing which character / actor uses which radio microphone throughout the show.
Vertically down the page are the scenes, musical numbers etc. 
Across the page are the numbered microphones. 
This enables the sound operator to instantly see who is using each microphone at every point during the show. 

MIC POUCH
A small fabric pocket that can contain a radio microphone transmitter pack. The pocket is often made of a slightly elasticated material (e.g. lycra) in black, and is attached to an elastic belt, or has a belt loop built in, if it's to be worn on the outside of a pair of trousers under (e.g.) a jacket. 
Mic Pouches from Canford Audio, UK

MIC UP
The process of attaching a radio microphone to a performer. The transmitter pack contains the battery and on/off switch, along with a short aerial cable and the microphone connection. This pack should be placed securely in a pocket, or in a mic pouch worn under the outer costume layer. The microphone head is connected to the transmitter via a cable, which should be run under the costume (with the cable held in place using micropore (surgical) tape if necessary) to the back of the performers' head, and the microphone should then be positioned either above an ear, in the middle of the forehead at the hairline. Having the microphone attached to a costume should be the last option, because the distance of the mouth to the microphone will change when the performer turns her head, making it very difficult for the sound operator to balance the wildly varying levels. 

MICROPHONE
A transducer which converts analogue sound vibrations into an electrical signal which can then be amplified or recorded onto tape. Signals from a microphone are very low level and are amplified in the mixing desk to line level.
There are many different types of microphone, each designed for a specific purpose. 
They can broadly be divided into three groups:
1) General Use - designed to be placed in front of and relatively close to a sound source, used for vocals and instrument mic-ing. 
2) Directional - also known as shotgun microphone - picks up from a longer distance away from the source
3) Body-worn - small size, consisting of a microphone head and a separate electronics pack.
General use and body-worn mics are available in wired or wireless (radio) versions. 
See Dynamic Mic, Condenser Mic, Phantom Power, Pick-up, Radio Mic.

MICROPHONE CAPSULE
An interchangable microphone head that fits onto a pre-amplifier. Many capsule types are available, all of which fit the same pre-amplifier.

MIDI
Musical Instrument Digital Interface. Control system established in 1983 for linking musical instruments or other electronic equipment and computers together and storing the control signals the equipment produces for subsequent playback.
See MSC, MMC, SYSTEM EXCLUSIVE.

MINI DISC
See DIGITAL RECORDING.

MINIJACK
Also known as a 3.5mm jack, this is found as a headphone outlet on many pieces of personal audio equipment or laptops. A minijack to twin-phono cable is used to connect from a laptop, phone or MP3 player into a sound system or mixing desk that has phono ('pin plug') input connections.

MIRROPHONIC
Trademark of Western Electric. Film recording and playback system which created variable density optical tracks on the film. Used from around 1933 - 1948. It produced higher-fidelity sound in comparison to the less complex variable area optical tracks.
1933: Logo appears in Motion Picture Herald [ref]
1938: Sound system installed in Brisbane [ref]

MIXDOWN
The process during which a multitrack recording is balanced and transferred to two tracks (stereo) for playback or reproduction.

MIXER
A desk comprising a number of input channels where each sound source is provided with its own control channel through which sound signals are routed into two or more outputs. Many mixing desks can also change the quality of the sound (see EQUALISATION).
A Powered Mixer has an amplifier built into it. Sound sources of varying levels are accepted which can be amplified if necessary.
Also known as a Sound Desk or Sound Board. (See Line Level, Gain).

MMA - MIDI Manufacturers Association
(From the MMA website) The MIDI Manufacturers Association (MMA) is the publisher and authoritative source of MIDI specifications. Manufacturers achieve interoperability through compliance with MMA Recommended Practices. We provide forums for developers to coordinate changes to the MIDI specification, which today remains one of the most relevant standards in the entertainment industry.
MMA website

MMC
MIDI Machine Control. A variation of the MIDI language designed for controlling mechanical equipment (eg Tape Players).

MONITOR
1) An onstage speaker which allows a performer to hear the output of the PA system, or other members of a band.
2) A video display screen (not normally able to receive broadcast TV pictures) used with a CCTV system or a computer.

MONITOR WORLD
The location on the stage / in the venue where the mixing desk and amplifiers for the on-stage monitor speakers is located. The monitor speakers are used to send a specific part of the audio mix to each musician/performer (or group of musicians). 
In-Ear Monitors are often used now, to reduce the overall volume on stage, and to give performers a better quality audio signal, with an easily adjustable volume control. These work like reverse radio microphones, where the output of the Monitor Mixing desk is sent to transmitters, which send to a receiver worn by each musician. 

MONOPHONIC (MONO)
Single channel sound recording, as opposed to STEREOPHONIC, which uses two channels (left and right).

MOTIVATED SOUND
A sound effect that is called for in the script of the play, or is motivated by the actions of a character. Examples include an actor switching on a radio to hear an announcement, an actor running a bath offstage, or a car pulling up outside the house. 
See also: ENVIRONMENTAL SOUND

MP3
Compressed audio file format, short for MPEG-1 Audio Layer 3. Enables 'good enough' audio quality when moving music around on portable devices. However, MP3 compression can sound awful through a theatre PA system, so ensure you are always using the best uncompressed version of music and sound effects tracks for a show.
The technological standard was agreed in 1991, and MP3s became widely used by the public in 1993. 

MP4
MP4 is a multimedia container format, which can store video, audio or still images.
See also MP3 (audio only)
What is MP4?

MS
1) MS stands for Mid and Side. It involves the use of two different types of microphone capsule - a cardioid for the M and a figure-eight for the S. The biggest advantage is that centre sounds are not 45 degrees off-axis as with XY, because the Mid capsule points along the centre-line. This means that there isn't so much of a 'hole' in the centre of the stereo image. The Side capsule is placed at right angles to the M capsule. The M is connected to a mixer channel. The S is split into two and connected to two mixer inputs. The M is panned centre. One of the S inputs must be phase-inverted. Find out which is the left and which is the right and pan hard left and hard right respectively. If set correctly, there will be no noise if the M is switched off because the two S channels cancel each other. Originally, there were problems with reflections and due to the use of two different capsules, although single-point MS mics have been developed which overcome the problem quite effectively.
2) Midstage (the area between upstage and downstage). 

MSC
MIDI Show Control. A control language which is an extended version of the original MIDI language. In addition to a 'go' command, cue numbers and other information can be sent as well (in addition to fault reports and safety checks).

MULTI
Short for MULTICORE.

MULTICORE
A flexible electrical cable composed of many well-insulated sets of cables covered in a strong PVC or rubber covering. Enables a number of different circuits to be carried down one piece of cable. Both lighting (power) and sound (signal) multicores are available.
Sometimes known as a Multi or Snake.

MULTIPAIR CABLE
See MULTICORE.

MULTITRACK
The process of recording a complex piece of audio consisting of multiple sound sources using a separate audio 'track' for each source (or section). The tracks remain separate and can be adjusted / modified to change the balance of the final mix, and additional layers / tracks can be added after the initial recording to correct mistakes or to build on the density of the mix. 
Multitrack recordings to download

MUSIQUE CONCRETE
(French) Music made from found sounds, originated in France & Germany in the 1940s & 50s (when audio tape came into prominence as a recording and editing medium) and was the basis of the groundbreaking work done by the BBC Radiophonic Workshop in the 1960s and 70s.

NAB
National Association of Broadcasters.
Also used as shorthand for the standard for tape recording equalisation characteristics that association developed..
NAB website

NAGRA
A portable audio reel-to-reel tape recorder, manufactured by Kudelski in Switzerland. The analogue Nagra was the industry standard for radio & TV reporters and for film location sound. The company now manufacture digital recorders to the same rugged build quality.
Nagra website

NLE
Acronym for Non-Linear Editor. This is audio, video or image editing software in which the original content is not altered in the editing process.

NOISE BOY
(Colloquial term) Theatre or concert sound engineer. Sometimes male, but not exclusively so! Also known as a Hum Head. See also Techie and Lampy.

NOISE GATE
A piece of sound processing equipment that reduces background noise by muting a sound signal when it falls below a certain level, restoring it when the level increases again. Must be used on vocal microphones with care, because it may cut the signal off, although the vocalist is still singing quietly. Also known as an Expander.

NORMALLING*
TO BE DEFINED

OCTAVE
A series of 8 notes on a piano keyboard which separate (and include) two notes, one of which is twice or half the frequency of the other. 

OG
1) Abbreviation used by the Phantom in The Phantom of the Opera, when he writes letters to the theatre managers. Short for Opera Ghost.
2) Urban slang 'Original Gangster' or 'Old Git' (from Internetslang.com), meaning a product which is now past its' prime, or was one of the first of its' type. 

OHM
The unit of electrical resistance.

OMNIDIRECTIONAL
See PICK-UP.

OPTO-ISOLATOR
Electronic component which transfers electrical signals between two isolated systems using light. This helps to prevent damage from high voltage spikes, and also isolates troubling ground loops in audio or lighting control signals from affecting audio quality and integrity of the control signal. 

OUTRO
A piece of music or media, or a part of the performance, which takes place at the end of the performance. The opposite of an INTRO. 

OVERHEADS
1) Microphones positioned above a drum kit to pick up the cymbals etc. without getting hit.
2) Microphones positioned over the stage to pick up the overall sound of the concert / production.

PA SYSTEM
Short for Public Address System.

PACK
See RADIO MIC.

PAD
A switch on a mixing desk input channel which attenuates (reduces the level of) a signal. Used if a loud / high level signal is causing the desk to be overloaded.

PAGE
1) See PAGING.
2) Some theatre announcement systems use the term 'PAGE' to mean making a call (e.g. 'Can you page Simon to come to the fly floor')
3) A way of increasing the functionality of a control on a lighting desk. For example, most computerised lighting desks with SUBMASTERS will allow you to store more than one lighting state in each submaster. Each group of submasters is given a page number which is used to select which set you want to use. See also SUBMASTER.

PAGING
The act of holding a tab etc. back to allow large items or actors offstage. Also preventing microphone etc cables from getting entangled by pulling / releasing them from offstage as performer walks around.

PAN
1) A control on a mixing desk which allows the operator to position the channel's output in the final stereo image (L - R).
2) A horizontal (side-side) movement of a camera or a moving light. Short for Panorama. See also TILT.

PANATROPE
Gramophone with built-in valve amplifier and speakers, used to play 78rpm discs for music and sound effects. Used in the late 1940s (and probably earlier) for playing sound effects on stage.  More information coming soon.

PARAMETRIC EQUALISER
Equalisation control where the range of frequencies to be boosted or cut can be selected. Allows the 'fine-tuning' of the equalisation.

PARAMETRIC SPEAKER
Highly directional speaker which produces a very narrow beam of sound using ultrasonic waves as carriers. When the ultrasonic waves collide with an object (or the listeners's head) the sound waves become audible to that person.

PASSIVE
Opposite of ACTIVE. See ACTIVE.

PASSIVE SPEAKER
A speaker that needs an external amplifier to operate. It requires a speaker-level amplified signal to operate, unlike an ACTIVE speaker, which has a built-in amplifier. 
See also ACTIVE SPEAKER.

PATCH
1) (verb) The act of plugging a lantern into a dimmer (e.g. 'Can you patch circuit 12 into dimmer 18 please') or on a lighting desk allocating control channels on the desk to dimmers or fixtures in the rig - this is known as a SOFT PATCH.
If written down, this is known as a Patch Schedule or Patch List. 
2) (noun) The system for connecting lanterns to dimmers (The Patch).
The term also applies to sound - a PATCH BAY is used to connect outboard equipment into the sound desk and to connect sound desk outputs to amplifiers, and amplifiers to speakers.

PATCH BAY
See PATCH.

PATCH PANEL
A board consisting of rows of sockets into which plugs can be connected to route sound signals or power for lighting circuits. Some American systems use a Pin Plug patching system. See also PATCH.

PATCHING
1) To cross-connect lighting circuits around the stage area to a chosen dimmer. Connecting lanterns to dimmers. This is sometimes known as a hot-patch (because you are potentially patching live power). The connectors used in a hot-patch system must not permit the user to touch live connections. 
2) Using a cross-connect panel which enables any stage lighting channels to the control desk to control any dimmer or group of dimmers. Some large lighting boards have the facility for soft patching - a totally electronic way of patching. Some Rock Desks have a pin patch which allows groups of dimmers to be allocated to a particular control channel. Also applies to routing of sound signals.

PCC
Phase Coherent Cardoid. See BOUNDARY MICROPHONE.

PFL
See PRE-FADE LISTEN.

PHANTOM POWER
Some condenser microphones require a power supply in order to operate. If this supply is not from a battery within the microphone body, it is known as a phantom power supply. It is usually 48 Volts DC (can be 9 - 52 volts from most mics), and is supplied either by a separate battery pack, or by the sound desk. The supply is termed 'phantom' because it is 'invisibly' carried down the same microphone cable as the sound signals.

PHASE
Two identical sound waves which are slightly apart in time are said to be out of phase; two identical waves are in phase.

PHASES
Electricity is generated and supplied to large installations as three separate supplies, known as phases, and labelled L1, L2 and L3 (for Line).
Until recently, the three lines were colour-coded Red, Yellow and Blue in the UK. Now, across Europe, the three lines are colour-coded brown, black and grey, with the neutral coloured blue.
Each of the phases and one neutral are supplied down a single multicore cable to the building, but effectively give three separate supplies. Because there is a potential difference (voltage) of 415 volts between any two phases and earth/ground, care must be taken that pieces of equipment powered by different phases are not capable of being touched at the same time in case of a fault.
This usually means that such equipment should not be on the same physical lighting bar, or in the same part of the studio theatre.

PHONE PLUG
(US) 1/4' Jack plug

PHONO
Short for Phonograph. Sometimes shortened further to just 'PH'. The inputs on a audio amplifier that a vinyl record deck should be connected to. The audio level of a standard record deck is much lower than (for example) a CD player, plus there is an equalisation circuit (or there should be), which is specified by the RIAA, to overcome the colouring that a record deck adds to a recording.

PHONO PLUG
An unbalanced audio connector used for connecting line-level equipment together (eg CD player, tape recorder). Unsuitable for professional use due to lack of durability. Also known as RCA connector, Pin Plug.

PICK-UP
1) Device which, when attached to an acoustic musical instrument, converts sound vibrations into an electrical signal.
2) A way of describing the directional sensitivity of a microphone. An Omnidirectional microphone has equal pick-up from all around, a Cardoid microphone is more sensitive from the front, a Super-Cardoid or Hypercardoid has very strong directionality from the front. A figure-of eight microphone picks up front and rear, but rejects sound from the sides.
3) The action of turning a followspot on a performer. (e.g. 'that was a good pick-up', 'your next pick-up is downstage left'). A BLIND PICKUP is on a moving performer and requires good hand-eye co-ordination. A SET PICKUP is on a specific area, is preset, and is made on a cue from the stage manager. A SIGHT PICKUP is made visually by the operator to a preset position.

PIN PLUG
See PATCHING, PHONO PLUG.

PINK CONTRACT
IATSE contract for Broadway or touring sound engineers between IATSE and the Broadway League. Known as a 'Pink'.  
Pink Contract on the IATSE website

PINK NOISE
Random sounding audio noise containing all frequencies in the audio spectrum tuned to the response of the human ear. Used with a Spectrum Analyser to set equalisation equipment for a large PA installation. However, the human ear is still a better judge of how a system sounds. See also WHITE NOISE.

PIT NET
Protective net across the orchestra pit to prevent any objects (or actors) falling from the stage and injuring musicians.

PITCH
1) The frequency of a sound defines the pitch. A higher frequency gives a higher pitch note. See PITCH CONTROL.
2) The seat pitch is the distance between one row of audience seating, and the same point on the next row. 

PITCH CONTROL
Facility on some sound playback devices for changing the speed of playback, and thus the pitch or frequency of the sound, to match an existing sound, or to fit a particular timeslot. Some Professional CD players have tempo controls which speed up the playback, and then compensate for the resulting increase in frequency using a pitch change. This results in the ability to match the beat of a CD in a disco situation, without the 'Pinky and Perky' effect.

PLASA / P.L.A.S.A.
Professional Lighting and Sound Association (UK).
See ESTA for the American equivalent.
PLASA website

PLATE REVERB
Reverb effect produced using a large metal plate. A signal is supplied to an acoustic transducer at the edge of the plate, causing vibrations which are picked up by transducers at other locations on the plate. This type of reverb can be simulated by some digital effects units.

PLOT
1) List of preparations and actions required of technical crews during the performance (eg Sound Plot = list of sound cues and levels in running order.) In the US, the term plot refers to a plan. (eg Light Plot = scale plan showing lighting instruments). See also RUNNING PLOT, STATE PLOT.
2) Session during which lighting states are created or checked with the director, on stage, with furniture and stand-in actors. This is also the name for the session during which sound levels are set (but this should not happen at the same time as the lighting plot!). 
3) The basic story thread running through a performance / play which gives the reason for the character's actions.

PLOTTING SESSION
Time during which the plot for each department is prepared (eg Lighting Plotting session). Also known as The Plot. 
See also PLOT. 

PLUG
A power or signal connector with a pin or pins which is used to make a connection from a power or signal source (the socket) to a device or another connector. 
Plugs are not used as a source of power, because of the risk of electrocution by touching the fully exposed pin connections. 
Sockets, where the connection is shielded, are used as the source. 

PMSE
Abbreviation for Programme-Making and Special Events. Licence required in the UK to use radio mics, walkie talkes etc of certain types for TV/Film/Events production.
UK Ofcom Page

POINT CUE
A cue inserted during / after plotting between two existing cues. (eg 8.5 is inserted between cues 8 and 9). Most computer lighting desks have the ability to either insert an additional cue in a sequence, or to link to another cue out of the sequence, and then link back again. Inserting cues into a plotted sequence on a manual lighting desk is more awkward, because it is a running plot (where only the changes between cues are noted down). Stage Management may prefer to call 8A instead of 8.5, but this is down to personal preference.
Sound cues which relate to an already-running cue within a sequence should have lettered cues (e.g. 8A is a fade up of Cue 8 and 8B is the fade out).

POP SCREEN
A thin gauze screen placed between a singer and a microphone to reduce vocal 'popping' and other breath noise. This noise is particularly produced by pronunciation of plosive sounds (P, B, T).

POP SHIELD / POP FILTER
A foam shield placed over the end of a microphone to reduce the pick up of vocal 'popping' and external wind noise.

POWER AMPLIFIER
Converts sound signals of line level (approx 1 volt) into tens of volts, with currents of around 1 Amp to drive speakers.

PPM
(Peak Programme Meter) Meter, often with green/red LED's, giving an accurate indication of the electrical nature of an audio signal (see also VU Meter).

PRE-FADE LISTEN
Often shortened to PFL. Control on a sound mixing desk which allows the user to check the presence of a signal, and its quality before bringing up the fader. Also vital for fault-finding, where the route of a signal can be PFL'ed around the desk until the point where the fault occurs. Also known as CHECK and CUE.

PREFADE / POSTFADE
An output from a sound desk is said to be prefade if it is independent of the channel fader. If it is postfade, the level of the output is relative to the channel fader.

PROCEDURAL AUDIO
Term for realistic sounding audio which is synthesised in real time on demand by software. This could be triggered by physical actions on a set or by movement sensors or infrared camera feeds, or at random. Seen as a possible future for sound design for theatre & film, and to increase the variety of audio present in gaming applications.

PRODUCTION SOUND ENGINEER
Often shortened to PE. Works alongside the Sound Designer to help in translating artistic ideas into equipment (and installing it).

PSU
Power Supply Unit.

PSYCHOACOUSTICS
Psychoacoustics is the branch of psychology concerned with the perception of sound and its physiological effects. 
The Haas Effect is used to trick audience members into believing the source of a sound is the stage, rather than a nearby speaker with a slight delay on the sound. 
MP3 audio compression uses psychoacoustics to remove sounds that are masked by others to reduce the file size. 

PUBLIC ADDRESS SYSTEM
The venue auditorium sound system. Usually shortened to "PA". Most theatres will have a separate sound system for emergency announcements in all public areas of the theatre. This system may also be used for Front of House calls. The Rear of House calls system often also acts as a SHOW RELAY, conveying the sound of the performance to remote parts of the theatre building.

PUNCH IN
A facility on multitrack recorders which allows you to 'drop in' a sound onto a track whilst playing through the tape, sometimes controlled by a footswitch. Useful for correcting mistakes in an already recorded tape.

PZM
Pressure Zone Microphone. See BOUNDARY MICROPHONE.

QUADROPHONIC
A sound system which uses four independent speakers (or sets of speakers). Each speaker replays a separate soundtrack, often fed by a four-track tape machine. The fore-runner of today's Surround Sound.
See also Stereophonic.

QUANTIZE
The process of imposing a rigid timing / rhythm onto a music track in audio composition / editing software.

RACK
1) A cabinet of standard width (19') into which various components can be bolted. Racks are ideal for touring equipment, are neat, and they allow easy access to the rear and front panels.
2) See Dimmer Rack.

RADIO MIC
Device consisting of a microphone head, transmitter pack with batteries, aerial and mains receiver unit which allows actors and singers to be amplified with no visible means of connection. Almost universally used in musicals where the singers have to be amplified to be heard over the orchestra / band. Used in non-musical shows for sound reinforcement.
Can be Handheld (where the microphone head, transmitter pack and batteries are all in one unit) or Lavalier (where a miniature microphone is either clipped onto clothing or body worn).
Radio mics use either VHF or UHF frequency bands to send the radio signals from the transmitter to the receiver. UHF systems tend to have better range than VHF, have more frequencies to select from, and are less susceptible to intereference from TV systems. Radio systems are being replaced in some situations, by digital wireless systems which use a digital wifi signal to transmit the audio. These can run into problems in areas with existing wifi networks and a lot of users with connected devices.

RAT STAND
Illuminated music stand (named after manufacturer).
R.A.T. website

RCA
See Phono Plug. (RCA = Radio Corporation of America)
RCA Corp website

RCD
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.

RECITATIVE
Musical terminology for a sung dialogue passage, in the rhythm of ordinary speech, during an opera, operetta or oratorio. Often shortened to RECIT.

REPETITEUR
Répétiteur is an accompanist, tutor or coach of ballet dancers or opera singers.

RESLO
Rugged microphone connector used on the Reslosound range of microphones, and in some theatres before the 3 pin XLR became ubiquitous. 

RESOLUTION
1) The point during a drama when the plotline reaches a conclusion, and conflict is resolved.
2) A measure of the quality of a video display / projection. Measured in the number of pixels width x height. 
3) 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).

RESONANCE
TO BE DEFINED

RETURN
1) Flats joined to the DS edge of flats of a set or unit that 'return' into the wings. They help mask and also keep the DS edge of a set from looking raw.
2) A financial report given to theatre management staff by the box office manager on a daily or weekly basis setting out the takings for performances (known as the Box Office Returns). 
3) Route for an auxiliary signal back into a sound mixer (see also SEND).

REVERB
(Reverberation) Effect which may be added to sound effects during recording or to a voice during performance. Sustains the sound longer than normal, as if the sound was reverberating around a large building (eg cathedral). Persistance of sound after the source has ceased.

REVERSE RADIO
A sound system that works opposite to a radio microphone - a sound signal is transmitted from the mixing desk to a battery-powered receiver, amplifier and speaker. Used for relaying a fully controllable sound feed to a remote location on stage - often used for an on-stage prop radio or tape player. This system is also used for in-ear monitoring (IEM).

REVOX
Brand name of the once industry standard reel to reel tape recorder. Still enormously popular and universally known.

RF
Radio Frequency.

RF CO-ORDINATOR
Member of the sound team on large scale events who ensures that all users of radio frequency devices (radio mics, comms, in-ear monitors, IFB etc.) have radio frequencies allocated to them which do not interfere with each other, and are covered by the appropriate licences in the region in which the event is taking place.

RIAA
Record Industry Association of America. The standard equalisation to be applied to a signal from a record deck pick-up. Phono pre-amps have RIAA circuitry built-in.

RIBBON MIC
Delicate mic not suitable for high sound pressure levels. Consists of a corrugated conductive foil strip suspended between opposing magnetic poles which is excited by pressure differences between the front and rear of the microphone and induces a current.

RIDING THE FADER
Sound operating technique where the operator constantly adjusts the fader level to maximise level while minimising feedback and background noise.

RIFLE MIC
See Shotgun Mic.

RING OUT
Process of maximising the volume of sound possible through a sound system before feedback ("ringing") occurs. The equalisation controls on the mixing desk channels are used, along with gain controls to reduce the chance of feedback.

ROUTER
Computer networking device which connects different networks together. Common uses in theatre are to connect technical networks to the internet, or to create wifi networks for technical purposes. Network cabling can connect lighting desks to dimmers and to additional interfaces to enable wireless control or computer-based control of systems. In sound, mixing desks and remote input/output interfaces can be connected via network cable, saving vast amounts of time connecting multicore audio cables, and again enabling wireless remote control of various systems. 

RT60
Also known as reverberation time, the RT60 is the time taken for an impulse sound to decay by 60 dB. For speech, the RT60 of a space should be lower than for a room used for music. In general, as the volume of a room increases, the RT60 time can be longer. The RT60 time of a room can be estimated using mathematical formulae.

RTA MICROPHONE
(Sound) RTA stands for Real-Time Analyser - a system that analyses the audio through a sound system and displays the result, or uses the result to calibrate the system. The analyser requires a 'reference' microphone of known type and quality, to enable the analysis to be accurate.
For example, the dbx RTA-M Measurement microphone is used with the DriveRack PA system to calibrate it for the environment. Pink Noise is played through the system, and the RTA mic 'listens' to the replayed audio and automatically calibrates the system for best audio quality. 

SAMPLER
Electronic device for recording a series of sounds digitally so that they are available instantly for playback. Samplers for theatrical use have a number of independent outputs (normally 8) to which any sound sample can be sent at any time. Samplers can be controlled by a MIDI keyboard or by computer control.

SAMPLING
The technique of recording a sound digitally (translating the analogue audio waveform into a series of electrical ons and offs that can be manipulated by a computer) for subsequent processing, editing and playback.

SCORE
1) The score is the written notation of a musical work. An arrangement of a piece of music for piano is called the Piano Score. An arrangement for a singer is the Vocal Score.
See also LIBRETTO.
2) A series of directions for a physical theatre / dance performance is sometimes called a 'score'.
3) A soundtrack running underneath a performance is called UNDERSCORE.
4) The music / sound tracks running during a performance is sometimes called the score.

SCRIBBLE STRIP
DIsplay window on a lighting, sound or automation control desk which enables the user to add a description of the function of that channel. Can be entered as text, or a hand-drawn image or text. This enables graphical characters (e.g. Chinese) to be used, or other symbols. 
On older analogue systems, the channel function was written on a piece of white PVC tape that was stuck on the control desk. Some systems had a white plastic strip on which chinagraph pencils (wax) could be used. 

SEND
See AUXILIARY OUTPUT.

SEQUENCING
A act of recording digitally and manipulating the MIDI information required to remotely play a synthesizer keyboard or similar device. A sequence of notes.

SFX
1) Abbreviation for SOUND EFFECTS.
2) Windows media playback software by Stage Research.

SHIELD
In an audio cable, a conductive cylinder around one or more center conductors that protects against unwanted electrostatic fields that could induce a signal, heard as a hum or buzz, across the conductors of the cable.

SHOTGUN MICROPHONE
A type of highly directional, high quality condenser microphone which can be placed a relatively long way from a sound source. A shotgun microphone uses a hypercardoid PICK-UP pattern.

SHOW CONTROL*
TO BE DEFINED

SHOW RELAY
A network of speakers carrying the sound of the show, and sometimes stage managers calls, to the furthest reaches of the theatre. (e.g 'Can we turn the show relay down please?')

SHURE
(Manufacturer) American sound equipment maker specialising in microphones (especially the industry standard SM58 vocal mic).
Shure website

SIBILANCE
Undesirable characteristic of some performer's speech when s, sh or ch sounds are emphasised.

SIGNAL PROCESSOR
Audio equipment that modifies or enhances the audio signal. Examples of signal processors include Graphic Equalisers, Noise Gates, Effect Processors, Delay Lines, Compressors and Limiters. 
Digital sound desks now have these functions built in, but separate (outboard) equipment is still required for many applications. 

SIGNAL TO NOISE RATIO
The ratio of the average signal (recorded or processed) to the background noise (due to the recording medium or electronic processing). The ratio is usually expressed in decibels.

SMPTE
(pronounced 'SIMPTEE') SMPTE stands for Society of Motion Picture and Television Engineers (US). 
The term refers to a timecode for synchronising pre-recorded show elements (e.g. sound or video) with other elements. For example, a timecoded 'click' is played to the musicial director to enable her/him to keep in time, and lighting and video cues are triggered at a particular time within the piece of music. Timecode is measured in hours, minutes, seconds and frames. There are usually 30 frames per second, meaning an accuracy of 1/30th of a second is possible. 
Where the timecode is played as an audio track, it's known as Linear Timecode (LTC). 
SMPTE website
Theatrecrafts.com: Controlling Lighting and Sound With Timecode

SNAKE
See MULTICORE.

SNAP
A lighting or sound cue with no fade time - the cue happens instantly.
This can be acheived on a computerised lighting desk by using a fade time of zero seconds.

SOCAPEX
A multipin connector which can carry a series of lighting or sound circuits. Very robust and designed for touring. Available in 19 pin (6 circuits) and 37 pin (12 circuits) configurations. Sometimes shortened to SOCA. See also LECTRIFLEX.

SOCKET
A power or signal connection point where a plug can be inserted to make a connection from the source of power. Sockets can be used as signal outputs or inputs, and are usually used as power outputs, due to the shielded connections, making it impossible to touch the live connections with fingers. 
Sockets are often wall or panel mounted, while plugs are used to connect portable equipment. 
There are exceptions of course - powercon connections which are panel mounted can be either power inputs OR outputs, and are differently colour coded to make it clear which is which, and the connectors are designed so they cannot be used incorrectly. 

SOFT KEY
Short for Software Key. A button on a lighting or sound desk whose function changes according to your last action. The function of the soft key is often shown on an adjacent display panel. The keys are often numbered rather than being labelled (e.g. on the ETC Express and Ion range of lighting desks, the soft keys are numbered S1 to S8).

SOLO
1) On a sound desk, the solo button on each input channel silences all other inputs so that channel alone can be heard. Dangerous to use during a show, but can be useful for fault-finding or testing equipment.
2) On a lighting desk, SOLO mode kills all other channels except the single dimmer you're working with. Again, can be useful for identifying a channel in a large rig, but can be dangerous during a show. Some desks allow you to assign flash buttons to SOLO mode which will turn off all channels except those loaded into that flash button or submaster. This can be used for a quick lightning effect (but it's a bit tacky). On Strand Lighting memory desks, the solo function is called REMAINDER DIM (or REM DIM).

SON ET LUMIERE
An audiovisual entertainment often based on an historical theme (and often produced in a historically relevant location). A voice narration is often used and lighting / special effects set the mood and portray certain events in time with the narration. Often used to refer to a performance with no performer where the meaning is communicated solely with technical effects.

SOUND BOARD
See MIXER.

SOUND CARD
Originally an accessory to a computer which equips the PC with the ability to play back and record sound. Early Windows sound interfaces were the Creative Sound Blaster (from 1981 - present) or cards made by Turtle Beach.
The term now (sometimes) refers to any external sound interface designed to allow multiple audio devices to connect to a Windows or Mac (or other) computer. External sound cards / audio interfaces were connected via FireWire, and are now connected via USB. 

SOUND CHECK
A thorough test of the sound system before a performance. This will include checking each speaker cabinet individually, and each playback device. In the case of a live concert, this is the session when each instrument is played in turn for the sound engineer to check and fine-tune the sound. A line check should be carried out methodically to ensure that every input to the sound desk is working correctly.

SOUND DESIGNER
Member of the production team who has the responsibility for planning and executing the layout of all sound playback and reinforcement equipment for the show. This role also includes the sourcing of music and sound effects for the production.
See also SOUND OPERATOR.

SOUND DESK
See MIXER.

SOUND EFFECT
See Effect, Sound.

SOUND ENGINEER
Member of the Sound Department / Audio Department, also known as Audio 1, who is responsible for operating the sound mixer to ensure that microphones and other audio sources are mixed to carry out the sound designers' vision for the show. Although many operations can be automated, to ensure that groups of microphones are unmuted at the right time, to ensure maximum quality and volume in the sound mix, faders must be continuously monitored and adjusted - only microphones that are needed at each precise moment should be 'live' so that no unwanted sounds are audible through the PA system.
The sound engineer on a musical will usually have an assistant working backstage, who ensures that radio microphones are working, and are fully charged, and allocated to the correct performers. Any faults during the show should be remedied (by changing batteries, adjusting aerials or replacing microphone heads) and communicated to the sound engineer immediately to adjust the mix accordingly. 

SOUND OPERATOR
Also known as Sound Op. The Sound Operator is responsible for operating the sound playback and mixing equipment for a show. They are sometimes a member of the Electrics department of the theatre and work with the sound designer for the production, or they may be employed just for the show. 
The main operator is called Sound No.1 (or Audio 1)
A standby / second operator is Sound No.2 and so on. 

SOUND REINFORCEMENT
Amplifying a voice just enough so that it can be heard, without the audience being aware that it is being amplified (ideally !).

SOUNDCRAFT
(Manufacturer) Maker of Sound Desks in the UK.
Soundcraft website

SOUNDSCAPE
A background sound that runs under a scene, to help establish a reality for the world of the play, and to immerse the audience in that world. It can also be used to heighten emotional moods and to emphasise important occurances. 

SPDIF or S/PDIF
Sony and Philips Digital Interconnect Format. Digital link between (usually) CD players and recording equipment. The S/PDIF format can cope with sample rates of up to 96kHz (CD is only 44.1kHz) and 24bit (CD is only 16 bit). S/PDIF followed on from AES/EBU (similar data stream, but different connector).
More about S/PDIF

SPEAKER
See Loudspeaker.

SPEAKON CONNECTOR
Manufactured by Neutrik. A type of shielded, locking multipin speaker connector which can safely carry the high currents from an amplifier needed to drive large speaker systems. Available in 4- or 8-way types, and ideal for bi-amplified systems. The cable version of the connector is male, and the panel mount connector is female.
Neutrik website

SPEED OF SOUND
The speed that sound travels through the air is around 343 metres per second (dry air, at 20 °C (68 °F).
At 0 °C (32 °F), the speed is about 331 meters per second (dry air). 
Wikipedia entry

SPL (Sound Pressure Level)
A measurement of the loudness of a sound.

SPLICE
1) A join or edit in a sound tape. A splice may be between leader tape and audio tape or between two pieces of audio tape. Splicing tape is the adhesive tape used, a splicing block is used to hold the tape and guide the single-sided razor blade when making the cut.
2) A join in two pieces of rope, made by tightly interweaving the strands from the two ropes so they become a single piece of rope.

SQ
Abbreviation for Sound Cue, used by stage management in the prompt book. The equivalent for lighting cues is LX. Avoid using abbreviations such as SX or FX for sound effect cues, as they sound similar to LX. When cueing the show, the member of stage management on the prompt book should say 'Sound Cue 12' rather than 'S. Cue 12', for clarity.

SQUELCH
Control on a radio microphone receiver for fine-tuning the reception according to the surroundings.

STAGE BOX
A connection box at the end of a lighting or sound multicore cable.

STAGE LEFT / RIGHT
Left/ Right as seen from the Actor's point of view on stage, when they are facing the auditorium. (ie Stage Left is the right side of the stage when looking from the auditorium.)
Stage Right = OP (Opposite Prompt) Abbreviated to SR. French: Cote Jardin, Netherlands: Toneel Links (translates to Stage Left!)
Stage Left = PS (Prompt Side) Abbreviated to SL. French: Cote Cour, Netherlands: Toneel Rechts (translates to Stage Right!).
NB: The Netherlands, Portugal and Germany use the opposite to the rest of Europe; i.e. Stage Left UK = Stage Right. The directions are seen from the director's and audience's perspective, NOT the actors. In Portugal Isquerda (left) is the equivalent of UK Stage Right and Direita (right) is the equivalent of UK Stage Left.

STAND-BY / STANDBY
1) A warning given to technical staff by stage management that a cue is imminent. The member of the stage management team calling the cues will say "Standby Sound Cue 12". Technicians acknowledge by saying "Sound Standing By".
In the US, the word "Warning" replaces "Stand-by".
2) A member of the cast of a musical or play who understudies one (sometimes more) of the principal roles but is NOT also in the chorus. A standby often will not even be required to be at the venue at each performance unless they are called in to perform in the role for which they are an understudy.
See also ALTERNATE, SWING, UNDERSTUDY.
Additional information submitted by Pierce Peter Brandt

STEREOPHONIC (STEREO)
A sound recording that uses two separate channels (left and right) which in combination, and especially when using headphones, can produce a sense of spatial separation of the different parts of the recording. 
The PAN control on a digital audio workstation or on a mixing desk can be used to set the 'location' within the stereo image of a particular sound source. 
See also MONOPHONIC, SURROUND SOUND. 

SUB-BASS
That part of a speaker system designed to extend the low frequency range of the system. See also SUBWOOFER.

SUBWOOFER
(often just SUB) - Speaker dedicated to reproducing very low frequencies. The large cabinet is often placed on the floor as the low frequencies radiate out, and the ear cannot detect their source, so the position of the Sub is not as critical as the rest of the sound system. 
See also BASS BIN. 

SURROUND SOUND
Originally from cinema, where various different types of surround sound system evolved. The most popular now is made by Dolby Laboratories, and provides 6 different sound sources around the cinema:
Front centre (main dialogue, from behind the screen)
Front left & Front right (music, effects and directional dialogue, from behind the screen)
Surround Left (auditorium wall)
Surround Right (auditorium wall)
Sub-Bass
This is known as 5.1 Surround sound.
Newer systems such as Dolby Atmos contain the above, as well as speakers above the audience, and provide a more immersive effect.

Theatre sound systems often contain a huge number of speakers in comparison, with localised speakers near each bank of seating (for musical theatre, particularly).
Any sound system where sound can appear to be all around the audience is said to be surround sound.

SX
Used by some as a shorthand for SOUND, in the same way LX is a shorthand for Lighting. However, when calling cues, stage management should always say 'Sound Cue 12 GO' rather than 'SX Cue 12 GO'. 'Sound' has one less syllable to say, and SX sounds too similar (no pun intended) to LX.
SXOP can be shorthand for Sound Operator. Many venues use FX in the same way, but this can also refer to Stage effects like smoke, pyro etc.

SYSTEM EXCLUSIVE
Part of the MIDI protocol which allows control of one device by another.

TAKE-DOWN
The same as a get-out, often used for live music events, this consists of removing all equipment and structures used for an event.

TAKE-UP SPOOL
The empty reel on the right hand side of a reel to reel tape deck onto which the tape is wound as it plays through the machine.

TALKBACK
1) On a sound desk, the talkback section enables the sound engineer to talk via a microphone to selected outputs of the desk. If the sound desk is used to feed on-stage monitor speakers for a musical group, the engineer can select a particular monitor feed (e.g. the drums) to politely ask the musician (drummer) to play quieter.
2) Term sometimes used interchangably with HEADSET for the communication system between technical crew on the production.

TAPE LOOP
A continuous loop of tape which produces an 'everlasting' sound effect when played. Used for any long sound needed (eg rain, wind) without having to continuously repeat a short effect.

TASCAM
Manufacturer of recording and mixing equipment.
Tascam website

TDIF
Tascam Digital Interconnect Format.
Tascam website

TECHNICAL REHEARSAL
(also known as the TECH RUN, or just TECH). 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.
A PAPER TECH is a session without the set or actors when the technical and design team talk through the show ensuring everything's going to work as planned. Stage Managers can use this session to ensure all is written correctly in the Prompt Book.

TELEX
A brand of wired or wireless intercom used on stage (predominantly US).

THREE TO ONE RULE
In order to get maximum gain (level) out of a PA system, microphones which are picking up the same sound source (e.g. a chorus on a large stage) should be three times further from each other than from the sound source. This minimises COMB FILTERING.

THUNDER RUN
Long series of channels down which wooden cannonballs are rolled to give a realistic thunder rumble effect. Built into the roof of some older theatres, but mostly now unused (for safety reasons).
The Bristol Old Vic has restored their Thunder Run in 2016 for their 250th anniversary.
History of Sound Effects for the Stage

THUNDER SHEET
Large suspended steel sheet with handles which produces a thunder-like rumble when shaken or beaten.

TIE LINE
A sound connection between two patch panels in different parts of the building. For example, there are tie lines between front of house mixing position and the stage to reduce the need for additional cables through the auditorium.

TIMBRE
A musical instrument (or voice) has a quality of character that separates the sound of different instruments from each other. That quality is known as the Timbre.

TRACK
1) Metal structure with rails on which curtain runners are placed to enable curtains to open and close smoothly.
2) A sideways movement of a flying piece, or flown actor. See FLYING HARNESS.
3) Separate audio recording channel. Most playback / recording devices have two tracks - left and right. Some are used for MULTITRACK RECORDING and allow either four or eight tracks to be recorded onto standard media (see also DIGITAL RECORDING). Many more tracks can be recorded onto computerised systems. The most important feature of a multi-track system is the ability to record and playback at the same time (e.g. Recording vocals on track two with a pre-recorded piano on track one.)
4) An actor's (or crew member's) path through an ensemble performance, indicating which roles they take in each section of the show. Having a flexible approach to such performances means the production can be agile, and have adequate cover for actor holiday periods and any illness whilst also keeping the show fresh for the ensemble. Shows that use this approach include Hamilton and The Lord of the Rings The Musical. Swing performers are told before the show which tracks they are covering that day. Sometimes if multiple people are away, swings perform multiple tracks simultaneously - they are then said to be covering Split Tracks. 

TRANSDUCER
A device that converts energy from one form to another. A microphone is a transducer that converts sound wave energy into electrical pulses.

TRIANGLE
(Musical Instrument) Metal bar in the shape of a triangle which is struck with a beater. 

TRIPE (bundle)
Bunch of cables tied or taped together into a single unit.
Also known as a LOOM, or HOD (USA).

TROUBLESHOOT
For lighting fault-finding / troubleshooting, please see the new page:
Lighting Fault-Finding:
https://www.theatrecrafts.com/pages/home/topics/lighting/fault-finding/

More coming soon

TWEETER
Part of a speaker system designed to handle the high frequency part of the signal.

TWISTED PAIR
Type of data cable consisting of multiple pairs of cable contained in a common sheath, often with a metallised screen around the cables to reduce interference. The fact that each pair of cables is twisted together also helps with rejection of errors and unwanted electrical interference / noise. Originally used for telecommunications, it is now used as computer network cable, where it's known as Cat5 or Cat6 (short for Category) cable. 
Wikipedia entry

UHF
Acronym for Ultra High Frequency. In theatres, it refers to a radio communication or radio microphone system using the frequency band between 300MHz and 3GHz (300 Megahertz to 3 Gigahertz). See also VHF. 

UNBALANCED LINE
A method of carrying sound or data signals cheaply. An unbalanced cable consists of two conductors - audio and screen/ground. Two pin connectors such as RCA/phono connectors are used, which are not suitable for heavy duty professional use. Commonly used for short distance hookups between audio or video equipment, unbalanced cables are subject to interference over long distances. See BALANCED LINE.

UNDERSCORE
Music used underneath dialogue or other stage action.

UPSTAGE
1) The part of the stage furthest from the audience. It's called Upstage because on a raked stage the stage slopes down towards the audience to improve sightlines. The furthest from the audience is literally higher due to the slope of the stage, so moving from close to the audience involves walking up the raked stage, towards 'Upstage'. 
US = Upstage, USC = Upstage Centre. USL = Upstage Left. USR = Upstage Right (see diagram)
See also DOWNSTAGE, ONSTAGE. 
2) When an actor moves upstage of another and causes the victim to turn away from the audience s/he is 'upstaging'. Also, an actor drawing attention to themselves away from the main action (by moving around, or over-reacting to onstage events) is upstaging.

VCA
Voltage Controlled Amplifier. Way of controlling sound level remotely from a physical fader. With a VCA sound desk, the faders control the VCA, which then controls the sound signal. Any faults etc in the fader do not affect the clarity of the output. More desk automation is possible with VCA's, as a particular VCA (or group of VCA's) can be allocated to any fader, or can be controlled by an outside controller.

VHF
Acronym for Very High Frequency. In theatres, it refers to a radio communication or radio microphone system using the frequency band between 30MHz and 300MHz (30 Megahertz to 300 Megahertz). See also UHF. 

VIDEO
See CCTV.

VISUAL CUE
A cue taken by a technician from the action on stage rather than being cued by the stage manager. Often abbreviated to "Viz" or "Vis".

VOICE OVER
Refers to a technique for recording an actor's voice and replaying it during the performance to indicate a thought process, or for more practical uses such as covering a scene change or costume change. Abbreviated to V.O.

VOLTAGE
The pressure at which electric current is available. The UK standard voltage is 230 Volts alternating current (AC). The American standard is 120 Volts AC.
The scientific name for Voltage is Electromotive Force. The frequency at which the current alternates (between positive and negative) is measured in Hertz (Hz) and in the UK is 50Hz, and in the USA is 60Hz. 
Named after Italian physicist Alessandro Volta (1745-1827). 

VOLUME
1) A measure of the loudness of a sound cue.
2) The amount of three-dimensional space an object takes up.
3) A large physical environment used for motion-capture or virtual reality production.

VPLT
German Professional Lighting and Sound Association.
VPLT Website

VU METER
(VU - Volume Unit). Pointer and scale meter which indicates the average level of a signal. Misses any transients and spikes that lead to a clipped signal. See PPM.

WALLA
General background hubbub sound effect - named after the sound actors make to create the effect.

WATTS
Unit of electrical power derived from the current (or 'quantity' of electricity) multipled by the voltage (or 'pressure' at which the current is delivered). Stage lighting equipment is rated in Watts (or Kilowatts - 1kW being equal to 1000W). This refers to the amount of power required to light the lamp. A higher wattage lamp requires more power and gives a brighter light output.

WAVE
Uncompressed audio format used on Windows computer systems, defined by IBM and Microsoft.
File extension: .WAV

WAVELENGTH
The distance from one point on a vibrating wave to the same point on the next wave. The lengths of the sound waves (wavelengths) we can hear range from one inch to 40 feet. High frequency sounds have short wavelengths (and are more directional), low frequency sounds have long wavelengths (and are less directional). In lighting terms, blue light is short wavelength, green is medium and red is long wavelength. Beyond visible light are the short wavelength Ultra Violet light and the long wavelength Infra Red light. Wavelengths of light are measured in Angstroms.
See also FREQUENCY.

WEDGE
A wedge-shaped foldback speaker. Angled so that it can sit on the stage floor and point up at musicians/cast.

WET
1) See DRY (Sound)
2) See TECH (Wet Tech).

WHITE GLOVE
A role is said to be 'white glove' if the person is not required or expected to help with setting up equipment, only in the operation of it. 

WHITE NOISE
A signal consisting of random frequencies at a uniform intensity. Used for audio system testing and also to signify overload or the static present on an untuned TV. See also PINK NOISE.

WOOFER
Part of a speaker system designed to handle the low frequency parts of the signal.

WORKSTATION
1) A PC and Monitor.
2) A synthesiser keyboard which also contains a sequencer and other MIDI software.

XFADE
See CROSS FADE.

XLR
Multipin metallic connector. (3 pin for normal sound use, 5 pin for DMX, Colour Scrollers etc). Sometimes called Cannons after the original manufacturer.
The audio standard for wiring the 3 pin connector is as follows : Pin 1 (Screen), Pin 2 (+ve / 'hot'), Pin 3 (-ve, 'cold'). (Xternal, Live, Return).
A 5 pin connector for DMX512 use has the following connections: pin 1 = screen, pin 2 = data -ve ('cold'), pin 3 = data +ve ('hot'), pin 4 and 5 are not used by many manufacturers. A comparison is made between the signals carried by the two data cables, and any differences are cancelled out, meaning that noise/data error reduction is very effective.
The connectors are available as either plug (with pins, sometimes known as Male) or socket (sometimes known as Female) variants, and are available as cable mounted (most common) or panel-mounted. The use of gendered terms (Male and Female) is being reduced as the industry catches up with the modern world. 

XY
A stereo technique whereby two identical microphones are placed next to each other with each mic being pointed 45 degrees off-axis from the centre-line of the action. This technique attempts to overcome the coverage problems of AB, although it is still affected by reflections off the two mics. The other disadvantage is that sounds from the centre of the stage arrive 45 degrees off-axis, where the response of a mic is not as good as 0 degrees. This can appear to leave a 'hole' in the middle of the stereo image. The mic on the left (as you are facing the action) picks up sounds from the right, so it is panned hard right at the mixer, while the other is panned hard left. See AB and MS.

YELLOW JACKET
US term for yellow plastic cable ramp sections.

ZERO DB
The common reference point when discussing sound levels. Levels above 0dB are expressed as positive (+5dB) and those below as negative (-20dB).