| Created: 24/09/05 | Last update: 17:03 01/12/08

A Glossary of PA terms

Terms that are Capitalised are defined in another entry.

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45/60 - a type of Horn loaded Loudspeaker with a nominal sound dispersion of 45 degrees vertical and 60 degrees horizontal, also come in 45/90, 60/90, etc; see also Long throw, Short throw.

Absorption - (coefficient of), the per-unit measure of how much incident sound an object absorbs, the balance being reflected. A hard object like a brick wall might be below 0.1, while a sofa might be as high as 0.6; see also Sabine, Reverberation.

AC - Alternating Current - a loose term for 240 volt Mains Power; a form of electrical energy transmission by means of a rapid push-pull action where the voltage swings alternately positive and negative, in the Australian Power system 50 Hertz or complete cycles per second; see also DC.

Acoustic - relating to sound; the science of sound (Greek); a guitar or other instrument designed to primarily produce sound rather than an electric signal, in contrast to an Electric guitar or synth.

Active - a device that requires power in some form; see also Passive, Phantom power.

ADT - Automatic Double Tracking - a vocal Effect produced by mixing the Dry signal with a very short delayed version (2mS) where the delay is slightly random, producing the effect of singing in harmony with yourself; see also Reverberation and Echo.

AGC - Automatic Gain Controls - a system of altering the Gain of an Amplifier or recorder to produce a fairly constant output Level with widely changing input; typical on most cheap tape recorders; uncommon and problematic in PA work; see also Compressor.

Aliasing - in a Digital system, an incorrect Frequency reproduced due to the input signal being Sampled too slowly; see also Nyquist.

ALC - Automatic Level Control - see also AGC, Compressor

Amplify - to make a signal larger in voltage; see also Power.

Amplitude - the strength, intensity or loudness of a signal

Analogue (UK)/ Analog (US) - a method of carrying signals that is smooth and continuous; a likeness or representation in another form; see Digital, Sampling.

Anti-node - a point in the air where the same signal arriving via two different paths cancel, causing a zone of silence; see also Node, Resonance.

Attack - the rate at which a signal rises to its peak Level; a control that sets the start response time; see also Decay, Compressor, Noise gate.

Attenuate - to cut down or reduce in strength or intensity; a Passive attenuator is sometimes required to reduce the output of some devices, such as CD players, to avoid Overloading the available inputs.

Audio - sound waves between about 20Hz to 20kHz.

Audiophile - “audio lover”, an irrational state where imagined equipment defects result in draining of the bank balance; see also Hi-Fi, Subjective, Objective.

Auditorium - a place for listening; the body of a theater or venue; see also FoH.

Backdrop - large generally canvass sheet which may be painted with a design or scene to cover the rear wall of the stage; see also Cyclorama.

Backline - amplifiers set up behind the players.

Baffle - any mounting or enclosure that inhibits the flow of air from the front face of a Loudspeaker to the rear face, traditionally simply a large flat surface with a speaker in the middle; any plate that carries a loudspeaker, such as the front plate of a sealed Cabinet.

Balanced - a method of transmitting signals as two identical but opposite Phase signals. This is received by an input amplifier that operates on the difference and ignores signals in common which are mostly due to external electrical noise. Balanced signals are used for their Noise immunity over Single-ended/Unbalanced, and from Earth-loop problems because the screening is isolated from the signal return or Cold.

Band, frequency - specified range of frequencies; see also Graphic.

Bandwidth - of a device is the Frequency range over which it will work, within defined Response limits. A typical Amplifier might be defined as 20Hz to 20kHz at -6dB ref 1kHz, meaning its output falls to half compared to 1kHz, at those frequencies. See also Bode.

Bass - lower part of the audio range; a control for Frequencies below 1Khz.

Baxandall - Peter, designer of the Tone control circuit in almost universal domestic use today.

Bin - term for a Loudspeaker box, often a Horn; see also Cab.

Bio-box - film projection booth; room that houses projectors in a cinema with glazed sound-proof projection and observation ports into the auditorium, from “Biograph”.

Bode plot - (mathematician), a graph that shows the Frequency and Phase response of a device or system. It is plotted with intensity vertically (linear in Decibels), and Frequency horizontally (log scale). These odd scales are chosen to make the most sense to the human ear, and provide a simple way to draw a picture of what you hear; see also Webers Law, Graphic.

Bomp/bump in/out - to move in and set up/pack up and remove show equipment from a venue.

Boom - a device to hold a Microphone, range from a simple cross-arm attached to a normal mike stand to the huge multi-operator Cranes used in TV and film studios.

Boost - to increase a range of Frequencies compared to others; see also Cut, EQ.

Braids - ultra-flexable wires that connect the user terminals of a Loudspeaker to the rear of the (moving) Cone.

“Break a leg” - traditional kindly encouragement from fellow performers to one who is just about to go on, normally in the Wings, sometimes together with pretending to spit on the person.

Burn - to record onto a CD (generally a copy).

Buss - the output path of a Mixing desk; range from simple Mono to several Stereo 'Subs' (output sub-busses to the master output).

c/b - see Circuit breaker

Cab - cabinet containing Loudspeakers; see also Enclosure.

Cannon - an equipment manufacturer (aka STC, now Alcatel) - designed the XLR type connector, thus XLR's (their type number) are also made by other companies, often better (Neutrix).

Cans - see Headphones, PAR cans.

Cart (Cartrage) - a plastic box containing a endless loop of quarter-inch magnetic Tape, used in radio stations for adverts and announcements, the playing machine running the loop back to the start point using a Cue track.

Cassette - Philips Compact Cassette, eighth-inch wide magnetic Tape in a pre-threaded plastic case normally running at 1 and 7/8 inches per second, better quality machines allowing double-speed operation at 3 and 3/4 inches per second for better Treble response; see also Cart, Reel-to-reel.

Cardioid - roughly heart-shaped - the shape of a sensitivity or response pattern, typically in a Microphone, taken in plan around the device; giving high sensitivity at the front and low sensitivity from the rear; Super-Cardioid has a greater front-to-side and front-to-back ratio of response.

CD - compact disk; a digital form of audio recording; see also Burn, Mastering.

Channel - a group of controls on a Mixing desk that control a single input Source; see also Buss.

Chip - slang term for an Integrated Circuit.

Chorus - an Effect created by a short delay with random variations that makes a single voice sound like a number of voices; see also Delay, Echo, Reverb, ADT.

Cinemoid - a brand of Gel.

Circuit - a pathway for electricity from the source to the destination, and back to the source; see also Open, Short

Circuit breaker - a switch that turns itself off in the event of excess current; see also Fuse.

Clap test - to estimate the Reverberation characteristics of a space by counting how many seconds the Ringing of a single loud handclap lingers; see also Sabine.

Clipping - a Distortion due to a device running out of Headroom; the hard limiting or 'flat-topping' of signal peaks due to drive in excess of capacity to deliver; see also Over.

Cold - in a balanced cable system the conductor that acts as the return or anti-phase, but is not the shield; see also Hot.

Companding - Complimentary Compressing and Expanding - of audio Level to artificially enhance the Dynamic range of a Media such as Dolby and dBX systems; see also Compressor.

Compressor - a device that reduces the Channel Gain as the signal gets louder to avoid Overload in following devices, common in PA work and universal in recording. The main controls are Threshold which sets the Level where gain reduction starts, and Ratio which sets the degree of gain reduction past that point; see also Expander.

Cone - the part of a Loudspeaker which acts like a piston moving back and forth to produce sound waves from the motion of the Voice coil; made of light fiber material, generally paper/cardboard.

Corner (frequency) - the frequency where a frequency-selective circuit such as a filter or Tone control starts to act; it comes from the corner created by a straight-line approximation of the response drawn on a Bode Plot; see also Filter, EQ.

Counter - a test instrument that accurately displays the Frequency of a signal as a number, an actual count of cycles per second; see also Sig gen.

CPS - Cycles per second - see Hertz, Hz

Crane - large operator driven arm carrying a camera or microphone; see also Boom.

CRO - Cathode Ray Oscilloscope/graph, aka “Crow”, “scope” - a test instrument that shows voltages on a calibrated screen plotted against time, or against other signals giving Lissajous figures (such as the ABC-TV logo); see also Sig gen.

Cross-over (network/filter) - a device that splits a signal into defined Frequency bands to drive the different elements of a Loudpeaker system such as Bass, Mids, and Treble Tweeters; may be passive (Hi-Fi) or active in the Amp or Effects rack (PA).

Crossover distortion - a type of Distortion caused by the imperfect transition or cross-over between the electronics that drive the positive half of the signal and the part that drives the negative half-cycle of the wave; really only significant in domestic Hi and Hyper-Fi; see also Clipping.

Crushing - distortion and Compression of dynamics and peaks due to gross overdrive, normally goes with very prominent background Noises during quiet passages; see also Trim, Compression, ALC.

Cue (up) - the moment when something is supposed to happen on stage; to pre-set equipment for that moment; a channel that allows reviewing a source before actually selecting it for output.

Cup test - to cup a hand over the face of a live Microphone as a test for Feedback Stability.

Cut - to reduce Gain in a Frequency band; see EQ.

Cyclorama, “Sike” - curved cloth Backdrop to cover the back wall of the stage, generally white, it may be curved forward at the floor to enhance the illusion that the stage has no back wall.

DAT - Digital Audio Tape - see also Digital, Analogue, Sampling.

dB - see Decibels.

dBA - A-weighting - a correction to wideband audio measurements to account for the nature of human hearing; see also Decibels, Fletcher-Munson.

dBX - a form of Companding; see also Dolby.

DC - Direct Current - a steady voltage supply of contant polarity where the current flows in only one direction.

Decay - the rate at which signal falls from its peak Level to silence; a control which sets the hold-on time after triggering; see also Compressor, Noise gate.

Decibels - a decibel is not an absolute measument, it is always a ratio like 'percentage', and since the human ear is itself much more sensitive to loudness ratio than absolute loudness level, the decibel is very useful. The ear has a 'logarithmic' response in that it requires four times the power to sound twice as loud; see also maths page.

Delay - used to produce several different Effects by Mixing a delayed version of the signal with undelayed including Reverberation, Phasing, Flanging, Chorus, and Echo, using different delay times.

Delay line - a Springline, Tape recorder, or Digital storage system that stores and reproduces the input a short time later; see Reverberation, Echo, Tape echo.

DI - Direct Interface - a device that allows instruments or amplifiers to be directly connected to the PA system without problems such as Earth Loops or excessive Level.

Digital - two state signal, on or off; a method of handling signals by rapid Sampling to produce a series of numeric values for points along the wave; see DSP, Nyquist.

DIN - Deutcher Instrie Norm - German standards association equiv ASA; foolproof compact multi-pin signal connectors for interconnecting various domestic devices such as Cassette Tape to and from Amplifiers; also the standard MIDI connector.

Dip - a fall in Frequency Response across part of the Bandwidth; a power outlet, often controlled by a dimmer, under a smnall trapdoor in the stage surface; a momentary drop in the mains supply voltage.

DIP - Dual Inline Package; a style of Integrated Circuit.

Direct radiator - most common type of Loudspeaker arangement where the speaker Cones radiate directly without any enhancement such as a Horn.

Distortion - lack of Fidelity to the original signal; see also Crossover.

Dolby - a form of Companding to increase Dynamic range and reduce the Noise floor; see also Noise gate.

Dome - a type of Tweeter with a hemispherical Cone, based on the false idea that moving a dome back and forth will produce a hemispherical radiation pattern, which it doesn't; see also Hi-Fi.

Double tracking - in recording, singing a second part to match the previous part; see also ADT.

Douser - a device, generally within a Follow-spot or projector, that interrupts the light output without turning the lamp off.

Driver - a name used for a Speaker when it is important to distinguish between the driving device itself and the cabinet or enclosure it is fitted in.

Dry - a signal with no Effects (particularly Reverb or Echo).

DSP - Digital Signal Processor - a Digital microcomputer Chip specifically designed to process audio signals in real-time; the core of most modern Effects units.

Ducking - reducing the Level of background under speech in time with the speech, manual or automatic; see also ALC, Pumping.

Duct tape - a poor quality imitation of Gaffer tape.

Dynamic (Loudspeaker) - and electro-magnetic device to convert electrical signals into sound; see also Driver, Piezo, Speaker.

Dynamic (range) - the available range of output intensity between the low limit of the Noise floor and the high limit of Overload or Clipping, typically expressed in Decibels. Live performances such as bands generally have a much higher dynamic range than the PA and Mixer.

Dynamic (Microphone) - an electro-magnetic device to convert sound into electrical signals.

Earth loop - a condition that imposes a Hum Noise on the signal path. It is a loop that can be created between two Mains powered devices where their Ground or common connections are joined via two paths, one via the Mains safety earth, the other via a signal lead screen, making a closed loop which then couples stray AC magnetic field from equipment power supplies into the desired signal path. See also Balanced.

Echo - the longest of the Effects produced by Delay; a distinct repeat(s) of the original sound; see also Reverberation, Effects, Tape loop.

Edgy - see Ringing.

Effects - can be added to the signals passing through the system, these include Reverberation, Echo, Chorus, ADT and Flanging.

Effects loop - or 'sidechain' is the path where signals are sent to be processed to add Effects; that part of the system included between the Echo or Effects Send output, and Echo (Effects) Return input on the main equipment.

Eigentones - the dominant Resonances in a space due to its basic dimensions; see also Honking.

Electret - a type of plastic with a permanent electric charge, the electrostatc equivalent of a magnet; capacitor Microphones made with this plastic.

Electrician (theater), Best Boy (film crew) - generally the person who takes care of connecting up the required lights, aka lighting tech.

EMK plate - a Reverberation device consisting of a steel plate suspended on springs, used in recording studios in the 60's and 70's.

Enclosure (speaker) - a box that contains a Loudspeaker.

EQ - Equalisation; PA term for Tone controls; controls that allow compensation for defects in the Frequency response of the system, particularly Microphones, allowing the overall response to be made Flat or even with frequency; Gain controls for specific bands of frequencies.

Equalise - the process of using EQ/Tone controls to correct uneven Frequency response so that the signal has equal strength at all Frequencies; the Boosting and Cutting of different frequency bands to achieve Flat response; correcting Feedback and other defects resulting from un-even response of Microphones and venue Rooms; see also Tone, Parametric.

Expander - a device that varies the Channel Gain to increase the Dynamic range; see also Compressor.

Fader - the main control for signal Level in a Channel, generally a Slider.

Feedback - a signal that passes from the output back to the input; a howling or whistling noise caused by having the Mirophone too close to the Loudspeaker.

Fidelity - faithfulness to the original signal.

FFT - Fast Fourier Transform - a method of decomposing a complex waveform into its sinewave components; see Fourier.

Filter - a frequency-selective circuit that pass some Frequencies while blocking others; come in low-pass, high-pass, band-pass, and band-stop flavors; simple versions are used for Loudspeaker Crossovers, Scratch, Rumble and Loudness filters on domestic Hi-Fi's; variable versions become Tone controls, Parametrics, and Graphic EQ's; see also HFP, LPF.

Flanging - an effect produced by mixing a signal with a slightly delayed version of itself; see also Effects, Reverberation, Echo, Delay, Chorus, ADT.

Flat - a Frequency response where all frequencies are at the same level; see also EQ, Tone, Bode plot.

Fletcher-Munson - Equal Loudness Contour; the sensitivity of human hearing to different frequencies changes depending on how loud the sound is.

Flights - an area above the stage to allow Backdrops to be lifted clear of the stage for storage. In big theaters the flights may be as much as three times the height of the stage allowing the storage of three stacks of Backdrops.

Fly - to suspend Loudspeakers on cables high above the stage; see also Rigger.

Flying faders - motorised faders used on more modern, generally Digital, Mixing desks that allow a few Faders to control a large number of parameters by switching or Multiplexing the faders to different functions. While these serve well in the studio they tend to age quickly and become sluggish, and Multiplexed controls are awkward in live Mixing.

FoH - Front of House - where the audience is; the Amplifiers and Loudspeakers that serve that area; see also Foldback.

Foldback - a secondary PA system for the stage, so that performers who require Pitching, such as vocalists, brass, and reed players, can hear themselves clearly against the other instruments, etc; see also FoH.

Follow spot - a large manually controlled light, typically at the back of the auditorium to highlight particular parts of a performance such as the lead singer.

Footlights - row of lights across the front edge of the stage facing the performers and shielded from the audience; see also Ground row.

Footswitch - generally used to control Effects in Backline Amplifiers; see also Stomp box.

Fourier - a French mathematician who first realised that any complex periodic function (signal) could be decomposed into basic sinewaves of various freqencies and amplitudes. Many Synths work in reverse, adding together simple electrical waveforms to produce complex ones, and thus complex sounds; see also Formants page.

Frequency - the inverse of period; the number of times a quantity varies periodically over one second, expressed in Hertz or cycles per second; the electrical Analogue of a pure note of Pitch A-440 is a voltage that rises and falls 440 times in one second; the range of human hearing is roughly 20Hz to 20kHz, but degenerates with age and abuse; see also CPS.

Frequency response - an expression of the range of Frequencies that a device or system will carry; see also Bandwidth.

Fresnel - a type of light lens made flat by forming many concentric rings of prismatic sub-lenses, favored for their wide aperture and thus efficiency.

Fuse - a device intended as a weak link that will melt if excessive current flows; see also c/b.

FX - see Effects.

Gaffer - person in theater or film production who Rigs equipment for a production.

Gaffer tape - Wide very heavy duty sticky tape used by Gaffers to hold cables to floor etc so they are out of the performers way. Traditionally black.

Gain - (voltage, power, SPL) - the increase or decrease of a signal between defined points in the signal path through the system, generally expressed in Decibels.

Gate - see Noise gate.

Gear - equipment.

Gel - thin plastic colour filter placed in a frame at the front of a light to give it a tint; note: these are high-temperature resistant - do not use substitutes such as cellophane; see also Cinemoid, Fire.

Gender - defines the pin/socket arrangement used; Jack plugs are obviously male and their sockets equally female, but with some shrouded connectors such as XLR's and DIN's it is defined by the actual connecting pins and sockets (and yes, there are also genderless connectors and gay and lesbian adaptors too).

Gods - the highest audience balcony.

GPO - General Power Outlet - a standard 3-pin 240 volt Power Mains wall socket; see also Three phase.

Grams - any pre-recorded material as part of a show (whatever the source); comes from the term 'phonogram' for a disc record player.

Graphic - a type of Equaliser that has individual slider controls for a number of frequency Bands, typically octave, third-octave, etc spacing, arranged to look like a graphical representation of the band-pass. Sadly this often has little relationship to the actual bandpass and even when set Flat still mangle the Phase response. More usefully applied to the Foldback Channel than FoH; see also Bode.

Ground row - lights, other than Footlights, on the stage surface facing upward, generally across the back to light the Backdrop or Cyclorama.

Group/sub - one of the output channels of a Mixer; see also Buss.

Hammer - a long handled socket wrench or spanner designed to fit the tuning pegs in a piano; the part of a piano that stikes the stings; see also Tuning fork, Pitch pipe.

Harmonics - signals with an integer, or whole-number, relationship to the fundamental Frequency, x2, x3, x4, etc. The harmonic content defines the sound of a musical instrument and is the basis of sound synthesis.

Hass Effect - a listener locates a sound source by the first arriving sound wave, intensity having little to do with source location; in PA Delay is sometimes used on reinforcement close to the listener to allow the wave to arrive from the actual source first, providing location, but the local reinforcement providing the primary sound level. Correct location of the source is important to intellegibilty even when the sound level is sufficient.

Head space - the space in a venue or room above the heads of the audience, often a major source of room Reverberation problems.

Headphones - Loudspeakers designed to fit on the head for personal listening; see also Cans.

Headroom - the difference between where a device starts to 'red-line', and where it actually starts to Distort or Overload; the real reserve for extreme conditions.

Hi-Fi - High Fidelity, originally a term used to describe a class of domestic sound equipment with superior technical specifications it has become meaningless as Audiophiles have totally lost touch with reality.

Hiss - high-pitched Noise like rain on a tin roof; produced by the random variation in the flow of electrons in electronic devices, and by magnetic 'granularity' in Tape coatings; see also Hum.

Honking - obvious Resonances in a performance space; spaces with large hard flat areas facing each other often produce one or more strong Mid-Frequency resonances with a nasal 'goose honk' sound.

Horn - a trumpet or flare added to a Loudspeaker to better couple it to the air; compared to the compliance of air a Loudspeaker is quite stiff and non-compliant ('high impedance') and therefore couples very badly. The difference in area between the mouth and the throat of the horn acts like a transformer or gearbox and translates the wavefront between the two and lifts the conversion efficiency (Watts in to SPL out) from around 2% for a conventional direct radiator cabinet to around 30% to 50%, but at the expense of Bandwidth. See also J-bin, W-bin.

Hot - the conductor or connector pin that carries the signal; excessive signal level.

HPF - High Pass Filter - a circuit that stops signals with Frequencies below its Corner or Cut-off frequency, passing those above; a Treble controls is a HPF with variable output; see also LPF.

Hubris - insolent pride, over-confidence, normally from a band or perfomer in the first flush of success; see Prima donna.

Hum - a low pitched sound of 50 or 100Hz, originating from the 50Hz Mains power supply.

Hz - Hertz, the unit of frequency; see also kHz, CPS.

Impedance - the Resistance of a circuit to current flow, expressed in ohms, specifically to AC signals of a reference or given Frequency; an expression of the ability of a Source to drive a Load or Sink, or of the drive required by a Load of Sink from a Source; see also Resistance.

Integrated Circuit - a circuit built on a single silicon slice in a sealed package.

Intermodulate - see Modulate.

J-bins - a type of Horn-loaded Loudspeaker Cabinet where the horn is folded back on itself to conserve space, forming a rough J-shape internally; see also W-bin.

Jack (plug/socket) - type of connector originally from telephone service, a poor imitation now common on musical instruments and amplifiers, consists of a sleeve which is common and a tip which is signal Hot. The common guitar size is nominally 6.5mm (1/4-inch originally). At best these are fairly poor connectors for any service, input or output, and prone to damage from cable pulls, XLR's being far superior. This style also comes in a common mini form and a less common sub-mini form. The standard and mini may also come with a ring just behind the tip for a second channel for Stereo or Balanced use. Caution: on domestic video Camcorders the ring on the “Stereo” mini mic connector may carry power for the active microphone; see also TRS, XLR.

K - kilo - x1000.

kHz - kilohertz - thousands of Hertz (cycles per second); a measure of Frequency.

Kick (drums) - a Microphone channel on the bass drum of a drumkit; see also Overhead.

Kick (VU, Level) - “Kicking the meters” - driving the system into overload, into the red area on the meters; in contrast to “licking the red” or only occasionally going into overload on signal peaks; see also Pin.

Lead sled - slang for a Rack amp (from their weight).

LED - Light Emitting Diode - a Chip that produces light, mainly red but now available in all colours, white, and some very high intensity types, efficient and almost indestructable.

Level - the strength or intensity of a signal at a given point, generally expressed in mV or Decibels.

Limiter - function in or type of Compressor that only acts on high-Level signals; see AGC.

Line array/source - a type of Loudspeaker system consisting of several radiators stacked vertically which produces a radiation pattern like a pie wedge with high horizontal dispersion and little vertical dispersion. These days big line arrays are back in vogue and usually consist of a number of Cabs in a shallow J shape Flown FoH above the side-stage. Straight Line arrays are particularly prone to Treble cancellations.

Line level - the signal Level output by devices such as tape and CD players, Echo units, Mixing desks and the like. Covers the range from old tape decks at 100mV up to CD players at 1 volt; implies a Sink Load Impedance higher than 10k ohm (light loading); see also Mic Level.

Lissajous - figures produced on a CRO from different Sinewave sources allowing the measuring of the ratio of the two frequencies, e.g. the ABC logo shows a lissajous figure of 3:1 frequency ratio.

Long throw - a Horn loaded Loudspeaker with a narrow sound dispersion intended to serve the rear of the audience from the stage area; see also Short throw.

Loudness control - on domestic amplifiers to allow the Boosting of Bass (and some Treble) to provide a corrected balance for material being replayed at a lower Level than the original, a form of pre-set EQ; see also Fletcher-Munson.

Loudspeaker - a device to convert electrical power into air pressure waves; an 'air motor'; generally consists of a powerful magnet with a coil of wire (the 'Voice Coil') Suspended in a circular gap. The voice coil is firmly attached to the apex of a cardboard Cone which is free to move forward and backward, and thus displace air like a piston. Electrical signals from a Power Amplifier are applied to the voice coil via Braids, causing it to motor back and forth in the magnetic field, thus driving the cone and producing sound. See also Driver, Baffle, Enclosure.

LP - Long Play - shorthand for 'microgrove' Analogue disc recording.

LPF - Low Pass Filter - a circuit that blocks high Frequencies while passing those below its Corner Frequency; a typical application is a Hi-Fi 'scratch' filter.

Lug, the - moving the Gear from storage to the show venue and back; see also Bomp.

Mains - normal household 240 volt 50Hz AC electric Power; see also Three phase.

Master - main Level control on a Mixer; the final recording from a studio session.

Mastering - the process of polishing a recording, generally following the final studio mix.

Media - the material that recordings are made on, Tape, CD, etc.

Mic - an abbreviation of Microphone.

Mic level - the voltage output by a Microphone under standard conditions, expressed in Decibels or Millivolts, typically 10mV peak; see also Line, Level.

Mic-line - a switch to change the sensitivity of a channel between Line and Microphone Level sensitivity, from about 100mV full scale to 10mV full scale; see also Trim.

Microphone - a device that produces a voltage related to the air pressure, thus the pressure waves of sound arriving are converted into an electrical Analogue. There are many types of microphone, but the most common one in PA work is the 'Dynamic' which is basically a tiny Loudspeaker acting in reverse; see also Electret, Dynamic.

Mid (middle) - control that acts on the Frequencies between the Bass and Treble controls, sometimes this is in turn split into upper-mid and lower-mid band controls; a Loudspeaker specifcally for those Frequencies; see also EQ.

MIDI - Musical Instrument Digital Interface - a method of connecting synthesisers together, it is now also being used to control lighting Rigs and PA Rack Amps.

Mixer - a device that allows the combining, proportioning, and routing of Audio signals. Defined by the number and type of inputs it will accept; how many output channels are available; and facilities for applying EQ and Effects to the signals being mixed; see also FoH, Foldback.

Mixer - the person running the Mixing Desk; see also Roadie, Therapist.

Mixing - the art of operating a Mixer (while dealing with musicians and members of the audience).

Modulate - one signal changes a property of a second signal, such as pitch or amplitude; see also Tremolo, Vibrato, Intermodulation, Ring mixer, Modulation page.

Monitor - to listen to a signal; Loudspeakers used in a studio.

Mono - a single audio channel; see also Stereo.

Multicore - a cable containing a number of individually Shielded conductors to carry signals between the stage and the Mixer.

Multiplex - to make one device do more than one task, generally by electronically sharing the resource between users at high speed; see also Flying faders.

mV - millivolt - 1/1000th of one volt.

Node - a steady pressure or SPL maximum, generally caused by a signal taking two paths by Reflection to the same spot where they reinforce; see also Anti-node, Resonance.

Noise - unwanted signal added to the original by the system. This may be Hiss, Hum, Crackles, or other Distortions like Tinfoil-in-the-Piano.

Noise floor - the level of internally generated noise, below which signals will be lost.

Noise Gate - a device that mutes the signal below a certain level thus hiding residual noise.

Nyquist - mathematician who discovered that for a Sampled signal to be reproduced it must be sampled at least twice as fast as its highest frequency - Nyquist's Sampling Law. This results in reproduction of the wave Frequency but not its shape. Fidelity requires sampling at least ten times the highest signal frequency.

Objective - evaluation of equipment using instruments; see also Subjective.

OFC - Oxygen Free Cable - alledged “low distortion” speaker cable, aka “Physics-free cable”, a Hyper-Fi con game with no basis in reality. Not often found around PA systems because PA operators normally have more sense than money.

Omni - in all directions, an Omni-directional Microphone is equally sensitive in all directions; see also Cardioid.

Op-amp - Operational Amplifier - an almost-ideal low power Amplifier on a single Chip with very high Gain, very low Noise, and very high Bandwidth/Frequency response, generally a voltage amplifier; see also Preamp.

Open (circuit) - the undesired interruption of an electrical circuit due to a broken connection; see also Short Circuit.

Over - in Digital recording a Sample that exceeds the available range causing a particularly nasty form of granular Distortion.

Overhead - a Microphone, generally on a Boom, positioned somewhere above the drumkit; see also Kick.

Overload - to drive outside the rated working range; see also Headroom, Clipping, Fuse, Circuit breaker, Speaker protector.

Pan control - a Mixer control that allows a Mono source such as a Microphone, to be proportioned or cross-faded between the Left and Right output channels, thus positioning the source in the reproduced stereo image.

PAR cans - stage lights; the PAR is derived from the type numbers used by Strand Electric for their theater lights; generally a cheap lowish power light intended for portable use such as bands.

Parallel connection - an arrangement where a signal is split to pass through two devices, such as Loudspeakers, before re-combining; see also Series.

Parametric - a Tone control that allows Cut and Boost to be applied by tuning a bell curve to the required Frequency, then shaping its sharpness and height or depth; identified by a “frequency” control and sometimes a “Q” or “resonance” control, as well as the normal control for the degree of Cut or Boost required. Uncommon and slightly odd in operation, but magical in effect.

Passive - a device that requires no power supply other than signals, such as a Line isolation transformer.

PCB - Printed Circuit Board - the replacement for point-to-point hand wiring in electronic assembly; a laminate of thin copper foil on a base of baked paper phenolic (brown or 'mud board'), fiberglass epoxy (green), or Teflon (non-stick, PTFE poly tetra fluro ethene) loaded epoxy (blue, expensive, tough, and sexy). The copper layer is photo-etched to leave all the interconnecting wiring, then the components mounted. Sometimes called a PWB or printed wiring board.

Peak level - the strength or intensity of a signal during impulses such as drumbeats, in contrast to average VU Level, and typically 8dB higher; see also Decibels, VU.

Pedal - (piano) - a control to lift the string dampers clear of the strings to allow notes that are struck to continue after they have been released, sometimes used to mean sustain.

Pedal - (stomp box) - an effects device with a footswitch, generally just in front of the guitarist; see also Stomp box.

PFL - Pre-Fade Listen - a Mixer facility that allows Headphone monitoring of individual signals in isolation from other signals.

Phantom power - a method of supplying power to an active Microphone, such as an Electret, over a standard signal cable, typically 48 volts. Note: phantom power should not be applied to any device that does not specifically require it.

Phase - the time difference between two forms of a given signal, normalised for Frequency by expressing the phase difference in angular degrees of one cycle, 360 degrees. Thus a Sine wave and its inverted form exactly out-of-step with the orginal is said to be “180 degrees out of phase”. Also loosely used to decribe signal inversion without time delay.

Phasing (effect) - an effect produced by mixing a direct and Delayed verson of the signal; see also Reverberation, Echo, Chorus, Flanging.

Phasing (speakers) - connecting all Loudspeakers in a system to operate in the same direction, that is a given signal polarity (+) causes all Loudpeakers to move in the same direction (forward).

Phones - see Headphones.

Phono - relating to LP disc turntables, and the special EQ needs of magnetic cartrages; a type of connector aka “RCA” (Radio Corporation of America) almost universal on domestic sound equipment, but rare in PA work due to its fragility.

Piezo - a ceramic element that flexes when voltage is applied, or produced voltage when flexed, used at the Driver in some Horn-loaded Tweeters; an early form of microphone and LP pickup, generally now only found as pickups in Acoustic guitars, generally capable of very high output Levels but without Preamp require very high Impedance inputs (greater than one megohm) to avoid Bass loss.

Pin (the meters) - to overdrive a signal meter so excessivly it is driven against its high end stop; a vastly excessive signal Level; see also Kick.

Pink noise - a Noise signal Filtered so that it has equal energy per octave; see also White noise.

Pitch - sound Frequencies defined as notes on a musical scale with A-440Hz being the standard (aka concert pitch).

Pitch-pipe - set of six tubes that when blown through produce the open string notes on a guitar for tuning.

Pitching - the ability of vocalists and players of wind instruments to adjust or “pull” their pitch into tune as they sing or play. This requires that they can hear themselves over the band; see also Foldback.

Playback - see Grams.

Plugpack - a small low voltage power supply designed to hang on the power point.

Polyswitch - a polymer-based device placed in series with a Loudspeaker that goes open circuit on overdrive and self resets when the excessive drive is removed. Not common in PA service; see also Protection.

Popping - a Bass Noise cause by the breath-blast of percussives striking the Microphone. Can be reduced by extreme low Frequency Cut and by using a Sock on the microphone.

Port (speaker) - an opening, duct or pipe used to tune an Enclosure to the resonant frequency of the Driver(s).

Pot - potentiometer, a rotary variable divider of voltage, a variable resistor generally used as a Level control; see also Slider.

Power - the ability to do work, measured in Watts.

Power amp - an Amplifier designed to deliver Current as well as Voltage into the Load, thus increasing the amount of Power available; see also Watts.

Preamp - a device that accepts a signal from a Source and Amplifies and conditions it with EQ and Effects, lifting it to a Level suitable to drive a following Power Amplifier, generally about 1 volt.

Prima Donna - Italian for “first singer” in an opera, it has come to mean a performer who is so far up themselves they can't see daylight; someone who has yet to learn how unwise it is to piss off the crew - they can do diabolical things to Props and Foldback to get even.

Props - short for properties meaning all the items required to dress the Set.

Protection, speaker - a device or circuit that protects the Loudspeaker in the event of Overload or Amplifier failure; see also Fuse, Circuit breaker, Polyswitch.

PSU - Power Supply Unit, generally to convert Mains power into Direct Current voltages for the equipment.

Pumping - an undesired fade up of background Level on a recording made using ALC/AGC, during breaks in the foreground; undesired action of Tremolo causing Loudspeaker Cones to move back and forth at a slow rate; see also Dolby, Compression.

Q - see Cue

Q - the magnification factor of a Resonance; see also Parametric.

Rack amp - term for a Power Amplifier with side brackets suitable for mounting in a standard 19-inch rack frame. Normally implies ruggedness and raw power. Controls are minimal such as on/off and perhaps Faders, but often have much better indicators than a domestic amplifier, such as output level, clip alert, output short circuit and over temperature indication and protection. They are almost always force air cooled with an internal fan.

Rake - the angle of the auditorium floor so the back seats are higher than the front; the slope of a stage downward from back to front.

RCA - Radio Corporation of America - a cheap form of audio connector designed by RCA and almost universal outside Europe on domestic equipment, aka “Phono”; see also DIN, Jack

Reel-to-reel - a form of Tape recorder where the magnetic Tape passes from a supply reel to a takeup reel, normally on quarter-inch tape at tape speeds of 3 and 3/4, 7 and a 1/2, or 15 inches per second, capable of producing very good recordings; see also Cassette.

Reflection - secondary sound that has bounced off a surface.

Refraction - bending of sound waves due to passing close to an object or edge such as the corner of a Speaker Cabinet, or due to passing through air at different tempratures, particularly at night when distant sounds are bent back toward the ground.

Resistance - opposition to the flow of current, expressed in ohms.

Resonance - the ability to store energy in an oscillation at a given Frequency; the Frequency at which mechanical and/or electrical actions combine to store energy; resonances have a characteristic Frequency and 'sharpness' or Q which defines its Bandwidth; the storage process takes time to charge or 'generate' and absorbs Power from the Source, once excitation stops it will then return this stored power as it 'decays'; acoustic resonances in venue spaces are a major problem in PA work; see also Node, Antinode, Q, Honking, Head space.

Return - a signal coming back from an external Effects unit.

Reverberation, Reverb - sound Reflected back into the venue; the time it takes for an initial impulse to die away to -60dB of its initial value; a device that delays the signal to mimic Reflections. see also Effects, Echo, Delay, Phasing, Flanging, Chorus.

Rig - equipment; to set up, particularly lights.

Rigger - a person who assembles scaffolding structures such as stage or light and Speaker towers at an outdoor venue.

Ring Mixer - a device that Modulates the amplitude of one signal with another; see also Effects.

Ringing - sound, not part of the original signal, coming from anything excited by that signal, typically the basic room Resonances themselves; marginal or incipient Feedback; see also Reverberation, Resonance.

Ringing out (the system) - a process of increasing system gain until Ringing occurs, killing the ring with EQ, repeating the process until it can no longer be EQ'ed. This increases the margin between operating level and Feedback level; see also Feedback.

RMS - Root Mean Squared - The effective DC voltage of an AC circuit; see also maths page.

Roadie - from “road crew”; person(s) generally on a small show who takes care of all aspects of setting up and running the show; see also Lug, Bomp, Mixer, Electrician, Therapist.

Room - venue, often a hotel lounge; the acoustics of.

Rumble - unwanted very low Frequency signals, typically from LP turntables; see also Popping.

Sabine - unit of Reverberation from the name of a researcher; see also Reverberation.

Sample - in a Digital system a single value of a signal.

Sampling - the process of converting an Analogue signal into a series of Digital values; see also DSP.

Screened (lead, cable) - cable with a conductive outer sheath to prevent capacitive pickup of unwanted signals.

Send - signal output to an external Effects unit; see also Return.

Series - a connection where a signal passes through two devices, each in turn; see also Parallel.

Set - a stage dressed with Backdrop and Props ready for a production; a group of songs played by a band between breaks; the arrangement of lights to light the stage or performance area.

Shadow - an area not being serviced with sound from a PA system, generally due to an obstruction such as a pillar, but sometimes due to Refraction.

Short (circuit) - the undesired connection of two wires, points, etc.; see also Open circuit.

Short throw - a type of Loudspeaker with a wide dispersion intended to serve the front aarea of the audience.

Shunt connection - see Parallel.

Sidechain - see Effects loop.

Sig gen - Signal Generator, Function Generator - a test instrument that produces simple standard signals of adjustable Frequency, Amplitude, and frequently wave shape; see also CRO, Counter

Sinewave - a signal that conforms to a Sine function, also known as Simple Harmonic motion; the position of a pendulum plotted over time; the apparent motion of a point on a rotating wheel, viewed edge-on; a pure musical tone free of Harmonics.

Single-ended - a method of sending signals where the signal return is shared with the Screening function; see also Balanced, Earth-loop.

Sink - a device that requires a signal to drive it; see also Source.

Slider - a type of Pot arranged to work in a straight line rather than rotate; see also Fader.

SMD - Surface Mounted Device(s) - new generation microscopic components that make modern consumer electronics possible, cheap, and un-repairable.

Sock - a breath-blast shield of cloth or sponge that fits over the face of a Microphone and reduces Popping.

Sonic - relating to sound (Latin); sometimes used as an overall term for the characteristic sound of a venue or equipment; see also Acoustic.

Source - a device that provides drive signals required by other devices; see also Sink.

Speaker - see Loudspeaker.

Speakon - a late generation connector of dubious merit specifically for Loudspeakers, and may prove to be fragile in service. Inspired by an equally dubious EU safety directive that all Amplifier output connections must be insulated from contact.

Spider - part of the Suspension of a Loudspeaker that locates the apex of the Cone and the Voice Coil in the correct position. It must hold the Cone assembly ridgidly centred in the magnet gap, but allow the Cone free movement in and out.

Spill - undesired sound coverage, generally from Backline amplifiers on-stage turned up too loud.

SPL - Sound Pressure Level - “how loud it is”; the sound level in Decibels above reference Level; see Decibels, dBA

Spring line - a type of Delay line consisting of one or more springs suspended between a driver and a pickup, generally magnetic, to cause random delays and reflections to simulate a Reverberant environment.

Stack - Loudspeaker enclosures placed on top of each other, generally at each side of the stage starting with the Bass Bins, then Mids, finally the Tweeters on top.; multi-Cab guitar Amplifier; tone controls within an amplifer.

Standing wave - a situation where two waves (or a Reflection of a wave) interact to produce a static pressure pattern, generally between two reflective surfaces; see also Resonance, Honking, Eigentone.

Stereo - a system where two different acoustic aspects of the same performance are available together, allowing the reproduction of a sound field that has a degree of directionality and depth. In PA work the use of stereo with Pan controls can help vocal definition by correctly placing the acoustic image over the performance; see also Hass Effect

Stomp box - any floor-dwelling Effects device with foot operated controls.

Strip - see Channel.

Subjective - evaluation of equipment using the ears alone, inherently unreliable; see also Objective, Hi-Fi, Audiophile, OFC.

Subs - a sub-Bass Loudspeaker; available output channels on a Mixer; see also Buss.

Super-Cardioid - see Cardioid.

Suspension - parts of a Loudspeaker around the rim and apex of the Cone, the Spider, that hold the assembly rigidly in-line with the magnet opening, but allow free forward and backward movement to produce sound. The suspension is important in Loudspeaker robustness and reducing distortion.

Tabs - tall narrow curtains to hide the side stage from the audience.

Tank - see Springline.

Tape - a recording Media consisting of an iron oxide layer on a flexable plastic base; see also Cassette.

Tape echo - see Tape Loop.

Tape loop - a method of producing Echo by recording the signal to rapidly moving endless magnetic tape loop then quickly replaying it again normally using a row of several replay heads following the record head. Multiple playback heads allow multiple delayed outputs from a single input. The tape is recycled using sprung rollers (short-loop) or an endless cassette format (long-loop), the latter giving better tape life. It is erased ahead of re-recording, cheaper machines use a small magnet which gives a high Noise Floor, better machines using a proper AC erase head. See also Effects, Moody.

Temper, Temperament - micro-adjustment of the tuning or other adjustment of an instrument (e.g. guitar bridge) so that chords played in all positions sound acceptable and not sour or out of tune; see also Prima Donna.

Three phase - a heavy duty Mains Power supply, generally for lighting Rigs at larger shows. Normal 'single-phase' Mains Power is only one of three phases generated in the power station, each 250 Volts, 50 Hertz, but exactly one-third of a cycle out of step with each other. The difference between each of the phases is 415 volts. An analogy is the difference between a single-cylinder engine, and one with three cylinders - more powerful and smoother.

Tinfoil-in-the-Piano - a distortion in Digital systems that sounds like distant crinkling alfoil; aka frequency-folding and Aliasing, a design defect. Comes from the trick of inserting a sheet of newspaper or foil between the dampers and strings of a piano to get a “honky-tonk” effect.

Tone control - a circuit that allows you to change the proportions of a signal at different Frequencies. Tone controls range from single top-Cut controls through the common Bass/Treble pair, to multi-band one-third Octave Graphic Equalisers; see also EQ.

Trap - a trapdoor in the surface of the stage to the understage.

Traps - a drumkit; sundry noise-makers with the drumkit such as wood block, cowbell, whistles, horns, etc, generally featuring during clown acts at the circus.

Treble - high pitched sounds; a control for Frequencies above 1Khz.

Tree - portable stand used to support lights, sometimes with an air cylinder to lift the lights into position.

Tremolo - slow variation (2-10Hz) in the amplitude of a signal. This produces a Subjective effect of Pitch shifting; see also Vibrato.

Trim control - a Mixer control near the input that allows the basic sensitivity of the Channel to be set. Setting the trim control too high and Crushing the signal as it enters the Channel has to be the most common PA operator fault.

TRS - Tip, Ring, Sleeve - a three contact Jack connector typically used for Stereo but can be used for Balanced and Phantom setups.

Tweeter - a Loudspeaker designed to produce only the higher part of the Audio range; see also Dome, Piezo, Horn.

Tuning fork - U-shaped device that when struck vibrates at the Frequency of its calibrated musical note.

Unbalanced - see Single-ended, Balanced.

Unscreened - a cable or device that has no conductive covering, such as a braid, connected to ground to shield the signal carrying wire.

Vent (speaker) - see Port.

Vibrato - slow variation (2-10Hz) in the Frequency of a signal, uncommon outside organs and synths; see also Tremolo.

Voice coil - part of a Loudspeaker that is attached to the apex of the Cone and is held in the circular gap of a magnet where it acts as a linear motor when current is passed through it; see also Loudspeaker.

Volume - see Level.

VOX - Voice Operated switch - not often used in PA; see also Ducking, Noise Gate, ALC.

VU - Volume Units - a measure of the strength or intensity of the average Level of a signal. VU or average reading programme meters have a longer response time than Peak Level reading meters and can be misleading on material with high dynamics or intense Bass. Mixers are normally fitted with peak reading meters for this reason.

W-bins - a type of Bass Loudspeaker Enclosure that uses Horn loading and compacts the horn by splitting it down the middle and folding it back on itself to produce a W-shape internally; see also Siamese page, J-Bin.

Wall wart - see Plugpack.

Watt - a unit of electrical power, the product of Voltage and Current; output drive rating of an amplifier; power consumed by lights, etc.

Weber's Law - “Where any physiological stimlus varies by equal steps in geometrical progression, perception of the stimulus varies by equal steps in arithmetic progression.” In pitch the perception of an an octave is a doubling of frequency. In amplitude a doubling of loudness perception requires four times the Sound Pressure Level (SPL) and therefore system power (watts).

Wedge (floor) - a Loudspeaker Enclosure with an angled front intended to go on the floor in front of performers who need Foldback.

White noise - Noise that has equal energy per constant Bandwidth; all Frequencies equally likely at any instant; see also Pink noise

Whizzer cone - a secondary smaller Cone on a Loudspeaker designed to act a Tweeter and extend the high Frequency Response of the speaker.

Wings - the sides of the stage hidden from the audience.

Wolf note - jarring discord caused by poor Temperament.

Woofer - Hi-Fi term for a Bass Driver, rarely used in PA; see also Bin, Horn.

XLR - a type of signal connector originally designed by Cannon/STC (now Alcatel) but since made better by Neutrix and others, featuring three pins for Balanced use, and a latching trigger release. Universally used on better quality Microphones and also make excellent Loudspeaker connectors.

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