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The glossary pages provide definitions for over 2680 PA-related terms and abbreviations. If you can't find the term you are looking for, or would like any of the existing definitions to be expanded, please email me − likewise of course if you find any errors in the links etc. Use of this information is conditional upon acceptance of the Disclaimer on the PAforMusic home page.

In the list below, the most commonly looked-up terms are in bold, lighting-specific terms are in pink, and video-specific terms are in orange.

Ear buds * Ear mix * Earhook * Early decay time * Early reflections * Earphones * Ears * Ears mix * Earth * Earth bonding * Earth-compensated * Earth fault * Earth fault loop impedance * Earth-free * Earth isolator * Earth leakage * Earth lift * Earth loop * Earth loop impedance * Earth potential * Earth rod * Earthed * Earthing * Earthing system * Earthy * EASE * EBU * EBU R 128 * Echo * ECIA * EDAC * EDID * EDM * EDT * Effects * Effects loop * Effects pedal * Effect return * Effect send * Effective series resistance * Efficiency * EFI * EFX * EIA * EICR * EIN * Electret * Electric bass * Electrical safety * Electrical safety tests * Electrical tape * Electrodynamic microphone * Electrolytic capacitor * Electromagnetic interference * Electromagnetic wave * Electromotive force * Electronically balanced * Electrostatic coupling * Electrostatic discharge * Electrostatic microphone * Element * ELV * EMAC * EMC * EMF * EMI * Emulated line output * Enclosure * End-firing * Energise * Energy * ENG * Engine * ENL * Ensemble * Envelope * Environmental noise pollution * EP * EP connector * EP[n] * EPD * Equal loudness curves/contours * Equalisation * Equaliser (EQ) * Equations * Equipment classes * Equipotential bonding * Equivalent input noise * Equivalent noise level * ERP * Error correction * Error rate * ESD * ESR * ESTA * ETH, Eth * etherCON * Ethernet * Ethernet cable * Ethernet connector * Ethernet protocol * ETS * ETSI * Euro connector * Euro thread * EWM * Exciter * Excursion * Expander * Expansion * Expansion ratio * Exponential horn * Extra low voltage

The definitions for these terms are given on the assumption of their use in the context of PA systems; many of the terms have more general meanings when used in a wider context. Where more than one definition is given for a term, the definitions are numbered (1), (2) etc.

Some of the definitions themselves use terms (such as "signal") in a specific way − most of these are links (just the first time they are used, in each definition), so just click on them to see the meanings that are intended.

Ear buds

An alternative name for earphones.

Ear mix

A slang term for a mix intended to be fed to in-ear monitors, or, less often, for a mix intended to be fed to headphones. See also Ears (2).


A device used to attach a head-worn device, usually a miniature microphone, by means of a stiff wire bent around the back of the ear. Or, describes such a microphone. Such microphones are usually radio microphones and are used in conjunction with a bodypack. See also Headset.


A more discrete alternative to headphones, typically used with in-ear monitoring systems and personal entertainment players. Earphones are a friction fit in the ear canal and so are self-supporting. They are also referred to as ear buds. Different types vary as to how much ambient sound they are designed to keep out. Minimum load impedance considerations apply in respect of earphones in the same way as for headphones − see Headphones for details. See also Ears (2) and Intraaural.

Early decay time

The time taken for the initial part of a reverberation decay curve. It is measured to the point where the sound level has reduced by 10 dB from its initial level, after a constant-level sound source has abruptly ceased. Commonly abbreviated to 'EDT'. A low EDT is desirable for good speech intelligibility. Compare Reverberation time.

Early reflections

Reflections of sound from nearby surfaces, resulting in reflected sound reaching the listener a relatively short time after the direct sound and substantially before the general reverberation of the space. See also Slap echo.

Ears (1)

Apart from the obvious meaning, a slang term for the flanges at the sides of the front face of equipment intended for mounting in a 19 inch rack system.

Ears (2)

A slang term for the performer-worn part of an in-ear monitoring system, sometimes referring specifically to the earphones worn for it.

Ears mix

See Ear mix.


Short for either 'safety earth' or 'signal earth'.

Earth bonding

See Bonding.


See Ground-compensated.

Earth fault, Ground fault

In mains electrical equipment and mains distribution arrangements, this usually refers to an excessive leakage of current from the mains supply to safety earth, occurring as a result of an equipment fault or as a result of unacceptably low insulation resistance in mains cables, connectors or distribution equipment. (A small amount of earth leakage is normal.) Excessive leakage currents may constitute a safety hazard, and may cause an RCD to trip and disconnect the power. Or, the term may refer to a short circuit from the supply live or neutral to a safety earth.

However, in PA work the term may be used to refer to any kind of problem associated with a safety earth or with a signal earth. See also Fault protection, Earth loop impedance and Megger.

Earth fault loop impedance

See Earth loop impedance.


An alternative term for 'floating'.

Earth isolator, Ground isolator

A device which is inserted into an interconnection between two items of equipment, in order to pass the required signal without a conducting signal earth connection. That is, to provide galvanic isolation of that interconnection's signal earth path.

The most common reasons for using an earth isolator are to avoid creating an earth loop through an interconnection (and so avoid or resolve mains hum problems) and to avoid or resolve problems due to interfering signals carried on the interconnection's signal earth conductor. Earth isolators are usually required only on unbalanced interconnections, as good quality balanced interconnections do not generally suffer from these problems. The device most commonly used for earth isolation is a signal isolating transformer. The equivalent US term is 'ground isolator'. N.B. Safety earths must never be disconnected to avoid hum or other problems. Not to be confused with the US-specific term isolated ground, which relates to mains outlets.

Earth leakage

Current that flows in a safety earth conductor from the mains supply. Such unwanted currents typically arise as a result of paths through capacitances between the live conductors of the mains supply and earthed points. These capacitances may be provided intentionally as part of mains interference suppression arrangements, but in any case will exist incidentally between the internal conductors of 3-core power cables and between the internal mains wiring of equipment and earthed chassis. When excessive earth leakage occurs as a result of a fault or low insulation resistance, this is termed an 'earth fault' and may be a hazardous condition.

Earth leakage can be a source of hum and buzz problems where earth loops exist, because the earth leakage currents develop a voltage across the safety earth path impedances and therefore cause voltage differences between different safety earth points in the power distribution system. Such differences in voltage may in turn cause mains-frequency currents to flow in the signal earth conductors of signal cables. As earth leakage can rarely be reduced (except by use of a balanced mains supply), solutions to these hum and buzz problems usually include the avoidance of earth loops as far as possible, and the use of balanced signal interconnections to reduce the effects of them.

Furthermore, the earth leakage currents arising from multiple items of equipment will tend to add up, and if the total value becomes excessive then spurious tripping of RCDs may occur.

Earth lift, Ground lift

On Class I mains-powered equipment, a switch which provides the facility to disconnect the equipment's signal earth from its safety earth, in order to avoid an earth loop. It should not disconnect the safety earth from the parts of that item of equipment which must remain earthed for safety reasons, and so operating an earth lift switch is not the same as using the equipment without a safety earth connection, which would present a serious electric shock hazard.

On Class II mains-powered equipment and on non-mains equipment (such as battery or phantom-powered DI boxes), a switch which provides the facility to disconnect the signal earth connection between other items of equipment, in order to avoid an earth loop. (Such a loop may exist through other signal earth paths, or through safety earth connections to Class I equipment.)

Although operating an earth lift switch should not in itself create a hazardous situation, it is strongly recommended that for maximum safety such switches are only set to the 'lift' position if it is certain that this does not disconnect the only safety earth connection to the signal earth (i.e. a safety earth connection is being provided from other equipment and is certain to remain connected during use). If no safety earth connection is being provided by another path, then a mains earth loop condition does not exist and operation of the earth lift switch is probably unnecessary; to operate it would remove the only safety earth connection from the signal earth, which as well as reducing safety could itself introduce a buzz or hum, confusingly similar to that which would be caused by an earth loop!

An earth lift switch may also be referred to as a 'ground lift switch' (originally a US-only term), and often will have just two positions typically labelled 'Earth' (or 'Ground') and 'Lift'. The 'Earth' position provides a low-impedance connection to earth, and the 'Lift' position provides a complete disconnection of the signal earth path. Note, however, that in the case of equipment which does not provide galvanic isolation (i.e. equipment in which the switch relates to an electronically balanced input or output), the 'Lift' position only breaks the earth path through the signal earth conductor, and a path to earth may remain (via some impedance) through the 'live' or 'signal' conductor(s).

In some cases (most often on DI boxes), the earth lift switch has three positions, typically labelled 'Earth' (or 'Ground'), 'Float' and 'Lift'. In these cases the function of the 'Earth' and 'Lift' positions is the same as in the case of a two-position switch, while the 'Float' position provides a 'medium impedance' connection to earth (typically through a parallel resistor and capacitor).

Earth loop, Ground loop

The situation that exists when two or more items of safety-earthed equipment are interconnected (either directly or via other equipment) by signal cables. This creates a continuous 'circular' path of earthy interconnections, made through the safety earth conductors of the equipment power cables and the signal earth conductors of the interconnecting signal cables.

For example, such a situation is likely to occur if a line output of a combo (or other item of Class I mains-powered stage equipment) were connected direct to an unbalanced line input of a mixer. This condition can sometimes result in the addition of hum to the wanted signal(s). An earth loop may also be referred to as a 'ground loop' (originally a US-only term).

The hum occurs because of mains-frequency voltage differences between the safety earths of the interconnected equipment, which arise due to mains earth leakage currents developing different voltages across the impedances of the safety earth conductors involved, and/or due to currents induced into the earth-loop path (e.g. from nearby mains transformers). Such voltage differences result in a voltage difference between the signal earths of the equipment, and therefore add to the voltage of any signals passed between them. Further, they result in the flow of earth currents along the signal earth conductor(s) of the interconnection, which may inductively couple into the signal conductors.

Earth-loop problems may be usually resolved by the use of good quality balanced or ground-compensated signal interconnections, to provide immunity against the earth voltage differences. Additionally, appropriate use is frequently made of DI boxes, earth lift switches, earth isolators, Class II mains equipment, and sometimes the physical disconnection of balanced cable screens inside connectors; these measures can provide galvanic isolation of signal earth connections and thereby break the loop. Note, however, that safety earths must never be disconnected, as to do this would create a lethal shock hazard. It is inadvisable to disconnect the cable screen of unbalanced interconnections. If the screen connection of a balanced cable is disconnected, this should be done at the destination end of the cable, which should be marked accordingly, and consideration should be given to installing a low-value capacitor (e.g. nF) between the screen and the connector earth terminal in order to provide a path for radio-frequency signals. Less common measures to reduce the likelihood of earth loop problems include the use of a technical earth and/or of balanced mains supplies. See also Pin 1 problem.

Earth loop impedance

A mains distribution term, essentially unrelated to the sound engineering term 'earth loop'. It is a shortened form of the 'official' term 'earth fault loop impedance', and relates to the total value of impedance around a notional electrical circuit completed through the live and safety earth conductors of the supply. It is measured, using specialist equipment, between the live and safety earth connections at distribution boards and at points of power utilisation. This value is required to be sufficiently low in order to provide safety by a sufficiently rapid automatic disconnection of the supply in the event of a short-circuit earth fault occurring from a live conductor to safety earth. Specific maximum values of earth loop impedance are required by BS 7671 and BS 7909, according to the type and rating of the circuit protection device.

Earth potential, Ground potential

A common reference point for the measurement of the voltage at other points; a point of assumed 'zero voltage'. In the context of power voltages referenced to a safety earth, earth potential is usually considered to be the potential of the general mass of the Earth. In the context of signal voltages, 'earth potential' usually refers to the potential of the relevant signal earth, which may or may not have a galvanic connection with the general mass of the Earth. The term 'ground potential' is more common in the USA. See also Potential.

Earth rod, Ground rod

A metal rod, usually of copper and about a metre long, which is driven into the ground and connected to in order to provide a local safety earth connection or in order provide a means of earthing for a locally generated electrical supply. May also be referred to as an earth spike, or (especially in the USA) as a ground rod or ground spike. In order to provide the required level of electrical safety, it must be verified that the impedance between the earth connection provided by the rod, and the general mass of Earth, is sufficiently low. See also TT.

Earthed, Grounded

Describes something that is suitably connected to a safety earth or to a signal earth, as appropriate to the purpose.

Earthing, Grounding

The process of providing a suitable conducting path to a safety earth or to a signal earth, as appropriate to the purpose. Or, the means that provides such a path. For a description of the most common safety earthing systems covered by BS 7671 see TN-S, TN-C-S and TT.

Earthing system

The particular means by which a safety earth is provided to an electrical installation. BS 7671 recognises several types of earthing systems, the most common of which are TN-S, TN-C-S and TT.


Describes a conductor that, in normal use, possesses an insignificant voltage with respect to the general mass of Earth, i.e. a conductor which is at essentially earth potential. Or, any conductor nominally at a 'zero' voltage, such as a signal earth. In an unbalanced connection, the earthy conductor is sometimes referred to as the 'cold' conductor. See also Safety earth. Compare Hot.


An abbreviation for 'Enhanced Acoustic Simulator for Engineers', a commercial software package that provides simulation of the acoustic behaviour of a specified room or space, under the influence of specified sound sources within it. Many speaker manufacturers provide acoustic data for their products in 'EASE format', for direct importing into the EASE package. For more information see the supplier's website at ease.afmg.eu (external link, opens in a new window). See also the Manufacturers' page and CLF.


An abbreviation for 'European Broadcasting Union', a body which sets technical standards for broadcasting in Europe. See also AES and ITU.

EBU R 128

An EBU recommendation for loudness normalisation and the permitted maximum level of audio signals, based on ITU-R BS.1770. Sometimes written as EBU R128. See also LUFS.


An effect unit that simulates a natural echoing of the sound signal supplied to it, or that provides effects of a similar kind. Or, such an effect itself. An echo is a delayed (and, usually, somewhat modified) copy of an original sound, providing one or more distinct repetitions of the original sound. A distinct repetition will typically only be perceived if the delay is greater than about 50 ms. The term 'delay' is now frequently used to refer to echo effects.

Echo effects are now more commonly provided either by more comprehensive outboard equipment generally referred to as delay effects units, which are also able to provide other delay-based effects such as reverberation, chorus and flanging, or by the multi-purpose onboard effects facilities of mixers. In most cases the facility is provided for single or multiple echoes. See also Haas effect.


An abbreviation for 'The Electronic Components Industry Association', an American organisation responsible for setting certain types of standards for electronics manufacturers in the USA. The ECIA now (since 2011) has responsibility for the standards produced by the now defunct EIA, and still uses the designation 'EIA' for certain new standards that it produces. Their website is www.ecianow.org (external site, opens in a new window or tab). See also TIA.

EDAC (1)

A manufacturer of connectors. In PA work, the term is most often used to refer to the screw-secured EDAC 516 series of rectangular multi-pole connectors, commonly used for the connection of multiple balanced circuits, e.g. on multicores and stageboxes. It should be noted, however, that this a general-purpose high quality 8.5 amp connector, that is also used in other applications. The most commonly used sizes in PA work are 38 pole (for 8 or 12 circuits), 56 pole (for 16 circuits), 90 pole (for 26 circuits) and 120 pole (for 32 circuits). 20 pole types are also available.

When used for balanced audio interconnections, the connectors are usually wired according to a standardised pin-allocation − see SAC (2). Cables are generally fitted with male types, designated '−MC' (male, cable). Panels are generally fitted with female types, designated '−FP' (female, panel). 'Compatible' connectors are produced by other manufacturers, though these may provide inferior quality connections − particularly when mated with connectors of a different make. However, the ELCO 8016 series is generally considered to be fully compatible. See also D-sub, MASS connector, Socapex and TCMCC.

View EDAC 516 series (56-MC) connector image

EDAC (2)

An abbreviation for 'error detection and correction', referring to the process of detecting and correcting errors in a digital bit-stream or in stored digital data. Error detection and correction is most commonly accomplished by use of a specific algorithm operating on additional bits inserted into the data according to clearly defined rules.


An abbreviation for 'extended display identification data', information that is exchanged during initialisation of an HDMI interconnection between two items of equipment. The EDID is supplied by the display equipment upon receipt of a request from the signal source, and provides the source with sufficient information to allow it to configure the HDMI signal it provides in such a way as to be compatible with the audio and video capabilites of the display equipment.

When an HDMI signal is to be supplied (via. an HDMI splitter) from a source to two or more items of display equipment having different capabilities, then it is necessary to make arrangements to ensure that the EDID provided to the source is appropriate, instructing it to provide a signal that is displayable by all the items of equipment receiving that HDMI signal.

The interface over which the EDID is carried is known as DDC; this interface is also provided by a VGA interconnection.


An abbreviation for 'electronic dance music', dance music that is partially or substantially generated electronically.


An abbreviation for 'early decay time'.

Effect, Effects

Onboard mixer facilities or outboard units whose purpose is to modify a signal − usually in such a way as to improve the interest or 'fullness' of the sound. Or, the part of the sound that is added by such facilities. Typical examples would be reverberation, echo, distortion, etc. Frequently abbreviated to 'FX' or 'EFX'. See the Effects page for further information. See also Wet, Dry, Signal processing, Serial effects unit, Parallel effects unit and Pedal. Compare Sound effects and Special effects.

Effect loop, Effects loop

The signal path that runs from an effect send output on some item of equipment, through one or more effects units, and back to an effect return input on the original item of equipment. On equipment such as backline amplifiers, the Send and Return connectors are usually 2-pole jack sockets, while on mixers the equivalent 'insert' facilty is usually provided by a single 3-pole jack socket − see Insert for further details.

It is usual practice for effects loops to be arranged for serial effects units. Therefore, when the loop facility is in use, there is usually no alternative path for a 'dry' signal provided through that equipment itself; any wet/dry mixing must usually be performed by the external equipment that is connected to the Send and Return connectors. In the absence of any effects being connected to the loop, the normal signal path through the equipment is usually provided via the switch contacts of the Return (or Insert) jack, which open to break that path when a plug is inserted (though in some cases the Send jack's switch contacts may also be involved). Oxidation of these switching contacts is frequently responsible for faults (often intermittent) that are only evident when the effects loop is not in use.

Effect pedal, Effects pedal

See Pedal.

Effect return, Effects return

An input, of a mixer or instrument amplifier, intended to accept the output signal of an effect unit.

Effect send, Effects send

An output, of a mixer or instrument amplifier, intended to supply a signal to an effect unit.

Effective series resistance

A parameter of some electronic components, most usually applied to capacitors and commonly abbreviated to 'ESR'. It indicates the amount of (unwanted) resistance that the component introduces into the circuit, appearing in series with the wanted effect of the component. The ESR of capacitors at some points within an audio circuit can be detrimental to sound quality if its value is too high. However, at many other points, the ESR value is of no great significance, typically because it is swamped by other circuit impedance values.


A measure of the proportion of the power supplied to an item of equipment (its 'input power') that is usefully converted or conveyed by the equipment (its 'output power'), expressed as a percentage. For example, if a particular power amplifier is providing 600 W of audio output power and (under those circumstances) is 60% efficient, then it will be consuming 1000 W from the mains supply. The efficiency of speakers and microphones is usually specified in terms of their sensitivity. See also the Amplifier Classes section on the Amplifiers and Speakers page.


See RCD.


An abbreviation for 'effects'. (More usually abbreviated to 'FX'.)


An abbreviation for 'The Electronic Industries Alliance', an American organisation previously responsible for setting standards for electronics manufacturers in the USA, including several important standards still applicable to audio and computer equipment. Although they ceased to exist in February 2011, the abbreviation continues to be used for their standards and also for new interconnection standards (and some others) created by the organisation now responsible, the Electronic Components Industry Association − see ECIA. See also TIA.


An abbreviation for 'electrical installation condition report'. See Condition report.


An abbreviation for 'equivalent input noise'.


See Condenser microphone.

Electric bass

The proper name for a 'bass guitar'; see Bass (2).

Electrical safety

See Electrical Safety on the Safety page.

Electrical safety tests

For fixed installation testing see Condition report and for equipment testing see PAT.

Electrical tape

See PVC tape.

Electrodynamic microphone

Another name for a dynamic microphone.

Electrolytic capacitor

See Capacitor.

Electromagnetic interference

Strictly, a general term for any interfering signal that is carried as an electromagnetic wave. Such interference may be continuous (e.g. caused by a radio transmission) or momentary (e.g. caused by the operation of a mains switch). However, in practice the term is very commonly used to refer to radio-frequency interference that is conducted through power cables or signal cables − regardless of whether or not the interference originated electromagnetically. Often abbreviated to 'EMI'. See also EMC, RFI, Longitudinal choke and ERP. Compare Inductive coupling and Capacitive coupling.

Electromagnetic wave

A more scientific name for a 'radio wave'. The strictly correct term is 'electromagnetic radiation'. See also Radio-frequency.

Electromotive force

Another name for voltage. Strictly, it is the value of a source voltage when no load is connected to that source, i.e. when no current is drawn from it. This term is most commonly used in relation to voltage supplies (such as batteries); when referring to the voltage at signal outputs the terms 'open-circuit voltage' or 'unterminated voltage' are usually employed. Frequently abbreviated to 'EMF'. See also Potential.

Electronically balanced

Describes an item of equipment's input or output when the equipment uses internal electronic circuitry to enable that input or output to provide the facility for balanced operation of its interconnection with other items of equipment. The term is usually used to emphasise that balanced operation is catered for by means of such circuitry, rather than by means of a transformer (compare Transformer balanced). The electronic circuitry will always require a source of power, so such an input or output can only be provided by active equipment. Most modern designs of mixer have electronically balanced microphone inputs.

An electronically balanced input or output may alternatively be described as 'transformerless', as it operates without the use of a transformer. For example, if the balanced output of a condenser microphone is described as being transformerless then it achieves the balancing of its output electronically, without the use of an internal transformer.

Note, however, that balanced operation of an interconnection is possible only when the equipment at both of its ends, and also the types of cable(s) and connectors used, are suitable for that type of operation.

Electronic balancing is in general neither 'better' nor 'worse' than transformer balancing. However, each type does have its own advantages and limitations; the relevance and importance of these varies with each application. There are some instances in which one or the other type may be preferable (or even essential), but in most cases the quality of the equipment's input or output design is likely to have more effect on the results obtained than the type of balancing employed.

Advantages of electronic balancing typically include:

Disadvantages include:

A particular type of electronically balanced output is the quasi-floating output. (The semi-balanced and ground-compensated types of output use an electronic drive circuit, but are not true balanced outputs as only one leg is driven.)

Two types of electronically balanced inputs are commonly used, which may be described as 'buffered' and 'unbuffered' types. The unbuffered type uses a basic differential amplifier design, in which the hot and cold legs are given equal and opposite gains but have different impedances to signal earth. This type is generally adequate only for balanced line level inputs, due to the inherent lack of symmetry between the hot and cold legs of the input. The buffered type uses a more sophisticated design which employs additional components to provide active 'buffering' between the differential amplifier and the input legs. This provides the two legs with (in principle) completely symmetrical input characteristics, which gives an improved common-mode rejection ratio. This is the type usually (except in the case of budget equipment) employed for microphone inputs, where optimum common-mode rejection is a necessity due to the very low signal levels present. Compare Transformer balanced.

Electrostatic coupling

Another term for capacitive coupling.

Electrostatic discharge

A flow of current from a very high voltage source that is able to sustain that current only very briefly. For example, the current flow from an object (such as clothing manufactured from some types of man-made fibre) that has become statically charged due to friction. Although the current flow is only very brief, the very high voltages involved (often many thousands of volts) can cause serious damage to electronic components, especially semiconductors. Electrostatic discharges can also generate radio-frequency interference, giving rise to the 'crackling' noise commonly referred to as 'static'.

Such very high voltages are able to overcome the insulating properties of insulators (e.g. air), enabling the current to 'jump' a gap between conductors. Such an event can cause permanent damage to nearby insulating material and/or to the conductors. Frequently abbreviated to 'static' or to 'ESD'.

Electrostatic microphone

Another name for a condenser microphone.


The specific internal part of a microphone that performs the function of a transducer, converting sound waves into an electrical voltage. There are three basic types of element, namely dynamic, condenser and ribbon, giving their names to these respective types of microphones (see the links below). In many cases the element is a self-contained part that is field-replaceable or even user-exchangeable, in which cases it is usually referred to as a capsule. A few types of microphone contain more than one element, for example both dynamic and condenser elements, a low frequency element and a high frequency one or, in the case of a stereo microphone, a Left and a Right element. See also Dynamic microphone, Condenser microphone, Ribbon microphone and Electret.


An abbreviation for 'extra low voltage'.


A trademarked abbreviation for 'extended multiply and accumulate', Mackie's proprietary 32-bit digital stereo effects processor.


An abbreviation for 'electromagnetic compatibility'. The degree to which items of equipment are immune from the effects of EMI, and/or are designed to reduce EMI effects they might have on other equipment. See also Longitudinal choke.


An abbreviation for 'electromotive force'.


An abbreviation for 'electromagnetic interference'.

Emulated line output

A line-level output, found on some combos and heads (especially those intended for guitars), that, when connected to a PA system, is intended to provide a sound similar to that produced by the speaker of the combo (or of the speaker connected to the head). That is, the results are intended to be similar to those obtained by miking-up the speaker, but without the associated problems such as leakage, cost of the microphone, space taken up by the microphone and its stand, etc.. Combos and heads vary in the degree to which the intended objective is actually achieved.

An increasingly common alternative (or additional) use for these outputs is to drive an FRFR amplifier and speaker system, in place of a conventional backline speaker cabinet.

Emulated line outputs can be either balanced (usually at low impedance) or unbalanced (usually at high impedance). If the connector is an XLR then the output is likely (not certain) to be balanced, and if the connector is a jack then it is likely (not certain) to be unbalanced − check the manufacturer's specification. Note that as these outputs are at line level, they are not suitable for direct connection to a mixer microphone input (or to a stagebox) unless the mixer is able to handle such high-level signals on its microphone inputs. (As a general rule, only mixers having 20 dB pad switches usually satisfy this condition.) In other cases, an attenuator or DI box must be used to reduce the level.


The case, housing or cabinet of an item of equipment, especially of a speaker. In the case of a speaker, the enclosure does not simply provide mechanical support and protection for the driver(s), but also affects the sound produced − especially as regards bass response. Speaker enclosures, often referred to as 'cabs', may be sealed to the passage of air (see Sealed box), or may be ported. See also Chassis.


Describes a microphone whose maximum sensitivity to sound is at the end of the microphone (rather than at the side). The end-firing design is the norm for PA microphones (with the exception of some types of drum microphones). Compare Side-addressed. See also Polar response.


To connect to a source of electrical energy, or to activate or switch on such a source so as cause electrical power to flow or to become available. In particular, to connect a mains power distribution arrangement to a source of mains electricity; the distribution arrangement is then said to be 'energised', or more informally, to be 'live'.


The ability (or potential) to do work, for example to create heat, light or sound, or to move objects. Or, the amount of work done. Electrical energy is stored in batteries or is obtained from the mains supply or from a generator. Energy is measured in joules: one joule is sufficient to sustain a power level of one watt for a duration of one second. Put another way, if energy is being transferred at a constant rate then the amount of work done (in joules) is the power (in watts) multiplied by the length of time (in seconds) for which that power level is sustained.


An abbreviation for 'electronic news gathering', a term used to describe audio, video and related equipment that is intended for (or is designated as being suitable for) use by roving news reporters or mobile news reporting crews. Such designation does not preclude the use of the equipment for other purposes unless the equipment makes use of transmitted radio frequencies that are specifically reserved for ENG purposes (or whose use would in any case be illegal) within the country or region of use.


The heart of a digital signal processing (DSP) unit, digital mixer or digital audio workstation (DAW), which performs high-speed mathematical operations on the digital signal(s) in order to achieve the desired results. The 'power' of the engine determines the amount of processing that can be performed in real time.


An abbreviation for 'equivalent noise level' (of microphones), an alternative term for 'self noise'. See Microphone Noise Levels on the Microphones page. See also Thermal noise.


A group of instruments that are played at the same time; a term generally used only for small groups of orchestral instruments, and often taken to refer indirectly to the musicians. Or, a small group of vocalists, not large enough to be considered a choir.


The way in which the level of a musical note changes, from the moment that the note is struck to the time that the sound produced completely dies away. Envelopes of electronically generated sounds are often described using the four parameters attack, decay, sustain and release − for details see ADSR.

Environmental noise pollution

Any man-made sound that is deemed to be a cause of unacceptable disturbance. Usually, the presence of absence of such disturbance will be determined by the local regulatory authorities, and in some circumstances immediate fines may be charged or prosecutions made. Often abbreviated to 'noise pollution'. See also Sound limiter.


Usually refers to a music track of longer duration than normal; a term derived from an abbreviation for the 'extended play' singles originaly distributed on vinyl records.

EP connector (EP3, EP4, EP5, EP6, EP8)

A series of high-power latching connectors manufactured by Amphenol®. This series has a rugged die-cast shell. A specific feature is their ability to accept large diameter cables. Once popular for connections to passive speakers, but now largely replaced by the Speakon. They are available in 3, 4, 5, 6 and 8-pole versions, referred to as EP3, etc. A further digit may be added to indicate male or female gender, cable or panel mounting, etc., e.g. EP5-12. The 3, 4, 5 and 6-pole versions are rated at 20 amps and at least 200 volts RMS; the 8-pole version is rated at 15 amps and 100 volts RMS. The 5-pole version was useful for amplifier-speaker combinations in which an additional 'sense' connection was required. The AP series of connectors is similar but has a durable plastic shell rather than die-cast metal; these types are fully compatible with the EP series.

View EP connector (EP5-12) image


An abbreviated name for The Event Production Diary, an on-line and annually printed resource that provides listings of subscribing event production companies and suppliers of associated products and services worldwide. Their website is www.epdweb.com (external link, opens in a new window). See also PLSN and FOH.

Equal loudness curves, Equal loudness contours

See Fletcher-Munson curves.


The facility provided by an equaliser, or the effect of such a facility on a signal − see the next definition.

Equaliser (EQ)

A dedicated item of equipment, or a section of a mixer or an amplifier, that allows control of the relative level of specific frequency ranges of a signal, whilst leaving other frequencies essentially unaffected.

The most basic equalisers just provide control over bass, mid-range and treble frequencies (loosely referred to as 'tone controls'), whilst more sophisticated units provide a finer degree of control. Most units provide, for each band of frequencies controlled, the facility to both cut (i.e. attenuate) and boost (i.e. amplify) the parts of the signal in that frequency range. Usually the cut and the boost are similar in the extent of control and in the width of the band of frequencies affected; where this is not the case the equaliser is described as asymmetric or non-reciprocal. (An example is where the cut applies to only a narrow band, for notching purposes.)

The term originates from telecommunications, where the purpose of an equaliser is to compensate for inadequacies in the frequency response of equipment, especially of long-distance cables, by providing an 'opposite' frequency response and thus making the overall response through the system substantially flat. It should be noted, however, that in PA work equalisers are more often used to alter the frequency response for artistic purposes rather than to flatten it (with graphic equalisers largely being an exception).

For further information, see the Equalisation section of the Mixing Facilities page. See also Sweep EQ, Peaking response, Shelving response, Parametric equaliser, Dynamic equaliser, RIAA and Tape equalisation.


For general audio and electrical equations see the Calculations page. For decibel equations see the Decibels page.

Equipment classes

See Class I and Class II.

Equipotential bonding

See Bonding.

Equivalent input noise (of pre-amps)

An indication of the level of noise that is added to a signal by a pre-amplifier, expressed in terms of the noise level that is apparently added at the input of the amplifier. Note that this figure is usually dependent upon the output impedance value of the signal source that is connected to the input. Often an A-weighted figure is quoted, usually in dBu. Often abbreviated to 'EIN'.

To take advantage of a low EIN value, it is necessary to use a low-noise signal source. For example, if the source is a microphone then it must have a low noise output level. (Microphone noise levels are usually quoted as an 'equivalent noise level' − or 'self-noise' − value, in dB SPL. For details of how to convert this to a value in dBu, for comparison with an EIN value, see Microphone Noise Levels on the Microphones page.)

To arrive at the noise level at the output of the amplifier, the equivalent input noise must be multiplied by the gain of the amplifier (in terms of decibels, this means adding the two quantities).

Equivalent noise level (of microphones)

An alternative term for 'self noise', abbreviated to ENL. See Microphone Noise Levels on the Microphones page. See also Thermal noise.


An abbreviation for 'effective radiated power'. A term used in radio transmission to indicate the level of radio-frequency (RF) power effectively emitted from a transmitter antenna. This value differs from the RF electrical power level provided by the transmitter, due to the effects of cable losses, impedance mismatches, antenna efficiency and antenna gain.

A maximum limit is set on the ERP of all transmitting equipment (radio microphones, in-ear monitoring systems, etc.) in order to reduce the likelihood of causing electromagnetic interference (EMI) to other equipment. Such limits apply to systems operating on both licensed and de-regulated frequencies. In the UK, the ERP limit for most UHF hand-held microphones is 10 mW, while for body-worn transmitters the limit is 50 mW to allow for increased RF power absorption by the wearer's body.

Error correction

A scheme in which additional information is added to a digital signal in order to allow the detection and automatic correction (within certain limits, dependent upon the particular scheme) of bits that are in error (i.e. a 1 instead of a 0 or vice versa). Used extensively in digital recording. See also Bit error rate and Interpolation.

Error rate

See Bit error rate.


An abbreviation for 'electrostatic discharge'.


An abbreviation for 'effective series resistance'.


The Entertainment Services and Technology Association, a non-profit trade association based in the USA. For a time this ceased to exist in its own right due to merging with PLASA, but has now come into existence again. Their website is www.esta.org (external link, opens in a new window).

ETH or Eth

An abbreviation for 'earth'. See Safety earth and Signal earth.


A type of connector, manufactured by Neutrik, that incorporates an RJ45 network connector into an XLR-type shell. They are available in several variants, to suit different category cables. Note that not all variants of etherCON connector are inter-mateable.


Originally a system for the interconnection of computer-related equipment, especially for the creation of computer networks, but which is now also used for the transfer of many other kinds of user data, including digital audio, video and DMX. Many different variants exist, operating at different data rates and using different cable and connector types. The most common arrangement is now 100Base-T or 1000Base-T, using 4 pair CAT 5e UTP cable terminated in 8p8c RJ45 connectors. The most common data transfer protocols used over Ethernet networks are TCP and UDP. See also AoE, SDVoE, Art-Net, sACN, ShowNet, TCP, UDP, IEEE 1394, USB and and the following definitions.

View ethernet connector (RJ45) image

Ethernet cable

Strictly, refers to any of the several different types of cable that may be used to make up one of the several different standard types of Ethernet network. However, in recent times this term is most commonly used more loosely to refer to a length of 4 pair UTP category cable terminated in 8p8c RJ45 connectors, regardless of whether the cable actually carries, or might be used to carry, Ethernet signals. See also QTP.

Ethernet connector

Most usually used as an informal term for an 8p8c RJ45 connector.

Ethernet protocol

The set of rules that allow Ethernet-equipped devices to communicate with each other in an orderly manner, in order to correctly route and convey user data. See also Protocol.


An abbreviation for 'European Telecommunications Standard'. Used as an identifying prefix for the telecommunications standards issued by ETSI, which include the allocation of the ISM band for licence-free use of radio microphone and in-ear monitoring systems. See also De-regulated frequency.


An abbreviation for 'European Telecommunications Standards Institute', a body that devises and issues telecommunications standards for Europe. Its standards have the prefix 'ETS' (see the previous definition). See also RED.

Euro connector

A vague term for a connector that is used in Europe (especially when not commonly used in the USA). It may be used to refer to many different types of connector, for example the IEC 320 mains connector, the Schuko mains connector or the SCART audio-visual connector.

Euro thread

A term for a screw thread that is used in Europe; in PA work it is most commonly used to refer to the 3/8 inch diameter Whitworth thread used for attaching microphone clips (and other accessories such as boom arms) to microphone stands. See also Thread adaptor. Compare American thread.


An abbreviation for 'ear-worn monitoring' − see In-ear monitoring.


An effects unit intended to modify a signal, most often so as to give greater 'body' or more 'cutting edge' to the sound. It usually operates by the judicious addition of appropriate harmonics, particularly even-ordered ones. Most commonly used on lead vocals, and more often used in the recording studio than with live performances.


The physical back-and-forth motion of a driver's cone or diaphragm, which is intended to generate sound waves. Or, the extent of such motion.


A signal processing facility whose purpose is to increase the dynamic range of a signal. An expander that applies expansion only when the signal level is below a specific value (the 'threshold') is called a 'downward expander'. See also Compressor, Compander and Noise gate.


A process that increases the dynamic range of a signal. The device that provides this function is called an expander, and the extent of expansion provided is called the expansion ratio. Compare Compression (1).

Expansion ratio

A measure of the amount of signal expansion taking place. The ratio control of an expander usually has settings labelled 1:2, 1:4, 1:6 etc, pronounced '1 to 2', '1 to 4', etc. 1:2 means that 1 dB of change in level at the input produces 2 dB of change in level at the output; 1:4 means that 1 dB of change in level at the input produces 4 dB of change in level at the output, etc. (For an explanation of decibels, see the Decibels page.) A setting of 1:1 means that the expander is providing no expansion (i.e. is inactive, or bypassed), whilst 1:Infinity means that it is acting as a noise gate. Compare Compression ratio (1).

Exponential horn

A horn whose cross-sectional area increases exponentially along its length. That is, its area at any given distance from the start of the horn is proportional to some number raised to the power of that distance. This design gives a high efficiency, but the directivity is not constant, increasing with increased frequency. This is not a problem for bass and lower mid-range horns, as the directivity of these frequencies is relatively unimportant. So, this type of horn is useful in those cases. However, at higher frequencies directivity is very important and so constant directivity types are more often used at those frequencies. See also Folded horn.

Extra low voltage

As defined by BS 7671, a voltage that does not exceed 50 V AC or 120 V ripple-free DC, whether existing between the current-carrying conductors or from them to Earth. Other definitions may differ. Such voltages are generally considered, under typical conditions of contact, unlikely to produce a fatal electric shock in a healthy person. Most signal voltages will fall into this category, with the notable exception of speaker-level signals. Commonly abbreviated to ELV. See also Voltage bands.

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