| Glossary of PA Terms - E
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The glossary pages provide definitions for over 2680 PA-related
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In the list below, the most commonly looked-up terms
are in bold, lighting-specific terms are in
and video-specific terms are in
Ear buds *
Ear mix *
Early decay time *
Early reflections *
Ears mix *
Earth bonding *
Earth fault *
Earth fault loop impedance *
Earth isolator *
Earth leakage *
Earth lift *
Earth loop *
Earth loop impedance *
Earth potential *
Earth rod *
Earthing system *
Effects loop *
Effects pedal *
Effect return *
Effect send *
Effective series resistance *
Electric bass *
Electrical safety *
Electrical tape *
Electrodynamic microphone *
Electrolytic capacitor *
Electromagnetic interference *
Electromagnetic wave *
Electromotive force *
Electronically balanced *
Electrostatic coupling *
Electrostatic discharge *
Electrostatic microphone *
Emulated line output *
Environmental noise pollution *
EP connector *
Equal loudness curves/contours *
Equaliser (EQ) *
Equipment classes *
Equipotential bonding *
Equivalent input noise *
Equivalent noise level *
Error correction *
Error rate *
ETH, Eth *
Euro connector *
Euro thread *
Expansion ratio *
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.
An alternative name for
A slang term for a mix
intended to be fed to
or, less often, for a mix intended to be fed to
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
and are used in conjunction with a
bodypack. See also
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
The time taken for the initial part of a
decay curve. It is measured to the point where the
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
sound from nearby surfaces,
resulting in reflected sound reaching the listener a relatively
short time after the direct
sound and substantially before the general
of the space. See also
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
inch rack system.
A slang term for the performer-worn part of an
system, sometimes referring specifically to the
earphones worn for it.
See Ear mix.
Short for either
'safety earth' or
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
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
from the supply live
or neutral to a safety
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
impedance and Megger.
fault loop impedance
See Earth loop
An alternative term for
A device which is inserted into an interconnection
between two items of equipment, in order to pass the
required signal without a
connection. That is, to provide
isolation of that interconnection's signal earth
The most common reasons for using an earth isolator
are to avoid creating an
earth loop through
an interconnection (and so avoid or resolve
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
interconnections, as good quality
do not generally suffer from these problems. The
device most commonly used for earth isolation is
The equivalent US term is 'ground isolator'. N.B.
must never be disconnected to avoid hum or other
problems. Not to be confused with the US-specific term
ground, which relates to mains outlets.
Current that flows in a
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
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
resistance, this is
termed an 'earth fault'
and may be a hazardous
Earth leakage can be a source of
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
currents to flow in the
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
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
equipment, a switch which provides the facility to
disconnect the equipment's
signal earth from its
in order to avoid an
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
mains-powered equipment and on non-mains equipment
(such as battery or
a switch which provides the facility to disconnect the
signal earth connection between other items of equipment,
in order to avoid an
(Such a loop may exist through other signal earth paths,
or through safety earth connections to Class I
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
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
(i.e. equipment in which the switch refers to an
balanced input or
'Lift' position only breaks the earth path
through the signal earth conductor,
and a path to earth may remain 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
The situation that exists when two or more items of
equipment are interconnected (either directly or
via other equipment) by
cables. This creates a
continuous 'circular' path of
made through the safety earth
conductors of the
equipment power cables and the
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
equipment) were connected direct to an
line input of a
This condition can sometimes result in the addition of
hum to the wanted
An earth loop may also be referred to as a 'ground loop'
(originally a US-only term).
The hum occurs because of
voltage differences between
the safety earths of
the interconnected equipment, which arise due to
mains earth leakage
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
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
the interconnection, which may
into the signal conductors.
Earth-loop problems may be usually resolved by the use of
good quality balanced or
signal interconnections, to provide immunity against the
earth voltage differences. Additionally, appropriate
use is frequently made of
earth lift switches,
II mains equipment,
and sometimes the physical disconnection of balanced cable
screens inside connectors;
these measures can provide
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
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
(e.g. 1 nF) between the screen
and the connector earth
terminal in order
to provide a path for
signals. Less common measures to reduce the likelihood of
earth loop problems include the use of a
and/or of balanced
mains supplies. See also
Pin 1 problem.
distribution term, essentially unrelated to the
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
of the supply. It is measured, using
specialist equipment, between the live and safety
earth connections at
boards and at points of
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
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.
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
earth potential is usually considered to be the potential
of the general mass of the Earth. In the context of
'earth potential' usually refers to the potential of the
relevant signal earth,
which may or may not have a
with the general mass of the Earth. The term
'ground potential' is more common in the USA.
See also Potential.
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
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.
The process of providing a suitable
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
The particular means by which a
safety earth is
provided to an electrical installation.
recognises several types of earthing systems, the
most common of which are TN-S,
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
Or, any conductor nominally
at a 'zero' voltage, such as a
In an unbalanced connection,
the earthy conductor is sometimes referred to as the
See also Safety earth.
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
(external link, opens in a new window).
See also the Manufacturers' page
An abbreviation for 'European Broadcasting Union',
a body which sets technical standards for broadcasting
in Europe. See also AES
An effect unit that
simulates a natural echoing of the sound
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,
though a distinct repetition of the original sound 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
equipment generally referred to as delay effects units,
which are also able to provide other delay-based effects
such as reverberation,
flanging, or by the multi-purpose
onboard effects facilities of
In most cases the facility is provided for single
or multiple echoes.
See also Haas effect.
A manufacturer of
In PA work, the term
is most often used to refer to the screw-secured
EDAC 516 series of rectangular
commonly used for the connection of multiple
on multicores and
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,
EDAC 516 series (56-MC) connector image
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 provided 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
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.
Devices 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 devices.
Examples would be
Frequently abbreviated to 'FX' or 'EFX'.
See the Effects page for further
Compare Sound effects and
An abbreviation for
'early decay time'.
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.
An input, of a
mixer or instrument
intended to accept the
signal of an
An output, of a
mixer or instrument
intended to supply a
signal to an
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
The efficiency of speakers
and microphones is
usually specified in terms of their
See also the
Classes section on the
Amplifiers and Speakers page.
An abbreviation for
(More usually abbreviated to 'FX'.)
An abbreviation for 'electrical installation
condition report'. See
An abbreviation for
The proper name for a 'bass guitar'; see
Safety on the
See PVC tape.
Another name for a
A general term for any interfering
signal that is carried as an
wave. Such interference may be continuous (e.g.
caused by a radio transmission) or momentary (e.g.
caused by the operation of a
Often abbreviated to 'EMI'.
See also EMC,
A more scientific name for a 'radio wave'. The strictly
correct term is 'electromagnetic radiation'.
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
drawn from it.
This term is most commonly used in relation to voltage
supplies (such as batteries); when referring to the voltage
outputs the terms
voltage' are usually employed. Frequently abbreviated to
See also Potential.
Describes an item of equipment's
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
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
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:
A particular type of electronically balanced output is
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
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
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.
Another term for
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,
Electrostatic discharges can also generate
giving rise to the 'crackling'
noise commonly referred
to as 'static'.
Such very high voltages are able to overcome the
properties of insulators (e.g. air),
enabling the current to 'jump' a gap between
Such an event can cause permanent damage to
nearby insulating material and/or to the conductors.
Frequently abbreviated to 'static' or to 'ESD'.
Another name for a
The specific internal part of a
that performs the function of a
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
element and a high frequency
one or, in the case of a
a Left and a Right element. See also
Ribbon microphone and
A trademarked abbreviation for
'extended multiply and accumulate', Mackie's
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
An abbreviation for
An abbreviation for
output, found on some
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.
Emulated line outputs can be either
balanced (usually at
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
(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
pad switches usually satisfy
this condition.) In other cases, an
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
Speaker enclosures 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).
See also Polar
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 be 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
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
one joule is sufficient to sustain a
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
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
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
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
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
EP connector (EP3, EP4, EP5,
A series of high-power latching
connectors manufactured by
Amphenol®. This series has a rugged die-cast
A specific feature is their ability
to accept large diameter cables.
Once popular for connections to
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.
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
(external link, opens in a new window).
See also PLSN and
curves, Equal loudness contours
The facility provided by an equaliser, or the effect
of such a facility on a signal
− see the next definition.
A dedicated item of equipment, or a section of a
mixer or an
that allows control of the relative
level of specific
ranges of a signal,
whilst leaving other frequencies essentially unaffected.
The most basic equalisers just provide control over
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
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
The term originates from telecommunications, where the purpose
of an equaliser is to compensate for inadequacies in the
of equipment, especially of long-distance
cables, by providing an
'opposite' frequency response and thus making the overall
response through the system substantially
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
largely being an exception).
For further information, see the
of the Mixing Facilities page.
See also Sweep EQ,
For general audio
and electrical equations see
this entry on the
FAQ page. For decibel equations
see the Decibels page.
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
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
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).
noise level (of microphones)
on the Microphones page.
An abbreviation for 'effective radiated power'. A term
used in radio transmission to indicate the
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
and antenna gain.
A maximum limit is set on the ERP of all transmitting
equipment (radio microphones,
in order to reduce the likelihood of causing
interference (EMI) to other equipment. Such limits
apply to systems operating on both licensed and
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.
A scheme in which additional information is added to a
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
See Bit error rate.
An abbreviation for
An abbreviation for
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
(external link, opens in a new window).
ETH or Eth
An abbreviation for 'earth'.
See Safety earth and
A system for the interconnection of computer-related
equipment, especially for the creation of computer networks.
Many different variants exist, operating at different data
rates and using different cable
and connector types.
The most common arrangement is 10Base-T
using UTP CAT 5e cable
terminated in 8-pole
See also IEEE 1394 and
ethernet connector (RJ45) image
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
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.
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
mains connector or the
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
(and other accessories such as
boom arms) to microphone
stands. See also Thread
An abbreviation for 'ear-worn 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
Most commonly used on lead
vocals, and more often used in the recording studio
than with live
The physical back-and-forth motion of a
is intended to generate
Or, the extent of such motion.
A signal processing
unit designed to increase the
dynamic range of a
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,
A process that increases the
of a signal.
The device that provides this function is called an
and the extent of expansion provided is called the
A measure of the amount of
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
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
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
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
directivity types are more often used at those
See also Folded horn.
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This page last updated 05-Sep-2017.