| Glossary of PA Terms - V
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The glossary pages provide definitions for over 2680 PA-related
terms and abbreviations.
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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
Vacuum tube *
Variable bit rate *
VCA group *
Velcro tie *
Velocity of sound *
Vocal band *
Vocalist set *
Vocalist system *
Voice coil *
Voice of God *
Voltage bands *
Voltage controlled amplifier *
Voltage controlled filter *
Voltage drop *
Voltage gain *
Voltage surge *
Volume control *
Volume leveller *
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 abbreviation for volt,
the unit of voltage.
Note: Due to font conversions, on some web pages the Greek
capital letter Omega, the symbol for ohm,
may be displayed by your browser as a 'V'; it should look like
a horseshoe shape with a flat base, which, if your browser displays
it correctly, now follows: Ω.
An abbreviation for 'volt-amperes', i.e. the
RMS value of the
multiplied by the RMS value of the
drawn (or available).
So, to determine the amount of supply current drawn by
that is rated in VA,
simply divide the VA figure by the
mains voltage. Likewise, to determine the amount of supply
current which may be supplied (or carried) by
power generation or distribution equipment (such as a
that is rated in VA, simply divide the VA figure by the
Also known as the 'apparent power'.
See Power factor for
further details. For further calculations involving voltage
and current, see the
How do I calculate ...?
question on the FAQ page.
Short for 'thermionic valve', a device generally
consisting of several electrodes spaced apart inside an
evacuated glass envelope. As valves require replacement
from time to time, to facilitate this its electrical
connections are made through a 'base' consisting of
several pins. The base plugs into a special socket
called a 'valve holder'. There is sometimes an
additional 'top cap' connection.
When replacing valves, be sure to heed the following
Consult the equipment manufacturer's instructions.
First switch off the equipment and disconnect it
from the mains supply.
Fragile glass − take appropriate precautions.
High temperatures during use − after operation
allow sufficient time to cool.
Lethal high voltages may
remain in the equipment long after it is switched off.
Do not open covers exposing any electrical connections
unless competent to avoid danger from these voltages.
Several different types of valves may be used within an
item of equipment.
Each one must only be replaced with a type approved by
the equipment manufacturer.
In equipment that incorporporates more than one
output stage valve,
it is usually important that a matched set of those
valves is fitted. For more information see
Some models of equipment require a
to be made after replacement of certain valves. (This
adjustment may only be accessible internally.) Failure to
do this correctly may result in improper operation of the
equipment and/or substantially shortened life of the new valves.
In a valve, a
current flows by means of a
movement of electrons from the cathode electrode
to the anode electrode. This flow of electrons
is controlled by the voltage applied to an
intervening 'control grid' electrode, so enabling the
amplification of a
signal applied to the grid.
This basic design is called a triode (meaning
More advanced designs (tetrode, pentode, etc.),
containing additional grid electrodes, are usually used
for high-power amplification.
In most valves, in order to facilitate the release of
electrons the cathode is raised to a high operating
temperature by a heater
− this is what produces the characteristic orange
Valves usually operate at high DC
supply voltages, produced within the equipment (see
These lethal voltages can remain present in the equipment
long after it is switched off, and may require to be
manually discharged. Servicing and repair of equipment
using valves must only be carried out by competent persons,
and even then only with extreme care.
The valve has a number of disadvantages (including fragility,
poor efficiency and a relatively short life), so is now
largely superceded by the
However, it is still used in some guitar
because of the particular
type of distortion that
it produces when operated at (or close to) its maximum
It is also used in some professional studio
and in a few models of outboard
equipment such as compressors.
The American term for a valve is a 'tube' (short for
'vacuum tube'). See also
Compare Solid state.
Variable bit rate
Describes a digital
signal having a
bit-rate that is not
constant, as in the case of a particular variant of
Or, describes a file containing data encoded in such
a manner. This type of coding is catered for by the
Often abbreviated to 'VBR'.
A 2-terminal electronic
according to the voltage
across it. For a practical application see
An abbreviation for
An abbreviation for 'voltage controlled amplifier' (the
term is rarely used in full). A
device whose gain (or
loss) is determined not
by a potentiometer
acting directly on the audio
signal, but by a
It has many applications, such as in
in enabling the level of a signal
to be controlled remotely, or in enabling some processing
(such as noise
filtering) of the control signal
to be carried out (as in an
A further application is when
the same control voltage is applied to several VCAs
simultaneously − this allows the level of several
different signals to be controlled together, even though
the signals themselves are not mixed (so effectively
forming a 'virtual group',
usually called a 'VCA group').
When incorporated as part of a more complex
(e.g. a compressor/expander
chip) a VCA is sometimes termed a 'gain cell'.
See also VCF.
An abbreviation for 'video
compact disc'. A standard for the recording of
information on a CD, giving a reduced picture
quality as compared to the DVD
See also AVCD.
An abbreviation for 'voltage controlled filter' (the
term is rarely used in full). A
device whose filtering
characteristics are determined not by physical
controls that are part of the filter
circuit, but by a
This allows the filter to be controlled remotely,
and also allows the control of several filters at once.
See also VCA.
An abbreviation for 'video
cassette recorder'. See also
A short narrow strip of fabric material, equipped
on one side with
miniature 'hooks' and on the other side with miniature
'loops', that engage with each other when the strip is
wrapped around something. Such strips are useful for
securing coiled cables
in transit or storage,
to prevent them becoming tangled, as an alternative to
the use of releasable
or PVC tape.
Strips designed for
this purpose usually incorporate a means of attaching them
to the cable, to avoid the strip becoming lost while the
cable is in use. This also has the useful effect of
keeping a tie of suitable length and width permanently
associated with each cable. For a list of the advantages
of using releasable ties such as the Velcro type
(as compared to using PVC tape),
see Cable tie.
The name Velcro is a registered trademark.
See Speed of
The location or premises hosting a
show or other event.
A slang abbreviation for
An abbreviation for the Video Electronics Standards
Association, an organisation which defines standards
for video source and
display equipment, and for
interfaces between such
equipment. As well as electrical aspects, its standards
include physical aspects such as display mounting methods.
Their website is www.vesa.org.
An abbreviation for 'video
graphics adaptor'. An analogue
computer graphics interface
standard for the connection of display
equipment (such as monitors and projectors) to
computers, now largely superceded by
digital interface standards
such as HDMI and
The VGA standard gives a resolution of
640 pixels horizontally
and 480 pixels vertically, producing a 4:3
However, note that as VGA was the 'original' standard,
its name has become something of a generic term that is
commonly used to refer to cables, connectors
(usually 15-pin high-density
D-sub types), etc.,
even though they may be used to carry the
higher resolution analogue computer graphics standards such as
UXGA (but not
DVI, which is a standard
with digital capability).
(HD15 / DE-15M) connector image
The most commonly encountered standards, their resolutions
and aspect ratios are tabled below.
|| Resolution (H x V)
|| Aspect ratio
||480 x 320
||640 x 480
||800 x 600
||854 x 480
|960 x 540
||1024 x 768
720p / 720i
|1280 x 720
||1280 x 800
|| 16:10 ||1.6:1
||1280 x 960
||1280 x 1024
||1400 x 1050
||1600 x 1200
1080p / 1080i
|1920 x 1080
||1920 x 1200
||2048 x 1152
||2048 x 1536
|2560 x 1440
||2560 x 1600
|3656 × 2664
||3840 × 2160
|3996 × 2160
|4096 × 1714
|4K DCI native
||4096 × 2160
Full aperture storage
|4096 × 3112
||7680 × 4320
An abbreviation for 'very high frequency'.
in the range 30 MHz to
300 MHz, used by some types of
wireless instrument systems and
systems. Most professional radio systems now use
UHF frequencies or operate in
the 2.4 GHz frequency
band. For more details, see the
radio mic information
on the Microphones page.
A deliberate repetitive variation in the
(frequency) of a musical
note, as an effect to improve the interest of the sound.
Most commonly encountered in the context of keyboard
Often confused with
tremolo (for example,
the effect produced by the tremolo bar of an electric
guitar is actually vibrato, not tremolo).
See also Leslie.
material (picture information) represented in an
electrical form for passing between items of equipment
or for storage. Depending upon the interconnection
format, used, video may be
digital and may be
carried using a single or multiple
signals. Some common
analogue formats are listed below in order of increasing
quality − follow the links for further information.
For digital video, in
consumer and semi-pro
applications the interconnections are now generally
HDMI, which is a development
of DVI. Professional digital
video interconnections use SDI.
See also Frame (2),
A term adopted to describe the 'original' type of
recording disc, having a continuous groove with physical
deviations to represent the audio information in an
The disc is played on a record
deck (also called a
turntable), in which the audio information is read
from the groove by a stylus and cartridge located
at the end of a
tone arm. The stylus
rests in the groove and physically follows its
deviations, the resultant vibrations being converted into
Left and Right audio signals
by the cartridge, to which the stylus is mechanically
The clarification became necessary to provide a distinction
from more recent 'disc-type' recording formats such as the
mini-disc, DVD, etc.
Although the very first continuously grooved discs
were not made from vinyl, most of those that remain in
use today are.
See also RIAA.
An abbreviation for 'violin'.
A small group of vocalists
who perform together as a fixed unit, often (for at least
part of the time) in harmony.
Their backing music is usually either recorded
or performed by musicians who are not considered to part
of the band. Often referred to as simply a 'band', or in
the case of same-sex groups, as a girl band or boy band.
See also Band (2).
A person who has an on-stage role as a singer. The term
is usually used only when singing is the person's only,
or primary, role, and is less commonly used for members
of a choir or chorus section.
A term commonly used by equipment manufacturers
to refer to a complete
system (or 'set') that includes a hand-held
suitable for use by a
vocalist. The radio
transmitter is incorporated within the microphone.
Compare Presenter set.
The human voice content of a complete sound
mix. The term usually refers
to singing, but may also refer to speech. Frequently
abbreviated to 'vox'. See also
Relating to human speech, sometimes also including human song.
For example, a recording of speech may be described as a
'voice recording' to distinguish it from a music recording.
A term referring to the particular type of
(as opposed to its pitch)
being created by a musical instrument, particularly a
programmable keyboard or an organ.
See also MIDI,
The coil of wire, inside a
driver or a
which carries the electric current
and is mechanically coupled to the
In the case of a driver, the voice coil generates a magnetic
field which interacts with the field of a stationary permanent
magnet, and the resulting mechanical force causes motion
of the cone (or of the diaphragm, in the case of a
that corresponds to the direction and magnitude
of the current, so producing sound
In the case of a dynamic microphone, sound
waves impacting on the diaphragm cause motion of the
voice coil within the field of a stationary permanent magnet,
and this causes a voltage
corresponding to the incident sound pressure to be
generated across the coil. See also
Voice of God
Speech spoken by a person unseen by the
audience − usually
amplified and often
heavily laden with
It may either be recorded or spoken
live by a person off-stage.
Or, a term used to refer to a
microphone used for
such a purpose.
A technique for setting the
equalisation of a
channel of a
PA system, or of a
for monitors or the
(FOH) speakers, in which
a microphone is spoken or sung into. Typically, one
person will speak into the microphone in situ on
stage while another listens at a location in FOH,
or else just a single person speaks into a microphone
temporarily located in FOH, and listens to their
own voice. The words "One" (for
treble response) and
are often used. See also
The process of obtaining a particular
voice, or set of voices,
from a musical instrument − particularly a
keyboard instrument. Or, the specific settings that
produce that voice or voices. See also
The unit of voltage − see the next
The 'pressure' of electricity. Measured in volts
or millivolts (a thousandth of a volt). No
current can flow without
a voltage to drive it around the electrical circuit.
Strictly, a voltage
can only be said to exist between two points
(usually two separate conductors),
rather than 'at' a single point, so another term for
voltage is 'potential difference'. In this differential
sense, voltage can be considered to be a relative quantity
(but measured in absolute units − see the last
paragraph of this definition).
However, when a particular
voltage is said to exist at a single point, it can usually
be assumed that the voltage relative to
earth is what is meant.
A voltage can be either DC or
or even a mixture of the two. In the case of AC
(such as an audio
value of voltage is continually rising and
falling, first in one direction and then with the opposite
Therefore, a special means is
needed to quantify the effective value of AC voltages,
over a complete cycle of change.
This is the RMS value. Furthermore,
in the case of an audio signal, there are usually constant
fluctuations in the effective value of voltage, as the
level of the represented sound
changes. Several measurement schemes have been developed to
accommodate this complexity, the main ones being
In general, the higher the voltage, the greater the capability
(when misused) for causing injury or death by electric shock,
so the greater the caution required. Voltages above 50 volts
can be considered hazardous from the perspective of shock,
however any voltage can be responsible for hazards such as
burns or fire − especially when the available current
is large. For further safety information
see the Safety page.
Audio signal voltages are usually less than 2 volts RMS −
except for the signals which directly drive
which may be as high as 100 volts RMS or more.
Mains voltage is 230 volts RMS
in the UK and Europe (400 volts RMS on
3 phase supplies),
and 110 volts RMS in the U.S.A.
For those with a scientific interest, the number of volts
between two points represents the amount of
(in joules) that
would be transferred per
coulomb of electrical charge
moving between those points.
For calculations involving voltage, see the
How do I calculate ...?
question on the FAQ page.
See also Electromotive
force and Potential.
Describes an interconnection in which the
of a signal source and the
input impedance of
the equipment that it connects to are co-ordinated so that
voltage of the source
equipment is not significantly reduced as a result of
making the interconnection. In practice, this usually
means that the input impedance of the destination equipment
must be at least ten times the output impedance of the
source equipment. Most
audio signal interconnections
are of this type. It is of course also necessary
for the source voltage (i.e. the signal
level) to be
compatible with the interconnected equipment (see
See also Load,
Designations of the bands (i.e. ranges) of
for which wiring is used, or is suitable, defined by
Band I (band one) −
limited so as to provide provide protection against
electric shock, or are limited for operational reasons
(e.g. to suit the requirements of the equipment
Note that, in the latter case, voltages in this band
may be sufficiently high to pose a shock
Most signals fall into
Band II (band two) −
voltages are not limited for either of the above reasons,
but will not exceed 1000 V AC
RMS or 1500 V
mains voltages fall into
BS 7671 requires that
wiring is suitably segregated from
Band II wiring, or else
is insulated to
standards, so as to reduce the likelihood of it
accidentally attaining a voltage above the specifically
i.e. to avoid it attaining a voltage that
does not provide the required protection
against shock or against damage to equipment.
(Such a voltage might otherwise be attained, for example,
in the event of damage occurring to the insulation of the
Band II circuit.)
Extra low voltage
The voltage that is
developed (or 'dropped') across a
an undesirable one such as the resistance of
cable conductors) as a result
of the current flowing
through it. The effect of voltage drop is that the
voltage available at the
load is less than that
provided by the voltage source.
Voltage drop is increased by increased current flow
or by increased series resistance − e.g.
by thinner or longer cable conductors.
Therefore, in order to keep the
voltage drop in cables within acceptable limits,
it is important to ensure that the
gauge of the cable is
sufficient to provide a low enough round-trip resistance,
taking into account the maximum current that will be
flowing and the length of the cable. Voltage drop
can be caculated using
The multiplying factor by which a
level is increased by
(or within) an item of equipment. It is
usually expressed as a value in
For fuller details see Gain.
A momentary increase in voltage
to a value substantially in excess of normal operating values,
occurring in a mains
arrangement. Large voltage surges most usually occur as
a result of switching operations occurring within the
high-voltage electricity distribution network, or faults
occurring within it, but may also result from lightning
strikes in the vicinity of overhead
power cables or
distribution equipment. Such voltage surges may be
damaging to electrical appliances such as
or computer equipment. Protection against them may
therefore be provided − see
MOV. Smaller and shorter
voltage surges, often known as
may result from the switching on or off of nearby
equipment such as motors or fluorescent lighting.
See also Power
A non-technical term for
loudness, deprecated by
A term used only with domestic
Hi-Fi equipment etc., to
refer to a control which is provided to enable adjustment of
the loudness of the
It is too general a term to be of any use in the context of
PA systems and the like, because
in such a system loudness is not a function of a single
control. The loudness of a particular amplified sound
source is affected by many controls in the
group fader, main fader,
etc.), and additionally the loudness at a given
listening position is affected by other factors
− especially by its distance from the
speakers and by the
See also Inverse
Short for 'voice' or 'vocals'. See also
Lead (2) and
An abbreviation for 'video
tape'. Often refers not to the tape itself but to a
recording on it, or to the machine it is to be
played on, as in the producer's phrase "Run VT",
meaning to start the playback of a particular recording.
Furthermore, it is now used to refer to a video recording
held on any type of media,
not necessarily tape.
An abbreviation for
'volume units', however the
abbreviation is most commonly used to refer to a type of
meter that is more properly
known as a "standard volume indicator".
This type of meter is typically found on
mixers used in broadcast and
post-production studios, and has a response that is
specially tailored to indicate the average (rather than
peak) level of the
signal in order to give an
indication of perceived
The required behaviour of the meter indication is detailed
in IEC standard
specifies a time of 300 ms
to reach a 99% indication (about
1 dB below 100%) when
suddenly subjected to a constant-level
The decay characteristic is similar.
As this response is unable to register short-term peaks
and transients, it is common
for a 'Peak' LED to be included in the meter to indicate the
presence of high-level peaks in the signal.
Although the meter has a scale marked 'VU', its reading is
actually a value in decibels
relative to an agreed
'0 VU' level. The standard scale runs from −20 to
+3 VU, with the portion above 0 VU being marked
in red. For broadcast equipment, a continuous
+4 dBu (equivalent to
1.23 volts RMS) is usually
arranged to register as 0 VU (though calibration standards
vary). However, because of the dynamics of a typical
programme signal, a programme
reading of 0 VU would be roughly equivalent to the
normal peak programme broadcast level of +8 dBu
(equivalent to 1.95 volts
RMS) as registered by a PPM.
See also SOL.
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This page last updated 21-Sep-2018.