| Glossary of PA Terms - N
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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
National Electrical Code *
Near field *
Necklace microphone *
Needed acoustic gain *
Negative feedback *
NL2, NL4, NL8 *
Noise boy *
Noise dose meter *
Noise dosimeter *
Noise floor *
Noise gate *
Noise pollution *
Noise reduction *
Noise squelch *
Noise weighting *
Non-destructive solo *
Non-polarised connector *
Non-polarised electrolytic capacitor *
Non-reciprocal response *
Notch filter *
Notch out *
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.
A type of connector
sometimes used with
interconnections, such as those to the
antennae of wireless
communication systems. N-connectors are available in both
50 ohm and
75 ohm impedance
versions and in order to avoid permanent damage to the
connectors of either the cable
or equipment it is essential
to ensure that only connectors of the same impedance are
mated. See also
(male, 50 ohm) image
An abbreviation for
'National Association of Broadcasters', an American
organisation which sets standards in broadcasting and
recording. In analogue
tape recording, NAB usually refers either to a particular
standard, or to the physical dimensions of a
reel-to-reel spool hub.
An abbreviation for
The International Music Products Association. The abbreviation
'NAMM' stands for the previous name of this association,
the National Association of Music Merchandisers. Their
website is www.namm.org.
Spoken accompaniment to a visual presentation,
usually performed by someone other than those with
key visual roles (where relevant). It is often performed
by a person who is not visible on-stage or on-camera.
Describes a signal
(often noise) or
equipment (often a filter) having a relatively
The specification of requirements for electrical
installations in the USA. Often abbreviated to 'Code'.
See also BS 7671 and
The region of 3-dimensional space close to a source
of sound; typically within
30 cm (1 ft) but dependent upon the dimensions
of the source and the
frequencies (or, more
accurately, the wavelengths)
Real sounds (e.g. of
acoustic musical instruments
or of speakers) do not
originate at a single point, but rather (as perceived
from a greater distance) consist of the different sounds
from different parts of the source, merged together.
Therefore, within the near field, where
this merging is not yet fully established, small
changes in the listening position (or
can substantially affect the
timbre of the sound that
is heard or picked up, and also its
level. See also
A sub-miniature microphone
that is equipped with an attached loop of cord, ribbon,
etc., or with a semi-rigid hoop.
This allows the microphone to be positioned at the front base
of the wearer's neck (or on the upper chest) by simply
placing the loop or hoop over their head. The microphone
cable typically exits the loop
or hoop at the rear of the neck. This design is particularly
suited to situations where a wearable microphone needs to
be placed and removed by the wearer, especially if this needs
to be done rapidly or frequently. See also
Needed acoustic gain
The amount of gain that
a PA system must provide
in order for the sound
level at the furthest required
distance from the source to be
equal to that at a distance at which the sound level
is adequate without any
Often abbreviated to 'NAG'.
By using the
square law, the needed acoustic gain in
dB can be
estimated mathematically as 20 times the log
(to the base 10) of the furthest required distance
divided by the acceptable distance without amplification.
For example, if the unamplified sound level is adequate
at a maximum of 10 metres, and the furthest listener
is at 50 metres, then the needed acoustic gain is
about 14 dB.
Note, however, that this is only an estimate, because
the effect of the acoustics
of the space concerned (reflection,
etc.) is not taken into account.
In order to estimate mathematically whether or not the
needed acoustic gain can be achieved by a given system,
acoustic gain (PAG) of the system can be calculated.
A slang term for 'minus'. A negative quantity,
most often used of a
level expressed in
decibels. For example,
"neg 15" would refer to a level that is
15 dB below the relevant reference level.
The situation in which a signal
is fed back to an earlier point in the
in such a way as to partially cancel the original
signal. Extensively used in
circuits as a method
of setting and stabilising the amount of
gain that is given to the signal
in each stage of amplification.
It is achieved by
ensuring that the signal that is fed back is in
to the original signal, at the point at which it is
If the gain of the amplifier without
any negative feedback in place is very much greater
than the gain with the
feedback applied (as is frequently the case),
then the effect will be that the amplifier
stage will produce just enough
output to cause the
feedback to very nearly cancel
the input signal.
In such cases, the overall gain and
characteristics of the amplifier will be predominantly
determined by the usually highly predictable characteristics
of the feedback path, rather than by the characteristics of
the amplification circuit itself, which are often somewhat
uncertain. See also
A material from which the magnet of many
microphones is now made.
It gives a stronger magnetic field (for a given
size and weight)
than earlier magnetic materials, and so enables the
design of microphones having a greater
A mains supply
connection point that carries supply
(in the case of a normal supply) whose
voltage with respect
safety earth is very
low − usually less than 5 volts. This low
voltage is due to the Neutral being connected with
safety earth at the supply source, the supply
transformer, or at the
entrance of the supply to the installation. In the UK,
these are the
only permissable locations for this connection (see
TN-S and TN-C-S).
Exceptionally, in the case of a
supply in which the two current-carrying conductors are
(erroneously) referred to as
'Live' and 'Neutral',
these conductors are at equal voltages with respect
to safety earth and must both be disconnected
by any switches provided for the purpose of safety
As the Neutral conductor is part of the mains supply
circuit, it should
be treated with exactly the same respect as a
'Live' conductor, and
should never be exposed to the touch (when
connected to a supply). See also
Phase (3) and
A German manufacturer of
most well-known for their
An abbreviation for 'nanofarad', one thousandth
of a millionth of a
A common unit for the measurement of
See also µF and
A group of 4 bits;
half of a byte.
NiCad or NiCd
An abbreviation for 'nickel cadmium'.
Describes a rechargeable battery that uses this
technology. As these batteries exhibit an undesirable
'memory effect', and cadmium is harmful to the
environment, they are gradually being superceded by
See also Alkaline
NICAM (NICAM 728)
An abbreviation for 'near-instantaneous companding audio
multiplex'. The system previously used in the UK and some other
countries to convey stereo
television channels (now redundant, replaced by all-digital
broadcast TV formats). The same system has also been
used to convey two independent
simultaneously, for example in different languages.
'Near instantaneous' refers to the
real time digital
processing in the TV receiver being sufficiently
simple to avoid introducing unacceptable
latency with respect
to the analogue vision signal (given the low-cost
hardware available at the date NICAM was first
introduced). 'Companding audio multiplex' refers to the
multiplexing of the
Left and Right channels into a single
transmission, corresponding decompression being applied
at the receiver
In the UK it employed a
at 6.552 MHz above the vision carrier,
a 728 kbit/s bit-stream.
The audio is
to 15 kHz and
It is then sampled
at 32 kHz with a
bit depth of
14 bits. This is then
digitally compressed down to 10 bits.
For further detail see the excellent article by
Steven Hosgood at www.qsl.net/zl1vfo/nicam.htm
(external page, opens in a new window). See also
An abbreviation for 'noise-induced hearing loss'.
A hearing deficiency (usually of the
SNHL type) that is the
result of damage caused by exposure to very high
levels, or by prolonged exposure to
moderately high sound pressure levels. The damage is
usually irreversible. See also
on the Safety page.
An abbreviation for 'nickel metal-hydride'.
Describes a rechargeable battery that uses this
technology. As these batteries exhibit no
'memory effect' and are not harmful to the
environment, they are gradually superceding
See also Alkaline
A commonly used but 'unofficial' unit of
equivalent to the 'official' unit which is
square metre (cd/m2).
A nits value is typically used to indicate the
brightness of display screens and projection screens,
either when viewed from a given direction or
averaged across the entire intended range of viewing
angles. Note, however, that no matter how bright a
screen image is, if it is swamped by an excessive amount
of ambient light
falling on the screen then the image quality is likely
to be perceived as poor.
When applied to a projection screen, the image
brightness in nits depends on the amount of projected
light striking the surface per unit area (measured in
and upon the optical characteristics of the screen surface,
typically quantified by a reflection factor
(Rf) value, which
is more commonly known as the 'screen gain'.
In such a case the nits value will be
lux x Rf / π.
NL2, NL4, NL8
The National Outdoor Events Association of the UK.
Their website is www.noea.org.uk (link to
external site, opens in a new window).
Any unwanted sound or electrical
signal, especially one that
does not carry (wanted) information.
When present (in significant proportions) along with wanted
sounds or signals (analogue or
noise is undesirable because of its tendency to mask,
to distract from, or otherwise to reduce the perceived
quality of, the wanted sound or signal. Usually the
level of the noise
itself is not what is important;
what is important is its level in comparison with
the level of the wanted signal that it is present with.
The amount by which the wanted signal level exceeds the
noise level is termed the
Noise originating from electrical sources may be random in
nature (e.g. hiss, or
crackles introduced by cables and
connections), may have a
(e.g. a hum or buzz), or
may be an interfering information-carrying signal such as
A certain amount of noise (especially hiss and hum) will
always be introduced by analogue equipment, but is not
normally noticeable unless the equipment
is either faulty or is not being used optimally. Such noise
can normally be rendered insignificant in relation to the
level of the wanted signal by
ensuring that the equipment is carrying a level of signal that
is well above the minimum level that the equipment is intended
to handle. For this reason, when the wanted signal levels are
very low (e.g.
signals), a pre-amplifier
is usually employed to raise the signal level to a suitably high
value before further processing − such a pre-amplifier
is often incorporated within other equipment such as a
mixer. For optimum results it is
very important that the pre-amplifier
gain control is correctly adjusted.
When noise is present along with digital signals, the result
is an increase in the
bit error rate (BER).
The usual behaviour is that noise present at low levels in
comparison with the digital signal (i.e. a high
signal-to-noise ratio) has very little effect on the bit error
rate, however when the signal-to-noise ratio starts to fall
below a specific value the bit error rate starts to increase
dramatically and a point is soon reached when the signal is
completely unusable. This effect is called the
and is in marked contrast to the gradual effect of decreasing
signal-to-noise ratio on the perceived quality of an analogue
(Note: In PA work 'noise' does
not refer to an unpleasant or
See also Noisy,
on the Microphones page.
Describes a microphone
that is designed to reject ambient sounds, being sensitive
only to very close sound sources, at typically less than
2 inches (5 cm).
Their main application is for speech pick-up in very
high ambient sound level environments, such as sports
commentary and aircraft cockpit communications.
A slang term for a
The term may be used to refer to male or female sound engineers.
See also Soundie and
Noise dose meter
The level of
noise that is
produced by an item
of equipment, or that is present at a particular point
in a system under specific circumstances. The term refers to
a 'floor' because this noise level effectively sets a 'base' level,
against which signal levels
are compared when evaluating the
of equipment or of systems. To obtain a satisfactory
signal-to-noise ratio, wanted signals must be at a
substantially higher level than the noise floor.
An item of
equipment intended to "close the gate" on
noise, i.e. to block its
whilst "opening the gate" to allow
through the wanted part of the
signal, the usual objective
being to improve the apparent
of the signal or to combat leakage.
It operates on the assumption that the
level of the noise is
significantly less than the level of the wanted part of the
signal, which is usually the case. The wanted signal, when
is present, therefore largely masks
out the noise − so the noise is only a real
problem when there is no wanted signal present.
By allowing the
user to set a 'threshold' level, which is higher than
the level of the noise but lower than the level of the signal,
the device can be arranged to only 'open' and let the
signal through (complete with its noise) when there is a
wanted signal present that is large enough to mask out the noise.
At other times the gate is 'closed' and the noise is
attenuated by the amount
set by the 'range' control. This may mean that some
low level signals are lost, and/or that sounds that pass
through the gate appear 'clipped' due to the attenuation
of their beginnings and/or endings.
Noise gates are particularly handy for use with
individually-miked drums and
guitar effects. In order to
establish appropriate dynamics for a gated sound source,
it is necessary to set appropriate
release (sometimes called 'decay')
times for the gate − or alternatively these parameters may be
adjusted for creative effect. Additionally, a 'hold' control
may be provided to enable the opening time of the gate to be
extended. Different models of noise gate may differ in
the precise function and effect of these three controls.
filter may also be incorporated,
to make the opening of the gate more selective to the wanted
sound and so reduce the likelihood of unwanted openings.
Effectively, a noise gate with its range control set to
maximum attenuation is a
downward expander set for
Any process or equipment intended to improve
ratio of a signal, but
particularly when used in order to accommodate the
poor dynamic range
of an audio storage or
transmission medium such as
analogue tape or
It usually operates by
signal (or a part of it) prior to recording or
transmission, and expanding
it again on playback or reception.
See also Dolby A,
Dolby C and
Describes a sound or a
signal that contains an excessive
amount of noise relative to the
wanted sound or signal level,
i.e. that has a poor
Or, describes equipment (or a part of an item of equipment)
that contributes an excessive amount of noise to the signal(s)
passing through it, resulting in a poor signal-to-noise ratio.
(Note: Does not mean
− see Loudness (1).)
Some types/parts of equipment that are particularly prone to
being (or becoming) noisy are cables,
Connectors and pots can readily introduce noise into the signal
being carried if they develop electrically poor point(s) of
contact; such problems are usually caused by wear and/or
contamination and are usually most evident when the
connector is moved around or the pot is adjusted.
A cable that introduces noise when moved around is sometimes
referred to as being
See also Dirty (2).
Compare Quiet (1).
An abbreviation for 'number of
microphones'. In a
before feedback decreases by
3 dB for every doubling
of the number of open microphones (assuming that
all microphones are given the same amount of overall
amplification through the system).
Describes the figure by which a particular value
is generally known, or the figure that is given to it
for the purposes of identification, without necessarily
being the precisely correct figure in reality. For example, a
mains supply referred to as
is rarely exactly that value in practice, due to
local differences and constant minor variations.
So, 230 volts is a 'nominal figure' for that mains supply
and the actual value at any point in time may be higher
or lower, within the limits set by the
are marked with their nominal value of
The nominal level of an
signal is sometimes
referred to as its 'average' level − see, for example,
Describes a system that does not incorporate a
See the radio microphone
information on the Microphones
Describes emergency lights, illuminated fire exit signs,
etc., that illuminate only in the event of a failure
of the mains supply. Whilst
the mains supply is operating normally, they charge their
internal batteries from that supply. If the mains
supply fails, they automatically illuminate by using
power taken from those batteries, and their illumination
continues (generally for at least 3 hours) until the
mains supply is restored. The correct operation of these
units must be regularly checked, and records kept of the
Usually refers to a 2-pole
incorporates no means to enforce or indicate a specific
when mated. Such connectors
are used for the mains power
connector on some types of
However, some types of non-polarised mains connector
such as Schuko
incorporate a third pole for the
connection required by
Non-polarised electrolytic capacitor
Describes a means of storage that is able to retain the stored
information indefinitely, even when the supply of power is removed.
Such types of storage are useful for retaining the settings of
between uses, or in the event of a power failure.
See also RAM.
To set all controls to their 'normal' or 'zero' positions.
For example, to normalise a
would be to adjust it to give a
flat response. The controls
of a mixer would typically
be set as follows:
All equipment should be normalised after use if
its next usage is to be in a different situation
− e.g. before returning hired or
borrowed equipment to its owner. Also referred
to as 'zeroing', or 'zeroing out', the equipment.
signal processing, the process of modifying the
of stored audio
data, so that all the data files that undergo this
processing have the same peak
signal level. Often this process may increase the
signal levels to the point where the peak level
is equal to 0 dB FS,
which reduces the headroom
to 0 dB − this may be a problem if the data
is to undergo further digital processing such as
Describes the internal connections to a socket
connector (usually a
jack socket) on an item of
equipment, where those connections are arranged to
route the signal
through the equipment in the usual (normal) manner if no
plug is inserted in the socket, but to interrupt
that normal path
if a plug is inserted.
In the case of a normalled
patch bay in which
source and destination equipments are permanently
wired to each
to the top and bottom sockets respectively), the
patch bay provides normal routing between those
items of equipment until a plug is inserted;
that normal path is then broken.
However, with most types of patch bay the
earth) connection between the relevant
pair of sockets is not broken.
Such patch bays may provide three possible types
Fully normalled (also called single normalled)
is where inserting a plug into
either the source (top) socket or the
destination (bottom) socket of a channel breaks the
patch bay's normal connection between the wired
source and destination equipments.
Half normalled is where the normal connection is broken
only by insertion into one of the channel's sockets,
usually the destination (bottom) one. This allows the other
socket to be used as a 'monitor' source without disrupting
the normal signal routing. (However, beware
Double normalled is where the normal connection is broken
only by insertion into both sockets of the channel;
this type is usually found only in broadcast applications.
Note that some patch bays have a third socket
on each channel − inserting a plug into just this
'monitor' socket (usually the centre one of the three)
never breaks the normal connection path.
Some caution must be exercised when passing
through normalled patch bays: When, as is usual,
there is no switching of the sleeve connection, which
provides a return path for the phantom power
issues may arise from the hot and cold connections
being diverted away from the sleeve connection by the
insertion of a jack plug. When patching occurs solely
between jacks of the patch bay, such problems may be
reduced by commoning
the sleeve connections of all circuits passing through
the bay (though this contravenes audio wiring conventions
requiring signal earths of separate circuits to
from one another along interconnection paths).
However, in any case phantom power should always
be switched off while making changes to the patching
of phantom powered
See also Insert.
An abbreviation for the Dutch national broadcasting system,
'Nederlandshe Omroep Stichting'.
Usually refers to the stereo
technique developed by them, in which two
are positioned with a spacing of 30 cm between the
and with their axes at an angle
of 90º. This technique gives similar results to the
ORTF method, and may be
useful for recording ensembles.
See also X-Y pair,
Mid-side pair and
a pictorial comparison of stereo microphone techniques.
(To view the image full-size in Explorer,
hover your mouse over the image and click on the green
'expand' icon that appears in the bottom right-hand
corner. Or, click when a magnifying glass containing a
An abbreviation for 'new old stock', used to refer
to items for sale (especially valves) that were manufactured
many years ago (typically by 'original' manufacturers no longer
in existence) but have never been used. The term distinguishes
these offerings from versions that have been recently manufactured
to the same, or a similar, specification as the original items
of that type. It is claimed by some people that NOS versions
of some valves (especially by certain specified manufacturers)
give significantly improved performance over recently manufactured
To significantly reduce the level
of a narrow range of frequencies.
This might be done,
for example, to increase the amount of
without feedback occurring.
It can be done with a
notch filter, a
(preferably a 31-band one), or a
(The same effect can be obtained to some degree using
sweep EQ, but the range of
frequencies affected would be rather too broad to be
described as a "notch".) See also
An abbreviation for 'National Television Standards Committee',
an American TV standards organisation.
Usually refers to the method used in the USA for coding the
prior to creating a colour
signal. Or, describes a
composite video signal that incorporates chrominance
information coded using that method.
Compare PAL and
[Noun:] A situation or location in which equal and
opposite values of some quantity (e.g.
cancel each other completely (or very nearly so),
giving an essentially zero result.
Or, [Verb:] To set something to zero (or, in some cases,
to the minimum possible value), or to arrange for a condition
of cancellation (as described above) so as to give an essentially
See also Dead spot,
Notch out and
The minimum rate at which the
of a repetitive-waveform
signal must be examined
(sampled) in order to correctly determine its
This rate was established by Harry Nyquist (along with
Claude Shannon) as being twice the actual frequency of the
signal being sampled. Note, however, that sampling at this
rate captures only the
of the signal, not the shape of its waveform. In order to
adequately capture the waveform shape, the signal must be
sampled at at least twice the frequency of the highest
harmonic that is present
at any significant level.
to digital conversion.
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This page last updated 20-Mar-2018.