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The glossary pages provide definitions for over 2680 PA-related terms. 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.

N-connector * NAB * NAG * NAMM * Narration * Narrow-band * National Electrical Code * Near field * Necklace microphone * Needed acoustic gain * Neg * Negative feedback * Neodymium * Neutral * Neutrik * nF * Nibble * NiCad * NICAM * NiCd * NIHL * NiMH * Nit * Nits * NL2, NL4, NL8 * NOEA * Noise * Noise boy * Noise-cancelling * Noise dose meter * Noise dosimeter * Noise floor * Noise gate * Noise pollution * Noise reduction * Noise squelch * Noise weighting * Noisy * NOM * Nominal * Non-destructive solo * Non-diversity * Non-linear * Non-maintained * Non-polarised connector * Non-polarised electrolytic capacitor * Non-reciprocal response * Non-volatile * Normalise * Normalling * NOS * Notch filter * Notch out * NTSC * Null * Nyquist frequency

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.

N-connector
A type of connector sometimes used with radio-frequency (RF) 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 BNC.

View N-connector (male, 50 ohm) image

NAB
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 tape equalisation standard, or to the physical dimensions of a reel-to-reel spool hub. Compare CCIR.

NAG
An abbreviation for 'needed acoustic gain'.

NAMM
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.

Narration
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.

Narrow-band
Describes a signal (often noise) or equipment (often a filter) having a relatively small bandwidth. Compare Wide-band.

National Electrical Code
The specification of requirements for electrical installations in the USA. Often abbreviated to 'Code'. See also BS 7671 and PAT.

Near field
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) produced.

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 microphone position) can substantially affect the timbre of the sound that is heard or picked up, and also its level. See also Close pickup.

Necklace microphone
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 Lavalier.

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 amplification. Often abbreviated to 'NAG'.

By using the inverse 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, reverberation, absorption, 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, the potential acoustic gain (PAG) of the system can be calculated.

Neg
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.

Negative feedback
The situation in which a signal is fed back to an earlier point in the signal path in such a way as to partially cancel the original signal. Extensively used in amplifier 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 anti-phase to the original signal, at the point at which it is fed back.

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 frequency response 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 Operational amplifier and Feedback. Compare Positive feedback.

Neodymium
A material from which the magnet of many dynamic 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 sensitivity.

Neutral
A mains supply conductor or connection point that carries supply current but (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 balanced mains 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 isolation.

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 RCD, Phase (3) and Basic protection. Compare Line conductor.

Neutrik
A German manufacturer of connectors and cables, most well-known for their XLR, Speakon and jack connectors. Pronounced "noy-trick".

nF
An abbreviation for 'nanofarad', one thousandth of a millionth of a farad, i.e. 10-9 farad. A common unit for the measurement of capacitance. See also F and pF.

Nibble
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 NiMH types. See also Alkaline battery.

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 audio digitally over analogue terrestrial television channels (now redundant, replaced by all-digital broadcast TV formats). The same system has also been used to convey two independent mono audio channels 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 digitally compressed Left and Right channels into a single bit-stream for transmission, corresponding decompression being applied at the receiver (see Compander).

In the UK it employed a carrier at 6.552 MHz above the vision carrier, modulated by a 728 kbit/s bit-stream. The audio is band-limited to 15 kHz and pre-emphasised. 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 Composite video, Lip sync and Compression ratio (2).

NIHL
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 sound pressure levels, or by prolonged exposure to moderately high sound pressure levels. The damage is usually irreversible. See also Audiology, Dosimeter, Tinnitus and Acoustic Safety on the Safety page.

NiMH
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 NiCad types. See also Alkaline battery.

Nit, Nits
A commonly used but 'unofficial' unit of luminance, exactly equivalent to the 'official' unit which is candela per 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 lux) 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
See Speakon.

NOEA
The National Outdoor Events Association of the UK. Their website is www.noea.org.uk (link to external site, opens in a new window).

Noise
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 digital), 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 signal-to-noise ratio.

Noise originating from electrical sources may be random in nature (e.g. hiss, or crackles introduced by cables and connections), may have a repetitive waveform (e.g. a hum or buzz), or may be an interfering information-carrying signal such as crosstalk or radio-frequency interference (RFI).

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. microphone-level 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 "digital cliff", and is in marked contrast to the gradual effect of decreasing signal-to-noise ratio on the perceived quality of an analogue signal.

(Note: In PA work 'noise' does not refer to an unpleasant or loud sound!) See also Noisy, Noise floor, Noise gate, Ambient noise, Tape noise, Thermal noise, Quantisation noise, Dynamic range, Equivalent input noise, Pink noise, White noise, Weighted noise measurement, IEC noise, HVAC, Earth loop, Leakage and Microphone Noise Levels on the Microphones page.

Noise-cancelling
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. See also Lip microphone.

Noise boy
A slang term for a sound engineer. The term may be used to refer to male or female sound engineers. See also Soundie and Techie.

Noise dosimeter, Noise dose meter
See Dosimeter.

Noise floor
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 signal-to-noise ratio 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.

Noise gate
An item of signal processing equipment intended to "close the gate" on noise, i.e. to block its path, whilst "opening the gate" to allow through the wanted part of the signal, the usual objective being to improve the apparent signal-to-noise ratio 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. This means that when the wanted signal is present it 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 − which will mask out the noise. At other times the gate is 'closed' and the noise is attenuated by the amount set by the 'range' control. Particularly handy for use with individually-miked drums and noisy guitar effects. In order to maintain the dynamics of the sound source, it is necessary to set appropriate attack and 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. An adjustable filter may also be incorporated, to make the opening of the gate more selective to the wanted sound.

Effectively, a noise gate with its range control set to maximum attenuation is a downward expander set for an infinite expansion ratio. See also Gain reduction, Gated reverberation and VCA.

Noise pollution
See Environmental noise pollution.

Noise reduction
Any process or equipment intended to improve the signal-to-noise 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 radio microphones. It usually operates by compressing the signal (or a part of it) prior to recording or transmission, and expanding it again on playback or reception. See also Dolby A, Dolby B, Dolby C and Compander.

Noise squelch
See Squelch.

Noise weighting
See Weighted noise measurement.

Noisy
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 signal-to-noise ratio. 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 "unpleasantly loud" − see Loudness (1).)

Some types/parts of equipment that are particularly prone to being (or becoming) noisy are cables, connectors and potentiometers (pots). 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 microphonic. See also Dirty (2). Compare Quiet (1).

NOM
An abbreviation for 'number of open microphones'. In a PA system, the gain 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).

Nominal
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 230 volts 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 tolerance. Likewise, resistors are marked with their nominal value of resistance.

The nominal level of an audio signal is sometimes referred to as its 'average' level − see, for example, Line level.

Non-destructive solo
See Solo.

Non-diversity
Describes a system that does not incorporate a diversity feature. See the radio microphone information on the Microphones page.

Non-linear
See Linear.

Non-maintained
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 tests. Compare Maintained.

Non-polarised connector
Usually refers to a 2-pole connector that incorporates no means to enforce or indicate a specific connection polarity when mated. Such connectors are used for the mains power connector on some types of Class II equipment. However, some types of non-polarised mains connector such as Schuko incorporate a third pole for the safety earth connection required by Class I equipment. Compare Polarised.

Non-polarised electrolytic capacitor
See Capacitor.

Non-reciprocal response
See Equaliser.

Non-volatile
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 digitally-controlled equipment between uses, or in the event of a power failure. See also RAM.

Normalise (1)
To set all controls to their 'normal' or 'zero' positions. For example, to normalise a graphic equaliser 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.

Normalise (2)
In digital signal processing, the process of modifying the digital signal level of stored audio programme 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 equalisation.

Normalling
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 channel (generally 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 sleeve (signal earth) connection between the relevant pair of sockets is not broken. Such patch bays may provide three possible types of normalling:

  • 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 termination of digital signals.)
  • 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 phantom power 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 current, 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 remain isolated 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 signal paths. See also Insert.

NOS (1)
An abbreviation for the Dutch national broadcasting system, 'Nederlandshe Omroep Stichting'. Usually refers to the stereo microphone recording technique developed by them, in which two cardioid microphones are positioned with a spacing of 30 cm between the microphone diaphragms, and with their axes at an angle of 90. This technique gives similar results to the ORTF method, and may be useful for recording ensembles. See also X-Y pair, A-B pair, Mid-side pair and Microphone technique.

View 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 '+' appears.)

NOS (2)
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 versions.

Notch filter
See Bandstop.

Notch out
To significantly reduce the level of a narrow range of frequencies. This might be done, for example, to increase the amount of amplification possible without feedback occurring. It can be done with a notch filter, a graphic equaliser (preferably a 31-band one), or a parametric equaliser. (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 Rejection.

NTSC
An abbreviation for 'National Television Standards Committee', an American TV standards organisation. Usually refers to the method used in the USA for coding the chrominance information prior to creating a colour composite video signal. Or, describes a composite video signal that incorporates chrominance information coded using that method. Compare PAL and SECAM.

Null
[Noun:] A situation or location in which equal and opposite values of some quantity (e.g. voltage or sound energy) 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 zero result.

See also Dead spot, Comb filter, Notch out and Calibration (1).

Nyquist frequency
See Aliasing.

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