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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.

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

V * VA * Vacuum tube * Valve * Variable bit rate * Varistor * VBR * VCA * VCA group * VCD * VCF * VCR * Velcro tie * Velocity of sound * Venue * Verb * VESA * VGA * VHF * Vibrato * Video * Vinyl * Vocal band * Vocalist * Vocalist set * Vocalist system * Vocals * Voice * Voice coil * Voice of God * Voicing * Volt * Volts * Voltage * Voltage-matched * Voltage bands * Voltage controlled amplifier * Voltage controlled filter * Voltage drop * Voltage gain * Voltage surge * Volume * Volume control * Volume leveller * Vox * VT * VU

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.

V
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.

VA
An abbreviation for 'volt-amperes', i.e. the RMS value of the voltage supplied multiplied by the RMS value of the current drawn (or available). So, to determine the amount of supply current drawn by mains-operated power-utilising equipment 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 AC power generation or distribution equipment (such as a transformer) that is rated in VA, simply divide the VA figure by the supplied voltage. 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.

Vacuum tube
See Valve.

Valve
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 Warnings:

  • 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.
  • Some models of equipment require a bias adjustment 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 'three electrodes'). 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 glow.

Valves usually operate at high DC supply voltages, produced within the equipment (see HT). 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 transistor. However, it is still used in some guitar amplifiers because of the particular type of distortion that it produces when operated at (or close to) its maximum output level. It is also used in some professional studio microphones and microphone pre-amplifiers, 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 Standby (1). 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 MP3 bit-stream. Or, describes a file containing data encoded in such a manner. This type of coding is catered for by the relevant codec. Often abbreviated to 'VBR'.

Varistor
A 2-terminal electronic component whose resistance varies according to the voltage across it. For a practical application see MOV.

VBR
An abbreviation for 'variable bit rate'.

VCA
An abbreviation for 'voltage controlled amplifier' (the term is rarely used in full). A signal processing device whose gain (or loss) is determined not by a potentiometer acting directly on the audio signal, but by a DC 'control voltage'.

It has many applications, such as in dynamics processors, 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 active fader). 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 integrated circuit (e.g. a compressor/expander chip) a VCA is sometimes termed a 'gain cell'. See also VCF.

VCA group
See Group.

VCD
An abbreviation for 'video compact disc'. A standard for the recording of digital video information on a CD, giving a reduced picture quality as compared to the DVD standard. See also AVCD.

VCF
An abbreviation for 'voltage controlled filter' (the term is rarely used in full). A signal processing device whose filtering characteristics are determined not by physical controls that are part of the filter circuit, but by a DC 'control voltage'. This allows the filter to be controlled remotely, and also allows the control of several filters at once. See also VCA.

VCR
An abbreviation for 'video cassette recorder'. See also VT.

Velcro tie
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 cable ties 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.

Velocity of sound
See Speed of sound.

Venue
The location or premises hosting a show or other event.

Verb
A slang abbreviation for 'reverb'.

VESA
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.

VGA
An abbreviation for 'video graphics adaptor'. A standard interface for the connection of display equipment (such as monitors and projectors) to computers. The standard gives a resolution of 640 pixels horizontally and 480 pixels vertically. The aspect ratio is 4:3. Note that as VGA was the 'original' standard, its name has become something of a generic term and so may be used to refer to cables, connectors (usually a 15-pin high-density D-sub), etc., even though they may be used to carry the signals of higher resolution analogue computer graphics standards such as SVGA, XGA, SXGA, WXGA or UXGA (but not DVI, which is a standard with digital capability).

View VGA (HD15 / DE-15M) connector image

The most commonly encountered standards, their resolutions and aspect ratios are tabled below.

    Resolution (H x V)     Aspect ratio  
HVGA 480 x 320 3:21.5:1
VGA 640 x 480 4:3   1.33:1   
SVGA 800 x 600 4:31.33:1
WVGA 854 x 480 16:91.78:1
qHD
'quarter HD'
960 x 540 16:91.78:1
XGA 1024 x 768 4:31.33:1
'HDTV'
720p / 720i
1280 x 720 16:91.78:1
 WXGA  1280 x 800    16:10   1.6:1
 QVGA  1280 x 960 4:31.33:1
SXGA 1280 x 1024 5:41.25:1
UXGA 1400 x 1050 4:31.33:1
SXGA+ 1600 x 1200 4:31.33:1
'HDTV'
1080p / 1080i
1920 x 1080 16:91.78:1
WUXGA 1920 x 1200 16:101.6:1
QWXGA 2048 x 1152 16:91.78:1
QXGA 2048 x 1536 4:31.33:1
WQHD
'Quad HD'
'1440p'
'QHD' (deprecated)
2560 x 1440 16:91.78:1
WQXGA 2560 x 1600 16:101.6:1
4K
Academy storage
3656 2664  1.37:1
4K UHDTV 3840 2160 16:91.78:1
4K DCI
flat cropped
3996 2160  1.85:1
4K DCI
CinemaScope cropped
4096 1714 ~12:52.39:1
4K DCI native 4096 2160 ~17:91.9:1
4K
Full aperture storage
4096 3112  1.32:1
8K UHDTV 7680 4320 16:91.78:1

VHF
An abbreviation for 'very high frequency'. Refers to radio frequencies in the range 30 MHz to 300 MHz, used by some types of radio microphones, wireless instrument systems and in-ear monitoring 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.

Vibrato
A deliberate repetitive variation in the pitch (frequency) of a musical note, as an effect to improve the interest of the sound. Most commonly encountered in the context of keyboard instruments. 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.

Video
Visual programme 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 analogue or 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), Field (2), Luminance, Chrominance, IRE, SCART, BNC, HDTV, Pixel, VGA, Scaler, Aspect ratio, VT, VCR, DVD, VCD, VESA, Sync, Raster, Grey scale, Contrast ratio, Lumen, Nits, Interlace, Progressive scan, Blu-ray and DL.

Vocal band
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).

Vocalist
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.

Vocalist set/system
A term commonly used by equipment manufacturers to refer to a complete radio microphone system (or 'set') that includes a hand-held microphone suitable for use by a vocalist. The radio transmitter is incorporated within the microphone. Compare Presenter set.

Vocals
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 Lead (2), Backing and Vocalist.

Vinyl
A term adopted to describe the 'original' type of audio recording disc, having a continuous groove with physical deviations to represent the audio information in an analogue manner. 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 coupled.

The clarification became necessary to provide a distinction from more recent 'disc-type' recording formats such as the compact disc, 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.

Voice
Apart from the obvious meaning (human speech or song), a term referring to the particular type of sound (as opposed to its pitch) being created by a musical instrument, particularly a programmable keyboard or an organ. See also MIDI, Patch (2), Timbre and Voicing (2).

Voice coil
The coil of wire, inside a driver or a dynamic microphone, which carries the electric current and is mechanically coupled to the cone or diaphragm.

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 high-frequency horn or tweeter) that corresponds to the direction and magnitude of the current, so producing sound waves.

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 Ferrofluid.

Voice of God
Speech spoken by a person unseen by the audience − usually amplified and often heavily laden with reverberation and/or other effects. 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.

Voicing (1)
A technique for setting the equalisation of a microphone channel of a PA system, or of a graphic equaliser for monitors or the front-of-house (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 bass response), "Two" (for treble response) and "Check" (for mid-range response) are often used. See also Ringing out.

Voicing (2)
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 Patch (2).

Volt, Volts
The unit of voltage − see the next definition.

Voltage
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 AC, or even a mixture of the two. In the case of AC (such as an audio signal), the instantaneous value of voltage is continually rising and falling, first in one direction and then with the opposite polarity. 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 PPM and VU.

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 passive speakers, 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 energy (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.

Voltage-matched
Describes an interconnection in which the output impedance of a signal source and the input impedance of the equipment that it connects to are co-ordinated so that the output 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 analogue 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 Matching). See also Load, Impedance and Open-circuit (1). Compare Impedance-matched.

Voltage bands
Designations of the bands (i.e. ranges) of voltage for which wiring is used, or is suitable, defined by BS 7671.

  • Band I (band one) − voltages are 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 concerned). Note that, in the latter case, voltages in this band may be sufficiently high to pose a shock hazard. Most signals fall into this band.
  • 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 DC. Normal mains voltages fall into this band.

BS 7671 requires that Band I wiring is suitably segregated from Band II wiring, or else is insulated to Band II standards, so as to reduce the likelihood of it accidentally attaining a voltage above the specifically required limit(s), 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.) See also Classes of wiring.

Voltage controlled amplifier
See VCA.

Voltage controlled filter
See VCF.

Voltage drop
The voltage that is developed (or 'dropped') across a series resistance or impedance (especially 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 Ohm's law.

Voltage gain
The multiplying factor by which a signal's voltage level is increased by (or within) an item of equipment. It is usually expressed as a value in decibels. For fuller details see Gain.

Voltage surge
A momentary increase in voltage to a value substantially in excess of normal operating values, occurring in a mains power distribution 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 PA or computer equipment. Protection against them may therefore be provided − see SPD and MOV. Smaller and shorter voltage surges, often known as spikes, may result from the switching on or off of nearby equipment such as motors or fluorescent lighting. See also Power conditioner. Compare Current surge.

Volume
A non-technical term for loudness, deprecated by sound engineers.

Volume control
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 sound produced. 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 audio chain (e.g. channel gain control, channel fader, group fader, main fader, crossover level adjustments, amplifier gain, 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 room acoustics. See also Inverse square law.

Volume leveller
See Leveller.

Vox
Short for 'voice' or 'vocals'. See also Lead (2) and Backing.

VT
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.

VU
An abbreviation for 'volume units', however the abbreviation is most commonly used to refer to a type of level 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 audio signal in order to give an indication of perceived loudness. The required behaviour of the meter indication is detailed in IEC standard 60268-17, which specifies a time of 300 ms to reach a 99% indication (about 1 dB below 100%) when suddenly subjected to a constant-level tone. 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 tone at +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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