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

B supply * B+ * B− * B-gauge jack * B-taper * B-type jack * B-weighting * Back electret * Back-emf * Background * Backing * Backing chorus * Backline * Backplate * Baffle * Balance * Balance control * Balanced * Balanced line * Balanced mains * Balanced pair * Balanced power * Ballsy * Balun * Banana plug * Band * Band track * Bandpass * Band-limited * Band-limiting * Bandstop * Bandwidth * Bank * Bantam jack * Bar * Bargraph meter * Barn doors * Barrel * Barrel connector * Barrier microphone * Barrier strip * Barrier tape * Baseband * Basic protection * Basket * Bass * Bass bin * Bass driver * Bass port * Bass reflex * Bass roll-off * Bass trap * Baxandall * BCD * BD * Be operating system * Beach * Beam blocker / diffuser * Beaming * Beamwidth * Beats per minute * Bed * BEIRG * Bel * Belden * Bell curve * Beltpack * BeOS * BER * Bessel * Beta microphones * Beta version * BFA * BGM * BGV * Bi-amping * Bi-phase mark code * Bi-polar electrolytic capacitor * Bias * Bidirectional microphone * Bifilar * Bin * Binary * Binary coded decimal * Binaural * Binding post * Bipolar junction transistor * Bit * Bit/s * Bit clock * Bit depth * Bit error rate * Bit-rate * Bit-stream * Blackout * BJT * Blacks * Blanking * Bleacher * Bleed * Blind test * Blinders * Block * Block diagram * Blocking * Blow * Blow up * Blown * Blown up * Blu-ray * Blue Book * Blue smoke * Blues harp * Bluetooth * BMC * BNC * BO * Board * Board tape * Bodypack * Bonding * Boom * Boom stand * Boomy * Boost * Boot * Booth * Bottom end * Boundary microphone * Box * Boxy * BPM * Bps * Braid * Brass * Break a leg * Break switch * Breaker * Breakout box * Breakout cable * Breakthrough * Breakup * Breath blast * Breathing * Brick wall filter * Bridge * Bridge-tied load * Bridged mode * Bridging * Briefcase engineer * British EQ * British terminology * Broadband * Brownout * BS * BS 1363 outlet * BS 1363A connector * BS 4343 connector * BS 7594 * BS 7671 * BS 7909 * BS 8300 * BS EN * BS EN 60118-4 * BS EN 60309 connector * BS.1770 * BSI * BT431a * BTL * Buffer * Build quality * Bulb * Bullet * Bum note * Burn * Burst error * Bus * Buss * Butterworth * ButtKicker * Buzz * BV * BVs * BVox * BWF * Bypass * Byte

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.

B supply, B+, B−

A term for the highest voltage DC supply present within an item of equipment.

In equipment that utilises valves, the B supply is the high voltage positive supply for the valve anodes, or plates (American term), more usually referred to as the 'HT supply' in the UK. For futher information see HT.

In transistor equipment, most commonly there are both positive and negative internal DC supply rails and these are sometimes referred to as the B+ and B− supplies, especially in American power amplifiers.

The term follows on from the term 'A supply' that was originally used for the low voltage supply to valve heaters.

B-gauge jack

See Jack.


See Taper.

B-type jack

See Jack.


See Weighting.

Back electret

See Condenser microphone.


An abbreviation for 'back electromotive force', the opposing voltage generated in an inductor when a change occurs in the current flowing through it. It is this behaviour which causes the effect known as 'inductance'.

Backing, Background

Describes an instrument or vocal part whose sound is intended to be non-dominant in the overall sound of the band, as perceived by the audience. For example, backing (or background) vocals − often abbreviated to 'BV' or 'BGV' − provide vocals support to the lead vocalist(s); backing guitar plays (mostly) background chords (rather than single notes) and does not normally have any solo parts. See also Rhythm guitar, Chorus (2), Harmony and the next definition. Compare Lead (2).

Backing chorus

A backing vocal part of a song, often sung while at the same time the lead vocalist(s) are singing a different lyric. The backing chorus lyric and/or melody may be the same as used in the main chorus of the song, or may be different.


The combos, and/or the speakers and their heads, that are provided for each individual musician (especially guitarists and bassists), to enable them to hear what they are playing and to enable them to make their own adjustments to the type of sound produced (in conjunction with adjustments on the instrument itself and on any effects they are using). This is in contrast to stage monitors, which are under the control of a sound engineer. The backline equipment is typically placed in a row across the back of the stage behind the relevant musician, hence the name. See also Pedal.


The rear, fixed, plate of the capacitor in a condenser microphone. The other plate of the capacitor (i.e. the one at the front) is the diaphragm of the microphone.


The surface on which a driver is mounted. This is usually a rigid board (typically of wood) forming the front face of a speaker enclosure. Its primary purpose is to very significantly reduce the amount of anti-phase sound coming from the rear of the driver that is audible from the front of the speaker, so avoiding the cancellation of the front and back sound waves at low frequencies and thereby dramatically improving the bass response of the speaker. In the case of a front-loaded speaker, the driver flange is seated on the outside of the baffle, whereas in the case of a rear-loaded speaker the flange is on the inside. When a speaker has one or more ports, these are often in the form of suitably sized holes in the baffle. A sealed box enclosure is sometimes referred to as an infinite baffle enclosure. See also Direct radiator.


A term sometimes used by non-technical personnel to refer to the relative levels of two or more sources in a mix, as in "The balance between the two guitars doesn't seem quite right". Technically, the term is more often used in the Left/Right sense of the following definition.

Balance control

A control used to adjust the relative level of two signals, most usually the Left and Right channels in a stereo configuration. Such an adjustment is made either to make the two signals equal in level, so compensating for an unwanted difference that was introduced earlier (e.g. differing Left and Right playback levels from a recording), or to intentionally make the two signals different in level, so compensating for a difference occurring later (such as a non-central listening position between the Left and Right speakers). A balance control is usually provided on stereo channel strips of mixers.

In analogue equipment, the control consists of two potentiometers mechanically linked such that, as the control is moved in one direction from the mid-point, the level of one channel is reduced without affecting the other channel − moving it in the opposite direction from the mid-point reduces the level of only the other channel. This is called an 'MN taper'. A balance control is often fitted with a central detent. Compare Pan.


Describes an interconnection between two items of equipment, in which two signal-related conductors are provided through the connectors and cable, separately from the signal earth or 'screen' of the interconnection (making three conductors in total), and in which the destination equipment registers the difference in voltage between those two signal-related conductors. In many such interconnections (but not all), these two conductors (known as a 'pair') carry signals of equal signal voltage but opposite polarity. They are usually referred to as legs, and are individually identified by the descriptions 'hot' (or '+', or 'in-phase') and 'cold' (or '−', or 'anti-phase'). The term 'balanced' emphasises the importance of each of the signal-related conductors having the same impedance to signal earth.

Or, describes an input, an output, a line or a cable that operates (or is intended to operate, or is capable of operating) with such an interconnection. Or, describes an item of equipment that is provided with such an input or output (e.g. a balanced microphone).

When good quality cable is used, this arrangement (properly termed a 'balanced line') is highly immune to the undesirable effects of earth loops and to the pick-up of interference, and so is commonly employed for low-level signals (such as between a microphone and a mixer) and/or when long distances (up to 200 metres) are involved. Picked-up interference originates primarily from RFI which succeeds in penetrating the screen of cables and connectors and from capacitively and inductively coupled signals from other nearby cables and equipment. However, it is important to understand that a balanced cable alone does not provide a balanced interconnection − balanced operation is possible only when such a cable is used with suitable source and destination equipment.

The immunity is achieved not (as commonly supposed) because of the opposite polarity of the hot and cold signals carried by the interconnection, but by the ability of a balanced input to 'reject' (or 'cancel') interference that arrives identically on its hot and cold terminals, termed common mode interference. The extent of this rejecting ability is specified by the input's common mode rejection ratio (CMRR). Such inputs are sometimes referred to as 'differential inputs', because (ideally) the input registers only the difference in voltage between its hot and cold terminals.

In order for this cancellation to occur satisfactorily, it is essential that the hot and cold legs of the interconnection pick up a near-identical level of the interference. This is achieved through the use of:

In fact, in some interconnections that are referred to as 'balanced', no signal is output on the cold leg of the interconnection by the balanced source. This has no effect on the input's immunity to the effects of earth loops and to picked-up interference, provided that the hot and cold legs are presented with the same value of impedance (to signal earth) by the balanced output. In such cases the differential input registers the difference between the hot leg signal voltage and a nominally zero cold leg voltage. Examples of this type of output are the semi-balanced and ground-compensated types. However, interconnections in which both legs are driven have the added benefits of reduced capacitive coupling ('crosstalk') into other circuits when not individually screened (such as inside stageboxes and multiway connectors), reduced signal current in the screen, and increased dynamic range; we shall refer to this case as 'fully balanced'.

A further advantage of a balanced interconnection is its ability to carry phantom power, useful for powering condenser microphones and active DI boxes. Caution: Phantom power may cause damage to equipment not intended to handle it.

The 3-pole (3-pin) XLR connector is almost always used for balanced audio interconnections − see the diagram. (A notable exception to this is on some patch bays, such as are frequently used in studios, where 3-pole jacks are often used.) However, an interconnection should not be assumed to be balanced solely because it uses an XLR connector (nor because it uses a 3-pole jack).

In a fully balanced interconnection there are two scenarios that can be encountered, depending on how the balanced operation is achieved by the equipment at each end of link. We can refer to these scenarios as 'isolated loop' and 'fully electronically balanced'.

The following table provides a comparison of the most common types of interconnections referred to as 'balanced'. The list includes types that provide a signal voltage on only one leg, and for completeness also includes the pseudo-balanced type even though it is not a balanced interconnection in the usual professional sense of the term. Interconnections between balanced and unbalanced equipment may perform unsatisfactorily or cause damage if phantom power is present, and are not recommended without use of a proper conversion unit; however some possible such interconnections are included in the table, shown in red. Note that, with the exception of pseudo-balanced, the type designations are strictly descriptions of the equipment output type only (not necessarily of the whole interconnection).

Diagrams showing the implementation differences between the various types of interconnections can be seen here (opens in a new window).

See also Multicore, FST, Drain wire, Differential input, One-legged and Pin 1 problem. Compare Unbalanced.

Type No. of
Cable connections
(see Key below)
No. of
+6 dB
(or SNR)

Balanced (fully) 3 2
3 Yes Good Good
2 No None None
2 No None None
Semi-balanced /

balanced /

3 1
3 No Good Good
2 No None None
2 No None None
Quasi-floating /

Servo balanced
3 2
3 Yes Good Good
2 No Fair to
2 No None None
3 1
3 No Good Good
2 No Fair to
2 No None None
Pseudo-balanced 2 1
2 No None Poor

Key to 'Cable connections' column:

Red text = balanced to unbalanced interconnection; see paragraph prior to the table.
1,2,3 = XLR pin numbers.
T,R,S = tip, ring and sleeve jack terminals (see TRS and TS).
−− (or more than 2 dashes) = cable conductor.
> = driven output pole.
< = voltage sensing via output pole.
X = cable conductor not connected.
Y = plug terminal should not be connected; do not use a 2-pole plug.
Z = plug terminal may be left disconnected or linked to S; or a 2-pole plug may be used.
# = to avoid shorting driven output, 3-pole TRS plug should not be inserted in 2-pole socket.
% = not driven, so no problem if 3-pole TRS plug is inserted in 2-pole socket.
¦ = linked connections (if R to S, may result from a 2-pole plug inserted in a 3-pole socket).
* inserting a 3-pole TRS plug into a 2-pole socket is unlikely to result in a reliable R to S link.
No cold conductor indicated = unbalanced screened cable used.

Balanced line

A line that operates in balanced mode. However, balanced operation of a line is dependent not only upon the line itself, but also upon being connected to suitable source and destination equipment. Therefore, the term 'balanced line' may be used to refer to a line that is intended to operate, or is capable of operating, in balanced mode − when connected to appropriate equipment.

Balanced mains

A special mains powering arrangement, in which the two conductors of the current-carrying power circuit have a voltage to earth that is equal in magnitude but opposite in phase. For example, in a 230 volt balanced supply, the two conductors would provide anti-phase voltages of 115 volts to earth − so the total voltage between them would be 230 volts (the same as in a normal unbalanced supply). This arrangement is in contrast to a normal mains supply, in which the Neutral conductor is at essentially earth potential.

Balanced mains supplies are provided by use of a centre-tapped mains transformer. The centre-tap of the transformer secondary must be adequately connected to the installation safety earth. Where a separate safety earth is provided for sensitive equipment, the centre-tap will typically be connected to that; a technical earth may not be used for this purpose unless it meets all the relevant requirements for a safety earth, and any other uses of the technical earth would not be adversely affected as a result of this use. The safety earth connection of all items of Class I equipment powered from the balanced supply must be adequately connected to the transformer centre-tap.

Such an arrangement is rarely used in mobile PA systems, but may be encountered in large fixed systems or in professional studios, where it can substantially reduce mains earth currents and so help to avoid problems from earth loops when a large number of unbalanced signal interconnections are in use between the items of equipment. In a PA context, earth loop problems are more usually avoided by use of balanced signal interconnections.

The reduction in voltage to earth in a balanced mains distribution arrangement gives an incidental safety benefit, but an RCD must nevertheless be used at the output of the transformer, to protect against earth faults occurring from either of the current-carrying conductors (which are both effectively 'Live' conductors). See also Distro, Power conditioner, Star point earthing and Technical earth.

Balanced pair

See Pair.

Balanced power

See Balanced mains.


A slang term subjectively describing a powerful, 'full-bodied' sound − especially one rich in bass and lower mid-range frequencies. See also Phat. Compare Thin.


A transformer arranged to provide conversion between balanced and unbalanced connections, with or without also providing a change in impedance. The name is most usually applied in radio-frequency situations such as radio aerial systems and computer network connections, rather than to audio-frequency transformers. It is sometimes a centre-tapped transformer, in which case the centre tap of the balanced side would usually be connected to signal earth.

Banana plug

A single-pole 4 mm connector, the male of which consists of a single exposed pin. Sometimes used (in pairs) for speaker connections, but now deemed unsafe for use in a domestic environment because they will fit into unshuttered European-type mains outlets (e.g. Schuko), which would result in a serious shock hazard (its replacement for domestic use is the BFA connector).

Unusually, in this kind of connector the spring(s) that provide a tight fit (and therefore a low contact resistance) are part of the male connector and are therefore visible. In the usual design, the spring(s) give the connector pin a slightly larger diameter towards the centre of its length; when the connectors are mated, this central part becomes slightly flattened-out and provides an outward pressure. This arrangement gives the pin a slightly curved profile, which is the origin of the connector's name.

Some 2-pole speaker connectors employ a pair of 4 mm pins mechanically linked; in this case the pin centres are normally 0.75 inches (approximately 19 mm) apart. See also Binding post and Speakon.

View banana plug image

Band (1)

A range of values between a lower limit and an upper limit, especially a range of frequency values. For examples of use, see Bandpass and the definitions following that one. For bands of voltage see Voltage bands. See also Graphic equaliser and Spectrum.

Band (2)

Strictly refers to a group of musicians who play together, but is usually taken to include any associated vocalists who do not also play instruments. Or, in pop music, a small group of vocalists who sing together, often (for at least part of the time) in harmony. In this latter case, which should be referred to as a 'vocal band', the backing music is either recorded or performed by musicians who are not considered to part of the band.

Band track

A recording of musical instruments without vocals, typically used to provide musical accompaniment to a vocalist singing live, but without a live band.


Describes a filter that allows a specific range (or band) of frequencies to pass through relatively unaffected, while frequencies significantly lower or higher than this band are significantly attenuated. The boundaries between the range of frequencies allowed to pass and those stopped are usually defined as the frequencies at which the attenuation is 3 dB greater than that at the centre of the band of passed frequencies (the centre frequency). For an explanation of dB see the Decibels page. Compare Bandstop.


Describes a signal whose frequency range (bandwidth) has been restricted by being passed through a band-limiting filter. The term is commonly used in relation to the effective removal of frequencies above a particular value, e.g. to avoid aliasing during analogue to digital conversion. See also the next definition.


The process of using a filter to restrict the frequency range (bandwidth) of a signal. Or, describes a filter essentially the same as a bandpass filter, but in which the emphasis is on excluding unwanted higher and lower frequencies rather than letting through specific wanted ones. Usually, the band of frequencies passed is quite wide, in relative terms, and sometimes it is the exclusion of just higher, or just lower, frequencies that is referred to. When both upper and lower filtering is required, the filter is often implemented using a high pass filter to stop the unwanted low frequencies, and a separate low pass filter to stop the unwanted high frequencies. An example of use of such a filter is in the restriction of the bandwidth of pink noise, e.g. to create a test signal for a specific frequency band of a speaker system. See also the pevious definition.


Describes a filter that provides a significant degree of attenuation to a specific range (or 'band') of frequencies, while frequencies significantly lower or higher than this band are allowed to pass through relatively unaffected. The attenuated frequencies are said to be 'rejected' by the filter. The boundaries between the range of frequencies rejected and those allowed to pass are usually defined as being the frequencies at which the attenuation is 3 dB greater than that at frequencies much lower or higher than the rejected band. (For an explanation of dB see the Decibels page.) The frequency midway between these two frequencies is called the centre frequency. If the band of rejected frequencies is quite narrow, and the transitions between the range of frequencies rejected and those allowed to pass are quite abrupt, then the filter is often referred to as a 'notch filter'. Compare Bandpass.


In an analogue context, a measure of the difference in frequency between a lowest and a highest frequency − i.e. a range (or band) of frequencies. Typically this would be the range of frequencies that exist within a signal, or the range of frequencies that are satisfactorily handled by an item of equipment or by an interconnection between items of equipment, or which are passed by a filter. Full audio bandwidth is generally recognised to be 20 Hz to 20 kHz.

A bandwidth value is determined by simply subtracting the lowest frequency of the range from the highest, these two frequencies usually being the lower and upper cut-off frequencies. Like frequency, it is measured in Hz or kHz. When an analogue communication channel is used for the transfer of digital data, the maximum achievable bit-rate will depend upon the analogue bandwidth and upon the data modulation method employed by the modems used. See also Half-power bandwidth and Q (1).

In a digital context, a measure of the maximum bit-rate that is supported by an item of equipment or by an interconnection between items of equipment. Digital bandwidth is usually measured in kbit/s or Mbit/s.

A larger bandwidth means that the maximum possible information transfer rate is increased, allowing, for example:


A set, or an associated group, of identical or similar items of equipment. Or, a store of several (usually different) control-settings of digitally programmed equipment such as digital mixers, lighting desks and electronic keyboard instruments. See also Patch (2).

Bantam jack

See Jack.

Bar (1)

A unit of pressure, equal to 100,000 (105) Pascals (Pa). As this unit is so very large, figures relating to sound pressure levels (SPL) are more frequently expressed in microbars (Ábar, 10−6 bar, equivalent to 0.1 Pa) or in picobars (pbar, 10−12 bar, equivalent to 0.1 ÁPa). Normal atmospheric pressure at ground level is variable around a value of approximately 1 bar (1000 mbar).

Bar (2)

The smallest section of a piece of music that contains a complete sequence of beats in the rhythm concerned (with rare exceptions). Bars are used by composers, musicians, singers and dancers as a convenient means of dividing up the music into small pieces that (by and large) each occupy the same amount of time − provided that the tempo remains constant. When musical beats are counted, the count is restarted at the start of each bar. (However, dancers often count over adjacent pairs of bars.) In professional music scores, the bars are often sequentially numbered to provide a convenient means of referring to any point within the musical piece.

Bar (3) (Lighting)

See Lighting bar.

Bargraph meter

A level-indicator that operates by means of a row (or, more usually, a column) of individual segments. Each segment is generally marked with a value of relative or absolute level, in dB or dBu respectively. The segments are usually activated progressively with increasing level, so that at the maximum displayable level they are all activated. The segments may be constructed using any display technology, but often use either discrete LEDs or an integrated LCD device.

The main advantages of the bargraph indicator over mechanical meters are ruggedness, low cost, accurate calibration and rapid response to changes in level.

More sophisticated versions of these indicators are now in common use, which include a 'memory effect' on the highest active segment, in order to give a clearer indication of the peak level reached. See also PPM.

Barn doors

Hinged metal plates, painted black, that are located around the edges of a lantern and which may be adjusted in order to selectively block the passage of light and so control the area that is illuminated by the lantern. A lantern normally has four barn doors.


A name for the main body of a microphone or of a cable-mounted connector (compare Shell), especially when this part is cylindrical. Or, the interference tube of a rifle microphone.

Barrel connector

A generic name for the style of 2-pole connector commonly used for low-voltage power supply connections to equipment, the plug of which has a cylindrical outer contact and a central hole for an inner contact. It may be used for supplies of various voltages, both DC and AC, but rarely exceeding 24 volts. In the case of DC supplies, the inner ('pin') connection is in some cases positive and other cases negative. WARNING: Therefore, before making connection it is always essential to be certain that the supply voltage, type, polarity and current rating of a power unit are correct for the equipment being powered, otherwise serious damage may be caused to the equipment and/or power unit, and there may be a safety hazard. It is strongly recommended to use only the equipment manufacturer's approved power unit, for each item of equipment. Notoriously, there are many different sizes of this type of connector, some of which look very similar to each other but are not compatible in terms of making a reliable connection and not damaging the mating connector. In this regard, note that the diameter of the inner hole must be correct, as well as the diameter of the barrel. In some cases the length of the barrel is also important, to provide sufficient reach into equipment where the socket is recessed. See also this question on the FAQ page.

View barrel plug image

Barrier microphone

See Boundary microphone.

Barrier strip

An American term for a row of screw-terminals on an item of equipment, provided to enable the direct connection of cables (that is, without the use of connectors). Generally used only for hard-wired connections in permanent installations. The name arises from the insulating pieces which project from the main body of the strip between each of the terminals; these pieces act as physical barriers to reduce the possibility of an accidental short circuit (e.g. due to a stray strand of a cable conductor).

Barrier tape

A self-adhesive tape with easily noticeable markings, usually red and white stripes, that is used at the boundary of areas accessible only to authorised persons. The tape is usually affixed to a physical barrier, but is sometimes stretched through the air between fixed points or affixed to the floor. See also Zebra tape. Compare Hazard tape.


Describes a signal which exists at its original range of frequencies, to contrast it with the case in which a signal has been processed to cause it to occupy a different (usually much higher) range of frequencies, as for example in the case of modulation onto a carrier.

Basic protection

In electrical safety, the collective name given to measures intended to provide protection against electric shock caused by direct contact. That is, electric shock occurring as a result of contact with conductive parts that are intended to be live (at a potentially dangerous voltage) in normal use, rather than as a result of an equipment or cable fault. This protection is provided by the presence of insulation or by the conductor being securely enclosed. Basic protection must be provided for the Neutral conductor of a mains supply as well as for the line conductor(s). Compare Fault protection.

Basket (1)

A term for the wire mesh grille of a microphone, located at the sound aperture(s). This term is generally used only in relation to 'hand-held' type microphones in which the mesh structure extends around to the sides at that end of the microphone, and is a separate component typically detachable (by unscrewing) for cleaning or replacement. The basket provides mechanical protection for the capsule's diaphragm while allowing sound waves to pass through relatively unhindered. It also usually supports an internal foam windshield.

Basket (2)

A term for the front part of a bass or mid-range driver, including the cone with its attached voice coil and the cone's surrounding metal support structure − i.e. all parts of the driver except the magnet assembly. Some types of driver are designed to allow the basket to be field replaceable; this means that the magnet assembly is attached to the basket with removable bolts and is arranged to accurately self-align around the voice coil without the need for an alignment jig. In the case of a driver failure, the old magnet assembly may thus be simply transferred to the replacement basket, allowing for a more cost-effective repair of a speaker than is the case when an entire driver has to be replaced.

Bass (1)

A low audio frequency, typically below 250 Hz. A mixer will usually provide the facility to cut or boost the relative level of these frequencies on each channel independently, leaving higher frequency ranges essentially unaffected. This facility is usually provided by an equaliser control having a shelving response and a cut-off frequency somewhere in the region of 60 to 250 Hz; such a control is often labelled 'LF'. More advanced mixers sometimes have an additional shelving control for bass frequencies, having an adjustable cut-off frequency. These controls, usually labelled 'Hi Pass' or 'HPF', often provide the facility to cut only (i.e. no facility to boost).

Some lowest fundamental frequencies are given below. Vocal ranges vary from person to person.

In a full-range speaker, the bass frequencies are handled by one or more drivers called woofers.

It is common practice for frequencies below around 100 Hz to be handled by separate amplifiers and speakers; these frequencies and the associated equipment are then described as 'sub-bass'. See also Bass bin, Treble, Mid-range and Crossover.

Bass (2)

One of several musical instruments designed to produce low frequency notes, including:

Bass bin

A speaker designed specifically to handle only bass and/or sub-bass frequencies. The type of driver(s) it uses are known as bass drivers, LF drivers or woofers. The term has most commonly been used to refer to the lowest cabinet of speaker stack systems, which for many applications have now been replaced by more modern arrangements incorporating full range speakers and/or line arrays. However, in such arrangements there is frequently a need for additional purpose-designed speakers to provide the required bass response, and though these are now more commonly referred to as 'subs', the term 'bass bin' may alternatively be used. See also Cardioid sub. Compare Tops. See the Amps and Speakers page for further information.

Bass driver

A driver designed specifically to handle only bass frequencies. It may also be referred to as an LF driver or woofer. Compare Horn (1) and Mid-range driver.

Bass port

See Port.

Bass reflex

See Port.

Bass roll-off

See Roll-off.

Bass trap

An acoustics modification device, installed or designed into the construction of a room, in order to absorb excessive bass frequencies. Such devices are usually employed only in a room such as an auditorium or a studio, where the acoustics are especially important. It is often part of the ceiling construction.


Describes a type of equaliser circuit, commonly used in simple 'tone control' arrangements, in which negative feedback is employed to provide for a variable cut (reduction) in level of the controlled bands of frequency, as well as a variable boost (increase). It often consists simply of bass and treble controls with shelving responses and fixed cut-off frequencies. Commonly used on 'Hi-Fi' equipment. Named after its inventor.


An abbreviation for 'binary coded decimal'.


An abbreviation for 'Blu-ray disc'.

Be operating system

An operating system popular for live performance software applications. Developed by Be Incorporated in 1996. Abbreviation BeOS.


A slang term for a particular location within a venue, especially for the location of specific equipment; an alternative to 'land' or 'world'. For example, 'monitor beach', 'dimmer beach' (vs 'monitor land', etc).

Beam blocker / diffuser

See the next definition.


The characteristic tendency of a speaker to have a decreased dispersion angle at higher frequencies. This effect is particularly evident when a single type of driver is used to cover a wide frequency range, as is usually the case with guitar combos and cabs. The result is that the on-axis sound has an excessive treble content, whilst the off-axis sound is lacking in treble. Such effects may only be noticeable at substantial distances from the speaker − perhaps in some cases greater than 5 metres (15 feet) or so.

To combat this effect some manufacturers incorporate an anti-beaming device in front of the driver(s); such devices, generally known as 'beam blockers' or 'beam diffusers' are also available separately for subsequent attachment. However, when the auditorium sound level from the guitar backline is low compared to that from the front-of-house speakers, the issue of backline beaming may be insignificant. Compare Off-axis colouration.


A measure of the dispersion angle of a speaker, usually expressed in degrees horizontally and vertically. For more information see 60x40. See also Directivity.


The part of a kick drum mechanism that makes contact with the drum skin.

Beats per minute

See BPM.


A fairly continuous 'background' of chords or synthesiser sounds on which other parts of a musical item (e.g. rhythm instruments, lead instruments, vocals) are 'built'.


An abbreviation for 'British Entertainment Industry Radio Group', a group representing the interests of radio spectrum users in the British entertainment industry. Their website is: http://www.beirg.co.uk (formerly beirg.org.uk). See also PMSE and PLASA.


A very rarely used term meaning ten decibels. For further information see the Decibels page.


A manufacturer of many different types of wire and cable. However, the term 'Belden cable' is often used to refer to a multicore, as Belden is a popular manufacturer of this type of cable. For multicore colour codes see Colour code.

Bell curve

See Peaking response.


A bodypack unit that is intended to attach to a performer's trouser-belt, or onto a body-belt worn specially for the purpose. Or, an alternative name for any bodypack.


An abbreviation for 'Be operating system'.


An abbreviation for 'bit error rate'.


Describes a class of filter having the minimum possible amount of variation (or 'ripple') of phase over the whole width of its passband, a so-called 'maximally flat' phase response. Named after the person first to document this design. Sometimes used for crossovers. See also Butterworth and Chebyshev.

Beta microphones

A range of high-performance stage microphones from Shure.

Beta version

In relation to software, a version released by the authors prior to final completion and testing, primarily in order to solicit comments from real users about any remaining problems. Such versions may not be fully functional or fully documented, and may contain features that are not present in the fully completed version.

In relation to hardware, it may have a meaning similar to that for software, or may refer to an improved or otherwise modified version of an earlier product.


An abbreviation for 'British Federation of Audio', an audio equipment manufacturers' association that ceased to exist at the end of 2010. This term is frequently used to identify a type of single-pole speaker connector most commonly found on consumer Hi-Fi equipment. The male connector has a 6 mm diameter hollow pin with a serated split along its length, allowing it to compress slightly and form a tight fit when inserted into a BFA socket; this design was developed to replace the use of the 4 mm 'banana' connector in domestic speaker connections.

4 mm single-pole connectors are now deemed unsafe for use in a domestic environment because they will fit into unshuttered European-type mains outlets (e.g. Schuko), which would result in a serious shock hazard. Further, the BFA connector is considered to provide a better quality of connection than the 4 mm connector for audio purposes. BFA and 4 mm connectors are not compatible with each other. See also Banana plug.


An abbreviation for 'background music'. See Musac.


An abbreviation for 'background vocal(s)', an alternative term for 'backing vocal(s)' (BV, BVox). Compare LV.


An arrangement in which low and high frequency audio signals are separated at line level by an active crossover before being amplified by separate power amplifiers and supplied through separate speaker cable conductors to suitable low and high frequency speaker drivers. These drivers may be incorporated within the same full range enclosure (e.g. a 2-way speaker incorporating woofers and horns), in which case the speaker must not incorporate a crossover (or must have a means of bypassing it) and must be provided with separate external connections to the two types of driver. Alternatively, the two driver types may be contained within their own separate enclosures.

The term is also used to refer to the internal arrangement of full-range active speakers that incorporate separate amplifiers for their low and high frequency drivers. However, some manufacturers use (or have in the past used) the term 'active' to refer to an unpowered full-range speaker that is intended for bi-amped operation, or to refer to the switch-selected bi-amped mode of operation of such a speaker.

By extension, tri-amping is an arrangement of three separate amplifiers driving low frequency, mid-range and high frequency drivers, and multi-amping is a generic term for a similar arrangement of any number of separate amplifiers from 2 upwards.

Bi-phase mark code

A data-bit coding scheme that is popular as a line code for synchronous serial digital audio interconnection lines, such as AES3 and S/PDIF. Its purpose is to facilitate bit-clock recovery and frame synchronisation by the equipment at the destination end of the line, to remove any DC component of the signal and to make the interconnection polarity-insensitive. Abbreviated to BMC.

It operates by using two consecutive logical states on the line to represent each data bit of the underlying signal. A state change always occurs at the start of each pair of logical states; a further state change occurs between the states of the pair if the represented data bit is a '1', but not if it is a '0'. So, a '1' is represented by the sequence '10' or '01' (depending on the preceding state), and likewise a '0' is represented by the sequence '11' or '00'. These coding rules have the effect that there are never more than two logical states before a state change, however the 'preamble' bits of AES3 and S/PDIF deliberately break the rules in order to be uniquely recognisable. Note that the use of two line states per data bit effectively doubles the bit-rate on the line.

Bi-polar electrolytic capacitor

See Capacitor.

Bias (1)

In analogue tape recording, a signal at ultrasonic frequency (typically in the range 50 to 100 kHz) that is applied to the recording head along with the audio signal to be recorded. The bias signal serves to mitigate against the inherently non-linear characteristics of the magnetic recording process. The correct adjustment of its level is critical in achieving the optimum compromise between dynamic range and frequency response. See also Tape equalisation and HX.

Bias (2)

In amplification using valves, the DC voltage that sets the required operating point on a valve's signal transfer characteristic, in order to provide optimum performance. In the small-signal stages (the pre-amp section) of valve amplifiers, bias values are most usually determined automatically by the circuit components. However, valve output stages such as are typically found in valve guitar amplifiers may be automatically biased or may require manual bias adjustment (e.g. on replacement of the output valves), depending on the model.

The means of manual bias adjustment is sometimes only accessible internally to the equipment. Warning: In this case the adjustment should be carried out only by skilled persons, taking into account that hazardous live parts may be exposed during the adjustment. Usually, where there is more than one output valve, a single adjustment serves for all of them, but in some cases there is more than one adjustment. One reason (among others) why it is important that a matched set of valves is fitted is so that they will all respond similarly to the bias value set. A typical setting arranges that the quiescent dissipation of the highest-dissipating output valve in the set is around 70% of the maximum for the relevant type of valve. This provides the maximum audio output level without stressing the valves.

Transistors used for amplification also require bias, but there is very rarely any need for this to be adjustable except in the case of the internal adjustment of quiescent current that is provided for the output stage of some types of power amplifier. Warning: As with valve amplifiers, internal adjustments to transistor amplifiers should be carried out only by skilled persons, taking into account that hazardous live parts may be exposed during the adjustment.

Bidirectional microphone

A microphone that picks up sound equally from the front and the rear, having a decreasing sensitivity towards the sides. The angle of least pick-up is at 90║ from the front (or rear) of the microphone, that is, directly at the sides. It is not often used in PA work. Also known as a 'figure-of-8' microphone, because its pattern of sensitivity, when plotted as a polar response graph, looks like the number '8'. See also Mid-side pair. For more information on microphones see the Microphones page.


Describes a coil wound back on itself in order to minimise its inductance. Used in wire-wound resistors, e.g. in crossovers. The term is from the French for 'two wires'.


A slang term for a speaker, especially one with a large (and often heavy) enclosure that caters for a restricted range of audio frequencies. Most commonly used as an abbreviation for 'bass bin'. See also Cab and Mid-range.


Describes a number that is expressed in base 2, i.e. using just the digits '0' and '1'. In such a number, each successive place, moving leftwards, has a significance twice as great. (Compare this with a normal decimal number, in which each place to the left is ten times as significant.) So, the right-most digit is the number of 1's, and successive places to the left are the number of 2's, 4's, 8's, 16's, 32's, 64's, etc.. For example, the number 375 would be written as 101110111 (= 256 + 0 + 64 + 32 + 16 + 0 + 4 + 2 + 1). The digits of a binary number are called bits.

This scheme is useful because it enables numerical information, such as a digital audio signal, to be conveyed and/or stored using just two values or 'states'. This minimises the probability of misinterpretation (which may arise due to undesirable modification of the signal or to the effects of added interference) and allows storage of the information using two-state media such as RAM or disc. See also the next definition and Hexadecimal.

Binary coded decimal

A numbering scheme in which each digit of a decimal number is represented in binary form, four binary digits being used for each decimal digit. For example, the number 375 would be represented as 0011,0111,0101. Often abbreviated to BCD. (Note that this is different to a binary representation of the number; for example 375 would be represented in binary as 101110111, requiring fewer bits than the BCD representation.) See also Hexadecimal.


Describes a stereo recording technique which makes use of a pair of microphones built into a model human head in such as way as to mimic the sound pick-up pattern of human ears. To achieve the desired effect, playback must be through headphones, so that the sound originally received by each microphone is reproduced directly into each ear of the listener.

Binding post

A type of connection terminal often used on power amplifiers and sometimes speakers, allowing the speaker cable to be connected directly − i.e. without the use of a connector. Alternatively, cables terminated with spade terminals may be connected. As it is a single-pole device, connection to a separate binding post is required for each conductor of the cable.

When using bare-ended cable, the insulation of the cable conductors must first be stripped back at the end of the cable to be connected − but only by just enough to avoid the insulation being gripped by the connector. Having careful regard to ensure correct polarity (see below), each bare conductor is then either wrapped around the appropriate binding post or more commonly is fed through the small radial hole that is revealed when the terminal is partially unscrewed. The terminal is then screwed-up by hand to securely grip the conductor (but not so tight as to damage it).

When used properly this method can provide a lower resistance connection than using a connector, but is not convenient for rapid connection and disconnection and is prone to polarity errors and other problems such as loose terminals, conductor damage and short circuits between adjacent conductors or to chassis. Binding posts are normally colour-coded red for the 'hot' or '+' connection and black for the 'cold' or '−' connection.

Some types of binding post are equipped with an axial hole for a male 4 mm connector (banana plug), as an alternative means of connection to the terminal. See also Speakon.

Bipolar junction transistor

The most common type of transistor, in which the main flow of current is controlled by a much smaller flow of current. The term is usually used to distinguish this type of transistor from FET types. Sometimes abbreviated to 'BJT'.


Short for 'binary digit'. When the term is used as a unit, i.e. preceded by a value, it is commonly abbreviated to 'b' (note lower case, to distinguish from 'byte'). A single digit of a number that is expressed in binary form − i.e. a '0' or a '1'. Digital signals consist of a consecutive stream of bits − see Bit-stream. See also Byte.


A unit of bit-rate, equal to one bit per second. Sometimes written as 'bps' (always with a lower-case 'b', to avoid confusion with Bps). Large values of data rate are usually expressed in kbit/s or Mbit/s.

Bit clock

A clock signal which indicates the rate at which bits are conveyed in a bit-stream or processed in a digital system. So, its frequency is the same as the bit-rate. See also Word clock.

Bit depth

The number of bits that are used to represent each sample in a digital signal or in stored digital programme material. In general, use of a greater bit depth provides an improved SQNR. For further information on sampling, see Analogue to digital conversion. Alternatively referred to as the 'sample width'.

Bit error rate

A measure of the rate at which bits that are in error (i.e. a 1 instead of a 0 or vice versa) are occurring in a bit-stream, expressed as a proportion of the total number of bits passing in the stream in the same period. For example, if over a certain period a total of 10,000 bits pass, and 3 of them are in error, then the bit error rate is 0.0003, more usually written as 3 x 10−4 or 3 x 10E−4. Commonly abbreviated to 'BER'. See also Parity and Cyclic redundancy check.


A measure of the rate at which bits are conveyed in a bit-stream, usually expressed in kbit/s or Mbit/s, sometimes written as kbps or Mbps (always with a lower-case 'b'). See also Bps and Bandwidth (digital).


A flow of bits from one point to another (often continuous), conveying some form of digital information. A digital signal. See also the previous definition and Streaming, Multiplex, Synchronous, Asynchronous, Bit clock, Byte, Word, Frame (1), AES3 and Subcode.


An abbreviation for 'bipolar junction transistor'.

Blackout (1)

A point during a performance when all stage lighting is switched off, for dramatic effect. Back-stage lighting remains on (as must all emergency lighting and fire exit signs). Often abbreviated to 'BO'. Compare Dead blackout and Dim out.

Blackout (2)

Sheet material, such as boarding or fabric, that is erected in a venue (typically over windows) in order to reduce the amount of natural light reaching a particular area. Blackouts may, for example, be used to increase the effectiveness of stage lighting, to increase the perceived contrast ratio of a projected image or to alter the visual ambience of a space. Blackout material is often matt black in colour, in order to minimise the amount of light reflected back from it.

Blackout (3)

An unintentional total loss of electrical power. Blackouts usually last for a relatively short period, but may nevertheless be extremely disruptive. For example, unprotected processor-based equipment will re-boot. See also Uninterruptible power supply and Power conditioner. Compare Brownout.

Blacks (1)

The black clothing worn by the stagecrew, to make them less visible to the audience.

Blacks (2)

Any black curtains or drapes used in a stage set.


See Raster. See also CVBS.


See Leakage.


See Riser (2).

Blind test

A test of equipment, usually a comparison test such as an A-B test, in which the person evaluating the equipment is kept unaware of the identity of each item of equipment during the test. See also A-B-X test. Compare Double blind test.


Originally, lanterns, facing towards the audience, that produce a white light so intense that it temporarily obscures their visibility of the stage. Such lanterns are usually arranged in rows or blocks, all being briefly illuminated together at maximum brightness − for either a single pulse or for several regular pulses. Or, any lanterns producing bright white light directed towards the audience.


An identifiable sub-unit, forming a part of the whole. For example, an internal section of an item of equipment (see the next definition) or a specific group of frames in a bit-stream.

Block diagram

A type of diagram, frequently found in equipment user guides, that allows the path of the signals though the various internal sections, stages or 'blocks' of the equipment to be visualised, but which omits the detail of the actual electronic circuitry. Each block of the equipment is typically represented by a rectangle or square, which may contain standard symbols for common functions such as amplification or filtering. Compare Circuit diagram.


The process of planning movements that are to take place during a performance. Usually refers to the movements of actors or dancers, often with specific refererence to lighting, lines of sight or camera angles. May also be used in reference to the planned movements of mobile cameras.

Blow (1)

A slang term meaning to play a musical instrument. Originates from the playing of wind instruments, but now gets applied to any type of instrument.

Blow (2), Blow up

Two equivalent slang terms meaning to cause sufficient damage to equipment to prevent its further (normal) use, as a result of actions taken during set-up or use of the equipment. These actions need not be reckless or even careless (though this might be so in some cases) − it may simply be normal operation. However, operation at or near the equipment's normal operating limits is often implied by use of these terms. The extent of damage to the equipment is usually much less than what these terms appear to suggest. See also the following two definitions.


A slang term describing a fuse that will no longer pass current or describing a driver, speaker or other component or item of equipment that is no longer operational. A blown fuse must be replaced with one of the correct rating and type − possible causes of the fuse blowing should first be investigated. See also Dead (3), Gone down and the next definition.

Blown up

A slang term describing an item of equipment that is no longer operational − particularly when a bang, flash or emission of smoke occurred at the time of failure. See also Dead (3), Gone down, Blue smoke and the previous two definitions.


A video disc recording format that is able to store an increased amount of data (25 GB single-sided), as compared to DVD. This increased capacity makes it suitable for storage of high definition video material (see HDTV). The disc is written and read using a shorter optical wavelength than DVD, and so is not compatible with it. However, a 'dual-standard' machine may be able to play back (or even to record) in both formats.

Blue Book

See CD standards.

Blue smoke

Usually refers to the smoke that is sometimes emitted from an item of equipment as it fails (regardless of the actual colour of the smoke). A reference to such equipment being no longer functional, or being unsuitable for (safe) use until repaired. In electronics folklore, blue smoke is considered to be the 'life-force' contained within all functional equipment, as 'evidenced' by the equipment's failure to operate after the smoke has been released. See also Blown up, Blown, Dead (3) and Gone down.

Blues harp

See Harp (2).


A standardised system for digital radio communication over very short distances, such as between nearby items of computer equipment. See also IEEE 802.11.


See Bi-phase mark code.


A bayonet-type connector often used for professional video and unbalanced digital audio interconnections. To connect it, place the slots of the male connector's locking ring over the lugs which protrude from the sides of the female connector, then push and twist the locking ring clockwise until the lugs lock into place. To disconnect, twist the ring fully anticlockwise to disengage the lugs, then pull the connector.

Note that there are two different versions, which look almost identical but should not be mated as they have different characteristic impedances: the 75 ohm version is always used in video and audio work, the 50 ohm version being used only in radio-frequency applications. For radio microphone antenna connections, check which type is required by your equipment. The two types of male connectors can be distinguished by the 50 ohm version having a plastic insert (usually white) inside its contact ring; the 75 ohm version does not have this insert.

This type of connector is also frequently used as a means of connecting and fixing gooseneck-supported illumination lamps over a mixing desk. BNC stands for 'Bayonet Neill-Concelman', Paul Neill and Carl Concelman being its inventors (though other explanations for the abbreviation are often quoted). See also N-connector, MUSA and Littlite.

View BNC image


An abbreviation for 'blackout'.


A slang term for a panel fitted with controls or switches. It is most commonly used as an abbreviated name for a sound board, a stage lighting control board or a distribution board for electrical power.

Board tape

Another name for console tape.


A small unit that is intended to be worn, usually to provide a communication fuction. Their most common uses are as transmitters for lavalier radio mics or for wireless instrument applications, receivers for in-ear monitoring systems, and pre-amps for wired instrument applications. They are usually powered by one or more internal batteries. Alternatively known as a beltpack. See also Condom and Pick-up.


A safety electrical connection between items of exposed metalwork, such as staging or gantry structures, or between such items and the main safety earth connection of the mains supply, in order to ensure that no harmful voltage can appear between those items in the event of an electrical supply fault. Particularly important in the case of a TN−C−S supply. The term 'earth bonding' is sometimes used, which is strictly incorrect; the correct full term is 'protective equipotential bonding' (often abbreviated to 'protective bonding'), as its function is to keep the interconnected items at essentially equal electrical potentials (i.e. voltages). See also Indirect contact.


Short for 'boom arm' − the part of a microphone stand that allows the position of the microphone to be offset horizontally from a position directly above the base of the stand. Although this part is usually supplied together with the stand, it may be purchased separately and attached to the top of a 'straight' stand − that is, a stand without a boom. (The threads might be different, but thread adaptors are available.) Some types of boom arm have two (occasionally three) telescopic sections.

Or, short-hand slang for 'boom stand'.

Or, in certain speech applications, a long hand-held pole (usually of multi-section telescopic construction) used to temporarily position a microphone close to (often just above) the person talking, while the operator remains some distance away, e.g. out of camera shot. Used in film sound, television interviews, live discussion forums (debates), etc.

Boom arm

See Boom.

Boom stand

A microphone stand that is equipped with a boom arm.


Describes a sound that has excessive or over-resonant bass content.


A common term for gain; an increase in level, usually specified in decibels. The term may be refer to an increase across the whole audio spectrum, or, more often, refers to an increase at specific frequencies only − e.g. by use of an equaliser. Or, as a verb, to make such an increase in level. Sometimes the term 'lift' is used. Compare Cut.

Boot (1) [Noun]

A protective enclosing cover for the point where two items are jointed, particularly the point at which a cable enters a connector. In such cases, where some degree of cable movement is expected, the boot needs to have some flexibility and is therefore frequently made from rubber or a similar material. Such a boot may also perform, or contribute to, a strain-relief function.

Boot (2) [Verb]

To start up a computer or a computer-based system such as a digital mixer. See also Reboot.


Any enclosure, or partial enclosure, for use by one or more persons. The term may be used to refer specifically to the front-of-house mixing location for a live performance event, when an enclosure or partial enclosure is provided for that location − typically within or at the rear of the audience seating area. Such an enclosure may well also accommodate other equipment, e.g. lighting desk, video equipment, etc. and the associated personnel. The term may also refer to an enclosure, or partial enclosure, provided for the purpose of acoustic isolation, particularly one used on stage for a drummer (more commonly called a drum screen) or one used in a recording studio for a vocalist or musician. In reference to live mixing locations, compare Control room (1).

Bottom end

The bass end of the audio-frequency spectrum. See also Top end.

Boundary microphone (Boundary layer microphone)

A special type of microphone which, when placed on or attached to a suitable surface, utilises the sound energy collected at that surface to provide an enhanced signal-to-noise ratio. Such microphones may be equally sensitive to sounds from all directions above the surface, or may exhibit directional characteristics. Typically used for speech, where a convenient surface such as a conference table, lectern or stage floor is available. Some types incorporate an integrated plate and so avoid the need for an external surface. Also called a 'pressure zone microphone' (PZM, a trade-marked term), a 'plate microphone' or a 'barrier microphone'. Patented by Ed Long and Ron Wickersham in 1982. For more information on microphones, see the Microphones page.


A slang term for a speaker (or, occasionally, for any item of equipment). See also Cab and Enclosure.


Describes a sound that has excessive or over-resonant mid-range frequencies, particularly in the 800 Hz to 1.5 kHz region.


An abbreviation for 'beats per minute', a means of specifying the tempo of music. A term mostly used by musicians, but also used by DJs as a means of comparing the tempo of recordings that are to be played sequentially without a gap, when a dance tempo is to be maintained.


An abbreviation for 'bytes per second', a measure of the rate of digital information transfer. However, note that when this abbreviation is written with a lower-case 'b' the meaning is then 'bits per second'. See also Bit-rate.


Another name for a screen, strictly one that consists of many fine strands of wire which are woven together around the insulated inner conductors, rather than being lapped.


Describes a particular class (or 'section') of orchestral musical instruments, including the trumpet, cornet, trombone, tuba, french horn and saxophone.

Break a leg

A theatrical term used in place of "Good luck!", for superstitious reasons.

Break switch

A button provided on some mixers, that typically mutes all inputs (apart from the 2-track inputs). Useful during performance intervals or other breaks. Not muting the 2-track inputs allows the playback of background music during such periods.


Short for 'miniature circuit breaker' − see MCB (or sometimes for 'moulded case circuit breaker' − see MCCB). Or, short for 'thermal circuit breaker'.

Breakout box

A general term for any adaptor box that enables the circuits (or, rarely, the individual connections) of a multiway cable to be accessed individually. For example, such a box may be fitted with a multiway connector to enable connection to the multiway cable, and also with several individual circuit connectors allowing the connection of several individual circuit cables.

Breakout cable

A general term for any adaptor cable that enables the circuits (or, rarely, the individual connections) of a multiway connector to be accessed individually. For example, such a cable may be terminated in a multiway connector at one end; the cable then splits into several tails, each terminated in an individual circuit connector.


Usually refers to the reception of an unwanted radio-frequency (RF) signal, that is being transmitted on a frequency other than that which a receiver (e.g. a radio microphone receiver) is intended to receive. This can occur when the unwanted signal is being transmitted at high RF power and/or from a nearby location, and is often due to the receiver being overloaded by the unwanted signal. Therefore, the unwanted audio may be distorted, and often starts and stops suddenly, as the changes in the unwanted RF signal level cause it to cross the overload threshold (in contrast to crosstalk, which is a linear phenomenon). See also RFI.


A term used by musicians, especially electric guitarists, to refer to the onset of distortion, especially in guitar backline amplifiers. Such distortion may or may not be desirable, depending upon the effect that the musician is aiming to achieve at the time. See also Overdrive.

Breath blast

The sudden burst of air that is expelled from the mouth when speaking or singing certain plosive sounds, particularly the letter 'p' but also the letters 'b' and 't'. When this burst of air hits the diaphragm of a microphone, it can cause a 'popping' sound to be generated. This effect can usually be adequately reduced by use of a suitable external windshield, though most good quality microphones intended for vocal applications are equipped with an internal windshield.


Undesirable audible changes in noise level that can occur during the operation of a compressor or a companding system. See also Pumping.

Brick wall filter

A filter that provides a very steep transition between its passband and its stopband. This is required when frequencies that must be passed are close to those that must be effectively stopped, for example in the case of some anti-aliasing filters.

Bridge (1)

The part of a stringed musical instrument on which the strings rest, at the sound board end of the instrument. The vibration of the strings is transmitted to the sound board largely through the bridge. In the case of classical instruments such as a violin, viola or double bass, specialised pick-ups are available for direct attachment to the bridge. In the case of an acoustic guitar, how a contact pick-up is placed in relation to the bridge has a substantial effect on the timbre of the sound that is picked-up.

Bridge (2)

An item of equipment that provides an interconnection between otherwise separate systems. Usually refers either to the interconnection of computers (or computer networks) or to the interconnection of audio equipment with a telephone network, enabling both sides of a live telephone conversation to be heard by the audience. See also Interface and Hybrid (2).

Bridge (3)

To connect or configure an amplifier in bridged mode − see Bridging.

Bridge (4)

An abbreviation for 'meter bridge'.

Bridge (5)

An abbreviation for 'cable bridge'.

Bridge (6)

A specific section of some songs. This section, when present, typically has a significantly different 'feel' to the other sections of the song − it is neither a verse nor a refrain. It most usually occurs just once in the song, and may or may not be included within the vocal part(s). It may sometimes be referred to as a 'middle 8', especially when it occurs near the middle of the song.

Bridge-tied load

See Bridging.

Bridged mode

The mode of a 2-channel power amplifier when it is set for single-channel bridged operation − see the next definition.


A technique to improve the matching between the impedance of a speaker (or the overall impedance of several interconnected speakers) and the optimum load impedance of the available power amplifiers, so as to increase the maximum amount of power that the amplifiers can provide to that speaker(s). It is most useful when it is required to use more of the power-handling capacity of the speaker(s), or more of the power-providing capability of the amplifiers, than could be achieved with a simple amplifier-to-speaker connection.

For example, if an 8 ohm speaker with a peak power-handling capacity of 2 kW is driven from one side of a 2-channel amplifier that can supply a maximum of 1 kW per channel into 4 ohms, but only 500 W into 8 ohms, then the maximum obtainable power into that speaker is 500 W, and clearly both the speaker and the amplifier are under-utilised. If a second identical speaker is available and is connected in parallel with the first one, then a further 500 W could be drawn from the same amplifier channel − this fully utilises that amplifier channel, but each 2 kW speaker can still only receive a maximum of 500 W. The bridging technique brings into play the second channel of the amplifier (assumed to be 'spare'!) and thereby allows the original single speaker to be provided with a maximum power of 2 kW while at the same time fully utilising both channels of the amplifier.

Bridging is possible only when each channel of the amplifier is capable of driving an impedance of one-half of the overall impedance of the connected speaker(s) (without stressing the amplifiers or causing an unacceptable reduction in their maximum power output capability).

It should only be employed if approved by the amplifier manufacturer and if the speakers are suitably rated, otherwise serious damage to the amplifier or speakers may occur. WARNING: The output voltage of bridged high-power amplifiers can be high enough to cause electric shock. The speaker cable used must be suitable for the voltage and current. Properly termed a 'bridge-tied load' connection, frequently abbreviated to 'BTL'. For a more comprehensive explanation, see Bridging on the Amps and Speakers page. See also Series-parallel.

Briefcase engineer

A sound engineer who has responsibilities only for mixing the sound (usually front-of-house sound), not for designing, assembling, modifying or dismantling a system, or for correcting physical faults. The term is sometimes used somewhat disparagingly by roadies or by other engineers having wider responsibilities, because such an engineer has to carry nothing heavier than a briefcase and/or because he/she doesn't "get their hands dirty" (in a similar sense to other briefcase-carrying personnel such as office workers). However, there are many situations in which it may be appropriate to use a briefcase engineer, for example when it has been established that a system has been properly designed and assembled, and other personnel can be called upon to correct faults or make physical alterations as required. See also Handover.

British EQ

Supposedly, an equaliser of a design popularised by British mixer manufacturers. In reality, a marketing term with little or no technical meaning.

British terminology

There are some differences in the PA-related terminology used in the UK, as compared to the USA. The most significant of these differences are listed under American terminology. As PAforMusic is a UK-based site, this glossary uses British spelling and the definitions reflect British usage and engineering practice. Where differences exist between British and American terminology, they are generally noted in the relevant entries of the glossary.


Describes a communications medium offering a high bandwidth.


An undesirable brief reduction in the voltage of the mains supply, typically caused by a fault occurring (possibly many miles away) within the power distribution network. Such reductions in voltage can have an adverse effect on the operation of equipment, which in some cases may be seriously disruptive. For example, power amplifiers may briefly enter 'Protect' mode and unprotected processor-based equipment may re-boot.

Brownouts typically last for less than 5 seconds, as within this time automatic equipment in the distribution network will usually have operated to clear the fault. The name arises from the effect of the voltage reduction on the light produced by incandescent lamps, which may be seen to change from 'white' to 'brown' during the brownout. See also Uninterruptible power supply and Power conditioner. Compare Blackout (3).


An abbreviation for 'British Standard', the prefix of the codes that are used to identify British Standards. See, for example, the following definitions. See also BS EN and BSI.

BS 1363 outlet

A standard UK 3-pole mains outlet, commonly referred to as a '13 amp socket' as its maximum current rating is 13 amps. These outlets accept BS 1363A plugs incorporating a fuse, one purpose of which is to protect the socket outlet against overload (see the next definition). BS 1363 outlets in fixed wiring installations are commonly installed on a ring main distribution circuit, and usually are either 'single' or 'double' types. The maximum current rating of most double types is 13 amps in total across both sockets (not 26 amps as is commonly thought), although a few models have a total rating of up to 20 amps.

BS 1363A connector

A standard UK 3-pole mains plug, incorporating a fuse. These are commonly referred to as '13 amp plugs' as their maximum current rating is 13 amps. The suffix 'A' refers to the version of the specification requiring insulated sleeving on the Live and Neutral pins, however as plugs without this sleeving are no longer available the suffix is often dropped.

Fuses used in this type of plug must be to BS 1362 and are available in ratings of 2A, 3A, 5A, 7A, 10A and 13A (of which the most popular are 3A, 5A and 13A). For adequate protection against the risk of fire, it is essential to ensure that plug fuse ratings are properly co-ordinated with the maximum current rating of the associated cabling and connectors, for example in accordance with BS 7671. Blown fuses must always be replaced with one of the correct type and rating. See also Mains cable/lead, Ring main, CEE-form and IEC 320.

View BS 1363A image

BS 4343 connector

See CEE-form connector.

BS 7594

A Code of Practice for the installation of induction loop systems in the UK. Internationally, standard IEC 118-4 (EN 60118-4 in Europe) also applies. See also BS 8300 and BS EN 60118-4.

BS 7671

The specification of requirements for fixed electrical installations in the UK, published by the IET. Informally known as the 'IEE Wiring Regulations', or, more recently, as the 'IET Wiring Regulations'. See also BS 7909, Periodic inspection (and test), PAT and National Electrical Code.

BS 7909

A code of practice for the safe provision of temporary electrical power distribution arrangements for entertainment and related purposes. BS 7909 applies only to distribution arrangements that are constructed by using pre-terminated and pre-tested cables to interconnect pre-assembled and pre-tested distribution units. A guidance book is available from the IET, entitled 'Temporary Power Systems: A guide to the application of BS 7671 and BS 7909 for temporary events'. See also BS 7671, PAT and the Safety page.

BS 8300

A specification of the requirements for buildings and other designed spaces in the UK to be fully inclusive to those with disabilities, including the provision of assistive listening facilities (e.g. induction loops) for the hard of hearing. BS 8300-1 relates to the external environment and BS 8300-2 to buildings. This standard must be applied in conjunction with the requirements of the Equalities Act 2010, Part M of the Building Regulations, BS 7594 and BS EN 60118-4. Assistive listening facilities are most often provided by means of an induction loop system, because most types of personal hearing aid have built-in loop receivers (see T setting). However, other assistive means are sometimes appropriate, such as systems using infra-red or radio, speech-to-text display services, or sign-language interpretation facilities.


An abbreviation for 'British Standard European Number', the prefix of the codes that are used to identify British Standards harmonised with European standards. See, for example, the following definitions.

BS EN 60118-4

A standard for the performance of induction loop systems. It specifies requirements for the magnetic field strength that will give adequate signal-to-noise ratio without overloading hearing aids. It also specifies the minimum frequency response requirements for acceptable intelligibility and methods for measuring the magnetic field strength, and gives information on appropriate measuring equipment.

BS EN 60309 connector

A mains connector that complies with harmonised British Standard 60309, otherwise known as a CEE-form connector. BS EN 60309 part 1 (60309-1) specifies the general functionality and safety requirements, while 60309-2 specifies the physical requirements, so enabling compatibility between connectors made by different manufacturers. The BS EN 60309 standard replaces BS 4343.


See ITU-R BS.1770.


An abbreviation for 'British Standards Institute', an organisation which sets technical standards for the UK.


The modern telephone line connector used in the UK, originally specified by British Telecom.

View BT431a image


An abbreviation for 'bridge-tied load'. See Bridging.


An item of equipment (usually an amplifier) intended to be connected in the signal path between two other items which cannot be connected together directly. Typically a buffer would be needed when the items of equipment have an incompatibility in level or impedance, or when their direct interconnection would cause the signal to be modified in an undesirable manner. Or, an internal stage of an item of equipment, provided in order to avoid the following stage (or an item of externally connected destination equipment) adversely affecting the signal from the preceding stage (or from externally connected source equipment), but which itself performs no intended modification of the signal − except, in some cases, a change in level or impedance. See also Matching.

Build quality

A subjective measure of the reliability and ruggedness of equipment, regardless of how well it performs its required function when in an 'as new' condition.


A slang term for a lamp, deprecated by lighting engineers.


A bullet-shaped piece often used in the throat of high-frequency horns to improve the acoustic coupling of the compression driver to the horn.

Bum note

A (British) slang term for a musical note that is flat, sharp or defective in some other way. See also Fluff.


To write a data file or a music or video track from a computer's hard drive or other storage device onto a compact disc or DVD. Compare Rip.

Burst error

In the transmission of digital information, bit errors (i.e. a '1' being received when it should have been a '0', or vice versa) do not always occur at a steady rate, but sometimes 'groups', or 'bursts', of errors occur over a short period of time. This is usually caused by some interfering signal of short duration, e.g. by the operation of a power switch. See also Bit error rate.

Bus, Buss

A conductor, or a set of conductors, which interconnect several (often many) sources and/or destinations of signals or power, usually internal to an item of equipment. Power buses are also known as 'rails'.

In a mixer, the term bus (or buss) usually refers to the conductors on which the signals from each channel are summed, forming the mixes; these are therefore sometimes given the more descriptive name of 'mix buses'. In a typical mixer there will be buses for the Left, Right (and possibly Mono or Centre) main mixes (see LCR (1)), for the audio groups (usually arranged in pairs), for the auxiliary (Aux) mixes and for the PFL facility. Channel signals are routed onto the main mix and group buses by the channel routing switches, and onto the auxiliary mix buses by turning up the channel's Aux Send controls.

The term 'bus' is also sometimes used to describe equipment that is meant to be used with a mix, rather than with a single channel's signal. For example, see Stereo bus compressor.

Within a computer or computer-controlled equipment, a data bus is a set of conductors enabling the interchange of data between any of the parts of the system that are connected to it. See also USB.


Describes a class of filter having the minimum possible amount of variation (or 'ripple') of attenuation over the whole width of its passband, a so-called 'maximally flat' amplitude response. Named after the person first to document this design. Often used for crossovers. See also Chebyshev and Bessel.


A trademarked name for an ultra-bass transducer that, when mechanically coupled to a chair or floor, enables a performer to feel (rather than hear) extremely low frequencies. It is available in various versions, to suit applications ranging from home entertainment to concert stages. Typically used for drummers (coupled to a drum stool) or for bassists (coupled to the floor), the 'Concert' version has a quoted response down to 5 Hz. Note that its quoted impedance is only 2 ohms so the power amplifier used to drive it must be suitable to drive that impedance value. For further details see the manufacturer's website: www.thebuttkicker.com (this link opens in a new window).


See Hum. See also Fret buzz.

BV, BVs, BVox

Abbreviations for 'backing vocals', an alternative term for 'background vocals' (BGV). Compare LV.


An abbreviation for 'broadcast wave format', an audio file specification based on the original WAV format, designed for use in broadcasting applications. It incorporates the facility for metadata such as the file creator's name, date of creation, etc.


A switch whose purpose is to enable the usual function of an item of equipment (or a part of it, such as an equaliser) to be made ineffective. Operation of such a switch allows signals to pass through the equipment unaffected by that function, regardless of the settings of the other controls associated with that function. An effect unit is said to be in bypass mode when its effect function has been disabled (usually intentionally). Unless a unit has a power-off bypass feature, it may be necessary for the equipment to be switched on in order to be able to pass signals in bypass mode. See also True bypass.


A group of 8 bits. When the term is used as a unit, i.e. preceded by a value, it is commonly abbreviated to 'B' (note upper case, to distinguish from 'bit'). Alternatively known as an 'octet'. See also Nibble and Word.

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This page last updated 24-Dec-2020.