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Glossary of PA Terms - T

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The glossary pages provide definitions for over 2270 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.

T-bar * T-position * Tab * Tail * Tails * Talent * Talkback * Tap * Tape equalisation * Tape hiss * Tape noise * Tape return * Taper * Tapping * TCMCC * Tech * Tech-head * Techie * Technical earth * Technical ground * Technical rider * Technophobe * Telephone jack * Telescoping shield * Tempo * Temporal * Temporised fuse * Terminal * Termination * Test signal * Test tone * TFT * THD * Thermal cut-out * Thermal noise * Thermal protection * Thiele-Small parameters * Thin * Third * Third harmonic * Third-octave * Third-order * Thread adaptor * Three-phase * Three-to-one rule * Threshold level * Threshold of hearing * THRO * Throat * Throw * Throw-to-width ratio * THRU * Thump protection * Tie-clip microphone * TIM * Timbre * Time alignment * Time code * Time difference stereo * Tinned conductor * Tinnitus * Tinny * Tiny Telephone jack * Tip * Title * TN-C-S * TN-S * TOC * Tolerance * Tonal colouration * Tone * Tone arm * Tone control * Top * Top end * Top hat * Toppy * Toroidal * TOSLink * Total harmonic distortion * TPI * Track * Trafo * Trailing edge dimming * Transducer * Transformer * Transformer balanced * Transformerless * Transients * Transient intermodulation * Transient response * Transondent * Transparent * Transport * Trapezoidal * Travel * Treble * Tremolo * Tri-amping * Triaxial cable * Trim * Trimmer * Trip * Trip switch * Trough * TRS * True condenser * True diversity * Trunking * Truss * TS * TSR * TT * TT jack * Tube * Tube amplifier * Tube bass * Tuning * Turnaround * Turnover frequency * Turntable * Tweak * Tweeter * Twisted pair * Tx * Type-A jack * Type-B jack

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.

T-bar
A horizontal metal bar, the centre of which fixes to the top of a floor stand. Commonly used as a mounting bar for lanterns, in small stage lighting rigs. See also Lighting bar.

T-position
The position to which the switch on a hearing aid must be set in order for the wearer to benefit from an induction loop. The original purpose of this switch was to activate a telephone pick-up coil in the aid, enabling the wearer to obtain a clearer sound from a telephone receiver (hence the marking 'T', which stands for telephone or telecoil).

Tab
A theatre curtain. (Usually used in the plural.) See also House tabs.

Tail
In reverberation, the decaying sound that continues after the original sound has ceased. (For the plural form, see the next definition.)

Tails
The set of individual cables which separate out at the mixer end of a multicore, each one having a connector (usually an XLR) suitable for connection to the mixer or patch bay. (For the singular form, see the previous definition.)

Talent
A performer or performers; an artist or artists.

Talkback
A facility whereby a sound engineer located at the mixer is able to talk to personnel on stage, typically via the monitors. Some mixers are additionally provided with a Clearcom interface. See also Comms.

Tap, Tapping (1)
A transformer terminal which connects to a point part-way along one of the windings of the transformer, rather than to the end of one of the windings. By wiring to the appropriate tapping, the required transformation in voltage, current or impedance may be selected. A tap located mid-way along a winding is called a 'centre tap', and a transformer having such a winding may be referred to as a 'centre-tapped transformer'. See also 100 volt line.

Tap, Tapping (2)
A facility that enables a timing parameter (such as the repeat time of a delay effect) to be set by repeatedly activating a sensor − usually a switch of some kind or a small microphone built into the unit − rather than by changing the position of a physical control or the setting of a digital parameter value. Or, the process of using such a facility (as in "tap it in"). Or, a connection point for a remote tap device such as a footswitch.

Tape equalisation
In analogue tape recording, the fixed equalisation that is applied, as part of the recorder/player's internal processing, to the signal(s) being recorded. An exactly opposite equalisation is applied on playback, to give an overall flat response.

The main purpose of this process is to boost the level of the treble frequencies on the tape and so enable the reduction of tape hiss in the playback equalisation, so improving the signal-to-noise ratio of the played back signal. For correct reproduction on playback, it is essential that the playback machine uses (or is set to) the same equalisation standard that was used when the tape was recorded.

For reel-to-reel tapes, either NAB or CCIR equalisation is normally used. The equalisation for ferric (Fe) cassette tapes is referred to as '120 µs' (micro-seconds), whilst for chromium dioxide (CrO₂) cassette tapes it is '75 µs'. See also Bias.

Tape hiss
See Tape noise.

Tape noise
In analogue tape recording, the hiss that is generated on playback as a result of random aspects in the magnetisation of the tape particles. See also Noise reduction and Tape equalisation.

Tape return
An input on a mixer, intended for the connection of a tape deck used for playback purposes. It is usually a stereo input, and often has less equalisation and routing facilities than the mixer's channel strips.

Taper
The nature of the variation in level obtained as a potentiometer (whether of the sliding or rotary type) is moved from one end of its travel to the other.

There are many kinds of taper in use, but the one most usually used for faders is a 'modified logarithmic' (or 'modified log') taper, in which, from any point in the upper two-thirds or so of the travel, a given amount of physical movement produces approximately the same change of level in decibels. This is the so-called 'audio taper', generally referred to as the 'A taper', and gives about 15% of voltage level (−16 dB) at its mid position, as compared to 10% (−20 dB) for a true logarithmic taper.

The two other most common kinds of taper are the linear or 'B' taper, in which the percentage voltage level is directly proportional to the physical position (i.e. 50% at the mid position), and the special 'MN taper' used in balance controls.

Tapping
See Tap.

TCMCC
An abbreviation for 'threaded cylindrical multi-pin coupling connector'. A class of connector used for multi-circuit mains supplies and other multi-circuit interconnections. See also Socapex. Compare QTBMC.

Tech
See Techie.

Tech-head
A slang term for a person who is very knowledgeable about technical things, and/or is experienced in their use. Particularly applied to computer-based equipment. Pronounced "tek-head". See also the next definition, also Guru and Soundie. Compare Technophobe.

Techie, Tech
A slang term for a technician; a person who is competent in the use, installation and/or repair of technical equipment, within their own particular field(s) of knowledge. For example, a soundie, a lampie, a repair technician, etc. The term 'techie' is more prevalent in the UK, and 'tech' in the USA. Pronounced "teky" and "tek", respectively. See also the previous definition.

Technical earth, Technical ground
A common signal earth connection point for all the equipment of a system (or sub-system), intended to provide a "clean" earth connection that is used only for the earthing of signal-cable screens and equipment chassis and racks that have no other galvanic connection path to earth. Its purpose is to provide a signal earthing arrangement that is uncontaminated by the mains-related earth currents and noise that are usually present on safety earth connections. Ideally, the technical earth is provided by a connection to a local earth rod that is entirely independent of the system safety-earthing arrangement. It is alternatively known as a 'functional earth'.

To be most effective, care must be taken to ensure that the technical earth connection is not used as the safety earth for any item of mains-powered equipment, and that the technical earth is not accidentally linked to the system safety earth. (The latter could, for example, occur if an item of Class II equipment, whose chassis has been connected to the technical earth, has a signal cable interconnection to an item of Class I equipment whose chassis is connected to the safety earth − assuming that the signal earth of both items of equipment is internally connected to their chassis, as is commonplace for radio-frequency screening purposes).

If an alternative strategy is adopted in which the technical earth also provides safety earthing, it is essential that the technical earth arrangements meet the relevant safety requirements for a safety earth (notably, the requirements for reliability and a sufficiently low impedance to the general mass of the Earth.

Comprehensive technical earth arrangements are usually only found in fixed installations such as studios, because of the practical difficulties of providing a separate earth rod and of ensuring that unwanted earth interconnections are not accidentally created through signal cables, equipment rack bolts, etc.

N.B. Every item of Class I mains-powered equipment must have its own independent safety-earth connection to an suitable safety earth point. (Usually this is achieved through the mains power cable and mains plug of the equipment, and the mains power distribution arrangements of the system.) WARNING: Never disconnect any safety-earth connections. 'Ground' is an alternative term for 'earth', and is the more common term in the USA. See also Balanced mains.

Technical ground
The US term for a technical earth (but is increasingly used in the UK).

Technical rider
A specification of what is expected of a venue by a performer, band, etc., particularly (but by no means exclusively) with regard to the technical facilities required. Usually forms part of the contract between the performer and the promoter of the event, and any variations from the specified requirements must be agreed with the performer well in advance of the event date. Often abbreviated to 'rider' by technical staff.

Riders vary widely in content and detail, but could typically include any or all of the following:

• A list of the equipment (sound, lighting, musical instruments, special effects, etc.) that the performer expects the venue to provide.
• A list of the equipment that the performer will bring to the venue.
• Minimum stage dimensions.
• Stage layout − location of performers, musical instruments (especially large items such as drum kits and pianos), backline, microphones, monitors, monitor mixer, etc.
• Riser requirements (size and height).
• Technical guidance for the venue's sound engineer and/or monitor engineer, such as channel allocations, monitor mixes, EQ settings, compressor patches and settings, etc.
• Technical facilities required, such as playback of tapes, CDs, Mini discs or DVDs; recording facilities; stereo or multi-channel speaker systems for special effects; etc.
• Mains power requirements, for on-stage equipment and/or for monitors / front-of-house PA / stage lighting.
• Lighting plots.
• Follow-spot requirements.
• Front-of-house speaker location requirements.
• House mixer location requirements.
• Cues for lighting changes, playing of pre-recorded tracks, triggering of special effects, etc.
• Crew to be provided by the venue.
• Set up and tear down timings.
• Piano tuning requirements.
• Transport and parking requirements.
• Security requirements.
• Green room facilities and refreshment/catering requirements.
• Requirements concerning supporting acts.
• Product promotion facilities required.
• Overnight accommodation requirements.

Technophobe
A person who has an irrational fear of technology, and/or of technical equipment. For example, a performer who is unreasonably nervous about the use of microphones, monitors, etc. Compare Tech-head.

Telephone jack
For the telephone connector, see BT431a. For the audio connector, see Jack.

Telescoping shield
Usually describes a cable whose screen (otherwise known as a shield) is connected to the relevant signal earth terminal of the connector at only one end of the cable. At the other end of the cable, it is unconnected. Such cables are sometimes used in an attempt to resolve earth loop problems in balanced interconnections, although in correctly designed systems this approach should not be necessary − and should be avoided as it can be the source of other problems such as radio-frequency interference (RFI) or signal crosstalk. Furthermore, where a signal earth must be disconnected this can often be achieved by use of an earth lift switch on an item of equipment. On an unbalanced or semi-balanced interconnection the cable screen should always remain connected at the source end of the cable, to provide a return path for current flowing through the capacitance between the hot conductor and the cable screen; this current will otherwise take an unknown path and may cause problems through common impedance coupling.

The term arises a) from the effectiveness of the screen gradually diminishing over the length of a cable connected in the way described above, but more graphically b) from the (very rare) use of a special type of cable having two concentric screens that are insulated from one another (i.e. a triaxial cable). In a telescoping shield arrangement using this type of cable, just the inner screen is connected to the connector's signal earth terminal at the source end, and just the outer screen is connected to the connector's signal earth terminal at the destination end. This arrangement provides better RFI performance than is obtained with a single screen disconnected at one end, because of the distributed capacitance that exists between the two screens. (The two screens are physically reminiscent of the two concentric tubes of a typical hand-held telescope.) See also Directional cable.

Tempo
The speed at which music is played, usually specified in beats per minute (BPM). See also Click and Bar (2).

Temporal
Describes something that relates to time. Compare Spatial.

Temporised fuse
A fuse that is designed to cater for short-term currents somewhat above its rating, without rupturing ('blowing'). Also referred to as a 'slow blow' or 'time delay' fuse. Such fuses are usually marked with a rating prefixed by 'T', for example T5A for a 5 amp rated fuse. The US spelling is 'temporized'. This type of fuse contrasts with 'normal' or 'fast' types, which are usually marked with an 'F' prefix (e.g. F5A).

Terminal
A point to which the conductor of a single core of a cable (or, less often, a wire) is securely connected − usually by soldering, screw-compression or crimping. Terminals are most often encountered inside the connectors attached to cables, but in some cases are fixed to the exterior (usually the rear) of equipment − see, for example, Binding post and Barrier strip. See also High resistance connection, Oxidation and Dry joint.

Termination (1)
The physical method of connection at the end of a cable, or the location of its destination. Examples of this usage are: "I need a cable with a BNC termination", or "Where is this cable terminated?". A cable, or a circuit (or line) within a cable, that is neither wired to a connector nor directly to any equipment is said to be 'unterminated'.

Termination (2)
A resistive load, connected at the destination end of an impedance-matched interconnection such as video, digital audio and DMX lighting control. Its purpose is to provide a load impedance equal to the source impedance and to the characteristic impedance of the cable, thereby reducing reflections of the signal back down the cable. An example of this usage would be: "This circuit requires a 75 ohm termination".

An impedance-matched circuit that is connected to an appropriate terminating load is said to be 'terminated', whilst one lacking an appropriate termination is said to be 'unterminated'. Usually the required termination is provided by circuitry within the equipment to which the signal is supplied. A switch may be provided which enables such an internal termination to be disconnected, allowing a daisy-chained 'through' connection of the feed to further items of equipment. In such cases care must be taken to ensure that the termination is connected at only the last item in the chain. (An example of this arrangement is where several lighting fixtures are connected to a single DMX control feed.) In the absence of such a facility, a distribution amplifier must be used if an impedance-matched signal source is required to supply several destinations. See also Double termination and Return loss. Compare Open-circuit (1).

Test signal, Test tone
See Tone (2).

TFT
An abbreviation for 'thin film transistor'; used mostly in the context of LCD displays.

THD
An abbreviation for 'total harmonic distortion'.

Thermal cut-out
A protective device, internal to an item of equipment, which operates at a preset temperature to shut down the operation of the equipment (or of a part of it) and so prevent the temperature from rising to a value which would damage the equipment. Such devices may reset automatically when the temperature falls to a sufficiently low value, or may require manual resetting. (Some devices, however, which operate at very high temperatures for back-up purposes, are non-resettable and must be replaced if their operating temperature is exceeded).

Most often encountered in power amplifiers, especially high-power types, to monitor the temperature of the output stages (and/or of the internal power supply). In such cases a front-panel indication is usually provided to warn the user when the thermal cut-out has operated − this is usually due to prolonged overload or to connection of an inappropriately low load impedance at the speaker output(s). See also Dissipation.

Thermal noise
The noise that is generated in a resistance by virtue of the random motion of the atoms that make up the material. It is usually heard as a hiss. The description 'thermal' arises because the extent of this motion increases with rising temperature. More properly, it is called Johnson's noise, after the person that first documented it.

The RMS noise voltage generated is (4kTBR)^½, where k is Boltzmann's constant (1.38 x 10⁻²³), T is the absolute temperature (i.e. degrees Celsius + 273), B is the bandwidth of interest (in Hz) and R is the resistance (in ohms). For example, the thermal noise level in a bandwidth of 20 kHz from a 600 ohm resistor at 20°C equates to −125 dBu unweighted (approximately −130 dBu A-weighted). The noise level increases by 3 dB for each doubling in source resistance, so (for the same temperature and bandwidth) would be approximately −128 dBu from 300 ohm and −113 dBu from 10 kohm (both unweighted).

Ideally, the equivalent input noise (EIN) of a microphone pre-amplifier would be no more than a couple of dB higher than the source noise level. See also Microphone Noise Levels on the Microphones page.

Thermal protection
See Thermal cut-out.

Thiele-Small parameters
The method of stating driver specifications that was devised by A. N. Thiele and R. Small, who did much of the foundational research into ported speaker enclosures.

Thin
Describes (subjectively) musical sound or speech that is lacking in 'body' and 'depth', typically due to a lack of bass and/or lower mid-range frequencies. Compare Phat.

Third
An interval of musical pitch that corresponds to a frequency ratio close to 1.25 (in practice the value is closer to 1.26). So, two frequencies are said to be a third apart when one frequency is around 11⁄4 times (or, of course, 4⁄5 of) the other.

For the musically minded, a third is so-named because this interval is reached at the 3rd note of a tonic musical scale. Between the lowest and highest of these 3 notes are 2 intervals, each of one tone. Since a tone is a ratio of the sixth root of 2, we can see that multiplying out these 2 intervals (i.e. 2^1/6 x 2^1/6) gives a resulting ratio close to a value of 1.25, i.e. a third. See also Octave. Compare Fifth.

Third harmonic
A harmonic whose frequency is three times that of the fundamental. It is most commonly encountered as a type of distortion. Compare Second harmonic.

Third-octave
Describes a graphic equaliser whose controls provide adjustment of frequency bands that are spaced a third of an octave apart. For further details see Graphic equaliser.

Third-order
See Order.

Thread adaptor
A device which enables incompatible threads of microphone stands, microphone clips, booms, etc. to be screwed together. The three most usually encountered threads are 5⁄8″ 27 threads per inch (sometimes referred to as an American thread), 3⁄8″ Whitworth thread (sometimes referred to as a Euro thread), and (less often) 1⁄2″.

Three-phase
See Phase (3).

Three-to-one rule
See 3-to-1 rule.

Threshold level
A level which acts as a boundary between two different behaviours or responses. That is, something acts differently depending on whether the actual level is above or below this level. Most usually encountered as a control on dynamics processors. For example, on a compressor it determines the level above which compression occurs. See also Knee, Limiter, Noise gate, Expander and Squelch.

Threshold of hearing
See dB SPL on the Decibels page.

THRO
See MIDI.

Throat
The flared part of a horn, to which a compression driver is attached.

Throw
The distance between a source of sound or light and its intended target, for effective operation. For speakers, the relative terms 'short throw' and 'long throw' are used to identify the intended application.

For video projectors and for some types of lanterns, the throw is adjustable (within the limits necessary to maintain focus) − see the next definition.

Throw-to-width ratio
The throw of a video projector divided by the width of the projected image. Usually, for a particular projector or lens, the throw-to-width ratio is adjustable between two limits − outside of which the image cannot be brought into focus. Therefore a throw-to-width ratio range is usually quoted for such equipment.

THRU
See MIDI.

Thump protection
See Speaker protection.

Tie-clip microphone
See Lavalier.

TIM
An abbreviation for 'transient intermodulation'.

Timbre
The tonal qualities of a sound (as opposed to its level). This is determined by the relative degree to which various harmonics are present in the sound. Most often used in the comparative description of the sound produced by acoustic instruments. See also Formant.

Time alignment
The introduction of a delay into one or more signals that drive power amplifiers, in order to compensate for other 'accidental' delays and so reduce the difference in time between the arrival of the corresponding sound waves at the listening location(s). Such 'accidental' delays may occur for one or more reasons, typically:

• A difference in distance between a listening point and two or more speakers at different locations.
• A difference in the response time of speakers covering different frequency ranges, e.g. due to the design of the enclosures.
• A difference in the signal delay of the different frequency ranges through the crossover(s) (whether active or passive).

Time code
A digital means of representing time (often elapsed time, rather than true clock time). See SMPTE, MIDI time control and Absolute time code.

Time difference stereo
See A-B pair.

Tinned conductor
An electrical conductor, typically of copper, that is manufactured with a very thin coating of tin, or a tin-based alloy, in order to prevent surface oxidation of the copper. In the case of stranded cores, each individual strand is separately tinned. The tinned design is used with some cable conductors and wires that are intended for soldering, as the absence of surface oxidation makes soldering easier and helps to avoid dry joints. Problems with oxidation are also reduced at spring-pressure terminals and binding posts.

Tinnitus
The sensation of a continuous sound in one or both ears, typically a buzzing sound, a steady note or a whistle, when no such sound exists in reality. Tinnitus may be permanent or temporary, typically occurring following an exposure to potentially damaging sound levels. It may only be evident when ambient sound levels are low. For further information see About Sound Levels on the Decibels page. See also Audiology, NIHL and SNHL.

Tinny
Describes a sound that is lacking in bass (or, less often, that has an excess of treble). See also Toppy.

Tiny Telephone jack
See Jack.

Tip
See TRS.

Title
A single complete recording on a DVD (equivalent to a compact disc 'track'). Titles are sub-divided into chapters.

TN−C−S
Describes a mains supply earthing arrangement recognised by BS 7671, the British wiring regulations. In this arrangement, the main safety earth connection of the electrical installation is provided by the electricity supplier through the same incoming supply conductor as provides the Neutral connection − i.e. effectively a 'combined neutral and earth' conductor is employed in the incoming supply. However, independent Neutral and safety earth conductors must be employed throughout the distribution cabling of the installation; the connection between them is made only at the incoming supply point. Also called a PME (protective multiple earthing) system. See also Bonding and BS 7909. Compare TN−S and TT.

TN−S
Describes a mains supply earthing arrangement recognised by BS 7671, the British wiring regulations. In this arrangement, the main safety earth connection of the electrical installation is provided by the electricity supplier through a separate earth conductor (usually the metallic armouring of the incoming main supply cable), independent of the supply's incoming Neutral conductor. The connection between Neutral and safety earth is typically made at the supply substation transformer. See also BS 7909. Compare TN−C−S and TT.

TOC
An abbreviation for 'table of contents', the area on an audio compact disc or mini-disc that indicates where on the disc the recorded tracks can be found. See also Finalise and PMA.

Tolerance
The degree to which an actual value may deviate from a nominal value. It is usually expressed as a percentage.

For example, a voltage may be specified as 20 volts ± 15%. This means that although the nominal value of the voltage is 20 volts, in practice it may be anywhere between 20 volts − 15% (i.e. 17 volts) and 20 volts + 15% (i.e. 23 volts). Sometimes different '−' and '+' tolerances are specified, e.g. 20 volts − 10% + 5%, which would indicate a possible value between 18 and 21 volts.

Tolerance values of electronic components such as resistors and capacitors are either marked as part of the colour code, or by using one of the following letters:

• M  20%
• K  10%
• J   5%
• G  2%
• F  1%
• D  0.5%
• C  0.25%
• B  0.1%

As there is little point in manufacturing close-together values of component that have a wide tolerance, sets of 'standard series' of values are used, according to the tolerance of the components. These series, for each decade of values, are as follows. (The tolerance indicated below for each series is a maximum figure, for example the E24 series may be available with 2% or even 1% tolerance.)

• E6 (20%): 100 150 220 330 470 680
• E12 (10%): 100 120 150 180 220 270 330 390 470 560 680 820
• E24 (5%): 100 110 120 130 150 160 180 200 220 240 270 300 330 360 390 430 470 510 560 620 680 750 820 910
• E48 (2%): 100 105 110 115 121 127 133 140 147 154 162 169 178 187 196 205 215 226 237 249 261 274 287 301 316 332 348 365 383 402 422 442 464 487 511 536 562 590 619 649 681 715 750 787 825 866 909 953
• E96 (1%): 100 102 105 107 110 113 115 118 121 124 127 130 133 137 140 143 147 150 154 158 162 165 169 174 178 182 187 191 196 200 205 210 215 221 226 232 237 243 249 255 261 267 274 280 287 294 301 309 316 324 332 340 348 357 365 374 383 392 402 412 422 432 442 453 464 475 487 499 511 523 536 549 562 576 590 604 619 634 649 665 681 698 715 732 750 768 787 806 825 845 866 887 909 931 953 976

It is useful to note that, when components having the same tolerance are interconnected in any series or parallel combination, the resultant combined value has that same tolerance value.

Tonal colouration
See Colouration.

Tone (1)
The relative degree to which various frequencies are subjectively perceived to be present in a sound. Or, the subjective effect that an item of equipment (especially a speaker) has on a sound by way of its reduced or emphasised handling of particular frequency ranges. See also Tone control, Timbre, Colouration and Frequency response.

Tone (2)
A continuous repetitive-waveform test signal, usually of a constant known level and frequency, which is typically used to check the operation of equipment and cables, and to align operating levels between different items of equipment. It is often a sine wave. See also Line-up (2), Gain structure, Oscillator and SOL.

Tone (3)
An interval of musical pitch, six of which make up an interval of one octave. In terms of frequency, a tone increase in pitch represents a multiplication factor of a sixth root of 2 (approximately 1.122). A half of a tone is a semi-tone.

Tone arm
The moving arm of a record deck, which supports the cartridge and exerts the appropriate vertical and lateral forces on the vinyl disc, via the stylus.

Tone control
A simple equaliser arrangement, usually giving control over just bass and treble frequencies. See also Baxandall.

Top
A speaker that reproduces the top end of the audio-frequency spectrum. May also be used to refer to a full range speaker, placed on top of the bass bins, when the bass bins are used to supplement the bass output of the full range speaker (rather than to provide the entire bass sound), or are used only to reproduce sub-bass frequencies.

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

Top hat
The hollow insert fitted to the bottom of a speaker to enable the speaker to be placed on top of the pole of a speaker stand, so-named because of its overall shape. Usually sized to accept a pole of diameter 1.375 inches (approximately 35 mm), the most common size for speaker stand poles. Note that this differs from the 1.25 inch (approximately 32 mm) diameter most commonly used for lighting stands. Alternatively known as a pole cup.

Toppy
Describes a sound that has an excess of treble frequencies. See also Tinny.

Toroidal
Describes a type of mains transformer often used in the power supplies of power amplifiers. These transformers have a circular core, giving a 'doughnut-like' appearance, and are usually mounted by means of a single bolt through the centre. N.B. To avoid a short circuit turn on the transformer, it is essential that any metallic contact to the fixing bolt is made at one end only.

TOSLink
A type of connector for optical-fibre cables, typically used for optical S/PDIF interconnections. The name is an abbreviated form of 'Toshiba Link', and is a registered trademark of Toshiba. It is variously written as TOSLINK, TOS Link, TOS-Link, TOS-link, etc. An alternative optical interface standard is the 3.5 mm optical connector.

View TOSLink image  View 3.5mm optical image

Total harmonic distortion
A measure of the amount of distortion present in a signal, expressed as a percentage of the overall level of the signal that is necessary in order to produce that amount of distortion. Often abbreviated to THD.

TPI
An abbreviation for 'threads per inch'. See Thread adaptor.

Track (1)
A section of a longer recording, able to be conveniently played in isolation (especially from a Compact Disc). In the case of an audio recording of music, a track is usually a single whole song (popular music) or a movement (classical music). The equivalent terms for a DVD are title and chapter.

Track (2)
A recording of a single voice or instrument, or a partial mix of such sources, made with the intention of later being combined with other tracks (in controlled proportions, and usually with the addition of effects and other processing) in order to create the final mix.

Such tracks may be recorded simultaneously (e.g. from a band performing at a live event), one at a time, or in groups. Or, a single channel of a stereo or surround sound recording. Or, the physical magnetic impression of any such recording on a tape. See also Reel-to-reel.

Track (3)
The resistive element of a potentiometer. The track is contacted by the wiper of the potentiometer at a point that is determined by the setting of its control knob. See also Dirty (2).

Trafo
A slang abbreviation for 'transformer'.

Trailing edge dimming
See Phase-angle control.

Transducer
Any device which converts energy from one form to another. Microphones and speakers are both examples of transducers. However, note that the term may be used more specifically to refer to the internal part of such a device, in which the conversion of energy actually takes place. In the case of a microphone this would be the capsule, and in the case of a speaker it would be the driver.

Transformer
A device which uses electromagnetic coupling to change the voltage of an AC power source, to change the impedance of a signal, to convert unbalanced signals to balanced ones (or vice versa) and/or to provide galvanic isolation (usually as a safety measure or to prevent a connection between signal earths and so avoid earth loop problems). Sometimes abbreviated to 'trafo'.

It consists of a winding of wire (called the primary winding) into which the supply or signal is fed, and one or more further winding(s) (called secondary windings, or secondaries) from which the output(s) are taken. One or more of the windings (primary or secondary) may be provided with one or more taps. In contrast with an autotransformer, a 'proper' transformer has no internal electrical connection between its windings.

A 'power transformer' is usually used to reduce the mains voltage to the specific voltage required for powering an item of equipment, and to provide isolation from the mains supply (an important safety feature). Note that although the input and output voltages (and currents) of a transformer may be very different, its power input will always be just a little greater than its total power output.

The impedance conversion property is used to enable the matching of the output of an item of equipment to an input which has a different impedance. For example, a passive DI box utilises the impedance conversion, balanced/unbalanced conversion and isolation properties. See also Balun, Toroidal, 100 volt line, Power supply and Balanced mains.

Transformer balanced
Describes an item of equipment's input or output that uses a signal transformer within the equipment to cater for balanced operation of an interconnection to other equipment. The term is usually used to emphasise that balanced operation is catered for by means of such a transformer rather than by means of electronic circuitry. For example, a passive DI box provides its balanced output in this way (and so avoids the need for a source of power to operate it).

Note, however, that balanced operation is possible only when the equipment at both ends of the interconnection, and also the cable(s) and connectors used, are suitable for it.

Advantages of transformer balancing include:

• It can provide a truly floating output or input, i.e. galvanic isolation from the equipment circuitry and from earth.
• A floating output maintains the same output level if one leg of the output is shorted to signal earth.
• Excellent common-mode rejection is possible, providing good immunity to earth loop problems.
• Good immunity to high levels of radio-frequency interference.
• Resilient to damage from large voltage transients, e.g. electrostatic discharges.
• Requires no source of supply power.

• May have a restricted frequency response.
• May have poor low-frequency linearity, causing sub-bass distortion.
• May be vulnerable to inductively coupled interference (e.g. from nearby mains transformers or from CRT computer displays), unless well magnetically screened.
• Relatively high cost.
• Relatively large size and weight.

Transformerless
Describes an item of equipment, or an input or output of an item of equipment, that operates without the use of an internal transformer. Most commonly used to describe a condenser microphone or a balanced input. For further information see Electronically balanced.

Transients
Strictly, very short duration changes in the instantaneous value of a signal's voltage or of sound pressure, often large in magnitude. Their very rapid rate of change means that they contain high frequency components. However, the term is also used to refer to very short-lived peaks in signal level, usually occurring at high frequencies. Common sources of these are percussion instruments and electronic keyboards. See also Slew rate. Compare Spike.

Transient intermodulation
A type of distortion, caused by intermodulation that occurs only during the transients of a signal. Often abbreviated to 'TIM'.

Transient response
The degree to which equipment is able to handle transients. See also Slew rate.

Transondent
Describes a material (such as a windshield fabric) that has little significant attenuating effect on the passage of sound through it. (Of course, what is a 'significant' effect is a matter of opinion!) Or, to be more technically correct, describes a material that is able to pass sound.

Transparent
A subjective term sometimes applied to amplifiers and other equipment, to indicate that its output is apparently a faithful replica of its input. See also Fidelity.

Transport
Originally, the mechanism of a physical recording or playback device, particularly a tape-based device, that supports and controls the motion of the media. However, the term may now also be applied to computer-based recording or playback applications, that use a hard-disk or memory as the storage media.

Trapezoidal
Describes a speaker whose opposite sides are not parallel with each other − most commonly such speakers are wider at the front than at the rear. This allows multiple speakers to be readily positioned in an arc, so forming an array (or cluster) having a large dispersion angle (usually in the horizontal plane).

Such speakers are notoriously difficult to accurately align directionally by walking the covered area and using a simple line-of-sight method, because their (non-parallel) sides do not become visible when the speaker is viewed from slightly off-axis locations, making their axis difficult to determine. Better results are often obtained by visually aligning from behind, or from above or below the speaker.

Travel
The distance that the knob of a slider potentiometer (such as a fader) moves, when pushed between its minimum and maximum settings. Typical values of travel for faders are 45 mm, 60 mm and 100 mm; the band controls of graphic equalisers often have a much smaller travel such as 35 mm, 30 mm or 20 mm.

Treble
A high audio frequency, typically above 8 kHz. A mixer will usually provide the facility to control the relative level of these frequencies separately for each channel, leaving lower frequency ranges essentially unaffected. This facility is usually provided by an equaliser having a shelving response and a cut-off frequency somewhere in the region of 8 to 15 kHz; such a control is often labelled 'HF'.

Appropriate adjustment of the high frequencies is essential for good clarity. A lack of them will produce an 'indistinct' sound, whilst an excess will give a 'harsh' one.

In a full-range speaker, the treble frequencies are handled by one or more drivers called horns or tweeters (depending upon their design). See also Bass (1), Mid-range and Crossover.

Tremolo
A deliberate repetitive variation in the level 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 vibrato (for example, the effect produced by the tremolo bar of an electric guitar is actually vibrato, not tremolo).

Tri-amping
See Bi-amping.

Triaxial cable
An unbalanced cable in which a single insulated central conductor is completely surrounded by a screen, which is surrounded by a layer of insulation and then a second screen which in turn is covered by an insulating sheath. It is so called because all three conductors (the central conductor and the two screens) all share the same axis. Normally used only for video signals in broadcast-quality applications. See also Coaxial cable and Telescoping shield.

Trim (1)
An alternative name for a gain control, favoured by some mixer manufacturers.

Trim (2)
An additional channel level control sometimes provided on digital mixers. This control typically has an identical effect to the channel fader. Its function is to pre-set the effect obtained from a particular setting of the fader; the overall effect obtained is the combined effect of the two controls. For example, if the required relative level in the mix of a particular channel is obtained by a fader setting of −15 dB, then setting that channel's Trim control to −15 dB would allow that same level in the mix to be provided by a 0 dB setting on the fader, making manual restoration of that level (after temporary adjustment of the fader) more convenient. N.B. Do not use channel gain controls labelled 'Trim' (see Trim (1)) in that manner, as they have a different purpose.

Trimmer
Usually refers to a potentiometer located inside an item of equipment, usually having no external means of access for adjustment. It sometimes refers to an internally-adjustable capacitor or inductor.

Trimmers are typically used to make fine adjustments to critical internal operating parameters of the circuitry. The correct initial adjustment is pre-set by the manufacturer of the equipment, so these internal controls are also referred to as 'presets'. To ensure continued safe and correct operation of the equipment, any subsequent adjustment must be made only by skilled persons, using suitable test equipment and an appropriate adjustment tool. See also Quiescent current.

Trip, Trip switch
A slang term for a miniature circuit breaker (MCB).

Trough
The lowest level reached (or expected to be reached) by a sound or by a signal. Or, a reduction in response, especially in frequency response. Compare Peak.

TRS
An abbreviation for 'tip, ring and sleeve', the names of the terminals of a 3-pole jack connector. The sleeve is always used for the signal earth connection. When used as a stereo connector, the tip is for the Left channel and the ring for the Right channel. When used as a balanced connector, the tip is for the 'hot' or '+' connection, and the ring for the 'cold' or '−' connection. When used as an insert connector, the tip is usually for the send connection and the ring for the return connection. Very occasionally the abbreviation 'TSR' (for 'tip, sleeve and ring') is used instead of TRS. Compare TS.

True condenser
See Condenser microphone.

True diversity
See the 'Wired or Radio' section on the Microphones page.

Trunking
A means of containment and mechanical protection for cabling fixed within a building, typically of rectangular cross-section, made of steel or PVC and provided with a removable lid along its whole length to enable the lateral insertion and removal of cables. (This lid must therefore remain accessible after installation.) Due regard must be given to the maximum capacity of the size of trunking being used and to the possible increased heating effect obtained when many cables carrying a substantial current are enclosed together. Metallic trunking for mains cabling must be connected to safety earth. Compare Conduit.

Truss
A long narrow metal structure, usually consisting of 3 or 4 parallel bars which are cross-linked by thinner strengthening members. Trusses are normally used horizontally and are typically used for the attachment of lanterns, other lighting fixtures and sometimes speakers. They may be flown on steel wires or fixed between vertical supports. They are manufactured in standard lengths which can be bolted together to give the required span (subject to the manufacturer's restrictions on maximum span and weight loading), but may also be custom-manufactured to a specified length. See also SWL.

TS
A rarely used abbreviation for 'tip and sleeve', the names of the terminals of a 2-pole jack connector. The sleeve is always used for the signal earth connection. Compare TRS.

TSR
See TRS.

TT
Describes a mains supply earthing arrangement recognised by BS 7671, the British wiring regulations. In this arrangement, the main safety earth connection of the electrical installation is provided by a local earth rod, independent of the incoming supply conductors. The supply Neutral is typically earthed at the supply substation transformer. See also BS 7909. Compare TN−S and TN−C−S. (See also the next definition.)

TT jack
See Jack.

Tube
An American term for a valve.

Tube amplifier
An American term for an amplifier that uses valves.

Tube bass
See Bass (2).

Tuning
In the context of PA systems, tuning a system relates to making adjustments to ensure optimum performance of that system in a particular venue − i.e. taking into account the acoustics of the space. This may include setting delays and graphic equalisers, and balancing the contribution of the various speakers. It may be carried out entirely by use of listening tests, or may include the use of formal measurement and analysis methods such as STI or MLSSA.

Turnaround
An American term for a gender changer.

Turnover frequency
An alternative name for a crossover frequency.

Turntable
A device for playing vinyl records. Also called a 'record deck'.

Tweak
Slang for 'to make a relatively small change or adjustment', especially to the setting of a control.

Tweeter
See Horn.

Twisted pair
A pair of insulated conductors that are twisted around each other throughout their length. Typically, the conductors are part of a cable and are used to carry balanced signals. The twisting reduces differential inductive coupling into the pair from other nearby conductors, and also from the pair into other nearby conductors. Capacitive coupling effects may also be reduced, especially when the pair are unscreened. For further information see Pair. See also UTP, STP and Lay length.

Tx
An abbreviation for 'transmission', or an identification of the transmit (or 'sending') direction of communication. Compare Rx.

Type-A jack
See Jack.

Type-B jack
See Jack.

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This page last updated 07-Feb-2012.