| Glossary of PA Terms - D
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In the list below, the most commonly looked-up terms
are in bold, lighting-specific terms are in
and video-specific terms are in
D-sub or D-SUB *
Damping factor *
Data compression *
Data rate *
dB, dBV, dBv, dBu, dBm, dB FS, dB SPL, dB (A) and dB (C) *
dB per octave *
DC protection *
De-regulated frequency *
Dead blackout *
Dead spot *
Delay speaker *
Destructive interference *
Destructive solo *
DI box *
DI output *
Differential amplifier *
Differential drive *
Differential input *
Diffuse field *
Digital amplifier *
Digital audio *
Digital audio workstation *
Digital black *
Digital cliff *
Digital gain *
Digital mixer *
Digital multicore *
Digital signal processing *
Digital snake *
Digital stagebox *
Digital to analogue convertor *
Digital video *
Dim out *
Dimmer buzz *
Dimmer fizz *
Dimmer noise *
Dimmer pack *
Dimmer rack *
DIN 45405 *
DIN 45412 *
DIN 45573 *
DIN 45596 *
DIN 651 *
DIN noise weighting *
DIP switch *
Direct box *
Direct contact *
Direct current *
Direct inject *
Direct output *
Direct radiator *
Direct sound *
Directional cable *
Directional microphone *
Discharge lamp *
Discrete circuit *
Distance factor *
Distant pickup *
Distributed public address *
Distribution amplifier *
Distribution board *
Divided pickup *
Dog box *
Dolby A *
Dolby B *
Dolby C *
Dome antenna *
Double balanced cable *
Double bass *
Double insulated *
Double normalling *
Double termination *
Downward expander *
Drain wire *
Drum cage *
Drum screen *
Dry hire *
Dry joint *
DSUB or Dsub *
Dual concentric *
Duck tape *
Duct tape *
Dummy load *
Duty cycle *
Dynamic equaliser *
Dynamic microphone *
Dynamic range *
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.
Alternative generic names for any of a number of
different types of
connector having a 'D-shaped'
shell surrounding either
2, 3 or (rarely) 4 parallel rows of pins (in the
male version). 'sub' is short
for subminiature, as at the time of its introduction this
was considered to be a compact form of connector.
In the UK, 'D-Type' was initially the most common term used
for it, but 'D-sub' is now more common.
These connectors are now
most commonly encountered in a 2-row 25-pole form as an
audio connector (usually
wired to the DTRS standard),
and in a 3-row ('high-density')
15-pole form as a 'VGA' connector.
Other variants, incorporating differently-shaped
signal earth pins,
are used for DVI
D-sub connectors are formally identified by a code of the
form Dx-n, where x is a letter indicating the size of the
shell and n is a number (of one or two digits) indicating
the number of poles (not including the shell, i.e.
the number of pins or holes). This may be followed by
the letter M or F to indicate the
For example, DE-15M is a male
VGA connector (though these are sometimes incorrectly
referred to as DB-15M) and DB-25F is a
female DTRS connector.
Various sizes were once in common use for low-speed
serial data interconnections
such as RS-232
(until the advent of higher-speed serial
interconnections such as USB and
IEEE 1394). Initially
the DB-25 was most commonly used for this purpose, but for most
applications was then largely superceded by the DE-9.
See also VGA and
D-sub / D-Type (9 pole) image
An abbreviation for
An abbreviation for 'digital audio broadcasting',
referring to the broadcast of public
digital radio services.
In the UK these broadcasts are in the
frequency range 217.5 to
230 MHz, but some other countries use other
An abbreviation for
to analogue convertor'.
A raised platform area or small stage, from which
lectures, presentations, etc. are delivered.
See also Lectern.
A method of interconnecting several items of equipment
such that an output of
one item feeds the
of a second item, the output of that one feeds a
third item, and so on in succession. Or, where several,
usually identical, items of equipment (generally their inputs)
are each connected at various points along the length of a
common set of cable
by means of a parallel cable
junction at the location of each item, but outside of it.
In the first-mentioned scenario, the term is used
of two distinct cases:
- Where the chained equipment 'outputs' provide an
identical copy of the
signal applied to their
inputs: either by a simple parallel connection between the
connectors inside the equipment
(as in the case of several daisy-chained
speakers fed from a single
or via a buffer
circuit (as in the case
of MIDI interconnections, where
such outputs are usually labelled 'THRO'). Another example
of this case is in DMX lighting
control, where many daisy-chained
lanterns may be separately
addressed through a single
- Where the chained equipment 'outputs' provide a
processed version of their inputs,
as in the case of daisy-chained
units. This interconnection arrangement is commonly used
with guitar pedals.
A reduction of something over a period of time −
especially a deliberate reduction of
echo, etc. that
would otherwise have continued for a longer period.
For example, the damping control on an echo
effects unit controls how
rapidly the echoes die away. Likewise, a pillow may be
placed inside a kick drum
to reduce resonances. The amount of damping of a
resonant system is often specified by a Q value −
see Q (3).
A measure of how well the motion of the
cone of a
speaker is controlled by
the power amplifier
driving that speaker.
If the damping factor is poor (a low number), the
speaker cones will continue to vibrate significantly
after a movement instructed by the amplifier,
and this will considerably impact on sound quality.
For 'Hi-Fi' applications a
sensible target value is 50, although in less critical
PA applications values of around
15 to 20 would usually be considered acceptable
and even as low as 10 may be tolerated. A very high value
may be quoted for an amplifier, but usually it is the
gauge and length of the
that have the most effect.
The overall value is calculated by adding
the output impedance
of the amplifier to the round-trip
of the speaker cable, and then dividing the speaker
impedance by the result of that sum. For example,
if an amplifier having an output impedance of
0.02 ohms is
connected to an 8 ohm speaker by a cable
with a total resistance of 0.05 ohms then the
damping factor is 114. But if the cable resistance
were 0.35 ohms then the damping factor would be
only 22. (As a guide, the round-trip resistance of
2.5 mm² cable is approximately 0.015 ohms
per metre length of cable, whilst for 4 mm²
cable the figure is approximately 0.01 ohms
per metre length). Note that for the calculation to be
accurate at treble
inductance of the cable
must be taken into account as well as its resistance.
See also Series.
A significant likelihood of injury or death
arising from a hazard.
N.B. This definition of the term may
differ from officially recognised definitions.
See also Risk.
For further information on safety see the
A trademarked name for a
over an IP network,
developed by Audinate
(external link, opens in a new window). The audio
interconnections provided by the network may be managed
by a computer connected to it.
Compare AES50 and
An abbreviation for 'digital audio reference signal',
signal used for
equipment. It is usually a
An abbreviation for 'digital audio tape', a
digital tape recording
standard which uses a 'mini cassette' tape format
and a helical scan technique.
The normal sampling rate for 2-track
is 48 kHz,
and the normal
is 16 bits.
However, other sampling rates are possible such as
44.1 kHz (for CD compatibility) and 32 kHz
operation). See also
to digital conversion.
See Compression (2).
An abbreviation for 'digital audio workstation', a
computer-based system for multi-track
audio recording and
the subsequent digital
mixing and processing of the recorded material.
See also Application,
Platform (2) and
dB (A) and
An abbreviation for 'decibel'.
The letter(s) following 'dB',
when present, indicate
the reference level or
For full information and value
conversion calculators see the
An abbreviation for
An abbreviation for
dB per octave
DB-9, DB-15, DB-25
Terms such as these are commonly used to identify particular
styles and sizes of D-sub
connectors (also known
as 'D-Type' connectors). For fuller information see
An abbreviation for
An abbreviation for 'direct current', a
or voltage which
does not reverse its polarity
(and usually has a substantially steady value).
This type of current is produced by batteries; alternatively
it may be converted from the
mains supply by using a
power supply unit (PSU).
It is used for powering
small items of equipment such as
phantom power) and guitar
pedals, and as a means of
remote control (especially in
analogue lighting systems).
An abbreviation for 'Digital Cinema Initiatives',
a standard for
video projection systems.
For a list of common video
VGA. See also the following
An abbreviation for 'Digital Cinema Package',
a file standard for
video projection systems,
orginally developed by Digital Cinema Initiatives to
use with their systems.
Several files are required to make up the
package for a particular film, providing information
for the video and audio
content and for the associated data needed by the
An abbreviation for 'Disability Discrimination Act',
UK legislation requiring (amongst other things) the provision of
facilities where speech-based services are provided to the
general public. Such 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
However, other assistive means are sometimes appropriate,
such as systems using infra-red or radio.
An abbreviation for 'digital delay line',
a delay unit that
(The term 'delay line' originates from an early
analogue delay technique,
in which a long line was
used to provide signal
An item of equipment used to reduce
Its basis of operation is the provision of
that is effective only at high audio
(e.g. greater than 4 kHz), and/or the
To disconnect two compatible
connectors from each other.
The term arises from the description of the connectors as
See also Gender.
The process of applying a lower
rating than the usual
value to an item of equipment or to a component.
This may, for example, be necessary as a result of
the item being operated under adverse environmental
conditions such as an elevated ambient temperature.
If in doubt as to whether or not any de-rating is
necessary in a particular case, consult the
A radio frequency
(e.g. for use by
or in-ear monitoring
that is free for use without any licensing requirement.
As the use of these frequencies is relatively uncontrolled,
interference from other users can sometimes be a problem.
Sometimes referred to as an 'unregulated frequency'.
For further details see
'Wired or Radio'
on the Microphones page. See also
To dismantle a system (such as a PA
system or a stage lighting system) that was erected
temporarily, specifically to meet the requirements
of a particular event. See also
Describes acoustics having a short
Describes a cable, a
mains supply point, etc.,
that is not presently energised
with electrical power.
A slang term describing equipment that is faulty,
usually to such an extent that it cannot be used at all.
See also Blown,
Blown up and
A point during a performance when all lighting that may
safely be switched off, is switched off, for dramatic effect.
This includes any back-stage lighting that may leak onto
the stage or into the
all emergency lighting and fire exit signs must remain on.
Often abbreviated to 'DBO'.
A point in space where a wanted
sound cannot be heard
as well as it can be heard at surrounding points;
typically due to physical obstructions or to the
interference between the sound from two different
sources (e.g. two speakers) or between
two sound paths (e.g. the paths of direct and
reflected sound). The locations and depth of dead spots
are likely to be heavily influenced by the location
and orientation of the speakers and, where reflected
sound is involved, by the
Informally, the period of time during which a
sound dies away
to silence. In this context, the notes produced by many
musical instruments (especially
instruments such as the guitar)
have a long decay time, in comparison with their
However, as a formal
parameter in the
definition of sound envelopes
the precise meaning of the term is different − see
This term may sometimes be used to refer to the
release control of a
A unit of relative measurement of effective
power, on a
For a comprehensive explanation and value
conversion calculators see the
See also Gain,
In general, an item of equipment for the recording
and/or playback of audio
or video material.
However, the term is frequently
used as an abbreviation for a
alternatively known as a turntable.
See also Vinyl and
A slang term for the floor, often referring to the
An effects unit that
provides delay-based effects
such as echo,
flanging. Or, a term
for such effects themselves. Such effects are most
commonly provided either by comprehensive
delay effects units or by the multi-purpose
onboard effects facilities of
Almost all delay units now function
digitally, and are sometimes known by
the abbreviation 'DDL' (for 'digital delay line').
See also Pedal and
A dedicated unit, or a feature of
management equipment, whose
purpose is to provide a delayed version of a
feeding to "secondary"
speakers that are
situated a considerable distance in front of
so that the sound heard from the secondary speakers is
closely synchronised with the sound heard from the main
The signal delay provided must be adjusted to match
the additional delay undergone by the
sound from the main speakers in travelling through the air
to listeners situated beyond the location of the
secondary speakers, as compared to the delay undergone by the
sound reaching those listeners from the secondary speakers.
As the exact value of that additional delay will vary for
different listening positions, it is necessary to adjust
the unit to provide the best match for the majority of listeners.
Approximately 3 milliseconds of delay is required per
metre of distance between the main and secondary speakers (see
Speed of sound).
Use of a delay unit would not normally be considered
for distances between main and secondary speakers
of less than about 10 metres.
See also the next definition,
Time alignment and
A speaker that is
fed with a
of a signal, as compared to
the signal fed to the
When a number of such speakers are being referred to,
this term is sometimes shortened to 'delays'. See also
See the previous definition.
The process of extracting the modulating
signal from a
i.e. the reverse process to
A device that extracts the modulating
signal from a
i.e. that performs the reverse process to
A device that separates out the component
signals of a
The process of separating out the component
signals of a
The extent to which an effect
such as chorus or
phase impacts upon the
An abbreviation for
Short for 'mixing desk' − see Mixer.
(In wider usage, may also be used to refer to a lighting control
desk, or to any form of control panel in which the controls
are mounted on a horizontal or slightly inclined surface.)
The phenomenon whereby certain
sounds seem to disappear, or to
significantly decrease in level,
at a particular position in a room (or indeed outdoors), even
though there is no physical obstacle in the way. This is
caused by the sound having arrived at this position along
two different paths − e.g. one a direct path
and the other a reflected one − such that the two
versions of the sound are of similar
level but opposite phase.
They therefore effectively cancel each
other out, and no sound (or only a much reduced one)
Since, for a given amount of delay, the phase relationship
varies with frequency,
usually only certain parts of a complex sound will seem
to disappear at a given point in the room −
but other parts may disappear at other points.
See also Dead spot,
and Comb filter.
A feature on a control (rotary or
slider types) which
defines a specific position in its
travel by requiring
a slightly increased mechanical force in order for
the control to be moved from that point.
Most usually, this feature is encountered
as a 'centre detent', a single detent that is provided
at the half-way point in the travel (e.g. on
Occasionally controls may be provided with many
detents, giving a 'click-click-click' feel as the control is
An abbreviation for 'direct inject'. See
An abbreviation for
input', used to
having that function.
See also AES3.
A device, usually used on stage, which allows an
signal source (such
as a keyboard or a combo
line output) to be
to a balanced
input, typically a
of a mixer.
The DI box also provides a
input, so that high impedance sources such as passive
guitar pick-ups can be
connected directly to the DI box if required.
Facilities are usually provided to help avoid
problems, and provision is usually made for adjustment
to the signal level
(often by means of a switchable
attenuator), to allow
a range of source levels to be catered for.
DI stands for 'direct inject',
so called because the instrument, guitar
etc. is connected
'directly' to the PA
system rather than its sound being picked up by
To avoid the need for use of a DI box, some instrument
amplifiers incorporate a DI facility and so provide
a balanced "DI Output"
(usually a male
DI boxes may be passive or active. Passive types
require no power source, and achieve the required
impedance conversion and isolation of the input and
connections by means of a
Active types contain electronic
circuitry which requires
power (supplied from an internal battery,
an external mains power unit
or by phantom powering).
Active types are able to provide a higher
than passive ones and also have the advantage that their
input impedance is unaffected by the
capacitance of the
balanced line or by the
impedance of the load(s)
that the line is connected to − these factors may be
of benefit when connecting high impedance passive guitar
pick-ups without using a pre-amplifier. However, many
active types fail to provide complete electrical isolation
between the input and output (which is only rarely a necessity).
DI boxes are most commonly single
channel units, but two and
four channel types are also available.
Note that use of a DI box is essential when connecting
an unbalanced source to a balanced input that provides
phantom power, or to a balanced line that carries
phantom power, as to make a direct-wired connection
(e.g. using an adaptor plug or cable) would
expose the source equipment to the phantom power
which may cause serious damage to that equipment.
that is intended to be connected directly to a
input, such as a
or to a stagebox input,
allowing the source signal
to be 'directly injected' into that equipment.
DI outputs are most often found on
occasionally on keyboards and rarely on guitars.
The connector is usually
XLR, and is connected
to the PA system using
a balanced cable
(such as a
check the manufacturer's instructions before applying
phantom power to
a DI output. See also
A surface that is intended to capture the motion of
sound waves, and so move
back and forth in sympathy with them. Or, a surface that
is intended to create sound waves by its own back and forth
motion. The former usage of the term is the most common,
and applies when the term is used to refer to the internal
part of a microphone that
vibrates in sympathy with the sound waves entering the
microphone. The latter meaning applies in reference to
a driver − specifically
referring to the internal part of a
horn driver that vibrates in
sympathy with the signal
applied to the driver, so creating sound waves. Other types
of drivers usually employ a conical diaphragm, which is
therefore more commonly referred to as a
In either case, it may also be called a membrane.
Usually, a diaphragm is very thin, and is circular in shape.
Usually refers to the
material between the two plates of a
Common dielectric materials for
capacitors are polystyrene, polycarbonate, polyester,
polypropylene, and ceramic.
types utilise an electro-chemically created dielectric of
The term is also used to refer to the internal insulation
between the inner and outer
of a coaxial cable
− particularly one of defined
impedance, generally used in
that amplifies the difference between the
signals present on its two input
connections (or 'legs'), neither
of which are permanently connected to
The input connections are generally referred to as
'+' and '−' or as 'Hot' and
The term most usually refers to the circuit that provides the
balanced operation of an
balanced input. See also
The type of signal
provided by a balanced
signal output that
legs. Or, a term
used to describe the nature of such an output,
by reference to the type of signal it provides. Note, however,
that not all such outputs behave in the same way under
various conditions of loading
or faulty interconnections. For further information
An alternative term for a
input. Such inputs are either
or transformer balanced.
Electronically balanced inputs operate using a
For further information
The phenomenon whereby
sound waves bend around
objects they encounter on their path. This is a
because it only occurs to any significant degree when the
wavelength of the sound
is larger than the physical size of the object.
The result is that treble
sounds are readily blocked by substantial obstacles in
their direct path, while bass
sounds are not.
See also Refraction.
Describes locations at which
energy from a particular sound source predominates over the
direct sound energy
from that source. Also known as the reverberant field
and as the ambient field (though some would argue that there
are subtle differences between the exact meaning of the
three terms). Within the diffuse field, the
inverse square law
does not apply. Note that within the diffuse field the
direction of the sound source may still be clearly
identifiable to a listener, because of the
Compare Free field.
See also Radius
Critical distance and
Describes anything which functions by means of numbers,
particularly when it is desired to contrast it with alternative
methods of funtioning that operate without numerical
tecniques (see Analogue).
Properly speaking, digital equipment is equipment that
processes, stores or conveys information that is represented
Sadly, the term is much misused, being sometimes applied to
equipment that is not truly digital according to the above
definition, but that merely incorporates a form of internal
or external control making use of digital
numerical) techniques −
or even that is simply claimed to be of a quality suitable
for use with truly digital equipment.
For information on digital audio,
see Digital audio.
A digital recording is one in which the
etc.) is stored as a sequence of numbers.
The storage media may be tape
removable disc (CD, Mini disc
or DVD) or a hard drive.
See also Analogue
to digital conversion,
and the relevant definitions following this one.
Properly speaking, an
accepts a digital
higher-level (and possibly
re-shaped and re-timed) version of that same digital
signal. More usually, such an amplifier is referred to
as a repeater or a
the latter term is strictly appropriate only when re-timing
In reference to audio
which by definition provide an
analogue output suitable
no such equipment as a 'digital amplifier' exists
according to the strictest definition of 'digital'.
Although the audio level represented by a
digital signal may be increased
by numerical means, within the limits of the coding
scheme (see Digital gain),
such an increased-level digital signal cannot directly
drive a passive speaker. In order to drive a speaker,
a power amplifier's primary function is to produce an
analogue signal of sufficiently high
sufficiently high available
and since this cannot be achieved through numerical
processing techniques alone, it is at best misleading
to refer to any power amplifier as one that provides
Nevertheless, the term 'digital amplifier' is commonly
misused to refer to a Class D power amplifier
(otherwise known as a 'switching amplifier'), some types
of which accept a digital input signal and/or make use
of digital processing techniques to produce an internal
PDM switching signal which
drives the output stage
The high-level switched signal so
produced is then subjected to analogue filtering within
the amplifier, in order to produce an analogue signal
suitable for driving speakers.
For more information on that type of amplifier see
modulation. For a list of common amplifier classes, see
Classes on the Amplifiers
and Speakers page.
Describes an audio
signal or recording in
which the audio information is represented in
form (i.e. numerically) rather than in
Or, describes equipment that processes, records or
plays back audio using digital processing or recording
In a digital audio signal, some parameter of the signal
voltage) makes rapid transitions
between just two states, which respectively represent a
'0' and a '1'. This sequence of 0's and 1's contains
a sequence of binary numbers, and the variations in the
value of those numbers indicates the variations in the
regular sample values of
that make up the sound
waveform being represented
by the digital signal (according to some agreed coding scheme).
In the simplest coding scheme, sometimes referred to as
linear PCM, each number
proportionally represents the voltage value of a single sample.
The level of digital signals
is usually expressed in
In a digital audio recording, the audio information
is stored as a sequence of binary numbers, typically including
additional bits to provide for
error detection and recovery and for auxillary data such as
track identity and copyright information.
The storage media may be
magnetic tape (see DAT),
removable optical disc (CD, Mini disc
or DVD) or a hard drive.
See also Digital mixer,
to digital conversion,
A digital audio
signal that represents
silence. Named by analogy with
video signals, in which
black is the lowest possible level of
A term used to describe the effect of decreases in the
quality of a digital
signal, for example,
decreases in its
ratio or increases in the amount of
If the signal quality progressively decreases from 'good'
towards 'poor', the effect on the perceived quality of the
conveyed information (e.g.
programme material) is
initially very slight, but at a specific signal quality
value the perceived quality of the conveyed information
abruptly reduces dramatically.
This is in marked contrast to the effect of an equivalent
progressive reduction in the quality of an
analogue signal, which is a
gradual reduction in the perceived quality of the
conveyed information. The term 'digital cliff' arises from
the cliff-like shape of a graph of conveyed information
quality against digital signal quality.
A control that, using numerical processing techniques,
operates on a digital
signal internal to an
item of equipment so as to enable adjustment
of the digital signal level
at that point. Such a change in
digital level does not in any way affect the
voltage level of a
digital signal passed over electrical interconnections
between items of equipment − it affects only
the numerical values conveyed by that signal.
When the digital signal is eventually converted to
an analogue one,
a corresponding change in the voltage level of that
analogue signal will occur (in the absence of other
factors affecting it).
As with other kinds of change in signal level, when
adjusting digital gain
care must be taken to avoid increases that would
bring the digital level to the point of
during signal peaks or
In the case of a digital signal, the clipping point
(0 dB FS) is
determined not by the maximum signal voltage
accommodated by the processing
circuitry, but rather
by the format of the
digital signal at that point. To avoid the possibility
of clipping, adequate
headroom must be
maintained at all points throughout the entire
during both analogue and digital processing.
Note that a digital gain control is unable to
correct for a substantially misadjusted analogue
Gain control at the
(i.e. prior to analogue
to digital conversion). Too little
pre-amp gain will result in a poor
ratio, while too much will result in clipping
at the pre-amp or during subsequent processing.
See also Over.
A mixer that functions
using digital techniques.
Usually the term refers to a mixer in which all mixing,
routing and other
within the mixer is performed digitally. This arrangement
has a number of important advantages, including:
- Many complex combinations of settings can be electronically
saved and restored at the touch of a button. This is especially
useful when several different acts are to use the same set of
mixer inputs during a show, or when a show such as a musical
has many different scenes.
(This is why the saved sets of
settings are often called 'scenes'.)
signal processing can be conveniently be employed
to enable the incorporation of functions such as
far more comprehensive
facilities than are generally provided on an
This greatly reduces the need for
- A common set of controls (which are often display-screen
based) can be used for adjustment
of any channel; on mixers handling a large number of channels
this greatly reduces the area of the
control surface and
- If required, the control surface can more readily
be located remotely from the signal processing equipment.
- As the signal does not pass through the control
levels are reduced and
potentiometer wear and contamination are less of an issue.
facilities are often provided with the mixer, most types
provide for integration with
('digital snake') systems in which each
signal is pre-amplified and
converted into digital form by an equipment rack located
at the stage. See also
Motorised fader and
to digital conversion. Compare
A system that uses digital
technology to provide a
audio link for
signals from the stage to a
mixer location, and often also
in the reverse direction
(for returns), taking the
place of a conventional
The 'send' signals are converted from
analogue to digital at a
(often in racked
equipment at the stage end of the link), which then
multiplexes them for
sending to the mixer location via a high-speed data
link, typically using a UTP or
and a protocol such as
AES50. Digital multicores
are nearly always used in conjunction with a
in which case the mixer end of the
cable is usually connected directly to the mixer.
An alternative arrangement is to use an analogue
multicore from the stage to a digital
and then a digital multicore to link the
monitor mixer to the
in which case a conventional analogue
stagebox is used on stage. Rarely, the digital
multiplex signal from a digital stagebox is
demultiplexed at the mixer location and
converted back to individual analogue channels for
connection to the FOH mixer in the usual way.
Typically such systems provide either
inputs for connection of
line-level sources such as instruments,
receivers and separate
pre-amps, or else they
incorporate microphone pre-amps to enable the
direct connection of wired mics to the stagebox.
to digital conversion and
performed by digital means.
Frequently abbreviated to 'DSP'. See also
A stagebox that employs
a digital interconnection to
the associated mixer,
which is usually a
Digital stageboxes are active
units, incorporating microphone
to digital convertors for the
to analogue convertors and
for the returns from the mixer.
The interconnection with the mixer is commonly an
utilising the AES50 standard.
to analogue convertor
An item of equipment, or a device within an item of equipment,
that converts a
digital audio or
signal into an
Often abbreviated to 'DAC'. Compare
to digital conversion.
Describes a video
signal or recording in
which the video information is represented in
form (i.e. numerically) rather than in
Or, describes equipment that processes, records or
plays back video using digital processing or recording
A typical label for a button or switch that activates a
dimming (1) or
dimming (2) function.
A period of very substantial reduction in lighting
but not to the extent of a
blackout. A dim out may
for example be called for during projection of a film or
Dimmer fizz, Dimmer noise
Alternative terms for the interfering
originating from lighting dimmers, that
is sometimes picked up by
and heard as a background
or 'fizzing' sound. This should not happen to
any significant degree if good quality audio
and dimming equipment and
audio interconnections are used, and proper
practice is followed.
An item of equipment, or a rack of several such items,
whose purpose is to provide a
stage lighting, typically under DMX
control. Dimmer packs usually provide independent dimming for
a group of dimmed output
circuits (often either 3 or 4),
each dimmed output being under the control of a different
DMX channel. They usually
A reduction in brightness of illumination,
e.g. as provided for
stage lighting by a
An alternative term for
An abbreviation for Deutsches Institut für Normung
(sometimes incorrectly written as Deutsches Institute für
Normalung), a German organisation which defines many types
of industrial standards, including electrical and audio-visual
In the context of connectors,
the abbreviation is most frequently used to identify a round
connector, available in many different configurations
from 2-pole to
including miniature versions (mini-DIN).
The 4-pole mini-DIN connector is frequently used for
The standard-sized 3-pole and
versions of this connector were once commonly found
on domestic audio equipment,
for mono and
stereo respectively. (These are now
largely superceded by the phono
connector.) The usual pin allocations for the stereo version were
as follows (in clockwise order, looking at the front of the
2-pole version (with a central flat
pin [− pole] and an offset
round pin [+ pole])
was similarly used for domestic
equipment speaker connections.
The standard-sized 180º 5-pole variety
is now used for MIDI interconnections.
See also IEC and
DIN (5-pole 180º) image
See IEC noise.
An electronic component
that conducts current
very well in one direction but very poorly in the other.
Diodes have a multitude of uses in electronic
circuits, but the most
common application is within
Diodes are usually
devices, but they are also available in the form of
valves. Special types of
diode include zener diodes and
LEDs. 'Normal' diodes are
usually rated in terms
of their maximum continuous forward current and their
maximum reverse voltage
(under specified operating conditions).
Same as Cut. See also
An electrical component
that incorporates several
sub-miniature 2-position switches in a single very
compact device. The switches are so close together that
they require a small tool to operate them, so applications
of this component are limited to settings that are very
infrequently changed, such as 'installation' settings.
Depending on the application, the individual switches
may have separate functions or may be used to set up a
numerical code such as an
address. Such codes
are effectively set up in
binary, but may be
recorded or displayed as
A common use for DIP switches is for setting the
address of addressable items of equipment such as
DIP stands for 'dual in-line package'; this relates
to the component having two parallel rows of pins that
connect it to the circuit board below (these are not
visible on an installed switch).
An American term for a 'direct inject' box −
see DI box.
safety, the potentially lethal situation where a person
comes into contact with a
conductor that is
intended to be live at a dangerous
voltage (e.g. at
This situation is protected against by
the presence of insulation
or by the conductor being securely enclosed; these measures
are referred to as 'basic protection'
against electric shock.
Supplementary protection against direct contact may be
provided by a suitable RCD,
but this must never be the sole means of protection
against direct contact. See also
output of a
mixer, provided on each
channel, which allows
signal on that channel
to be supplied to other equipment such as a multi-track
recorder or another mixer.
The direct-out signal may be
or post-EQ − on some
mixers this is panel-switchable while others provide that
choice by means of an internal switch or
Channel feeds for live recording of professional performances
are more usually obtained by use of a multi-channel
See also Insert.
Compare Split output.
Describes a speaker in which
the driver(s) are located at the
front face of the enclosure,
and create sound by acting directly
on the air in front of the enclosure. This contrasts with the
use of horns, diffractors and other
devices that are sometimes employed to couple a driver to the
air surrounding its enclosure. Note that a
full-range speaker may
utilise a mixture of coupling methods; in the case of low and
PA speakers a
direct-radiating woofer and
a horn-loaded HF driver is
commonly employed. See also
Sound that has travelled
on a single essentially straight-line path from its source to
the listener or to a
specifically without having undergone any
sound. See also
Diffuse field and
Strictly, no such thing. It is claimed by some
audiophiles that some
types of cable may give better
performance when an audio or
is passed through it in a particular direction −
that is, with a specific end of the cable connected to
the signal source.
Considering the cable alone (i.e. without
there is no technical justification for such a claim
because, as such signals are AC,
the current flows equally
in both directions (when averaged over time) −
regardless of the direction of signal flow.
However, when considering a cable with connectors
attached, directional factors may be introduced. This
may be through obvious means such as different connector
types at each end (e.g.
or by more subtle factors such as differences in the way
that the two connectors are wired (for example,
screened cables which
have their screen connected at one end only − see
shield and Pseudo-balanced).
A microphone whose
to sound varies according to the
angle at which the sound strikes the microphone,
relative to the microphone's axis.
For further information:
See also Rejection. Compare
The extent to which a
speaker, or one of its
has narrowed dispersion
angles. A narrower dispersion angle results in the
emitted sound energy being
more concentrated and so (potentially) provides an
and therefore a corresponding increase in the
sensitivity of the speaker.
The directivity may be expressed as a Q value or as a value
in decibels, either of which
may be referred to as the directivity index. This index
value indicates the increase in on-axis sound
level as compared to the level that would have been obtained
(at the same distance) if that speaker had been radiating
the same total sound energy spread equally in all
directions; this value is usually
So, it can be seen that a
long throw speaker
has a higher directivity than a
short throw one.
The correspondence between (circular) dispersion angles and
the Q and decibel expressions of directivity is illustrated
in the table below.
Note that the Q value of directivity index is not
in any way associated with the Q
values that are used to describe the degree of
damping of a driver's or
See also Constant
and Line Array.
Describes a signal or
other electrical interconnection (including an
earth connection or
a power source)
that is contaminated with
Or, describes a signal or
in which distortion
is significantly present − whether undesirably so
or deliberately introduced. See also
Describes an electrical contact (especially the
mating surface of a
conductor or the
wiper of a potentiometer)
that is physically contaminated with material that
impairs the quality
of the electrical contact, typically causing a
resistance connection (with the possible effect
of overheating in some situations),
unreliability of the connection, and/or the introduction
of distortion or
noise. In the latter event,
the contact or potentiometer may be described as
In the case of metallic
contacts, a frequent cause of such contamination is
A lamp in which the
electric current flows
through a gas enclosed within the lamp envelope,
rather than through a metallic filament. In constrast to
discharge lamps cannot be operated
direct from the supply: the
or fixture incorporates
'control gear' specifically designed to suit the
appropriate type and power
of the lamp. The control gear provides a
high initial voltage
to start the discharge and 'ballast' to limit the
current once the discharge is established.
Common types of discharge lamp are low and high
pressure mercury vapour and low and high pressure
sodium vapour; most types cannot be operated from
dimmer-controlled supplies. Discharge lighting can
sometimes be a source of interference affecting
PA systems. Compare
An electronic circuit
that is constructed using a number of individual
connected together, often by means of a
The 'spreading out' of
sound from a source; the
extent to which the sound from a
speaker effectively covers
the area in front of it. As the distance from the source
increases, the sound will have spread its energy over a
larger area and so the
level decreases − this happens according to the
A speaker with large dispersion
angles (horizontal and/or vertical) will spread its sound
over a larger proportion of the total area in front of it,
even when the distance between the speaker and the target
area is quite small − it is therefore
described as a 'short throw' speaker. A speaker with small
dispersion angles is able to accurately direct its sound
to a target area some distance away, and is therefore
described as a 'long throw' speaker.
See also Directivity.
interface used on some
compact mobile devices such as smartphones and tablets.
Adaptor cables are available to enable interconnection
with HDMI compatible
The conversion of electrical
power into heat (or
by an item of equipment. Or, the total amount of electrical
power absorbed from the circuit by a component, or
from the supply by an item of equipment − minus
any power that is usefully converted into forms other
than heat or light (e.g. sound or motion)
or that is passed on in electrical form.
In the case of non-transducer
components such as resistors
all of the power absorbed from the
circuit by that component is dissipated by the component
In the case of transducer
components such as
some power will always be dissipated by the component
as heat (as no transducer is 100% efficient).
The remainder of the power absorbed from the circuit is
passed on in the form into which it is converted.
In the case of electrical equipment that passes on no
substantial amount of power in electrical form
(such as an unpowered mixer),
essentially the whole of the power drawn from the
supply is dissipated by the equipment as heat
In the case of electrical equipment that does pass on a
substantial amount of power in electrical form
(such as a
or a transformer),
the proportion of the power drawn
that is dissipated by the equipment as heat will be
determined by the efficiency of the equipment.
The power that is dissipated as heat within electrical
components or equipment must be adequately removed,
e.g. by means of natural air circulation,
in order to avoid an unacceptable rise in temperature
which may result in damage and/or the operation of a
In theory, purely reactive
no power. However, as in practice these components
possess some inherent series
resistance, they do
dissipate some power − though usually only
A value describing the extent of directionality provided
by a directional
The distance of such a microphone from a
sound source must be
this many times greater than the distance of an
microphone in order to provide the
of direct sound
to natural reverberation
as would be obtained using the omni-directional microphone.
Typical distance factors for various
are as follows:
For example, this means that a super-cardioid microphone,
when pointed at a sound source and placed 1.9 times further
away from it than an
omni-directional microphone, will pick up about the same
ratio of direct to reverberant sound as the
See also Critical
distance (1) and
Describes the placement of a
microphone at a
distance of around 2 feet (60 cm) or more from a sound source.
Compare Close pickup.
A modification of a signal,
caused by the equipment handling it, in which new
frequencies are added
that are related in some way to the original signal
but which themselves were originally not present to any
significant degree. This is usually undesirable.
A distorted sound
or signal is sometimes described as
dirty, whereas one
that is free from distortion may be
described as clean.
Distortion may be caused when the
or processing circuits within equipment are
excessive signal levels.
Such an overload situation is most usually due to
equipment being incorrectly adjusted or wrongly
connected, and in extreme cases results in signal
In this type of distortion,
(primarily odd harmonics) of the frequencies
originally present are added. At the point of clipping,
the level of these odd harmonics dramatically increases.
Such distortion may be avoided by ensuring that adequate
headroom is maintained
throughout the entire
(see Gain structure).
An essential element in this is the correct adjustment
gain controls. It is also
necessary to be sure that any
microphones used are not subjected to excessive
(some are fitted with pad switches).
There are also other types of unwanted distortion,
that are not caused by overload. Two possible sources
of this are faulty cable
connections (see High
resistance connection) and defective equipment
(notably worn or dirty
signal-carrying switches and potentiometers).
Some specific types of distortion are
Sometimes distortion may be deliberately introduced,
for example in order to produce a richer or harsher
sound from an instrument such as an electric guitar.
To allow the extent and type of distortion
to be carefully controlled, this would normally be done
using an effect
designed for the purpose (see
but may often be produced simply by
increasing the gain of the
so as to deliberately cause signal overload.
It should be noted that any item of electronic equipment
will always introduce at least a small amount of distortion,
but with good quality equipment, correctly used and adjusted,
this is usually too small to be noticeable.
It is only when the distortion reaches unacceptable
(that is, audible) proportions that the equipment is
said to be "distorting" the signal.
The overall amount of distortion that is present in a
signal, or that is introduced into a signal by a
specific item of equipment, is usually indicated by
a THD value.
Distributed public address
that provides independent multiple
outputs for each
input that it has,
so as to enable one or more sources to (each)
supply its signal
to several destinations. An important feature is
the isolation between its outputs, which means that
if a fault occurs on the
feed to one of the destinations
then the feed to the other destinations will be unaffected
Use of a distribution amplifier is essential when
multiple destinations are to be supplied with the same
signal such as video or
digital audio, in order
to avoid double
termination of the feed.
(The only exception to this is where the equipment
allows for a
of the signal, as in the case of
DMX lighting control and
some video equipment.)
A distribution amplifier intended for use with the
signals picked-up by an
antenna is frequently
referred to as an
distribution unit, or ADU.
Note that the term 'amplifier' could be considered to
be strictly incorrectly applied here, because the
equipment often provides no
gain. However, the term
is justified by the fact that, in total across all
its outputs, the equipment is generally able to
supply more current
than would be available from the source that feeds it.
An item of equipment containing an arrangement
protection devices such as
Commonly abbreviated to 'DB'.
See also the next definition.
A slang abbreviation for 'distribution',
usually relating to equipment and
cabling for the
See also the previous definition and
In general terms, describes something that is
separated, or spread out. In relation to its application
to radio microphone
receivers, the term generally refers to an arrangement in
which the radio signal is picked up on two aerials
each connected to a separate set of receiving electronics
− the audio
output of the unit
is obtained from the aerial which is giving the best
quality signal at any moment in time, or else is a
combination of the results obtained from both aerials.
These types of receivers are much less prone to
types having a single set of receiving electronics.
The aerials are generally
best set at between + and − 30 to 45 degrees from the
vertical, i.e. spreading apart at between 60 and 90
degrees to each other.
Some single-channel receivers are equipped with two aerials,
even though they have only a single set of receiving
electronics − these may perform a little better
than receivers with only one aerial, but fall far short of
the performance obtained from 'true diversity' receivers.
See also the 'Wired or Radio'
section on the Microphones page.
A guitar or bass
pickup that provides a
signal from each
string of the instrument. These multiple signals may
then be processed separately, or may be used as separate
controlling inputs to a synthesiser.
A medium-sized percussion drum of African origin,
typically having a skin of either 10" (25 cm)
or 12" (30 cm) diameter and a body that narrows
from the skin downwards towards a half-way point, and
then widens again.
An abbreviation for 'double layer' (or 'dual layer').
A type of recordable DVD
that incorporates two layers of information on the same
side of the disc, giving nearly twice the information
capacity (8.5 GB as compared to 4.7 GB for the
single-layer type). See also
An abbreviation for Digital Living Network
Alliance®, an organisation that sets
standards for the interoperability of networked
equipment. Their website is www.dlna.org
(opens in a new window).
An abbreviation for 'digital multimeter';
a multimeter that provides
its readout of measured quantities via a
digital (i.e. numeric)
display. Such multimeters are frequently equipped with
an 'autoranging' facility, which largely avoids the need to
manually select the appropriate value-range of the quantity
to be measured (although the type of quantity
− e.g. voltage,
resistance − must
still be manually selected). DMMs are sometimes referred
to as DVMs (digital voltmeters), because the very earliest
types were able to measure only voltage. See also
A standardised digital
control system interface for stage lighting and
similar equipment, originally developed by
USITT and capable of
carrying up to 512
channels of data per
control cable (termed a DMX
'universe'). DMX is an abbreviation of 'digital
DMX equipment is set up, at the time of installation, with
a specific address that
allows the controller to direct commands to each particular
item of equipment. The address is the channel ID of the first
channel in the set of channels implemented for each item.
The addresses of equipment are typically set up using
DMX uses balanced
most usually 5-pin
The cable screen connects
to pin 1,
'Data −' to
pin 2 and
'Data +' to
The shell is normally
left unconnected. Pins 4 and 5 are desinated for a
second balanced data circuit, but are rarely used.
The DMX standard does not permit them to be used to
Some DMX-compatible equipment is equipped with
3-pin XLRs of the same type as used for
even though the DMX standard does not permit this.
In this case, pins 1, 2 and 3 serve the same functions
as on the 5-pin connector (i.e. pin 3 is '+', the
opposite of audio usage) − though some equipment
has pins 2 and 3 reversed.
Regardless of whether 5-pin or 3-pin connectors are used,
control signal sources are equipped with
and destinations with male
connectors − note that this is the opposite way
round to audio XLR connections. However, some devices
connected to DMX links may communicate bi-directionally −
The electrical interface standard is
(previously known as RS-485),
and the bit-rate is
This high rate means that a suitable type of cable must be
used to avoid deterioration of the signal quality,
especially if long distances are involved −
under perfect conditions the maximum theoretical
transmission distance is 1 km, but 500 m is a more
The cable must have a
impedance of 120 ohms
and must be daisy-chained
from equipment to equipment −
not branched along its length.
Only the last item of equipment in the chain
must have its
in the 'On' position (or have a 120 ohm terminating plug
fitted if it has no such switch).
A slang term for a
The digital audio
encoding schemes for 5.1 and
surround sound systems
developed by Dolby. Compare DTS.
A trademarked name for the original
reduction scheme from Dolby Laboratories, intended for
audio recording on
tape. It operates by dividing the audio
spectrum into several
and applying appropriate
to each band during recording. To achieve the
reduction in noise, the corresponding
expansion must be applied during playback
(failure to do so will result in incorrect
reproduction of the recorded material).
See also the next two definitions.
Similar in principle to
but simplified for use with consumer cassette recorders.
It applies compression
to the higher frequencies
only. It gives an improvement in
ratio of about 10 dB
at high frequencies. See also the next definition.
An improved version of
It gives an improvement in
ratio of about 20 dB
at high frequencies.
Recordings made using Dolby C must be played back
using Dolby C.
A realm (or 'world') of operation, or of
significance. For example, "signal processing in the
refers to the processing of a signal while it is in
digital form, i.e.
A device that records the total exposure to a particular
quantity received by a person over a given period, usually
one working day. In PA work the
term usually refers to an audio
dosimeter, sometimes referred to as a 'noise dosimeter'
or a 'personal sound exposure meter' (PSEM).
These are devices that are worn in order to record
the wearer's total daily exposure to
sound, so as to assess the
potential for damage to hearing. See also
on the Safety page.
An alternative name for star
A musical instrument; the
member of the violin family, most often encountered in
the strings section of a classical orchestra but also used
in other settings such as jazz bands and swing bands.
See also Bass (2).
See Class II.
An undesirable condition in an interconnection
that is meant to be
caused by the connection of an
output to two (or possibly
inputs. The effect is that
the overall load
impedance is no longer equal to the
and to the
impedance of the cable,
of the signal back down
the cable which may seriously impact upon the quality
of the interconnection. Additionally, a double termination
will result in the received signal
level being too low.
Where an impedance-matched source needs to feed several
destinations, typical solutions are use of a
amplifier or, where applicable, use of a
signal routing in which the input
are disconnected at all but the last item in the chain.
See Gone down.
Further towards the audience − towards
the 'front' of the stage. So-called because of the
slight downwards incline ('rake') in this direction
on a theatrical stage.
The additional sound
that is required in order to provide
fill at the very front of
the audience, provided by downwards-angled
typically located beneath a
Employing such speakers (referred to as downfills)
means that the curvature of the
line array can be reduced, enabling it to be more effective
in its mid- and long-throw
coverage. (This is especially relevant when the line array
is flown high.)
Note that the downfills are not part of the line array
proper, and would usually be driven by a separate
An abbreviation for 'digital phantom power', a standard
for remote powering of
microphones that have
a digital audio
For details see AES42.
In mains power
distribution, describes a
connector that is
wired (ultimately) to
It may be a fixed connector or may be attached to a
connector is described as a
See also Distro.
An uninsulated conductor
that is sometimes included inside the
screen of a screened
cable (e.g. a
and in electrical contact with it,
in order to ensure a continuous
conductor path throughout the cable length and to facilitate
termination of the
screen to the cable's
A drain wire is usually
provided only in cables that employ a foil screen or a
semiconductor screen (not in cables employing a screen
that is formed of braided or lapped copper strands).
As a verb, to cause a flow of
power in a
circuit that connects
a source of electrical
energy to a
load, usually with reference
to the typical or maximum current or power requirements
of the specified load. In this context,
the source referred to is most likely to be the
a power unit, a
battery, or a signal
output of an item of
Or, much less commonly, as a noun, the typical or
maximum level of
current or power that is caused to flow. See also
An abbreviation for 'dress rehearsal'.
To arrange cabling
(especially when fixed, e.g. to racking) in an
[Noun:] A signal,
especially in reference to the requirements of an
input, or to the capabilities
of an output, of an item
of equipment. For example, "There's insufficient drive
for this effects unit", or
adequate drive for those
speakers". See also
Or, [Verb:] To supply a signal
to an item of equipment. For example, in a particular
signal chain, a
drive an active crossover,
which drives the
which in turn drive the
A slang term for "operate" an item of
equipment, as in "Do you know how to drive this
The part of a speaker
that performs the conversion of electrical
sound waves. This conversion
is usually achieved by means of a
voice coil causing the
motion of a cone or
speakers often contain several drivers − typically
some combination of woofers,
mid-range drivers and
horns (or tweeters).
See also 2-way,
An abbreviation for 'digital rights management'.
Any scheme intended to
prevent the use of an item of software or other
recorded information (e.g. music) from being used
other than by a legitimate user.
See also SCMS,
A momentary or intermittent interruption in normal
In recording, a short disruption in the played-back
information, caused by a physical anomaly of some kind on
the recording surface. In
may be compensated for (either completely or partially) by
the operation of
In signal transmission systems
(especially radio systems), a loss of acceptable signal
for a short duration or under specific circumstances
(for example, at a particular location of a
See also Diversity.
Drum cage, Drum screen
An acoustic screen, usually made of a transparent plastic
such as Plexiglas®,
that is placed around a drum kit and drummer to reduce
sound level and
to reduce leakage of drum
sound into other instrument
microphones and vocal
microphones. Preferably these screens are partially lined
with sound-absorbant panels − often just at the
lower front, the sides and the back. Some types have a
'lid', preferably also lined.
Describes a sound that is free from
effects, especially from
See also Clean.
Hiring of individual items of equipment from a
hire company, on a 'self assemble and operate' basis,
as compared to hire (usually of a complete system) that
includes the personnel to assemble and operate it. See also
Compare Wet hire.
A soldered electrical joint of poor quality,
resulting in problems such as an intermittent
inconsistent operation, etc.
Often the problems are not apparent until months,
or even years, after the joint was made.
When making your own soldered joints, the two
most important factors in avoiding dry joints are
to ensure that both parts being joined are
sufficiently heated, and that they remain
completely stationary whilst the joint
An abbreviation for 'direct stream digital',
a term describing a particular format
for audio storage or interconnection
in which audio data is represented in a
modulated (PDM) form. (More academically speaking,
it is a delta-sigma modulation scheme.) This is the format
in which audio is represented on an
It can be considered
to occupy a position half-way between an
analogue and a
of the original audio.
It has similarities with an analogue
signal in that the
pulse density is directly representative of the audio signal
− simply low-pass
filtering a DSD signal will produce the analogue
waveform, without any
'decoding' being involved.
It has similarities with a digital signal
in that it is a representation of constant-rate
samples and that the
signal voltage has only two
states. However, it should be noted that,
or other such codes
(but rather like PWM),
DSD is not a true digital format
as the sample values are not represented numerically.
DSD signal interconnections are not normally encountered in
PA work, being limited to
SACD conversion, mastering and duplication equipment,
where a physical interface
in the form of SDIF
is usually employed.
An abbreviation for 'Deputy Stage Manager'.
See also SM and
An abbreviation for
signal processing' or 'digital signal processor'.
An abbreviation for 'Digital Tape Recording System',
originally referring to a range of Tascam 8-track tape-based
obsolete). However, the term is still in use to refer
to the recording format
used by those machines and also to refer to the
connection scheme used for the
on those machines, carrying 8
became an informal standard for 8-channel analogue audio
interconnections between multi-channel items of
equipment such as
analogue to digital convertors and recording
systems. This standard is now formalised by
For details of the internal wiring for DTRS
DB-25 connectors (and also for a 4-channel bi-directional
digital interconnect) see
this PDF file on the Tascam website: DB-25_Pinout
(external link, opens in a new window).
See also SAC (2).
A trademarked name for a series of
encoding systems, most frequently used in conjunction with
video programme data (such as on
DVDs or within an
signal) as an alternative to
encoding. Like Dolby, it supports
7.1 systems, though the 5.1
system is the one most commonly referred to.
It was developed by
Digital Theater Systems Inc. of the USA (also known as
'Dedicated to Sound'), now renamed
DTS Inc. See also Codec.
A trademarked name for a particular brand of
waterproof adhesive tape, intended for general-purpose use.
It is sometimes used as
though is not as strong as the gaffer tape usually
used in the entertainment industry.
Note that only tape that is specifically
intended for use as an electrical
should be used for that purpose.
Use of the silver-coloured variety of Duck
tape is not recommended for use on
cables − see
Gaffer tape for
further information. Often confused
with duct tape,
because of the similar-sounding name.
The intentional temporary reduction of a
level for an period
during which another signal has precedence. Alternatively
referred to as 'dimming'. For example,
in a DJ console,
the music level may be automatically
reduced while the DJ speaks. Or, in a studio the normal
monitoring feed may be
reduced in level while a producer or recording engineer
speaks to the performers. Another possible application
would be in a
public address system,
where the musac level
may be reduced during announcements. Ducking may be
achieved by passing through a
compressor the signal
that is to be controlled, and applying the controlling
signal to the compressor's
side chain input.
An airtight (and often waterproof) adhesive tape,
usually silver-coloured, intended for sealing the joints
of air-conditioning and ventilation ducts.
However, the name has come to
be used to refer to any kind of strong adhesive tape.
with Duck tape,
because of the similar-sounding name.
Note that only tape that is specifically
intended for use as an electrical
should be used for that purpose.
As duct tape is intended for permanent application,
when removed it may leave a residue or cause damage
to the surface finish. High-quality
gaffer tape is
recommended for general
Further, use of the silver-coloured
variety of duct tape is not recommended for use on
cables − see
Gaffer tape for
A load connected
to an amplifier
for test purposes, in order to make test-bench measurements
such as maximum power output
a consistent manner and without creating high
The simplest dummy load consists of a
resistor of the appropriate
impedance and having a suitably
high power rating.
However, more sophisticated versions attempt to simulate
of the load's impedance value.
Describes an interconnection or
a communications link) that is able to pass information
in both directions. Often sub-categorised as follows:
- Half-duplex: Information may be conveyed in both
directions, but not simultaneously.
- Full-duplex: Information may be conveyed in both
An interconnection or interface that is able to pass
information in one direction only may be described as
simplex, but this term is rarely used.
See also I/O.
The proportion of time, usually expressed as a percentage,
that an item of equipment or a
component is actively in
operation. For example, a 25% duty cycle refers to the
item being actively operational for a quarter of the time.
Duty cycle limitations are imposed on some types of equipment
(such as some motors, generators and transformers)
− usually to avoid an
unacceptably high operating temperature being reached
as a result of the power
being handled or delivered by the equipment. Therefore,
maximum duty cycle figures are frequently dependent upon
power levels and ambient
An abbreviation for
Supposedly an abbreviation for 'digital versatile disc',
but really more of a name in its own right. Nevertheless, a
disc which is able to support a variety of
recording formats. Its capacity is 4.7 GB (single
layer). See also DL and
An abbreviation for 'digital
A standard for
between a computer and display equipment
(monitor screens and projectors), providing an improvement
in image quality over the earlier analogue-only
standard. Several variants are available, including
DVI-I, DVI-D and DVI-A.
See also HDMI.
DVI connector image
An abbreviation for 'digital voltmeter' − see
An abbreviation for
See also PVR.
equaliser (Dynamic EQ)
An item of equipment, or a facility of one, that
which automatically varies according to the
level of the
signal being equalised.
The most common arrangement is that the
and Q of the equalisation are
set by manual adjustment, and the extent of the
boost varies automatically
within manually-set limits. Such an equaliser
can be arranged to provide many different results,
A common application is in the boosting of
(and sometimes treble)
frequencies at low levels, in order to compensate
for the reduced sensitivity
of the ear at these frequencies (see Loudness (2)).
Frequently abbreviated to 'DEQ'.
A type of microphone in which
sound is converted to an electrical
by causing the vibration of a
conductor in a magnetic field,
so inducing a voltage in the
Most dynamic microphones that are used in
PA work are of the 'moving coil'
type − this means that the conductor is in the form
of a coil of wire which is attached to the
This coil is called the 'voice coil'. (Another, less common,
kind of dynamic microphone is the
As this process
generates sufficient signal level
for direct connection to a PA
amplification of the
signal is required within the microphone.
This type of microphone is most
close pickup applications
such as lead vocals,
guitar amplifiers, etc. (see the
Microphones page for more information).
The name is a shortened form of 'electrodynamic microphone',
which indicates that sound causes a movement of electrons
through the microphone capsule
(when connected to a load).
When describing a sound or an
signal, dynamic range refers
to the difference in level
between the quietest and loudest periods of the
usually measured in
See also Peak,
When describing an item of equipment, in general terms
its dynamic range
is a measure of the extent of variation in level that
the equipment is able to handle (without
further manual adjustment, once correctly set up), while
maintaining an acceptable
ratio and an acceptable degree of
Numerically, it is the difference (in decibels) between the
noise floor of the
equipment and the signal level at which unacceptable distortion
clipping) would occur.
(Note that this means that specified equipment dynamic range
figures are meaningless unless details of the noise measurement,
such as weighting, are given,
along with the relevant distortion figure.)
Put another way (using figures in decibels), dynamic range
is the sum of the signal-to-noise ratio
and the headroom. In
regard to digital equipment,
see also the comments on this term under
The natural variations in
level that occur
in most sounds such as music
and speech, and therefore occur in typical
signals. For more information
see Dynamic range.
A signal processing
unit that modifies the
dynamic range of a
signal, such as
noise gate or
See also Compander
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This page last updated 15-Sep-2017.