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Glossary of PA Terms - L |
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The glossary pages provide definitions for over 1900 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.
L * L<number> * LAT * Leq * Lamp * Lampie, Lampy * Lantern * Lapel microphone * Lapped screen * LAT * Latency * Lavalier * Lavaliere * Lay * Lay length * Lay-up * LCD * LCR * LD * Lead * Leakage * Lectern * LED * Leg * Legacy * LEQ * Leslie * Level * Level meter * LF * LFE channel * Lift * Light * Lighting fixture * Lighting plot * Limiter * Limiting * Lin * Lin pot * Line * Line-up * Line array * Line check * Line filter * Line input * Line level * Line microphone * Line output * Line sync * Linear * Linear phase response * Linear potentiometer * Linear power supply * Linear taper * Linearity * Link * Linkwitz-Riley * Lip microphone * Lip sync * Listen wedge * Littlite * Live * Lively * LM * LMID * Lo-Z * Load * Load impedance * Load-in * Load-out * Lobar * Lobe * Log * Log pot * Log taper * Long throw * Longitudinal choke * Longitudinal wave * Loop * Loop amplifier * Loop driver * Loop system * Loss * Lossless * Lossy * Loudness * Loudspeaker * Low cut * Low end * Low frequency * Low impedance * Low pass * Low-Z * Lower mid-range * Lows * LPF * LR * LR-4 * LSF * Lumen * Luminaire * Luminance * LV
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.
L
An abbreviation for 'Left
channel'.
See Stereo.
Compare R.
L<number>
In sound
level measurement,
the level that is exceeded for <number> percent
of the time, over the period of the measurement,
usually expressed in
dB SPL.
For example, the L10 figure is the level that is
exceeded for 10% of the time during the
measurement interval.
See also Sound
level meter. Compare
Leq.
Leq
In sound
level measurement,
the continuous level that is equivalent to the average
of the actual levels over a stated period of measurement,
usually expressed as an
A-weighted value in
dB SPL. A measurement
period of the order of 1 to 3 minutes might
typically be considered appropriate for
PA applications. This method
of measurement is more properly called LAT,
and is defined by standard IEC 61672-1. See also
Sound level meter.
Compare L<number>.
Lamp
The component, within a
lantern, that converts
electrical energy into light.
Frequently called a 'bulb' by non-technical personnel
(a term deprecated by lighting engineers).
Does not refer to the complete lantern.
See also LED.
Lampie, Lampy
A slang term for a lighting engineer.
Compare Soundie.
Lantern
The 'proper' name for a 'stage light' − an
enclosure
containing one or more light sources (and
possibly other devices such as lenses, shutters,
gobos etc.),
arranged to emit light
in a controlled way.
Many different kinds of lanterns exist − see, for
example, PAR can and
Fresnel.
Sometimes called a luminaire. With the advent of lighting
and other equipment that is directly controllable using
DMX, the term 'fixture'
is now commonly used to refer to all such equipment;
lanterns are therefore now often referred to as 'lighting
fixtures'. The US term is 'lighting instrument'.
See also Lamp
and LED.
Lapel
microphone
See Lavalier.
Lapped screen
See Screen.
Latency
The time delay introduced in a
signal by
digital
signal processing
(or communications) equipment, generally due to the complex
arithmetic operations which must be performed on the signal
(or due to relatively low communications
bit-rates).
The delay is more likely to be significant when some but
not all signals are processed (or digitally communicated)
by equipment with a high latency,
because the time difference may then be more apparent
(for example, poor lip sync).
As an example from digital communications, consider a MIDI 'note-on' message sent from a keyboard to a sound generator over a single MIDI link. This message consists of three bytes, each of 11 bits (including the start and stop bits). At the standard MIDI data rate of 31.25 kbit/s, the message will therefore take just over 1 ms to be sent. So even ignoring processing delays within the keyboard and sound generator, the latency between pressing a key and the sound beginning will be at least 1 ms. See also Time alignment.
Lavalier
(or, less commonly, Lavaliere)
Originally, described a small
microphone that was worn
by being suspended from a cord around the wearer's neck,
to allow hands-free
use − e.g. by presenters or actors.
However, this method of attachment is now relatively
uncommon, and the term is now used to refer to any
chest-worn microphone − usually miniature types that
are attached to clothing by means of a clip.
As they are often clipped to a lapel or a tie,
they are alternatively known as lapel microphones,
clip microphones or tie-clip microphones.
They are usually
radio microphones,
and are used in conjunction with a
bodypack.
In some situations these microphones can be prone to problematic variations in output level, due to the changing distance from the wearer's mouth as their head is moved. To minimise this effect they should ideally be worn centrally, just below the point at which the wearer's chin would touch their chest. If they must be attached to one side, then this should be the side that the wearer predominantly faces (e.g. in an interview situation). Level variations can be further reduced by the use of omni-directional types, but these are more prone to feedback and leakage problems, especially when a high gain needs to be employed. A preferable approach is often a headset microphone.
The term 'lavalier' was taken from the name given to a type of single-stone pendant necklace (by visual similarity), originating from the French word 'lavalličre' for a necktie with a large knot, popularised by the Duchesse de La Valličre.
Lay
See the following two definitions.
Lay length
The distance taken up by each complete twist of the
insulated
signal
conductor
wires within a
balanced
cable.
Sometimes just referred to as the 'lay'.
See also Pair and
Star quad cable.
Lay-up
The particular physical arrangement of the
conductor
wires or
pairs within a
cable.
Sometimes just referred to as the 'lay'.
See also the previous definition.
LCD
An abbreviation for 'liquid crystal display',
a device in which liquid crystals are placed under
the influence of an electric field in order to control
their polarisation and hence their ability to pass
light
(when used with appropriate polar filters).
By division of the display area into segments or
pixels, each under
separate electrical control, information such
as numbers, characters or full images can be formed.
When each pixel has its own adjacent controlling
transistor(s) fabricated
into the LCD, the display
is described as 'TFT', an abbreviation of 'thin
film transistor'.
The liquid crystals themselves do not emit light; the display must either incorporate a source of light (e.g. a 'back-lit' display) or rely on the reflection of ambient light. See also LED.
LCR (1)
An abbreviation for 'left, centre and right'; describes
a routing
arrangement that in addition to the facility for
providing Left and Right
mixes
(for eventual delivery to the Left and Right
speakers of a
stereo
PA system), also
provides the facility for a Centre mix (for eventual
delivery to centrally located speakers).
Some mixers that provide such routing arrangements have pan controls that are configured to pan from a Left-only feed (when fully anti-clockwise), to a Centre-only feed (when at the 12 o'clock position) to a Right-only feed (when fully clockwise). The lack of any feed to the Left and Right mix buses when the control is at 12 o'clock is in contrast to the usual stereo routing arrangement, in which an equal feed is supplied to those buses when the control is in that position. Some mixers providing LCR routing have the facility to select whether the pan controls operate in LCR mode or in stereo mode. See also Cluster.
LCR (2)
A combination of the component designations for
inductors (L),
capacitors (C) and
resistors (R).
Usually used to describe a
filter which makes use
of all three of these component types.
LD
An abbreviation for 'lighting designer'.
See also Lampie.
Lead (2)
Describes an instrument or vocal part whose sound
is intended to be dominant in the overall sound
of the band, as perceived by the audience.
For example, lead vocals (LV) sings the main melody
line; lead guitar plays (mostly) single notes
(rather than chords) and often has a solo part
in at least one song.
See also Rhythm guitar.
Compare Backing.
Leakage
Pick-up by a microphone
of sounds other than those intended to be picked-up by that
microphone, particularly musical instruments situated close
to the target instrument. Usually undesirable in
PA work (but see
Creative leakage).
In the sense that leakage constitutes a part of the unwanted
signal present, it may be
considered to be part of the
noise. Alternatively known
as 'spill' or 'bleed'. See also
Noise gate.
Lectern
A stand which supports books, documents, a laptop
computer, etc., used by a person delivering a
presentation. It may also support a
microphone, often a
gooseneck type.
A lectern is often located on a
dais.
LED
An abbreviation for 'light-emitting diode',
a semiconductor
device that emits light when a
current is passed
through it. High brightness LEDs are now increasingly
used as light sources in lanterns,
where they can provide multiple colours and much greater
efficiency and longer life than a conventional
lamp.
See also LCD.
Leg
One of the signal-carrying
conductors of a
balanced
pair. The two legs of
the pair are commonly referred to as the
'hot'
and 'cold' legs, or as the
'+' and '−' legs. Note that in a
star quad cable
two wires are used to make
up each leg of the pair (making four wires in total).
See also One-legged.
Legacy
Describes equipment of an earlier design or style
than what is now being manufactured. This may mean
that the equipment is many years old, but in the case
of equipment using rapidly-changing technology
(such as effects units
and computer-based equipment) the term might be used
of equipment even less than a year old. The term is
most frequently used in a comparative sense, to refer
to the earlier equipment that remained installed,
or in use, after some refurbishment or extension of the
system (often by new owners or new operators of a venue).
Such a description does not necessarily imply that the
equipment referred to is no longer fit for purpose.
Leslie
Describes a speaker
that incorporates an internal motor-driven rotating device
which interferes with the passage of the
sound emerging from the
driver. A means is usually
provided to switch the motor on and off, and to control
its speed of rotation (e.g. start/stop and
fast/slow foot switches). Effective miking of these
speakers can be difficult, and is sometimes achieved
by use of two microphones,
e.g. at the top and side apertures of the
cabinet.
Such speakers were originally used with early electric organs to produce a rapid 'vibrato-like' sound effect typical of classic 'theatre organs'. The effect is now produced internally in keyboards by digital means. Named after its inventor.
Level
The amount of something; a measurement or indication
of its magnitude. In particular, the magnitude of
an audible sound
(usually expressed in
dB SPL) or of a
signal (usually
expressed as RMS values in
volts,
dBV,
dBu
or dBm).
Also called the 'amplitude'.
See also Line level,
Microphone-level,
Instrument-level,
Metering,
PPM and
VU.
Level meter
See Metering.
LF
An abbreviation for 'low
frequency'.
See Bass.
LFE channel
A surround sound
recording channel
used solely for
sub-bass
signals,
typically for the low-frequency effects added
to film sound-tracks. Use of a separate channel for this
purpose enables
high-level
sub-bass signals to be recorded at a lower level without
having to record the entire programme at a lower level,
and therefore provides an improved
signal-to-noise
ratio at the
higher frequencies,
where noise is more prevalent
and more noticeable. For proper reproduction of the LFE
channel a sub-woofer
is required.
See also 5.1 and
7.1.
Lift
Same as Boost.
See also Earth lift.
Light
Visible electromagnetic radiation, emitted by a
source such as lantern.
Not the lantern itself (though non-technical
personnel frequently use the term in that way,
as in 'a stage light').
Lighting fixture
See Lantern.
Lighting plot
A diagram (or set of diagrams), produced during the
planning of an event, to indicate the stage area that is
to be illuminated by each
lantern during each scene,
and to specify the lighting colours, textures, special
effects, etc. that
are to be used. Often abbreviated by lighting engineers
to just 'plot'.
Limiter
A signal processing
unit that prevents the peak
level of a
signal from significantly
exceeding a pre-determined value (the limiting
'threshold'),
either as an effect or to
restrict its
dynamic range in order
to avoid the overload of
amplifiers,
speakers, recording
equipment or broadcast equipment.
If the limiting threshold is crossed by the
input signal, the limiting
action that takes place will reduce the difference between
the signal's average level and its peak level, so the
required headroom is reduced.
Limiting
The effect on
dynamic range that is
intentionally produced by a
limiter, or that is
caused by some other means (intentional or otherwise)
that has a similar effect.
Lin
An abbreviation for 'linear'.
Lin pot
An abbreviation for 'linear
potentiometer'
− see Potentiometer.
Line (1)
A physical
signal-interconnection
between two points (usually a significant distance apart),
made by means of a cable.
In the case of a multicore
cable, the same cable incorporates several lines.
Note that a line may carry any type or
level of signal for which
the cable is suitable (not just
line-level
analogue signals).
The signal path over a line may be referred to as a
circuit or a
channel. To assist
in the reduction of interference picked-up on the
line, lines are often screened
and/or balanced.
See also Link (1),
Feed,
Pair,
Leg,
100 volt line,
Termination (1) and
Termination (2).
Line (2)
The mains power for an
item of equipment, or a cable
carrying such power. See also
Line filter.
Line-up (1)
The particular set of musical instruments used by a
band during a performance.
Line-up (2)
The process of adjusting the relative
signal
levels throughout a
system, so as to achieve the required
gain structure.
See also SOL and
Programme level.
Line array
A speaker system
consisting of a vertical column of
drivers, either all contained
within a single enclosure or
(more usually) each driver having its own enclosure.
The array is usually flown, and may hang straight downwards or be 'articulated' into a curved shape. A common shape is the so-called 'J-curve', in which the units are angled increasingly downwards towards the lower end of the array, forming the shape of the letter 'J' when viewed sideways from stage right. (The amount of curvature necessary can be reduced by use of downfill or front-fill speakers.)
The resulting sound field has very limited dispersion in the vertical plane, but provides a broad horizontal coverage. It can be pictured as a segment of a horizontal slice of a vertical cylinder (i.e. like a wedge-shaped piece of a circular cake). The result is that, for a particular range of frequencies and up to a particular distance (the 'critical distance'), the on-axis sound level decreases by 3 dB for each doubling in distance, rather than by the 6 dB that is applicable to a point source (see Inverse square law).
The critical distance is dependent upon the length (i.e. height) of the array and upon frequency, but opinions differ as to how best to define this distance and calculate its value. Mark Ureda (of JBL) proposed in a 2001 AES convention paper (preprint 5304 − click to open in a new window) that a suitable approximate calculation would be (array length2 x frequency) / 700, where the array length and the resulting distance are in metres, and the frequency is in Hz. However, in a 2002 paper (AES ref 5649 − click to open in a new window) he proposed a revised approach giving a significantly increased critical distance, calculated (as an approximation) using 0.006 x array length2 x frequency. These calculations show that quite long (i.e. tall) arrays are needed to obtain any useful effect at low frequencies. The high-frequency limit of the effect is determined by how close together the individual drivers of the array can be placed. See also Column speaker. Compare Cluster.
Line check
A specific part of the
sound-check procedure,
during which the allocation and correct operation of the
lines from the stage is
checked. At the conclusion of the line check, it will be
proven that each
microphone and
instrument source is connected to the correct
input of the
mixer (or to the correct
inputs of the
front-of-house and
monitor mixer, where
these are separate) and that there are no problems with
the connections.
Line filter
A filter that is intended to
be used in a mains power
feed, with the intention of
reducing mains-borne
radio-frequency interference
(RFI). Such filters must be
rated adequately for the
current demands of the
equipment supplied through them. See also
Power conditioner,
Distro and
VA.
Line input
An abbreviated form of
'line-level
input'; an input that is
intended to accept a line-level
signal. The
connector is usually
a quarter-inch (6.35 mm)
jack
or a female
3-pole
XLR. Line inputs may be
intended for the connection of
unbalanced or of
balanced signals.
However, inputs that are intended for balanced signals
can usually accept unbalanced ones, provided that the
connector is appropriately wired − check the
equipment manufacturer's instructions. Compare
Microphone input.
Line level
Usually refers to a signal
whose nominal
level is in the region of
0.3 V to 2 V
(−8 to +8 dBu),
or refers to an input or
output
connection intended to carry such a signal.
Typically, line-level signals are used for interconnections
between mixers,
power amplifiers,
graphic equalisers,
effects
and active
crossovers.
Nominal levels for these signals are standardised at either −10 dBV or +4 dBu.
- −10 dBV (equivalent to approximately −8 dBu or 0.316 V) is used by most semi-professional equipment, home studios, etc. These connections are typically of the unbalanced type.
- +4 dBu (equivalent to approximately +2 dBV or 1.23 V) is used by most professional equipment. These connections are typically of the balanced type, in which case +4 dBu refers to the level between the hot and cold conductors (not from these conductors to signal earth).
Line
microphone
An alternative name for a
rifle microphone.
Line output
An abbreviated form of
'line-level
output'; an output that
provides a line-level
signal.
Line sync
In an analogue
video
signal, the
synchronisation
pulses that indicate the start of each horizontal
line of the picture.
In a 625-line picture, the pulses occur at
a frequency of 15.625 kHz,
an interval of 64 µs.
The short black-level interval preceding the line sync pulse
is called the 'front porch'.
The slightly longer black-level interval following the line
sync pulse is called the 'back porch' and in a
composite video
signal carries the
chrominance
reference burst; it is also used for black-level
clamping.
Both line and field sync
pulses occupy the negative-most
0.3 volts of a
standard 1 volt peak-to-peak video waveform.
Linear
Describes a system, or a component of a system, that has a truly
proportional response. That is to say, the output of the system
is always perfectly in direct proportion to the input
(under normal operating conditions and within practical and
appropriate limits of detection). So, a doubling of input
produces a doubling of output, etc. Such a component
or system has the important property that no new
frequencies are introduced
into the signal by it.
A system or component which does not behave in this way
is (in general terms) described as 'non-linear'.
See also Taper,
Potentiometer,
Power supply,
Intermodulation and
Interpolation.
Linear phase
response
If the phase response
of a system whose
group delay
is constant over a particular
frequency range is plotted
against frequency, the result will be a straight line over
that frequency range; this is described as a 'linear phase
response'. So this term is just another way of saying
'constant group delay', which is a good thing in high-quality
audio systems.
A system having a linear phase response over a particular
frequency range is sometimes described as being
'phase linear' over that range. A system having a linear
phase response is not necessarily a
minimum phase system.
Linear
potentiometer
See Potentiometer.
Linear
power supply
See Power supply.
Linear taper
See Taper.
Linearity
The degree to which a system or component behaves in a
linear manner. See also
Intermodulation.
Link (1)
An interconnection path between equipment or between
locations, a term often used when there is a
considerable distance
involved. Although sometimes used as short for 'radio link'
(i.e. a wireless interconnection), it may also
be used to refer to a physical interconnection −
see Line.
Linkwitz-Riley
Describes a crossover which
uses 4th-order
Butterworth
filters. So-called because the
engineers S. Linkwitz and R. Riley determined that this
arrangement gives an improved result over 3rd-order designs
− not only by virtue of a steeper
slope, but also in that the
low-pass and
high-pass outputs are well
co-ordinated in amplitude and
phase through the region of
the crossover
frequency. This is important because in this region
both drivers
are operating simultaneously, and so problems in
co-ordination of their drive signals can lead to
undesirable variations in the overall output
level and in the
directivity of the
speaker. Abbreviation LR, or
LR-4.
Lip microphone
A microphone which is
intended to be held extremely close to the mouth. It usually
has a shield protruding from its top surface; this is intended
to touch the user's face between the upper lip and the nose −
hence the name. It is generally used only for
sports commentary applications, and is usually of the
noise-cancelling
type.
Lip sync
In audio-visual applications (such as TV or film), the
degree to which the sound and vision tracks are in
synchronism, characterised by the degree to which the
sound of a person's voice corresponds with the movement
of their lips. It may be adversely affected by the
latency of
signal processing
equipment such as digital
vision mixers.
Listen wedge
The monitor
speaker
that is provided for use by the
monitor engineer.
It enables him/her to listen to a particular performer's
monitor mix − this is especially
useful when making adjustments to the mix. Typically the
listen wedge is fed from the 'control room' output of the
mixer, and the mix to be
monitored is selected by activating the
AFL of the appropriate
aux send. The monitor
should be of the same type as those used by the performers,
and any outboard
processing (most commonly
graphic equalisers)
that is used for the monitor mixes should be
patched into the aux send
inserts of the mixer, so
that their effect is apparent in the listen wedge.
See also Wedge.
Littlite
A trademarked name for a particular brand of miniature
illumination devices for equipment and for musicians'
music stands. The gooseneck
variety is frequently used for illumination of
mixer control surfaces, where
it is often powered and supported via a
BNC
connector. The most
popular lamp rating
is 12 volts
5 watts.
Live (1) (electrical)
Describes an item of equipment that is currently
in use, or that is connected to a source of electrical power
− especially mains power.
(More formally, live mains supply distribution equipment or
cabling is described as
'energised'.)
Or, describes a conductor
that is at (or is intended to be at) a significant
voltage with respect to the
general mass of earth; that is, a
non-earthy
conductor, sometimes referred to as a
'hot'
conductor, or marked '+'.
Warning: In energised mains supplies, the live conductor
is at a dangerously high voltage with respect to earth.
See also
Phase conductor.
Live (2)
(microphones)
Describes a microphone
that is currently 'open' − i.e. the sound that it
picks up is currently being used in some way (amplified,
recorded, broadcast, etc.).
See also NOM.
Live (3) (programme)
Describes a programme
originating from a performance, or other event, that is
happening at essentially the present time; not one
previously recorded.
Live programme material must be handled in
real time.
Lively
Describes acoustics
having a long
reverberation
time.
Compare Dead (1).
LM
An abbreviation for
'lower
mid-range'.
LMID
An abbreviation for
'lower
mid-range'.
Lo-Z
See Low
impedance.
Load
The item of equipment, or an
input
of it, which is the destination of a
signal or of a
source of electrical power.
The impedance of the
load is often significant (see the
next definition), particularly in regard to
speakers.
Or, as a verb, the effect that connection of one or more
loads has on the output
of the source equipment − particularly as
regards the resulting reduction in output
level.
Load impedance
Usually, the combined
input impedance
value of all the loads
that are connected to a particular
output.
Or, the input impedance value of a particular load.
Load impedance is of particular importance in the
interconnection of speakers
and power amplifiers
− see the
Impedance
section on the
Amplifiers & Speakers page.
See also
Input impedance,
Output impedance,
Parallel and
Series.
Load-in
The process of moving a performer's equipment,
or a rig, from the transport
vehicle(s) into position in
the venue before an event.
Compare Load-out.
Load-out
The process of moving a performer's equipment,
or a rig, from its location
in the venue into the transport
vehicle(s), after an
event. See also De-rig.
Compare Load-in.
Lobar
Describes a
microphone whose
polar response
contains multiple lobes.
An alternative name for a
rifle microphone,
as these types have such a polar response.
Lobe
An imaginary 3-dimensional area in space,
emanating from a speaker
or a microphone,
the boundary of which area defines a given degree of
sensitivity of that
particular device.
For example, the rear lobe of a microphone is the
region of pick-up on the microphone's rear axis, which
occurs in the case of
super-cardioid and
hyper-cardioid
polar responses.
Log
An abbreviation for 'logarithm'. The mathematical power to
which some number (called the 'base') must be raised in order
to give a particular value. Logarithms to the base 10 are
generally assumed, so the log of a number is the power
to which 10 must be raised to give that number.
For example the log of 1000 is 3, because
103 = 1000. Similarly, the log of 0.01 is
-2, and the log of 1 is 0.
Or, an abbreviation for 'logarithmic', which describes a component, scale, or response in which the 'output' varies in accordance with the logarithm of the 'input' (or approximately so, or within defined limits). An example of this usage is 'log pot' (see Potentiometer).
The main relevance to sound engineering is in relation to decibels, which is a logarithmic scale − see the Decibels page. See also Taper.
Log pot
See Potentiometer.
Long throw
Describes a speaker
that has narrow dispersion
angles, enabling it to provide sound effectively to an
audience at some distance from it (say, greater than 12
metres). See also
Directivity.
Compare Short throw.
Longitudinal
choke
An inductor whose
purpose is to introduce an opposition to
signals carried by
all the conductors
of a cable, rather than to the
signals appearing between the conductors.
Most often used to reduce
common-mode
radio-frequency (RF)
electromagnetic interference (EMI) picked up by,
or radiated by, computer equipment or other
digital
signal processing
equipment. In such cases the choke is usually implemented
as a ferrite cylindrical or
toroidal core through which the whole cable is
passed either once or twice; this is seen as a cylindrical
'bulge' close to one (or both) ends of the cable.
Sometimes called a 'common mode choke'.
('Choke' is just another term for an inductor.)
Longitudinal
wave
A wave in which the variations in the medium occur
along the length of the wave in its direction of travel.
For example, a sound
wave in air is a longitudinal wave consisting of alternate
regions of compression
and rarefaction.
See also Speed of sound.
Loop (1)
Short for
Induction loop.
Loop (2)
Short for Effects loop.
Loop (3)
A recording that, when played, is arranged to restart each
time that it reaches the end of the recorded material.
Loop amplifier / driver
See Induction loop.
Loop system
See Induction loop.
Loss
The amount of
attenuation given to a
signal between two specific
points in a system or within an item of equipment.
Or, the amount of reduction in response (or
sensitivity) of an item
of equipment at a particular
frequency, as compared to its
response at another frequency (often a standard reference
frequency such as 1 kHz)
− see
Frequency response.
Loss is usually measured in
decibels.
Compare Gain.
Lossless (1)
See
Compression (2).
Lossless (2)
Describes equipment or an interconnection having
no attenuation.
Lossy (1)
See
Compression (2).
Lossy (2)
Describes equipment or an interconnection having
a significant
attenuation.
Loudness (1)
The apparent magnitude or 'volume' of an audible
sound, as perceived by an
average human ear (therefore also called 'perceived
level', or 'perceived volume').
On average, loudness is subjectively judged to double for
each 10 decibels
increase in
sound pressure
level.
Usually measured in phons
(occasionally in sones).
Contrast with sound pressure level (SPL), which is the
actual magnitude of the sound.
See also VU.
Loudness (2)
A control, usually found on a domestic
Hi-Fi
amplifier,
which may be operated to activate
equalisation
that partially compensates for the apparent
reduction in sound quality which occurs when
listening at low
sound pressure
levels.
It works by boosting
the bass
frequencies
to compensate for the ear's reduced sensitivity to
those frequencies at low
levels, and also
boosting the treble
frequencies to compensate for the
masking effect
of low-level
ambient noise.
Loudspeaker
See Speaker.
Low cut
The operation of reducing the
bass content of a
signal.
Or, the name of a switch or control(s) that provides
this function (e.g. on a
mixer, where it may be
considered to be a part of the
channel
EQ section). May be abbreviated
to 'LC', or may alternatively be referred to as
'high pass' (HP).
On a mixer, a variety of forms are found, depending
on the mixer sophistication − for details see
Equalisation
on the Mixing Facilities page.
For cross-references to more filtering-related
terms see Filter.
Compare High cut.
Low end
The bass end of the
audio-frequency
spectrum, also called the 'bottom end'.
Compare High end.
Low frequency
See Bass (1).
Low impedance
Usually describes equipment or interconnections in which the
source impedance
is, or is intended to be, no greater than
600 ohms.
Sometimes written 'Low-Z' or 'Lo-Z', because Z
is the symbol for impedance.
Note that inputs intended
for the connection of low-impedance
microphones usually
have an
input impedance
significantly greater than 600 ohms (typically
2 kilohms),
but are nevertheless referred to as 'low-impedance inputs'.
For further information on the impedance of microphones,
see the Microphones page.
A speaker that is not
a 100 V line
type is sometimes referred to as a 'low-impedance speaker'.
See also Matching.
Compare High
impedance.
Low pass
Describes a filter that
attenuates
('cuts')
frequencies higher
than a particular value, but allows frequencies lower
than that value to pass through relatively unaffected.
The boundary between the range of frequencies allowed to pass
and those cut is called the
cut-off frequency,
however in practice the transition between 'cutting'
and 'passing' is not abrupt, but takes place over a range
of frequencies.
The cut-off frequency of a low pass filter is usually
considered to be the frequency at which the
attenuation
is 3 dB greater
than the average attenuation at frequencies that
are low enough to be clear of the transition region.
A low pass filter is sometimes referred to as a 'high cut'
filter. For cross-references to more filtering-related
terms see Filter.
Compare High pass.
Low-Z
See Low
impedance.
Lower mid-range
Describes an
audio frequency
at the lower end of the mid-range
frequencies, typically between 250 and
800 Hz.
Often abbreviated to 'LMID' or 'LM'.
Compare
Higher mid-range.
Lows
Another name for bass
frequencies.
Compare Highs.
LPF
An abbreviation for
'low pass
filter'.
LR, LR-4
See Linkwitz-Riley.
LSF
An abbreviation for 'low smoke and fume'. Describes a
cable that emits little
smoke or hazardous fumes when exposed to extreme heat
or fire. Such cables are sometimes specified for
permanent PA
installations in certain types of building.
Lumen
The unit of measurement of light intensity, commonly
used to specify the intensity of video projectors.
As there are several possible ways to make the measurement,
the method laid down by ANSI
is often indicated.
Luminance
The part of a
composite video
signal that carries the
monochrome (i.e. black and white) information,
that is, the brightness information.
Abbreviation 'Y' (sad, but true!).
Compare Chrominance.
See also S-video.
LV
An abbreviation for lead
vocal(s). Compare BGV
and BV.
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This page last updated 10-Nov-2009.