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Home entertainment glossary
The really easy guide to terms and technologies
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by: Jim Sommerville
Confused by jargon
and technobabble? Here's a guided tour of the major terms and technicalities
you'll encounter in the world of home theatre.
Every area of specialised interest invariably
incorporates its own often particular collection of words, phrases
and terms to efficiently quantify and qualify technical information.
The arena of home entertainment is no different, with myriad associated
words that mean plenty to those people involved but often leave other
people scratching their heads.
Some of the terms you'll encounter in home entertainment are self
explanatory, while others have entered the world of common usage.
Many people, become downright confused and, ultimately, frustrated
in an endeavour to become 'informed' on the subject.
This is where our glossary comes to the rescue, by highlighting
various words and terms and then providing as clear a definition
of their meaning - in 'lay' language - as possible. We've avoided
scraping away at the essence of home entertainment words and
terms and providing a 'Cat in the Hat' interpretation of their
meaning.
[
A
]
AC (ALTERNATING CURRENT):
An electrical potential with periodically changing polarity. Often
used as synonym for electrical house current. <<<
AC-3: Dolby Laboratories' new method of encoding full-range
digital sound on film and consumer software and of decoding it for
home theatre. <<<
ACOUSTIC FEEDBACK: Unwanted mechanical interaction between
output and input of an audio system, such as that between loudspeaker
and microphone or turntable cartridge. Also called Positive Feedback.
<<<
ACOUSTICS: The science of sound. Also, referring to the acoustical
character of venues and spaces. <<<
AMPLIFICATION:
A device that increases electric voltage, current, or power, or the
loudness of sounds. <<<
AMPLITUDE: Strength or magnitude of a signal. <<<
ANALOG: In the audio field, signals in which the sound level variations
and pitch of the sound are represented by amplitude level and frequency
variations. This is as opposed to 'digital' signals, which consist
of coded groups of numbers that represent these variations mathematically.
<<<
ATTENUATOR: Any device used for decreasing the strength of
a signal. <<<
AUDIBILITY THRESHOLD: The minimum sound intensity the average
human ear can hear. <<<
AUDIO-VISUAL: A term used to describe the synergy between and
amalgamation of sounds and images. Usually used in reference to amplifiers
and receivers which have connection, switching, interaction and processing
facilities for audio and video components. <<<
AUTOMATIC LEVEL CONTROL: A circuit which automatically keeps
the amplitude of a signal within a present range. <<<
AUX (AUXILIARY) INPUT: An input stage that accepts line-level
signals, for example those with average amplitudes in the 0.750-volt
range, and further characterised by fairly high (50k-100k ohm) input
impedance. <<<
AZIMUTH: The angle of a tape head's gap relative to the tape.
<<<
AZIMUTH ERROR: Refers to the lack of parallelism or to the
difference in angular measurement between the magnetic gaps of the
record and playback head. If the record head is just slightly askew
with respect to the play head, high-frequency response is diminished
and the two channels are not reproduced at the same time (in phase).
<<<
[
B
]
BALANCE CONTROL:
Device used to adjust volume difference of left and right stereo channels.
<<<
BANDPASS FILTER: A circuit which will transmit signals at particular
frequencies or groups of frequencies (bands) while attenuating others.
<<<
BASS: The particular low-range area of the sound spectrum where
low musical notes and sounds are located. <<<
BEAT: A pulsation caused by the interaction of two separate
frequency waves. <<<
BIAS: In tape recording, a high-frequency signal applied to
the tape to induce its magnetic particles to operate in a magnetically
linear region. <<<
BLOCK DIAGRAM: A graphic illustration of the main electronic
circuit sections and signal flow in an electronic device. <<<
BUFFER 1: A digital stage which temporarily stores signal information.
2. An amplifier stage used to match impedance (resistances) between
two circuit stages. <<<
[
C
]
CAPSTAN:
Driving spindle in a tape deck: the tape is pressed against the capstan
by a pinch roller. <<<
CARDIOID MICROPHONE: A microphone with a directional characteristic
that resembles the shape of a heart. <<<
CHASSIS: The mainframe of an audio component, usually including
a baseplate, side walls, front and rear panels and a cabinet. <<<
CHUCKING ARM: Device used to convey the disc clamping mechanism
onto the rotating spindle of a compact disc player. <<<
CLIPPING: The inability of an electrical stage to amplify an
input signal linearly, due to voltage or current limitations. Clipping
results in high distortion. <<<
COIL: A spool of wire wound around a centre bobbin; has properties
of inductance that modify frequency of the signal passing through
the wire. Used in some amplifier output stages and in most loudspeaker
crossover networks. <<<
CONDENSER MICROPHONE: A transducer utilising a change in capacitance
to produce an output voltage. <<<
CONTOUR EFFECT: Also known as 'shoulder effect' or 'head bumps',
this phenomenon is characterised by unevenness in the low-frequency
range, often seen in a frequency response curve as small, undulating
bumps occurring below 100Hz. <<<
CONTROL AMPLIFIER: A preamplifier. <<<
CROSSOVER FREQUENCY: In loudspeaker systems and multi-amplifier
audio installations, the borderline frequencies between low/medium
range and medium/high range speakers or amplifiers. <<<
CROSSTALK: Leakage of right channel signal into left channel,
and vice versa. Expressed as level of unwanted signal in relation
to wanted signal channel, measured in decibels (dB). <<<
CUT-OFF FREQUENCY: The point at which frequency response is effectively
limited, generally defined as the point at which level is reduced
by 3dB. <<<
[
D
]
DAMPING:
Reduction of resonant effects by use of resistance or its mechanical
and acoustic equivalents. <<<
DAMPING FACTOR: Ratio of loudspeaker impedance to amplifier's
output impedance. Denotes amplifier's ability to damp unwanted, residual
speaker movement. <<<
dB (DECIBEL): A logarithmic unit used to express the ratio
between two power, voltage or current levels.
<<<
DIFFERENTIAL AMPLIFIER: A type of amplifier consisting of two
transistors in which the difference in the transistor's input signals
is amplified. Because of their excellent thermal characteristics,
differential amplifiers are used in the first stage of some power
amplifiers, phono stages, etc. <<<
DIGITAL: In audio, a class of signals composed of number groups
that represent musical values mathematically rather than through a
directly analogous relationship between pitch and frequency, amplitude
and loudness. <<<
DIN (DEUTSCHE INDUSTRIE NORMEN): German Industrial Standards.
In audio, the German standard of plugs, sockets, performance ratings,
etc. <<<
DISTORTION: An alteration of a desired signal which occurs
when a component, in reproducing a signal, adds its own harmonics
or modulation by-products. <<<
DOLBY NOISE REDUCTION: A proprietary form of reducing noise
and hiss found in the cassette medium.
<<<
DOLBY HX: Dolby Laboratories' system of extending treble performance
from cassette tapes. <<<
DOLBY PRO LOGIC SURROUND: The original system of producing
surround sound in cinemas and in home theatre systems.
<<<
DROP-OUT: A loss of signal caused by thin or bare spots on
a tape or compact disc or by an intermittent contact in a circuit.
<<<
DYNAMIC RANGE: In program material, the range of signal amplitudes
from highest to lowest; the range (in dB) which a device will handle.
<<<
DVD: A medium that provides digital quality sounds and images
on standard-size (120mm diameter) discs.
<<<
[
E ]
EFFICIENCY:
The acoustic power delivered by a speaker for a given electrical input
- that is, the amount of sound out for the amplifier power input.
<<<
EQUALISATION: 1. Correction for the frequency non-linearity
found in various recording media. 2. Alteration of the frequency response
characteristics of a circuit to achieve a desired effect.
<<<
EUROCONNECTOR: A 21-way connector for linking television, video
and audio equipment together. Mostly fitted to European equipment
but increasingly common in good audio-visual electronic components.
Also called SCART connector. <<<
[ F ]
FIELD STRENGTH:
The intensity of an electrical or magnetic field.
<<<
FILTER: A circuit which attenuates signals above, below or
at a particular frequency. <<<
FLUTTER: See 'Wow and Flutter'.
<<<
FLUX: Magnetic lines of force.
<<<
FLYWHEEL: A disc of large mass which, when rotating, has the
tendency to maintain its rotational velocity. This effect is utilised
in tape equipment and turntables to maintain constant speed.
<<<
FM (FREQUENCY MODULATION): A class of radio waves in which
the frequency, not the amplitude of the carrier, is varied (modulated)
by the audio signal. FM broadcasting achieves higher sound quality.
<<<
FREQUENCY: Rate or number of occurrences in a specific period
of time. <<<
FREQUENCY RESPONSE: Measurement of the ability of a component
to pass signals. This is depicted as a curve which assumes that the
input signal is of equal strength at all frequencies.
<<<
[
G ]
GAIN: Degree
of signal amplification achieved in an amplifier circuit. Expressed
in dB. <<<
GAP: Vertical slit in the core of a tape head. In the gap,
a magnetic field occurs during recording, and a magnetic signal is
induced during replay. <<<
GROUND: A point, usually of zero voltage, used as a reference
for other voltages. <<<
GROUP DELAY: The condition when a circuit produces a shift in
phase dependent on the frequency of the signal passing through it.
<<<
[
H ]
HARMONIC DISTORTION:
The sum of all signals in an output which are multiples of the input
signal frequencies ('harmonics') and not part of the input signal.
Their intensities are expressed as a percentage of the total output
intensity. <<<
HEAD: The erasing, recording and playback transducers used
in tape equipment; they function by inducing a magnetic field that
magnetises the tape particles in record mode and senses these magnetic
variations in playback. Erase heads essentially record a very high
level (ultrasonic) signal as a means of deleting the previously recorded
magnetic information, rendering the magnetic particles random in their
polarisation. <<<
HEAD ALIGNMENT: Mechanical adjustment of the angular relationships
between the head gaps and the tape.
<<<
HEAT SINK: A device used to remove heat from electronic components
such as tubes, transistors and the like.
<<<
HERTZ (HZ): Unit of frequency, equal to one cycle per second.
<<<
HUM: Unwanted low-frequency tone. Usually caused by 50Hz or
60Hz AC and its harmonics. <<<
[
I ]
IC (INTEGRATED CIRCUIT):
Solid circuit block containing the functions of numerous transistors,
diodes, resistors, capacitors, etc.
<<<
IMAGE REJECTION: The ability of a tuner to reject an RF signal
which appears to be received but which is actually a sum of reception
differences in a tuner. <<<
IM DISTORTION: Signals in output caused by interaction of two
or more input signals, but not harmonically related to them. Expressed
as a percentage of total signal intensity. IM distortion is known
to cause listener fatigue and irritation.
<<<
IMPEDANCE: Resistance to the flow of alternating current. Measured
in ohms. It may vary with the frequency of the applied current.
<<<
INTEGRATED AMPLIFIER: Unit combining a preamplifier and power
amplifier. <<<
INTERFERENCE: Unwanted influences on desired signal by extraneous
signals, for example from electrical appliances, motors, automobiles
as well as from undesirable signals generated within the audio equipment.
<<<
[
L ]
LED (LIGHT EMITTING DIODE):
A semi-conductor device that produces light when an electrical current
is passed through it. <<<
LIMITER: Any circuit used to set a restriction on a signal's
amplitude. Usually used to set an upper limit.
<<<
LINEARITY: The tendency to follow a course in a fixed direction:
(a) Amplitude linearity: distortion of which produces harmonic distortion
and intermodulation; (b) Frequency linearity: referring to the straightness
of a frequency response curve. <<<
LINE OUTPUT: Output terminal of a preamplifier, tape deck, etc,
providing a signal for monitoring, tape recording or supplying to
a power amplifier. <<<
LOUDNESS CONTROL (CONTOUR): A circuit which counteracts the
reduced sensitivity of the ear to very low and high frequencies at
low volume levels, but which can be abused and cause damage to speakers.
<<<
LOW FILTER: A filter circuit designed to remove low-frequency
noises (rumble, hum, etc) from the program.
<<<
[
M ]
MAIN AMPLIFIER:
Amplification stage which produces the output power required for driving
speakers. Commonly referred to as a Power Amplifier.
<<<
MIDRANGE: 1. The middle area of the sound range (between bass
and treble) where the ear is most sensitive. 2. The name for the driver
in a speaker system used to reproduce this area of the sound spectrum.
<<<
MONAURAL: 1. One-eared. 2. Monophonic.
<<<
MONITOR: 1. A television display screen where the channel-tuning
section has been replaced by direct video input facilities. 2. Nomenclature
for a high end speaker. <<<
MONOPHONIC: Recording, transmission or reproduction of sound
via a single channel. <<<
MOVING MAGNET (MM) CARTRIDGE: Magnetic cartridge in which the
magnet moves and the coils are fixed.
<<<
[
N ]
NEGATIVE FEEDBACK: Signal
from output of amplifier or electronic network applied to input in
anti-phase (hence negative feedback) to reduce distortion and noise
and to flatten or otherwise shape frequency response.
<<<
NOISE: Unwanted signal consisting of a mix of random electrical
agitations. Also the sum of all unwanted signals such as hum, hiss,
rumble, interference, distortion, etc. NTSC: The television standard
adopted by Japan and America. <<<
[
O ]
OMNI-DIRECTIONAL:
Equal sensitivity or output in all directions. Said of antennas, microphones
and loudspeakers. <<<
OSCILLATOR: An electric circuit which generates an alternating
current by use of positive feedback.
<<<
OUTPUT IMPEDANCE: Resistance across the output terminals of
a device as 'seen' by the load. <<<
OUTPUT STAGE: Final circuit of a power amplifier which supplies
power to a loudspeaker. <<<
OVERTONE: A frequency accompanying the fundamental in a musical
note. May or may not be harmonic. Usually refers to the secondary
vibrations from the body of a musical instrument.
<<<
[
P ]
PAL: The
television standard adopted by Australia and a good deal of Europe.
<<<
PHASE: The order of arrival of a signal or pressure wave. When
multiple signals or waves arrive in synchronisation, they are said
to be in phase. If there is any variance in the sequence of arrival,
they are out of phase to some extent.
<<<
PHASE SHIFT: The relative change in timing (phase) of a signal,
or group of signals, at the output in relation to its input as the
signal passes through a circuit. Phase shift in an amplifier, compact
disc player or cassette deck results in blurring of stereo spatial
localisation and, in serious cases, can cause unstable amplifier performance
and distortions. <<<
PINCH ROLLER: A rubber or neoprene wheel, which presses the
tape against the capstan during recording or play.
<<<
PINK NOISE: Artificially created noise for testing equipment.
Contains equal energy in each octave band.
<<<
POLARITY: The relationship of the positive and negative terminals
of a battery or power supply, or the north and south poles of a magnet.
Often used in reference to the phasing of phono cartridges, stereo
connecting leads and speakers. <<<
POWER AMPLIFIER: See main amplifier.
<<<
POWER HANDLING ABILITY: Maximum amount of power that can be
safely fed into a loudspeaker. <<<
PREAMPLIFIER: A circuit unit which takes a small signal from
a component such as a CD player, tuner or tapedeck and amplifies it
sufficiently to drive a power amplifier for further amplification.
<<<
PRESSURE PAD: A device, usually made of a felt-like material,
designed to force the tape into intimate contact with the head gap,
usually by direct pressure at the head assembly.
<<<
[
Q ]
QUADRAPHONIC:
Defunct system of creating four channels of sound with no attempt
to capture real acoustic effect in the process.
<<<
QUANTISATION: The processing technique which divides an analog
signal up into small time fragments and assigns those fragments a
digital code. <<<
[
R ]
RESONANCE: The
tendency of a mechanical or electrical device to deliver maximum energy
at a particular frequency. Generally, this tendency should be suppressed
for maximum sonic accuracy. <<<
REFLEX: A form of bass loading in speakers where a small tube
and port are used to channel bass sound and enhance the low notes
being produced. <<<
RESOLUTION: 1. A measure of picture quality in a television
screen - the better the resolution the better the image. 2. A measure
of acoustic accuracy - the better the resolution the more accurate
sounds, instruments and voices are.
<<<
REVERBERATION: The acoustic effect caused by sound waves bouncing
between surfaces and the time it takes those reflections to die away.
<<<
RF (RADIO FREQUENCY): A frequency or band of frequencies used
as radio carrier waves, for example FM occupies 88-108 MHz.
<<<
RMS (ROOT MEAN SQUARE): The effective amplitude of an AC voltage
waveform; equal to the DC current or voltage that, in any given load
or resistance, would produce the same power.
<<<
ROLL-OFF: The frequency at which an equaliser, tone control
or filter begins to work. <<<
RUMBLE: Low frequency noise resulting from vibrations in the
platter and motor of a turntable and from record warp.
<<<
[
S ]
SAMPLING: The
rapid measurement of a signal in its discrete time segments (see quantisation).
<<<
SATURATION: The condition of a tape coating or head that has
accepted its maximum degree of magnetisation, or of an amplifier that
is at the point of clipping. Distortion increases sharply as signal
level approaches the point of saturation.
<<<
SENSITIVITY: 1. The input signal level required by a tuner,
amplifier etc, to be able to produce a stated output. The lower the
necessary output, the higher the sensitivity required.
<<<
SEPARATION: Degree to which two or more individual signals
are isolated; such as channel separation between the left and right
circuits of a stereo amplifier or CD player. 2. The volume level of
sound produced by a speaker for a given input, usually a 1-watt input.
<<<
SETTLING TIME: The period required for a signal to assume its
correct value after a change of state. In digital applications, the
length of time needed for a digital-to-analog converter's output voltage
to reach a stable value. <<<
SIGNAL-TO-NOISE RATIO: Ratio between a reference output level
and the background noise of an amplifier circuit or storage media.
<<<
SYNCHRONOUS MOTOR: Type of AC electric motor in which rotational
speed is related directly to frequency of power supply.
<<<
[
T ]
TAPE GUIDES:
Grooved pins mounted in the tape path of most tapedecks to position
the magnetic tape correctly as it passes over the head assembly during
recording or playback. <<<
THX LUCASFILM: A proprietary form of manipulating Dolby Pro
Logic sound in home theatre systems to provide better quality and
surround sound effects. <<<
TONE CONTROL: Circuits with frequency response variable over
a fixed range, used to vary the proportion of bass and treble in the
audio signal. <<<
TORQUE: 1. The force that tends to produce a rotating motion.
2. Rotation of the plane of polarisation of light by some crystals.
<<<
TRANSDUCER: Device for converting energy from one form to another,
eg a loudspeaker converts from electrical to acoustic, a playback
tapehead converts from magnetic to electrical.
<<<
TRANSIENT: Abrupt change of state; sudden change in signal
amplitude as might be caused by percussion instruments, plucked strings,
etc. <<<
TRANSIENT RESPONSE: The ability of an amplifier, cartridge
or speaker to follow sudden changes in amplitude.
<<<
TREBLE: The high notes of the sound spectrum.
<<<
TUNER: The part of a receiver, or a separate unit, which receives
radio broadcasts and converts them into audio frequency signals.
<<<
TWEETER: The driver in a speaker system used to reproduce treble
music notes. <<<
[
V
]
VHS: Video
Home System: the world's domestic standard for the video cassette
medium. Also stands for 'vertical helical scan'.
<<<
VHS-C: A compact version of the VHS video system which is used
in some video movie systems and is replayable on a VHS domestic video
recorder via an adaptor. <<<
VIDEO-8: Compact form of video storage and retrieval used extensively
in video camera systems. It
is not compatible with domestic VHS stationary machines.
<<<
[
W ]
WHITE NOISE: Random
noise that contains every frequency across the acknowledged sound
spectrum and used to test equipment.
<<<
WEIGHTING: Alteration of the conditions of a test in order
to produce specific results, usually by application of a non-linear
curve. <<<
WOOFER: A driver in a speaker system used to reproduce low music
notes and lower frequency sounds. <<<
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