A: Common abbreviation for ampere (see ampere).
AB Switch: A coaxial cable switch capable of switching
one cable to one of two branch cables, A or B.
AC: Common abbreviation for alternating current.
Acoustic: Pertaining to sound; usually refers to the
specific characteristic sound in a particular place (e.g.
cathedral acoustic; concert hall acoustic; listening
room acoustic etc). See Reverberation also.
A/D: Analog/Digital; an integrated circuit device that
converts analog signals to digital signals
Alternating current: Electricity in the form of sine
wave (ie. with positive and negative halves of a
continuous waveform). Mains electricity is in
the form of alternating current (AC).
Ampere: Measure of electrical current (Often abbreviated to A).
Analog: Literally analogous to the waveform of
the original source signal. An analogue waveform is
usually a composite of many sine waves and sudden
or transient signals such as a struck cymbal. See also
Digital.
Aerial: An array of metal wire used primarily to help a
radio or television tuner locate and tune into broadcast
signals. A complex multi-element FM aerial or yagi is
required in areas far from radio transmitters. It
comprises reflectors and directors, as well as the
standard dipole.
Ambisonics: A recording/replay system developed in
the Seventies to improve three dimensional stereo
definition by means of a special microphone recording
technique, encode/decode electronics and a multiple
surround sound loudspeaker playback system.
Amplifier: An electronic device or product designed to
turn a small signal into a larger one. An integrated
amplifier accepts input signals, has source selection
and volume controls and provides an output sufficiently
high to drive loudspeakers. A power amplifier, simply
the loudspeaker driving half of an integrated amplifier.
A pre-amplifier, the first half of an integrated amplifier,
provides inputs for the various source signals,
switching between sources and a number of controls
(eg volume, balance, tone and other signal processing).
Most hi-fi amplifiers contain two channels (left and right
stereo). A monoblock power amplifier is a single channel
amplifier. Two are required to drive a stereo pair of
loudspeakers. Multi-channel amplifiers are required
for surround sound systems. For instance a fully
fledged Home THX system requires five channels
of amplification (left, center and right front, plus
two rear channels). An extra power amplifier is
sometimes required if a subwoofer (very deep bass
loudspeaker) is used to supplement the low frequency
output of the system.
Amplitude Modulation: A form of radio broadcast,
(abbr: AM); literally means that the carrier frequency is
modulated, or varies, in size (amplitude) according to
the content of the transmitted signal.
Anechoic: Non-reverberant. An anechoic chamber is
an acoustically dead room designed primarily for the
purpose of accurate loudspeaker measurement.
ATRAC: The system of data reduction used by Sony
in its MiniDisc format.
Audio: A term used to describe sounds within the range of
human hearing. Also used to describe devices which are
designed to operate within this range.
Auxiliary Bass Radiator: A loudspeaker drive unit fitted to
a box loudspeaker, coupled acoustically but not electrically
to the input signal. Functions somewhat like a port or
tuned tube in the loudspeaker cabinet supplementing
bass output and aiding loudspeaker sensitivity.
AWG: American Wire Gauge; a wire diameter specification,
the lower the AWG number the larger the wire diameter.
B
Back EMF: The rear electromotive force from loudspeakerC
drive units.
Baffle: A board or panel designed to separate the front
and rear output from a loudspeaker drive unit.
Balanced: In a balanced electrical circuit the positive
and negative conducting paths are referenced to
earth equally. The advantages of balanced operation
are improved signal to noise ratio and distortion
compared with unbalanced circuits.
Bandwidth: A range of frequencies defined by its highest
and lowest limits. The audio bandwidth of human
hearing has traditionally been defined as 20Hz to 20kHz.
In pure electronic terms, the width of a communication
channel, measured as frequency (in cycles per second,
or hertz). A channels bandwidth is a major factor in
determining how much information it can carry.
Bass: The bottom octaves of human hearing.
Bass Reflex: A type of box loudspeaker whose bass
output is supplemented by a port (a hole or tube) tuned
to a particular frequency to extend bass below the
resonant frequency of the bass drive unit, and to help
improve the overall loudspeaker sensitivity.
BER: Bit Error Rate. The ratio of received bits that are
in error, relative to a specific amount of bits received;
usually expressed as a number referenced to a power
of 10.
Bias: A high frequency AC signal applied to the record
head of a tape recorder to help it record a wide bandwidth
linear signal onto magnetic tape.
Binaural: Associated with a type of recording made using
a dummy head fitted with microphones located at
the position of the two ears. Replay of binaural recordings
via headphones is considered to enhance a sense of
'out of the head' definition in contrast to the normal
'inside the head' sound using headphones.
Binding Post: A device for clamping or holding electrical
conductors, such as wire, in a rigid position.
Belt-drive: Turntables fitted with a belt between the
drive motor pulley and the record-supporting platter. A
belt is used to isolate the pickup cartridge from motor
noise. It is traditionally regarded as the best way to
maintain rotational speed stability at audio frequencies.
C: Symbol for capacitance and centigrade.D
Cantilever: Arm on which is fitted the stylus of a
pickup cartridge.
Capacitance: A measure of reactance
(units: Farad, pF, uF etc).
Capacitor: Solid state device used in electronic circuits
and loudspeaker crossover networks to introduce a
required level of capacitance.
Cartridge: The small component fitted to the front end
of a tonearm. Contains the stylus and electro- magnetic
system required to track a vinyl record (LP or single) and
feed output to an amplifier phono stage. There are two
main types of hi-fi pickup cartridge - the 'moving magnet'
and 'moving coil'.
Cassette: Audio cassette or analogue cassette. Contains
blank or pre-recorded tape on spools constrained
within a case or cassette.
Cassette deck: The machine required to play and/or record
onto an audio cassette.
CD: Compact Disc. (see Compact Disc).
CDi: Compact Disc Interactive. An offshoot technology
from CD, developed by Philips as an educational and
entertainment format providing interactive still and moving
pictures and audio sound.
CD-ROM: Compact Disc Read Only Memory is an
audio/video offshoot technology from CD. Now an
established multimedia source, CD-ROM is now an
accepted extra source for Macintosh and
Personal Computers.
Chip: A silicon chip on which is etched a microcircuit.
May perform a variety of functions from amplification to
signal processing.
Clipping: The type of distortion caused by gross overload.
The resulting loud, harsh and unpleasant sound may
cause damage to a hi-fi system, particularly loudspeaker
drive units. Clipping is so named because of its reference
to the sharp truncation of the AC signal waveform.
Coloration: A term used to describe the added color or
artificial character superimposed on the pure, true
sound of an audio signal as it is reproduced by hi-fi
components. Loudspeaker colorations are perhaps
more pronounced and easily identified than other types.
Compact Disc: The first commercially available digital
audio playback format. Software is a 12cm diameter
single sided silver disc containing digitally encoded
signal to a 44.1kHz, 16-bit standard. Optical playback
is by means of laser beam. Developed jointly by Philips
and Sony CD has spawned a number of offshoot
audio/video technologies such as CDi and CD-ROM.
Compliance: A measure of the springiness in a
component. A cantilever suspension, moving coil
speaker drive unit suspension, CD player isolation feet etc.
Compression: A measure of the dynamic range of a
signal. A compressed (or reduced) dynamic range
may be required of some broadcast signals to prevent
overload during some radio transmissions. However
it is anathema to high fidelity reproduction, since low
level signals are raised and high level signals lowered
so that the full power and subtlety of the sound is lost.
Conduction: Electrical signal transmission.
Conductor: A material suitable for carrying an electric
current.
Crossover: A network of components, usually
capacitor(s), inductor(s) and resistor(s) arranged on a
circuit board inside a box loudspeaker to divide the
incoming signal from a power amplifier into discrete
frequency bands appropriate for each loudspeaker
drive unit. In simple terms in a two-way loudspeaker,
the crossover feeds treble to the tweeter and
midrange/bass to the main cone drive
unit.
Cycles per second: More commonly known as
Hertz (abbr: Hz) after the German who discovered
the nature of audio frequencies. It is the speed of
movement of a sine wave or cycle that determines
its frequency, and in turn the musical pitch of a note.
D/A: Digital to AnalogE
DAC: Digital to Analog Converter. A chipset or circuit
or audio product whose primary function is to convert
a digital signal into an analog form.
Damping: A process whereby the amplitude of a
vibration or resonance is reduced. This may be required
in tonearms or loudspeaker cabinets for instance.
Resistors may be used in circuits to provide electrical
damping. The pros and cons of damping have
generated heated debate among audio enthusiasts.
Damping Factor: A measure of the control an amplifier
exerts over a loudspeaker drive unit. Damping factor
is a measure of amplifier output impedance relative to
loudspeaker impedance.
DAT: Digital Audio Tape. This format introduced in the
late Eighties makes use of a rotating drum containing
a helical scan head similar to the sort used in video
cassette recorders. Unfortunately disagreement
between the recording and hi-fi industries led to a
refusal by the major record companies to produce
pre-recorded DATs or to sanction the release of a
non-copyright protected digital tape recorder hardware.
By the time a copyright protection system had been agreed,
DAT was dead on its feet as a mainstream consumer
format, though it is widely used by professionals and
semi-professionals today.
DCC: Digital Compact Cassette is Philips' backwards
compatible digital cassette format. In addition to
playing and recording Digital Compact Cassettes,
DCC recorders also play standard analogue cassettes.
Hence the term backwards compatible. DCC tapes work
to 16-bit 44.1kHz sampling. It also features Philips' PASC
data reduction system. PASC selectively discards signals
thought to be below the threshold of audibility. Soft signals
audible in isolation may be masked by louder signals.
In such circumstances PASC eliminates the masked signals.
dB: abbreviation for decibel
DC: abbreviation for direct current
Decibel: A measure of loudness (abbr: dB). The decibel
scale is such that 3dB represents a doubling of amplifier
power from say 50W to 100W), while 10dB represents
a doubling of perceived loudness.
Dielectric: The non conducting space/insulation between
two conductors in a cable.
Digital: A sampled analogue waveform encoded in the
form of on/off pulses. The frequency with which the
analog waveform is sampled is its sampling frequency
which, in the case of Compact Disc, is set at
44.1kHz (44,100 samples per second). The accuracy
of sampling is determined by the word length of each
sample. For Compact Disc it is 16-bit. Modern
professional digital recorders are capable of
almost 24-bit resolution as of this date (12-15-96).
Diode: The thermionic diode invented in 1904, marks
the start of the electronics era. It is the first device for
controlling the flow of current in relation to applied voltage,
and comprises two electrodes, the heated cathode
(electron source) and anode (electron receptor).
Direct Current: Current that does not have a positive
or negative value. Usually referred to as DC.
Diaphragm: The surface of a loudspeaker drive unit.
Most moving coil bass drive unit diaphragms are cones
while moving coil tweeters are invariably domes.
Ribbon and electrostatic drive units are flat.
Directionality: The tendency in some loudspeakers to
beam sound like a laser rather than radiate it equally in
all directions. Horn, ribbon and electrostatic speakers
tend to be more directional at high frequencies than
well designed dome moving coil tweeters, a factor
that in extreme situations can impose restrictions on
listening and speaker position.
Distortion: Any loss or addition to the audio signal is a
distortion. Various amplifier distortions have been
identified, the most commonly measured being
intermodulation, transient intermodulation and
harmonic distortion.
Dither: A low level random noise added to a digital
signal to mask highly audible forms of digital distortion.
DMM: Direct Metal Mastering. An LP disc mastering
process in which silvering and electroplating stages
are eliminated.
Dolby® B, C & S: Three types of noise reduction system
featured on cassette decks. The highest amount of
processing occurs with Dolby S, the least with Dolby B.
Dolby A is a noise reduction system sometimes used
in professional recording situations.
Dolby HX Pro®: A form of signal processing during
recording which prevents self biasing of the signal. HX Pro
thus protects loss of high frequency signals through
unwanted compression, a useful feature in cassette
decks.
Dolby Stereo® & Dolby Surround®: All Dolby Stereo encoded
cinema sound tracks contain a surround channel. This may
be recovered from video recorder sound tracks by a
Dolby Surround Decoder.
Dolby Pro-Logic®: A more advanced form of Dolby Surround
encoding and decoding in which there is an additional
front center channel containing dialogue information.
Drive unit: One of the most important components in a
loudspeaker. The drive unit turns electrical power,
fed to it from an amplifier, into acoustic power. Most
drive units operate over a limited frequency bandwidth.
Tweeters handle treble frequencies, Woofers operate
over the bass frequency range.
DVD-Audio: At the time of this writing, this 12cm disc offers
5.1 and 7.1 channels (the .1 is for subwoofer) and digital
audio specifications of signals including 16/20/24-bit
with 44.1/48/96/192kHz sampling rate. This format also
includes Dolby AC-3, linear PCM, and MPEG-2.
Dynamics: The level changes present in music.
Dynamic range: A useful definition is the difference
between the quietest and loudest sound of a music signal.
Earth: Sometimes called ground, earth is the zeroF
reference point for electrical circuits including the
mains electricity supply.
Earth Loop: A source of hum audible through the
loudspeakers, at mains frequency (or multiple thereof),
and caused by failure to find a common single earth.
Incorrect earthing of tonearms and turntables
is perhaps the most common source of earth loops.
Echoic: Literally prone to echo. Hard surfaces in
listening rooms will result in a lot of high frequency
reflections and a generally echoic sounding acoustic.
The technical term for this is a long reverberation time.
It is to be avoided if possible.
EIA: Electronic Industries Association. The United States
national organization of electronic manufacturers. It is
responsible for the development and maintenance
of industry standards for the interference between
data processing machines and data communication
equipment.
Efficiency: A measure of the proportion of electrical energy
fed to a loudspeaker that is turned into acoustic
energy. Most loudspeakers are very low efficiency
transducers (typically around 5 per cent). Only
horn loudspeakers manage a much higher efficiency
(sometimes around 30 per cent).
Eigentone: A standing wave set up between two parallel
room surfaces. The frequency of a standing wave is
determined by the distance apart of the parallel surfaces.
A listening room where the long axis is double that of the
short axis is likely to have acoustics problems since the
first standing wave will be augmented by one at twice the
frequency. This second harmonic will be difficult for the
ear to differentiate and the effect will be a pronounced
and audibly intrusive bass resonance easily excited
by music signals.
Electromagnetic induction: The process whereby an
electrical current is induced in one of two ways. Either
a magnet moves within a structure of coiled wires, or
vice versa. It is the foundation stone or underlying
principle of all moving coil loudspeaker drive units,
moving coil cartridges and moving magnet cartridges.
Electrostatic:The electrical force induced when friction
is applied between two nonconductive materials
(eg plastic and paper). The principle has been applied
to loudspeaker design. The Electrostatic loudspeaker
works by applying a fixed or polarizing voltage to an
electrostatically charged flat diaphragm mounted between
two transformer coupled plates fed anti-phase signal.
EMI: Electromagnetic Interference. External signals that
disrupt the data being transmitted on the local area
network or electronic device being operated.
Equalization: A correction made on playback of tape
recordings to restore correct linear frequency balance
Feedback: Acoustic or structure-borne vibrations thatG
interfere with the operation of audio equipment. For
example loud deep bass emanating from a loudspeaker
may upset the performance of a turntable such that the
pickup stylus reads the interference as bass signal. In
extreme instances a loop of sound may be created
resulting in high frequency instability; the more usual
effect is a loss of clarity to the music signal. Bass
becomes woolly and the rest of the signal unfocused.
See also Negative Feedback.
Fiber Optics: Transmission of energy by light through
glass fibers. A technology that uses light as an
information carrier.
Filter: An electrical circuit which blocks signal below
or above a predetermined frequency. The filter rate
may be shallow, steep, or in the case of a digital filter
of 'brick wall' type.
Frequency: The number of cycles per second
(Hertz or Hz) of a vibration, resonance or sine wave.
Audio frequencies range up to 20kHz (20,000Hz), though
many experts believe humans may be able to detect
far higher into the supersonic spectrum. Radio frequencies
(RF) extend from around 70kHz into the MHz. FM stereo
broadcasts are typically in the 87.5 -107MHz
frequency bandwidth. In some countries such as Japan,
FM broadcasts are at a slightly lower bandwidth.
Frequency response: The measured accuracy within db
limits of a piece of audio equipment. For instance, hi-fi
loudspeaker manufacturers specify the tolerance limits
(usually +/-3dB) of each model alongside the
operating frequency range (typically 50Hz - 20kHz).
Front end: Traditionally used to designate the input
stage of a radio tuner. More broadly it refers to the source
component in a hi-fi system. This could be one of a
number of product types from CD player and turntable
to tuner and turntable.
Fuse: Protection device containing thin wire within
glass case. The fuse wire will break under high stress
conditions preventing overload of the component
(eg Loudspeaker or amplifier).
Gain: An objective measure of voltage amplification.H
GHz: Gigahertz. 1,000,000,000 cycles per second
Grid: The perforated element in a triode tube (valve).
The addition of the grid to the diode thermionic valve
meant that in the triode, the first building block to
the invention of an electronic amplifier had been
discovered.
Ground Loop: The generation of undesirable current
flow within a ground conductor, owing to the
circulation currents which originate from a second
source of voltage.
Harmonics: Multiples of the fundamental sine waveI
frequency. A 50Hz sine wave has a second harmonic
at 100Hz, a third harmonic at 150Hz, a fourth harmonic
at 200Hz, a fifth harmonic at 250Hz and so on. The
timbre of a musical instrument is defined by the
complex mix of harmonics overlain on each note.
In amplifiers, harmonic distortion is the addition of
unwanted harmonics to the signal. Total Harmonic
Distortion is the summation of all harmonic distortions.
HDTV: High definition television.
Hertz (Hz): Cycles per second. Named after Hienrich
Hertz.
Hi-Fi: Abbreviation of High Fidelity. Literally means
honesty or truthfulness. In audio terms the context is
accuracy to the original recorded signal, or more
broadly authenticity to the composed music.
Horn: A flared structure often used to assist a
loudspeaker. Horn-loaded loudspeakers are
considerably more efficient than ordinary moving coil
loudspeakers in turning electrical into acoustic energy.
Hz: Shortened form of Hertz (cycles per second).
I2R: Formula for power in watts, where i=current in amperes,J
R=resistance in ohms.
IF: Intermediate Frequency to which RF signals are
converted in a radio tuner.
Impedance: A measure of resistance and reactance
to the flow of electricity. Measured in Ohms.
Inductance: A measure of reactance with comparable
but different audio effects to capacitance. The measuring
unit of inductance is the Henry.
Inductor: Solid state component with a particular Henry value.
Infinite Baffle: Sealed box loudspeakers work on the
infinite baffle principle. The idea is to isolate the rear
radiation and front radiation from a loudspeaker.
In theory an infinitely large baffle board will perfectly
achieve this goal.
Jitter: The slight movement of a transmission signal ink
time or phase that can induce errors and loss of
synchronization in high-speed synchronous communications.
kHz: 1000Hz or kiloHertz. or 1000 cycles per second.L
kOhm: 1000Ohms or kiloOhm.
kWatt: 1000W or kiloWatt .
L: Symbol for inductance.M
Lacquer: The soft disc cut on a lathe from the master
tape. It is the first disc stage in the production of LPs.
From the lacquer are made a number of negatives and
positives before the negative metal stamper
can be created to press vinyl discs.
Linearity: A general term referring to the accuracy of
response of an audio component in terms of a particular
measured parameter, such as frequency response.
Line Stage: Another name for a preamplifier. A unit that
controls the volume and allows for selection of various inputs
(CD player, Tuner, etc).
Load: Electrical resistance is often referred to as the load.
Loudspeaker: A device for converting electrical energy
into acoustic energy.
LP: Long Playing record. Usually a 12 inch diameter
vinyl disc.
LW: Long Wave band (one of three AM radio bands,
the other two being Short Wave and Medium
Wave).
Magnetic flux: The measure of strength of a magnet.N
Unit of measurement is Gauss (G).
Mastering: The process of recording and mixing that
leads to the production of a master tape and finished
pre-recorded cassettes, LPs, Compact Discs, DCCs
and MiniDiscs are mass produced copies derived
from the mastering of studio mix.
MHz: Megahertz (one million cycles per second).
Microphony: Unwanted microphone like behavior of
components in the audio replay system. In effect
sound causes these components to vibrate at their
resonant frequency and the vibration modulates the
signal waveform. Tubes (also called valves) are
known to behave microphonically but so too do
some solid state components.
MiniDisc: A record/playback system developed by Sony
using a small silver disc as software and a data
reduction technology known as ATRAC. Seen by
many as a rival to Philips' Digital Compact
Cassette. MiniDisc is incompatible with CD since it
is a magneto-optical record/playback format.
Monitor: Loudspeaker used to gauge quality in a
recording or broadcast studio.
Mono: Single channel record/replay standard. All
commercial recordings were mono until the early Fifties
when stereo was introduced.
Moving coil: Operating principle of moving coil
loudspeakers and pickup cartridges. Wound around a
permanent magnet a loudspeaker's voice coil is
fed electrical input signals. The resulting electro-motive
force induced in the coil forces the loudspeaker
diaphragm to move. In the cartridge, the mechanical
movement of the pickup stylus translated to the moving
coils located next to a fixed permanent magnet causes
the production of an analogous electrical signal.
Moving magnet: An alternative and cheaper form of
pickup cartridge to the moving coil is the stylus assembly
moves in precise relation to fixed coils causing the
generation of analogous electrical signals.
Multibit: A type of digital to analogue conversion in
which ladder resistor networks are used to read the
14, 16, 20, or 24-bit words of a digital bit stream.
mV: Millivolt. (1000mV = 1V); 1000uV = 1mV)
Near field: The region within approximately two metersO
of the loudspeakers. Listening tests conducted in the
near field reveal different aspects of a loudspeaker's
performance compared with listening in the far
field.
Negative feedback: An amplifier circuit configured so
that the output signal is fed back to be compared with the
input signal and any error signals cancelled. Easier to
imagine than to achieve the desired results without
unwanted side effects.
Noise: Any unwanted sound other than the signal.
Examples include tape hiss, electronic noise generated
by amplifier circuits, earth loop induced hum, and random
hums, hiss and spurious electronic clicks
and pops (e.g. from static electricity on vinyl records).
NTSC: National Television Standard Committee. The
United States TV standard.
Ohm: The electrical unit of resistance. The valueP
of resistance through which a potential difference
of one volt will maintain a current of one ampere.
Ohm's Law: Stated V=IR, I=V/R, or R=V/I where
V is voltage, I is current, and R is resistance.
One-bit: Also known as BitStream, one-bit digital to
analogue conversion is an alternative method to
multi-bit d/a conversion developed to improve low
level signal resolution.
Output: The audio signal exiting a component.
Output impedance: The source impedance an amplifier
presents to a loudspeaker. The lower the source
impedance the greater difficulty a loudspeaker will
have in feeding Back EMF to the driving amplifier, and
the greater the level of control the amplifier will be able
to exert over the loudspeaker.
Parallel/Series: All electrical components can beQ
connected in series or in parallel. Their effect on signal
may reverse depending on the type of connection. An
inductor connected in series with a woofer will
provide a simple low pass filter. A capacitor connected
in series with a tweeter will provide a high pass filter. An
inductor connected in parallel with a series capacitor will
help create a 12dB/octave high pass filter for a tweeter.
A capacitor connected in parallel with a series inductor
will help create a 12dB/octave low pass filter for a woofer.
Band pass filters can be created by means of a series
capacitor and series inductor, or by a mixture of series
and parallel capacitors and inductors.
Passive: A component unconnected electrically to the
signal source, such as an Auxiliary Bass Radiator.
Or a component unconnected to a source of mains
power, such as a passive pre-amplifier which acts
purely as a source signal switching/routing device
providing control functions for a power amplifier.
PCB: Printed Circuit Board.
PCM: Pulse Code Modulation. Pioneering form of
digital recording.
Peak output: Sudden bursts of power are required in
response to certain types of music. Loud drum beats
and percussive piano playing demands a high peak
output power from an amplifier. Failure to do so
causes signal compression, resulting in a squashed,
thick sound as if the drum sticks or piano hammers
are made of sponge.
Pentode: Commonly used valve type. Contains cathode,
anode, grid and two further electrodes.
Phase: Measured in degrees up to 360, as in a circle,
phase refers to points in a sine wave cycle. The
crossover point between positive half of the cycle and
negative half cycle is 180 degrees. If the left channel
is shifted by 180 degrees relative to the right channel,
and identical information is fed to both channels,
assuming the two loudspeakers are perfect and turned
to face each other, the signal will be self-canceling.
No sound should be audible. If a system is connected
out of phase, music signals fed through a normally
positioned pair of loudspeakers will sound unfocused with a
monotonous undifferentiated bass. It is easy to accidentally
connect a system out of phase by wiring the positive
lead of one channel to the negative socket. If both
channels are accidentally connected this way, the
system will be in-phase, but strictly speaking in reverse
phase. Some amplifiers feed a reverse phase signal to
the loudspeakers. Users should check the manufacturer's
owners' manual for optimum mode of connection. Some
products are fitted with a phase inverter switch to enable
direct comparison.
Phono stage: The extra equalization and gain stage
required to amplify signal from a pickup cartridge to line
level. The RIAA equalization is necessary because bass
signals are compressed to allow them to be cut onto
vinyl records. There would be insufficient space
otherwise. Moving magnet cartridges, which typically
deliver output in mV (for 5cm/sec standard acceleration)
require less amplification than most moving coil cartridges
which deliver output typically in uV for the same acceleration
standard.
Pilot tone: The 19kHz tone carrier tone on which stereo
sum and difference signals are broadcast. It is removed
by the stereo decoder of FM tuners.
Pre-amplifier: The control amplifier featuring source
switching , volume and signal processing circuitry.
Polarity: The difference between positive and negative.
Potentiometer: The device used to provide volume level
setting. Ideally a potentiometer is a variable resistor. Often
shortened colloquially to 'pot'.
Power output: The amount of power, usually measured
in watts per channel, delivered by a power amplifier
or integrated amplifier to loudspeakers. The rated
maximum rms or continuous sine wave power output
is a less relevant indicator of the dynamic range
capability of an amplifier than its peak output power
capability or its peak current delivery measured in
Amps. Amplifier power output is usually specified
relative to an 8 Ohm resistive load. However the
majority of loudspeakers present a load that varies
according to audio frequency, rising at loudspeaker
drive unit resonant frequency but often decreasing
elsewhere across the bandwidth. Impedances lower
than 4 Ohms require an amplifier to have considerable
current drive capacity.
Power Supply: Electronic components deriving their
power from a mains source require a transformer,
smoothing capacitors and rectifier to turn the mains
AC into a stable DC rail voltage. Amplifiers in particular
are heavily dependent on a stable rail voltage.
However components as varied as CD players, DACs
and turntables also benefit from well configured power
supplies often as separate items. Power supplies can
be a useful retrofit upgrade.
Power amplifier: The amplifier required to drive a loudspeaker.
Preamplifier: Another name for a line stage. A unit that
controls the volume and allows for selection of various inputs
(CD player, Tuner, etc).
Presence band: The middle range of audio frequencies
to which the ear is most sensitive. Typically taken to mean
the 1-4kHz frequency range.
Printed Circuit Board: (Abbr: pcb). The board onto which
a conducting track and solid state components - resistors,
capacitors and the like - are mounted. pcbs may be single
sided or double sided, fitted vertically or
horizontally.
Psycho-acoustics: The overlapping branches of acoustics
and psychology where research is conducted into
human perception of sound.
PWM: Pulse Width Modulation. A form of digital recording
which makes use of the width of a digital pulse.
Q: The sharpness of a peak.R
Quadraphonic: Four channel audio. Various rival
quadraphonic audio formats including QS, SQ and CD4
were proposed in the Seventies. Many broadcast
companies experimented with four channel FM
transmission, the BBC, for example, favoring a format
known as Matrix H. No quadraphonic format survived
as a viable commercial entity into the digital age.
R: Symbol for resistance or resistorS
Reactance: A frequency selective resistance.
Inductance and capacitance are the two forms of
reactance. The combination of resistance and
reactance is impedance.
Rectification: An essential process in the conversion
of AC to DC by means of a half wave rectifier, a form
of diode which is a key element in a power supply.
Resistance: Pure resistance is measured in Ohms.
Resistance in the form of resistors blocks the flow of
electric current in a linear or non frequency selective
manner.
Reverberation Time: The time it takes for a sound
generated in a room to drop to 60dB below its original
level. It is a measure of the size and reflectivity of the
room boundary surfaces. A typical listening room
measuring about 2.5 X 6.5 X 3.75 meters (HLW) will have
a Reverberation Time of about 0.4 seconds.
Major concert halls have a far longer RT in the region
of 1.5 to 2.5 seconds.
RF: Radio Frequency. Typically frequencies upwards
of 70kHz through to MHz.
RFI: Radio Frequency Interference. The disruption
of radio signal reception caused by any source which
generates radio waves at the same frequency and
along the same path as the desired wave.
RIAA: Record Industry Association of America. It is
the RIAA disc equalization curves that are almost
universally followed by record companies making LPs,
and by hardware manufacturers configuring their
phono amplifiers.
rms: Root Mean Square. rms qualifies an amplifier
power output specification to signify continuous power
output as opposed to peak or transient power.
Rumble: Turntable rumble is a very low frequency noise
caused usually by main bearing noise. It is usually a
sign of poor bearing lubrication.
SACD (Super Audio Compact Disc): A dual-layer 12cm discT
developed by both Philips and Sony. This new dual layer
disc employs a 1-bit Direct Stream Digital (DSD) for
higher resolution audio with upwards of six channels while
the second layer adheres to the two channel 16-bit/44.1kHz
compact disc standard.
Screening: A form of protection of conducting cable
from radio interference.
Selectivity: The ability of a radio tuner to select or
separate stations transmitting on nearby frequencies. By
reducing the IF (intermediate frequency) bandwidth to
sharpen selectivity, there may be a tradeoff in the
form of increased distortion. Some sophisticated tuners
provide switchable selectivity so that when two adjacent
stations are required to be separated, users may do so by
choosing narrow IF selectivity, at other times reverting
to wide selectivity to benefit from the natural reduction in
distortion.
Sensitivity: A measure of the efficiency of a loudspeaker.
A typical sensitivity figure for a loudspeaker is 87dB.
A high sensitivity 94dB or more. A low sensitivity is
80dB or less. (See Efficiency). Low sensitivity
loudspeakers require a high amplifier power output to
obtain realistic volume levels. High sensitivity
loudspeakers will be happy working with low power
output amplifiers (20W per channel maximum
or lower).
Separation: Stereo separation is a measure of the success
in isolating left and right channel stereo signals. The
higher the dB specification the better.
Series/Parallel: See Parallel/Series.
Signal to noise ratio: Abbr: S/N ratio, measured in dB, it
is an indication of the level of unwanted background
noise generated by a hi-fi component (eg a tuner or
amplifier). Again, the higher the number the better.
Sine wave: Continuous waveform of a particular
frequency (cycles per second).
Smoothing capacitor: An important component in a
power supply, the smoothing capacitor(s) eliminate(s)
unwanted ripple, the remains of the positive half cycle
of AC mains following rectification.
Square wave: A waveform designed to simulate a
transient impulse such as that of percussion instrument.
Derived from a sine wave, a square wave can be
shown by technical analysis to contain a multitude of
harmonics. It is a very difficult test of hi-fi equipment
and therefore particularly useful.
Stereo: Literally means solid. Usually taken to refer to
two channel stereo, though developments in digital
audio will facilitate multichannel stereo.
Stylus: The needle part of a cartridge, the tip of which
makes contact with a vinyl record. Elliptical, and
super-elliptical (e.g.. fine line and Shibata) tipped styli
are preferable to conical styli (found only on the
cheapest, most unsophisticated cartridges.
Tape deck: Machine for playing magnetic tapeU
recordings. Tape decks range from conventional cassette
decks, old-fashioned open reel analogue tape recorders,
to DCC and DAT tape decks to professional studio
tape decks. Most modern studio tape recorders are digital,
the conventional storage medium being U-matic tape
(a format originally developed as a professional video
recording standard).
Tetrode: A four electrode tube (valve) based on the triode.
Tonmeister: Literally tone master. The term used by
Deutsche Grammophon to describe the function
performed by the professional recording engineer.
The role requires microphone positioning and choice,
operation of tape recorders for all takes during a recording
session. Ultimately the Tonmeister or recording engineer
is responsible for the sound quality of the master tape.
Tracking: The ability of a cartridge to track the record
microgroove. A down force or tracking force is
applied by a counterweight on the end of the tonearm
to which the cartridge is attached. An appropriate
side force (bias) is also applied to ensure the cartridge
is not dragged towards the center of the disc.
Typical downforce values of around 1.8 to 2.0gm
are used today, depending on the mass of the
arm and cartridge and the compliance of the cartridge
suspension system. A high mass cartridge
(10gm or more) and high mass tonearm
(15gm or more Effective mass), low compliance
(10 cu or less) combination may require a down force
in excess of 2.0gm.
Triode: The first electronic amplification device.
Invented in 1907 by Lee de Forest who called it the
audion, the triode is a diode with an extra perforated
electrode, the grid, whose function is to vary the
amount of current flowing from anode to cathode.
Transient: A sudden sound.
Transistor: There are numerous types of transistor,
all designed to amplify an electrical signal. The most
common form used today is the bipolar transistor. There
are also j-fets, mosfets hexfets and many other generic
types with particular applications.
Transmission line: A type of box loudspeaker in which
a folded chamber leading from the rear of the bass unit
exits in the form of a vent. The aim of a transmission
line is to make the chamber sufficiently long and
filled with sufficient material such as acoustic fibre,
to prevent rear radiated sound exiting the cabinet.
Ideally all the sound will have been converted to
heat by the acoustic fibre.
Tweeter: High frequency loudspeaker drive unit.
Usually a dome diaphragm moving coil unit of either
doped fabric or plastic construction.
Unbalanced: A form of cable and electrical circuit in
which only one half of the positive/negative signal is
referred to a zero reference earth.
V: Symbol for Volt.W
Valve: Known as tube in America, the thermionic valve
is the earliest form of electronic amplification. At its
simplest in the form of a triode, the valve comprises
an evacuated glass case containing three electrodes
(conducting elements), the cathode, anode and grid.
VHF: Very High Frequency. The early terminology for
FM radio broadcasts.
Volt: Unit of electricity (Abbr: V). A unit of electrical
"pressure" . One volt is the amount of pressure
that will cause one ampere of current to flow through
one ohm of resistance.
Volume: Subjective term for loudness; more accurately
the signal level setting of an amplifier.
W: Symbol for watt or wattageX
Watt: A measure of electrical power defined by Current
multiplied by Volts (A X V).
Woofer: Low frequency or bass loudspeaker drive unit.
Wow and Flutter: Measures of speed instability, typically
of turntables and cassette decks.
X: Symbol for reactance.Z
Z: Symbol for impedance.
