Audio Terminology

  Below are the definitions to various audio related words and phrases. If you don't see the answer to that tricky word or phrase below, please feel free to e-mail your question(s) to me.

Click here to see a graph that depicts the equivalency of sound pressure levels and also how various acoustic instruments are placed within the frequency range.

A   B   C   D   E   F   G   H   I   J    k   L   M   N 

O   P   Q   R   S   T   U   V   W   X   Z

A

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 loudspeaker
  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

C: Symbol for capacitance and centigrade.

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

D/A: Digital to Analog

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.

E

Earth: Sometimes called ground, earth is the zero
  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

F

Feedback: Acoustic or structure-borne vibrations that
  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).

G

Gain: An objective measure of voltage amplification.

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.

H

Harmonics:  Multiples of the fundamental sine wave
  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).

I

I²R: Formula for power in watts, where i=current in amperes,
  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.

J

Jitter: The slight movement of a transmission signal in
  time or phase that can induce errors and loss of
  synchronization in high-speed synchronous communications.

k

kHz: 1000Hz or kiloHertz. or 1000 cycles per second.

kOhm: 1000Ohms or kiloOhm.

kWatt: 1000W or kiloWatt .

L

L: Symbol for inductance.

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.

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).

M

Magnetic flux: The measure of strength of a magnet.
  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)

N

Near field: The region within approximately two meters
  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.

O              

Ohm: The electrical unit of resistance.  The value
  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.

P              

Parallel/Series: All electrical components can be
  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.

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              

Q: The sharpness of a peak.

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              

R: Symbol for resistance or resistor

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.

S              

SACD (Super Audio Compact Disc): A dual-layer 12cm disc
  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.

T              

Tape deck: Machine for playing magnetic tape
  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.

U              

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                

V: Symbol for Volt.

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              

W: Symbol for watt or wattage

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              

X: Symbol for reactance.

Z              

Z: Symbol for impedance.