Glossary

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A	Common abbreviation for ampere (see ampere).
A/D	Analog/Digital; an integrated circuit device that converts analog signals to digital signals.
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 (eg cathedral acoustic; concert hall acoustic; listening room acoustic etc). See Reverberation also.
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.
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).
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.
Ampere	Measure of electrical current (Often abbr to A).
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.
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.
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.

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.
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.
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.

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, CDROM 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 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 tone arms 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.
db	abbreviation for decibel.
DC	abbreviation for direct current
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.
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.
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.
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.
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 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 Pro-Logic�	A more advanced form of Dolby Surround encoding and decoding in which there is an additional front center channel containing dialogue information.
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� 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.
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.
Dynamic range	A useful definition is the difference between the quietest and loudest sound of a music signal.
Dynamics	The level changes present in music.

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 tone arms 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.
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).
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.
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 electro statically 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.
Equalisation	A correction made on playback of tape recordings to restore correct linear frequency balance.

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).

Gain	An objective measure of voltage amplification.
GHz	Gigahertz. 1,000,000,000,000 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 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�R	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.

kHz	1000Hz or kilohertz. or 1000 cycles per second.
kOhm	1000Ohms or kiloOhm.
kWatt	1000W or kilowatt.

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).

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. All finished prerecorded cassettes, LPs, Compact Discs, DCCs and MiniDiscs are mass produced copies derived from the master tape.
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 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 (eg from static electricity on vinyl records).
NTSC	National Television Standard Committee. The United States TV standard.

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.

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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.

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 equalisation and gain stage required to amplify signal from a pickup cartridge to line level. The RIAA equalisation 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.
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 amplifier	The amplifier required to drive a loudspeaker.
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.
Pre-amplifier	The control amplifier featuring source switching, volume and signal processing circuitry.
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.

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 metres (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 equalisation 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.

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 (eg. 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 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 downforce 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 centre 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 downforce in excess of 2.0gm.
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.
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.
Tweeter	High frequency loudspeaker drive unit. Usually a dome diaphragm moving coil unit of either doped fabric or plastic construction.

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 wil 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 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.

Glossary

Hi-fi, home cinema, multi-room terminology explained with our a-z index