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AC: Alternating current. An electric current with periodically changing polarity. In popular parlance, often used as a synonym for electrical house (or mains) current.

Acoustic Feedback: Unwanted acoustic interaction between output and input of an audio system, usually between loudspeaker and microphone or turntable cartridge. Can lead to "howl".

Acoustics: The science of sound. Also, the acoustical character of halls and rooms.

Active Filter: See filter.

Aerial: Synonym for antenna in British English.

AF (Audio Frequency): Frequency within the range of human hearing - approximately 20 - 20,000 Hz.

AFC (Automatic Frequncy Control): An AFC circuit of an FM tuner corrects for an inaccuracy in tuning by locking in the station being tuned.

AM (Amplitude Modulation): Modulation accomplished by varying the amplitude (intensity) of the carrier.

Amplification: Increase in signal magnitude.

Amplifier: Unit providing amplification of signal, from low to higher voltage or current (preamplifier) or power (power or main amplifier).

AM Suppression: Characteristic of an FM tuner to suppress changes of amplitude in received signals, thereby improving the signal-to-noise ratio by rejecting noise and intereference.

Anechoic Chamber (Room): A specially designed room, used for testing microphones and speakers, rendered acoustically "dead" by sound absorbing material.

Antenna: Assembly of metal bars, wires or loops for picking up radio waves. dimensions depend largely on the wavelengths to be received.

Antenna Directionality: The characteristic of certain antenna configurations, including most FM and TV antennas, to receive radiowaves reaching it within certain defined angles more strongly than those coming from other directions.

Antenna Gain: An indirect measure for an antenna's output level, i.e. the strength of the signal supplied by the antenna when compared to a standard antenna and at certain frequency. Expressed in dB.

Anti-Skating Device: Mechanism exerting a small outward force on a tonearm to compensate the inward thrust caused by groove/stylus friction and tonearm geometry.

Antistatic Fluid: A fluid (or spray) used to prevent phonograph records from becoming electrically charged, as an electrical charge would attract dust.

Audibility Threshold: The minimum sound intensity that the average human ear can hear. Approximately 0.0002 microbar at a frequency of 1000 Hz.

Automatic Level Control: A circuit which automatically keeps the level of a signal within a certain range. Examples: automatic gain control in AM radios, ALC in portable tape recorders.

Automatic Record Changer: Record player which can change from disc to disc automatically.

Aux (Auxiliary Input): Input on amplifier etc. Accepts extra signal source such as cassette tape player etc.

Baffle: The board on which one or several loudspeakers are mounted. Separates the radiations from the front and back of the speaker.

Balance Control: Potentiometer used to adjust volume difference of left and right stereo channels.

Bandpass Filter: A circuit which will pass signals above (high bandpass) or below (low bandpass) a certain frequency while attenuating others.

Bass: A fine English ale. Low audio frequency range, below approximately 200 Hz.

Bass Reflex: Loudspeaker enclosure with an outlet permitting sound from the rear of the speaker cone to be radiated to the front.

Beat: A pulsation caused by interaction of two waves of different frequencies.

Bias: In tape recording, a high frequency signal applied to the tape to optimize its frequency response. Also, the side thrust on a tonearm.

Bias Compensator: See anti-skating device.

Bi-Radial Stylus: See elliptical stylus.

Block Diagram: A schematic diagram illustrating the main circuit blocks and signal flow in an electronic device.

Capacitor: A device which can store an electric charge. Permeable to AC, impermeable to DC.

Capstan: Drive spindle in a tape deck. The tape is pressed against the capstan by a pinch roller.

Capture Ratio: An FM tuner's ability to reject unwanted FM stations and interference occuring on the same frequency as the desired station.

Cardioid Microphone: A microphone with a directional characteristic that resembles the shape of a kidney.

Carrier: Main radio signal from a transmitter. Can be modulated in different ways (AM, FM) to convey sound or picture information.

Cartridge: (a) phono pickup; (b) endless loop tape in a packaged, standardized container.

Cassette: Preloaded container with tape and spools for use on cassette tape recorder.

Center Channel: An output terminal found on some stereo amplifiers which supplies a monophonic L+R signal.

Channel Separation: Degree to which left and right channel signals are separated in a stereo pickup, FM stereo tuner, amplifier, etc.

Characteristic: Refers to a characteristic curve which conveys information about an amplifier or other item.

Chrome Tape: A newly deveolped tape using the chromium dioxide particles, and offers excellent frequency response and wide dynamic range.

Coaxial Cable: A cable consisting of an inner conductor and an outer screen. Used as antenna leads and for interconnecting audio units.

Coaxial Speaker: A loudspeaker consisting of a bass cone with a concentrically mounted tweeter.

Compatible: (a) FM multiplex signal receivable as mono by a radio or tuner. (b) Stereo disc playable with a mono pickup. (c) Stereo pickup suitable for playing mono records, too.

Compliance: The flexibility of phono cartridge. The unit of compliance is 10(-6)cm/dyne.

Component System: An audio system consisting of separate units: turntable, tuner, amplifier, speakers, etc.

Condenser Microphone: A microphone utilizing the changes in capacitance caused in a condenser if one of the plates - the microphone membrane - vibrates in rythym with sound waves. Same principal can be applied to a condenser type phono cartridge.

Control Amplifier: A preamplifier and amplifier combined in one unit.

Cost-Performance Ratio: A way of evaluating a unit's over-all performance by grading its characteristics with points, and dividing the sum of accrued points by the cost. Naturally, highly individualistic.

Counter Weight: Weight fitted at rear end of tonearm behind the pivot to counter the weight of the arm/head assembly and to permit adjustment of the tracking force.

Crossover Frequency: In loudspeaker systems and multi-amplifier installations, the borderline frequencies between low/medium range and medium/high range speakers or amplifiers.

Crosstalk: Leak of right channel signal into left channel, and vice versa. Expressed as level of unwanted signal in relation to wanted signal channel, measured in dB.

Cutting: The process of engraving undulating grooves in a rotating, wax coated disc. An important step in the manufacture of phonograph records.

Cutting Angle: See vertical angle.

Cutting Stylus: Stylus used for cutting of phonograph records.

Damping: Reduction of resonant effects by use of resistance or its mechanical and acoustic equivalents.

Damping Factor: Ratio of loudspeaker impedance to amplifier's internal impedance. Denotes amplifier's ability to damp unwanted, residual speaker movement.

DB (Decibel): A logarithmic unit used to express the ratio between two power, voltage or current levels. Mathematically: 20 log(10) x level1/level2 or 10 log(10) x power1/power2.

Decoder: In an FM stereo tuner, the circuit that extracts the left and right channel signals from an FM MPX broadcast signal. Or matrix decoder for translating matrix 4-channel program sources.

De-Emphasis: Attenuation of high sound frequencies in an FM tuner, to counteract the boosting of these frequencies ("pre-emphasis") done at the FM station.

Demodulation: The process of "extracting" from a modulated high or intermediate frequency wave the original audio signal which it was modulated with.

Derived Center Channel: See center channel.

DIN (Deutsche Industrie Normen): German Industrial Standards. In audio, the German standard of plugs, sockets, etc.

Dispersion: Distribution of sound from a speaker through a room.

Dolby System: A unique noise reduction system, which electronically eliminates the irritating noise (tape hiss, circuit noise, etc.) without sacrificing the original tonal quality.

Drift: Tendancy of a tuner to move away from optimum adjustment as its components warm up. Compensated by AFC.

Drop Out: In tape recording and playback, the "holes" in the sound caused by thin or bare spots on the tape.

Dual Cone: Two scoops. Speaker consisting of separate bass and treble cones mounted concentrically and driven by the same coil. See also Coaxial. Mechanical 2-way speaker.

Dynamic Mass: The effective mass of the moving parts of a pickup cartridge. This is not simply the sum of the masses of each component, but rather the equivalent mass that determines the mechanics of its behavior.

Dynamic Range: In program material, the range of signal amplitudes from highest to lowest; the range (in dB) which a device will handle.

Efficiency: Ratio of output to input power in a transducer. In loudspeakers, the percentage of electrical power available as acoustic output.

Electrostatic Speaker: A loudspeaker utlizing the principal of a membrane vibrating in a strong electric field.

Elliptical Stylus: A pickup stylus shaped so that its width across the groove is greater than the width of its sides. Claimed to have better high frequency characteristics than round styli.

Enclosure: The cabinet which houses one or more speaker units. Has great influence on bass response of speaker.

Equalization: Correction for frequency non-linearity of recordings. Phonograph records are cut with low frequencies attenuated and high frequencies boosted. Equalization compensates for this, producing a flat frequency characteristic.

Equalizer Amplifier: In a pre-amplifier, the circuit which amplifies and "flattens" the phono input signal. Needed because phonograph records are not cut with flat frequency response but according to a standard "equalization" curve.

Feedback: Signal from output of amplifier or electronic network applied to input in anti-phase (hence negative feedback) to reduce distortion and noise, and to flatten or otherwise shape frequency response. Also, unwanted acoustic feedback.

Ferrite Coil Antenna: An antenna, used chiefly for AM reception, consisting of wire windings around a core of ferrite. Advantages are: compact size, good sensitivity and high directionality.

FET (Field Effect Transistor): Special kind of transistor consisting of metal oxides. Amplifies voltage, not current. Used in audio equipment because of its good linearity and stable impedance.

Field Strength: The intensity of an electrical or magnetic field.

Field Strength Meter: See signal strength meter.

Filter: A circuit which attenuates signals above, below, or at a particular frequency.

Flutter: Quick waver of pitch caused by speed fluctuations in the movement of tapes or discs. Heard as a sort of quiver.

Flywheel: A disc of large mass which, when rotating, has the tendancy to maintain its rotational velocity. This effect is used in tape equipment and turntables to maintain constant speed.

FM (Frequency Modulation): Type of modulation of radio waves in which the frequency, not the amplitude of the carrier is modulated by the audio signal. FM broadcasting achieves higher sound quality.

Four-Channel Stereo: A newly developed audio technique using four (instead of two) channels for sound reproduction.

Frequency Response: The frequency range which a unit will reproduce or respond to.

Front End: Section of a tuner that selects the wanted station from the radio band and converts the RF signal to IF.

Function Selector: In an amplifier or receiver, the switch or knob which selects the different program sources such as phono, FM, AM, aux, etc.

Gain: Degree of signal amplification achieved in an amplifier circuit. Expressed in dB. Opposite: negative gain or loss.

Gap: Vertical slit in a tape-head. In the gap, a magnetic field occurs during recording, and a magnetic signal is induced during playback.

Ghost: In TV, the appearance of a secondary picture slightly to the right of the main picture. Similarly, ghost can be used to mean multipath FM reception. Also, the "images" of the true station frequency that an FM tuner purports to receive.

Harmonic Distortion (Total or THD): The sum of all signals in an output which are multiples of the input signal frequencies ("harmonics"). Their intensities are expressed as a percentage of the total output intensity.

Head: a) the erasing, recording and playback heads in tape equipment; (b) the shell-cartridge assembly of or attached to a tonearm.

Headphones: Small transducers, usually mounted in pairs on a bracket to fit over the head and designed to make intimate contact with th ears.

Head Shell: The -often detachable- part of a tonearm which carries the cartridge.

Heat Sink: A device used to remove heat from electronic componenets such as tubes, transistors, etc.

Hertz (Hz): Unit of frequency, equal to one cycle per second.

Horn: Speaker using a trumpet-bell shaped, flaring funnel to couple its sound vibrations to the surrounding air.

Hum: Unwanted low frequency tone. Usually caused by 50 Hz or 60 Hz AC and its harmonics.

Hysterisis Motor: A motor used in high quality turntables. Characterized by very constant speed regardless of power voltage fluctuations.

IC (Integrated Circuit): Solid circuit block containing the functions of numerous transistors, diodes, resistors, capacitors, etc.

IF (Intermediate Frequency): The frequency which results in a tuner when the incoming signal from the antenna is mixed with the oscillator frequency.

IF Transformer: Component in tuner or radio receiver used to couple or feed IF signal between succesive amplifying transistors or tubes. Windings usually tuned with capacitors to resonate at the fixed IF frequency.

IHF (Institute of High Fidelity): Institute founded by American manufactuers of audio equipment, devoted to the improvement of audio technology, standardization of test and measuring methods, etc. "IHF" in audio specifications means that values were obtained in measurements according to IHF satandards.

Image Rejection: The ability of a tuner to reject an RF signal which appears to be received, but is actually a sum or difference of the tuner's oscillator and intermediate frequencies.

IM Distortion: (see Distortion) Signals in output caused by interaction of two or more input signals, but not harmonically related to them. Expressed as a percentage of total signal intensity. IM distortion is know to cause listener fatigue.

Impedance: Resistance to the flow of alternating current. Measured in ohms. It may vary with the frequency of the applied alternating current.

Induced Magnet Cartridge: A pickup cartridge in which both magnet and coils are fixed. The moving part is a tiny iron sheet.

Infinate Baffle: Life. Type of loudspeaker mounting without an air path between front and rear of speaker cone.

Integrated Amplifier: Unit combining a preamplifier and power amplifier. Also called pre-main amplifier.

Interference: Unwanted influences upon desired signal by extraneous signals, for example from electrical appliances, motors, automobiles as well as from undesirable signals generated within the audio equipment.

Limiter: Circuits in an FM tuner that reject unwanted amplitude variations caused by atmospheric or ignition noise, producing an FM signal of constant amplitude.

Linearity: (a) Amplitude linearity, distortion of which produces harmonic distortion and intermodulation; (b) Frequency linearity referring to the straightness of a frequency response curve.

Line Output: Output terminal of a preamplifier, tape deck, etc., providing a signal for monitoring, tape recording or supplying to a power amplifier.

Loudness Control (Contour): A circuit which counteracts the reduced sensitivity of the ear to very low and high notes at low volume levels.

Low Filter: A filter circuit designed to remove low frequency noises (rumble, hum, etc.) from the program.

Magnetic Cartridge: A cartridge which derives its electrical output signal from change effected in a magnetic circuit by means of some mechanical device such as a moving coil, moving magnet.

Main Amplifier (Power Amplifier): Amplifier unit which produces the output power required for driving speakers.

Monaural: One-eared. Sometimes erroneously used to mean monophonic.

Monitoring: Listening to a program to judge or control the sound quality.

Monophonic: Recording, transmission and reproduction of sound via a single channel.

Moving Coil (MC) Cartridge: Magnetic cartridge in which the coils move and the magnet is fixed.

Moving Magnet (MM) Cartridge: Magnetic cartridge in which the magnet moves and the coils are fixed.

Multiplex: Transmission of two or more channels on a signal carrier so that they can be independently recovered by the receiver. In FM stereo: transmission of L + R (sum) signal and L - R (difference) signal on main carrier and subcarrier, respectively.

Mutipath Reception: Arrival of FM or TV signal via several paths of different length, due to obstructions, reflecting objects, etc.

Multiplex Decoder: See decoder.

Music Power: The maximum power available temporarily from a power amplifier. Also called "dynamic-power".

NAB: (National Association of Broadcasters) Most widely used standard of tape recording techniques.

Network: In audio, a frequency dividing network in a speaker system, or an electronic crossover network in a multi-amplifier installation.

Noise: Unwanted signal consisting of a mixture of random electrical agitations. Also, the sum of all unwanted signals such as hum, hiss, rumble, interference, distortion, etc.

Omni-Directional: Equal sensitivity or output in all directions. Said of antennas, microphones and loudspeakers.

Oscillator: An electronic circuit which generates an alternating current, e.g. the oscillator in a tuner produces the frequency used to mix with incoming radio signals.

Output Impedance: Impedance at output terminals of a device as "seen" by the load.

Output Stage: Final stage of a power amplifier which supplies power to a loudspeaker.

Output Transformer: Transformer in tube power amplifer to couple output tubes to loudspeaker.

Overtone: A tone accompanying the fundamental in a musical note. May or may not be harmonic.

Phasing: Connections between power amplifier and speakers in a stereo system must be made in such a way that signals representing a central sound source cause the speakers to move equi-directionally, i.e. in phase.

Phase Shift: As a signal passes through a tuner, amplifier, etc., some frequencies may lag behind others. In a tuner, this phase shift can, in extreme cases, cause loss of channel separation of FM stereo broadcasts. Phase shift in an amplifier results in blurring of stereo spatial localization and, in serious cases, can cause unstable amplifier performance and distortions.

Polarity: Positive and negative terminals of a battery or power supply, or the north and south poles of a magnet. Sometimes refers to phasing of cartridges and loudspeakers.

Power Amplifier: See main amplifier.

Power Bandwidth: The frequency range over which a power amplifier will produce at least half of its rated output power (according to IHF standard).

Power Handling Ability: Maximum amount of power that can be safely fed into a loudspeaker.

Preamplifier: A circuit unit which takes a small signal, e.g. from a tuner or turntable, and amplifies it sufficiently to be fed into the power amplifier for further amplification.

Quietening: Term sometimes used instead of "muting" in FM tuners.

Quieting: See wife. See limiter.

Rated Output Power: The maximum power that an amplifier will deliver continuously without exceeding its specified distortion rating. Also called continuous power output or RMS power output.

Ratio Detector: Circuit in an FM tuner for extracting audio signals from modulated radio or intermediate frequency signals.

Resistor: Circuit device which offers resistance to the flow of electric current. Resistors may be made from wire, metallic film, carbon and other materials.

Resonance: The tendancy of a mechanical or electrical device to resonate at a particular frequency.

Response: See frequency response.

Reverberation: Reflection of sound from walls or ceilings. Echo. Can be created artificially by electronic or mechanical devices to imitate the effect of large halls.

RF (Radio Frequency): The frequency of a radio carrier wave. AM (MW) covers 535-1605 KHz, FM occupies 88-108 MHz.

RIAA (Record Industry Association of America): Usually refers to the disc recording and replay frequency response curves established as standards by this association.

Rumble: Low frequency noise resulting from vibrations in platter and motor of a turntable and from record warp.

Selectivity: The ability of a tuner to receive only the desired station while rejecting stations which are not required. Measured in decibels (dB).

Sensitivity: The input signal level required by a tuner, amplifier, etc., to be able to produce a stated output. The lower the neccessary input, the higher the sensitivity.

Separation: See channel separation.

Signal-To-Noise Ratio: Ratio of desired signal voltage to unwanted noise and hum voltage. Expressed in decibels (dB).

Solid-State: Circuits using semi-conductors, e.g. transistors and integrated circuits (ICs).

Speaker System: Enclosure containing two or more speakers and a crossover network. Speaker box.

Stereophonic: Recording transmission and reproduction of sound via two or more independant channels.

Stylus: A finely machined piece of sapphire or diamond. The part of a phono pickup that traces the record grove.

Synchronous Motor: Type of AC electric motor in which rotor speed is related directly to frequency of power supply.

Tape Deck: Tape equipment comprising complete tape transport system, with motors, drive pulleys, linkage etc., as well as preamplifiers for recording and playback, but no power amplifer or speakers.

THD (Total Harmonic Distortion): See distortion.

Tone Control: Control circuits used to vary the porportion of bass and treble in the sound.

Trackability: Ability of phono cartridge to track record grooves of high amplitude and velocity. Also, see compliance.

Tracking Error: Deviation of center-line of phono cartridge from tangential of record at point of stylus contact. Caused by tonearm geometery.

Transducer: Device for converting energy from one form to another; e.g. a loudspeaker converts from electrical to acoustic, a tape head converts from magnetic to electrical.

Transient: Abrupt change of state; sudden change in signal amplitude as caused by percussion instruments, "attack" of plucked strings, etc.

Transient Response: The ability of an amplifier, cartridge or speaker to follow sudden changes in the level of a sound.

Tuner: The part of a receiver, or a separate unit, which receives radio broadcasts and converts them into audio frequency signals.

Tuner-Amplifier: Unit combining the functions of a tuner, preamplifier and power amplifier. Also called "Receiver".

Tweeter: A speaker designed to reproduce the high part of the sound spectrum.

Vent: Opening or port in a bass reflex loudspeaker enclosure.

Voice Coil: A coil of wire attached to a speaker cone. When placed in the field of a magnet, the coil responds to the alternating signal from the amplifier, moving the speaker cone back and forth in accordance with the frequency and intensity of the signal.

Woofer: A speaker designed to reproduce the low part of the sound spectrum, e.g. organ, bass, etc.

Wow: Wow indeed, that was a lot of typing. Slow variation of pitch caused by speed fluctuation in tape or record movement.