Don't know your RDS from your RMS, confused by Peak Power or got yourself in a Wow & Flutter over all these terms then this guide is for you!

AF: Alternate frequency. Allows a receiver to re-tune to a different frequency that provides the same station, when the first signal becomes too weak (e.g. when moving out of range).

Attenuate: To reduce volume through the reduction in amplitude and intensity of a signal. The opposite of amplification.
 
Automatic Volume Control: Automatically adjusts the volume depending on the cars speed.

Autostore: Automatically scans the airwaves and stores the strongest signals in the station presets.

Azimuth: The angle of contact between a tape head and the cassette tape. The more similar this is between record and playback the better the reproduction.

Band-pass filter: A device that passes frequencies within a certain range and rejects (attenuates) frequencies outside that range. Used as a way of filtering out certain frequencies, often used for the mid range in a 3 way component system.
 
Bass: The lower end of the sound spectrum (usually under 150 Hz).

Bass Reflex: A type of loudspeaker enclosure that utilises the sound from the rear side of the speaker to increase the efficiency of the system at low frequencies as compared to a typical closed box loudspeaker.
 
Bridgeable: The ability to combine the stereo outputs of an amplifier into one mono output with double the output power.

Coaxial: Speakers with more than one drive unit built in, eg. a woofer combined with a tweeter. Gives better frequency response and clarity that a single cone.

Component Speakers: A set of speakers with seperate bass, mid range and high end speakers.

Continuous Power: See RMS.

Crossover: A device that filters out certain frequencies so they can be fed to particular types of speakers eg. so that only high frequencies are fed into a tweeter. A passive crossover filters signals after they have been amplified and an active crossover filters signals before amplification.

Crosstalk: The level of stereo separation between the left and right channels of a stereo.

CT: Clock time and date set from an RDS signal.

DAC: Digital to Analog converter, a device for converting a digital code (eg. data on a CD) to an analog signal.

DNR: Dynamic Noise Reduction, a method of reducing background hiss on cassette tapes.

Dual Cone: A single speaker that has two cones the smaller of which produces the higher frequencies. Not as effective as coaxial speakers.

DIN: The standard size of most car stereo units.

Double DIN: The size of most double height car stereo units, often seen on Japanses import vehicles.

DSP: Digital Sound Processing, used for creating simulated acoustic environments such as rock, pop, theatre etc.

EON: Enhanced Other Networks, allows the radio to interrupt what you are listening to with news bulletins from local stations.

Face Off: A security system that allows the front panel of a car stereo to be removed so it is less attractive to thieves.

Fader: Controls the amount of sound coming from the front or rear speakers in the same way as a balance control affects the left/right speakers.

Free Air: A subwoofer speaker which is able to work efficiently by not being enclosed in a box.

Full Logic Control: A cassette deck with electronic touch control instead of mechanical buttons.

Full range: A speaker designed to give a wide frequency response.

Gain: The degree of signal amplification provided by an amplifier. Expressed in decibels (dB).

Hertz: The frequency of a sound, usualy given as a range that an amplifier or speaker can reproduce.

High Pass Filter: Filters out low frequencies, usually used with tweeters.

Infinite Baffle: See Free Air.

Intro Scan: Plays the first few seconds of a track on CD or tape.

Local/DX: Two levels of sensitivity for scanning for radio stations, local and distant.

Loudness: Boosts low frequencies at low volumes.

Low Pass Filter: Filters out high frequencies, usually used with a subwoofer.

Mid Range: A speaker designed for producing frequencies in the mid range of the frequency range.

MOSFET: A type of transistor used in amplifiers for superior sound reproduction.

MSS: Music Search System, see Track Search.

Ohm: A measure of a speakers resistance. If a signal is sent into two speakers, one of which is rated at 4 ohms and the other at 8 ohms twice as much current will flow through the 4 ohm speaker as the 8 ohm speaker, requiring twice as much power.

Over sampling: A method of achieving higher quality Digital to Analogue conversion.

Peak Power: Often used by manufacturers in an attempt to look better in print. Peak power has no bearing on the actual performance of a product and usually works out to be approximately twice the continuous power (RMS).

PLL: Phase Locked Loop, keeps FM signals locked on to a station.

Port: The hole in a Bass Reflex speaker enclosure to give extra bass.

Pre-Amp: Boosts an audio signal before it gets to the main power amplifier.

Pre-Amp Output: An output from a head unit that can be connected straight to an external power amplifier.

Presets: The number of stations that can be programmed into a radio for instant recall.

PTY: The type of program that a radio station transmits eg. popular music, allows the radio to automatically tune into a station broadcasting a particular type of music.

RDS: Radio Data System, allows the radio station to send extra information to the radio eg. the station name, current song playing etc.

RMS: Root Mean Square, an accurate way to measure the output of an amplifier. The higher the figure the more powerful the amplifier is.

Signal To Noise Ratio: The ratio between the music you hear and the noise that the system produces, the higher the signal the better, anything above 70db is acceptable.

SPL: Sound Pressure Level, the amount of volume produced in decibels (dB).

Subwoofer: A speaker designed for very low frequencies.

TA: Traffic Announcement, switches the radio to a local station when there are traffix announcements.

Track Search: Allows you to rewind or forward to the next track on a tape.

Tweeter: A small speaker designed for high frequencies.
 
Wow & Flutter: The accuracy and stability of the speed of a cassette player, the lower the figure the better.

THD: Total Harmonic Distortion, the difference in quality between the output of a stereo and the original recording.