AAD :	Seen on CD cases, meaning the music was recorded and mastered in analogue form - the first two As - but stored digitally (on the CD).
AC-3:	See Dolby Digital
ADD:	Music recorded in analogue form (A), mastered or remastered digitally (D), and stored digitally on CD (the third D).
Alignment:	Adjustment of a record-player cartridge relative to the groove on the disc. Bad alignment causes distortion. Tape heads also need alignment, but it's best left to the experts.
Amplifier:	Boosts signals to drive speakers. Can be one-box (integrated) or have separate pre and power sections.
Analogue:	LPs/cassette tapes store audio in non-digital form directly related to the signal.
Anti-skating:	Applied to arms on turntables to prevent them from swerving towards the centre.
Balanced connections:	Positive and negative wires are shielded (for better interference rejection) in balanced connections. Normal connections use the negative to shield the positive cable. Use a three-pin XLR type plug to connect from the amplifier - also used in the AES/EBU digital format.
Bass:	Low frequencies, often tricky to reproduce. A review that says bass is slow means it goes 'whoompa-whoompa' and can dominate the music. The ideal is good bass extension (ie low down) allied to speed and rhythm.
Bass reflex:	A speaker design using air-flow from a port in the cabinet to help low frequencies.
Biamping:	Each drive unit of a speaker is driven by a separate amp channel, so a pair of two-way speakers needs two stereo amps, and two runs of cable to each speaker. See biwiring.
Binding post:	Speaker terminal with threaded collar for gripping bare wires and sometimes a socket for banana plugs, too.
Bit:	A single piece of digital information, basically an 'on/off' signal. Digital-to-analogue converters turn strings of bits into audio signals.
Bitstream:	One method of turning digital CD data into analogue signals. Bitstream digital-to-analogue converters process single bits of digital data much faster than multibit DACs, which work on chunks of digital data.
Biwiring:	Some of the benefits of biamping but at a lower cost. You need speakers with two sets of inputs and a split crossover, then send twin runs of cable from amp to each speaker.
Bridging:	Increasing power by connecting a stereo power amp for use in mono, then adding a second bridged-stereo amp for the other channel. Power typically triples, but the amps must be designed to be bridged in the first place.
Cables:	Copper conductors are mostly used with purity expressed as a number of 'nines'. So 'six nines' or '6N' purity might be 99.99997 per cent pure copper. Good speaker cables can have many strands (multistrand) or one or more thick wires (solid core). Look for arrows, which should point from the amp to the speaker, on directional cables. Directional interconnects have arrows that point from source to amp.
Cable TV:	Multi-channel TV down a wire to your home. You pay for different combinations of services. Stereo provision varies between companies.
Cartridge:	The device which actually plays the record. It converts the wobbles in the record's groove into electrical signals for your amp. See moving magnet and moving coil.
Compact Disc:	Standard 12cm disc, which stores information digitally, read by laser optical system. Originally designed for music storage the CD is now used for many applications, some of which follow...
CD-R:	CD-Recordable. Uses a special blank disc in a recording CD player. Once recorded it can't be erased, but plays in standard CD players when 'fixed up'. CD-R discs look green. Comes in two flavours, professional and consumer. Discs and machines are not interchangeable
CD-ROM:	Uses CD as a Read Only Memory for computers. Vast storage capacity - around 600MB - on single disc.
CD-text:	New system which allows CD players to display a limited amount of text such as track names or lyrics. Being introduced shortly by Sony
Class A:	Amp in which positive and negative half cycles are amplified together. Runs hot, as the transistors in the power amp are on all the time, but has high sound quality.
Class B:	Positive and negative halves of the signal dealt with by different parts of the circuit, the output devices switching continually. Runs cooler, but the sound is not as pure.
Coloration:	A shift away from the natural rendition of music. Coloration is undesirable - 'boomy' bass, a 'nasal' midband or a splashy treble, for instance. All colorations get in the way of the music.
Compression:	Used by radio stations to reduce level differences between loud and soft parts of music. Helps in-car and transistor sound, but can be awful through a hi-fi
Crossover:	Circuit inside speakers which splits high frequencies to the tweeter and low to the woofer.
DAB:	Digital Audio Broad-casting: digital stereo on both FM and AM. Currently broadcast by the BBC to a limited area, it banishes hiss and interference. No tuners yet out.
DAC:	Digital-to-analogue converter, turning on/off pulses into analogue sound. CD players have DACs built in. Separate DACs can upgrade a CDplayer or other digital player/ recorder, or can be used with dedicated CD transports.
DAT:	Digital Audio Tape. A digital recording system now used mainly professionally. Uses a revolving recording head similar to that used in a VCR.
Data reduction:	Lowers the amount of data needed to store music. Sony's MiniDisc uses an in-house system called ATRAC (Adaptive Transform Acoustic Coding) while the PASC (Precision Adaptive Sub-band Coding) used in Philips' DCCformat serves a similar function, removing signals its designers think you can't hear.
DCC:	Digital Compact Cassette - Philips' home digital tape system, now rather knocked out by Sony's MiniDisc
DDD:	On CD cases - music recorded and mastered digitally and stored digitally on CD
Decibel:	(dB) Measures changes in sound pressure. A change of 1dB is just about audible, while 10dB sounds like the level has been doubled.
Digital:	Method of storing data used by CD players, DAT, DCC, MiniDisc etc. The sound or picture is converted to a stream of digits - effectively 1s and 0s representing on/off pulses. Bane of vinyl lovers
Digital output:	Allows the digital signal to be recorded or processed by an offboard DAC. Electrical or optical (fibre optic) outputs are provided.
Distortion:	Unwanted signals or signal changes added by equipment.
Dolby Labs:	Developed noise-reduction and cinema surround systems.
Dolby B, C S:	Noise-reduction to boost quiet signals when recording and reduce them on playback, cutting hiss.
Dolby Digital:	Also known as AC-3, this is the latest home cinema sound system from Dolby, using five discrete channels of digital sound plus a separate subwoofer channel
Dolby HX Pro:	Not noise reduction, but a way to record more high frequency information without distortion (often called 'increasing headroom').
Dolby Surround:	Encodes sound for rear effects channels into the stereo tracks. Needs to be replayed through a decoder to produce surround.
Dolby Pro-Logic:	Uses an extra centre speaker at the front, which locks dialogue to the screen.
Dolby 3 Stereo:	In cinema sound amps, delivers the surround channel information through the front left and right speakers, while providing centre channel information.
Drop-out:	Momentary loss of signal during tape recording or playback from a defect in the magnetic coating or from the tape briefly losing head contact. Drop-outs can also occur on CDs, but it takes fairly serious disc damage.
DTS:	Discrete-channel home cinema digital sound system - rival to Dolby Digital
Dual mono:	Some amplifiers are designed to keep the left and right signals separate throughout the amp - this helps avoid possible interference between the two channels.
DVD:	Video Designed for home entertainment, they play on consumer DVD players that plug into TV sets, or on desktop PCs equipped with a DVD-ROM drive and the requisite hardware/software.
DVD-ROM:	Like CD-ROMs but better! Read by DVD-ROM drives installed in PCs, DVD-ROM discs exist in various capacities from one-sided single-layer (4.7GB) to dual-layer, dual side (17GB).
DVD Audio:	The specification for DVD Audio (version 0.9) is still being finalised as we go to press. It is thought the standard will be based around 24 bit/96kHz sampling. Some audio-only discs have already been produced using the DVD Video standard.
DVD-R:	This is a type of DVD that allows once-only recording of data. DVD-R discs will store 3.95GB on a single-sided disc, and 7.9GB on a double-sided disc.
DVD-RW:	A 3GB erasable and rewritable format under development by Sony, Philips and Hewlett-Packard as an alternative to the DVD RAM storage format (see below). Sony is also developing a 12GB DVD-RW disc that will give five hours of TV recording, and predicts this will be available in two years. DVD RAM This is a version of computer DVD that is erasable and can be rewritten. The specification for DVD RAM enables users to store 2.6Gb on a single-sided disc and 5.2Gb on a double-sided disc. DVD RAM drives are expected to be released in the US in 1998.
Divx:	Recently announced by US company Circuit City, this is a low-price DVD format that allows only a 48 hour viewing period. It's an alternative to rental, but you keep the disc - if you rewatch, your DVD player rings DIVX headquarters by phone and charges your account. Scary! The discs won't play on non-DIVX DVD players.
Dynamic range:	The range, in dB, between the largest and smallest signals reproduced by hi-fi.
Electrostatic:	Speakers that use the force of high voltages to push and pull a thin light diaphragm, which produces the sound.
Flutter:	Rapid speed instability on tape or vinyl leading to fluctuations in pitch. This is caused by transport problems.
Frequency:	High-pitched sounds have a high frequency, low-pitched ones a low frequency. Audible sounds range from around 16Hz to 20kHz.
Front end:	The signal source in a system, eg LP or CD. Also the stage in a tuner which handles signals from the aerial.