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).3

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 center.

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.

Bo lart
Amplifier has no strength or sounds weak.

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 (scv). 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.

Class D
Digital switching of power into speakers using Pulsed Width Modulation. Digital signal direct from digital domain and no analog amplification is used.

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 tuner.

Crossover
Circuit inside speakers which splits high frequencies to the tweeter and low to the woofer.

DAB
Digital Audio Broadcasting: digital stereo on both FM and AM.  Currently broadcast by both the BBC and independent stations, it banishes hiss and interference. At time of writing - March 2000 - four tuners available, from  Arcam, Cymbol, TAG McLaren Audio and Technics.

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.

Delta Sigma
One type of DAC conversion method, used by Crystals Inc.

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 standard is 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. Talking of recordable, DVD  RAM 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.

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 and usually heard on older tape decks or turntables.

Frequency
High-pitched sounds have a high frequency, low-pitched ones a  low frequency. Audible sounds range from around 20Hz to 22kHz.

Front end
The signal source in a system, eg LP or CD. Also the stage in a  tuner which handles signals from the aerial.

HDCD
High Definition Compatible Digital - a coding system for CD which aims to get better sound. Needs a decoder to hear the full effects.

Hertz (Hz)
Unit of measurement for frequency. One Hz means a signal has one cycle per second.

Horn loading
Improves a drive unit's efficiency and output, using a structure within the speaker shaped like a horn. Works like the trumpet on an old-fashioned gramophone.

Impedance
Electrical property. A low impedance draws a high current flow from the source, while a high impedance draws a little. This means that speakers with a low impedance (lower than 6-8ohms) are more difficult for an amplifier to drive.

Line level
Describes inputs to amplifiers which don't need amplifying before the amp can use them.

Midband
Frequency range where most of the instruments and voices are heard. Vital if singers, etc, are to sound natural.

MiniDisc
Sony's 64mm disc that can record up to 74 minutes of sound. Looks  like a mini computer disc but works optically, like CD, on prerecorded discs, or magneto-optically in the case of blank software.

Monobloc
An independent mono power amp, so two are required for a stereo system. Advantage is a lack of interaction between channels.

Moving coil
Cartridges with a stylus connected to coils which move in relation to fixed magnets, creating electrical signals. Lower output than moving magnet.

Moving magnet
Record-playing cartridge (pickup) design in which a tiny magnet connected to the stylus moves relative to a fixed coil in the body, thus generating the signal.

Nicam
CD-quality digital stereo television sound transmitted alongside the picture.

Ohm
Unit of resistance to current. Impedance of a speaker is measured in ohms - generally the lower the figure the harder it is to drive.

Oversampling
Used in DAC systems. Increases signal frequency, making it easier for conversion circuitry and ancillary systems to filter out unwanted signals.

Passive
A circuit or component which does not amplify the signal.  Introduces very little distortion.

Phono stage
Cartridges output signals at much lower levels than CD players and tape decks. Many amps have the extra amplification built-in, but increasing numbers don't, and require an add-on phono amplifier.

PMPO
Stands for peak music power, used on gear that needs to look more  powerful than it is. If you see a ghetto-blaster advertising 160watts output, ignore it.

Power amplifier
Supplies audio signals to the loudspeakers.

Power handling
The maximum safe power for speakers. But be aware that it's  easier to damage speakers with an amp of too low power driven hard, than with  too much power.

Preamplifier
The control part of an amp. Built into integrated amps, but can be separate and used with power amp or active speakers.

Pro-Logic
see Dolby

RDS
Radio Data System: data piggybacked on FM radio allowing RDS tuners to display the names of stations, and perform a range of station-seek and switching  functions.

Reclock
A process, device or system that redo the timing information from the SPDIF or AES transimission system. It will reduce jitter and improve definition.

Sampling rate
How fast a digital recorder or player samples a signal. CD,  DCC and MiniDisc use a rate of 44.1kHz - ie 44,100 samples per second - while DATrecorders offer a choice of 48kHz or 44.1kHz, and Digital Audio Broadcasting will work on 32kHz. A digital-to-analogue converter needs to work on all three rates. The sampling rate determines the highest frequency recordable a digital system can carry - hence the development of higher-sampling formats, such as Pioneer's 96kHz system, for better treble extension.

Shielding
Keeps a conductor or equipment away from interference.

Signal-to-noise ratio
Describes the difference between the level of the  audio signal and the level of unwanted noise. The larger the figure, measured in dB, the lower the noise will be.

Subwoofer
A separate woofer box to produce the deep lows smaller speakers  can't reach.

Tape loop
A pair of sockets on an amp letting the signal out for recording on a tape deck and another pair to let the signal back in for replay.

THX
Developed by LucasFilm, this is basically a set of standards for Dolby Pro-Logic gear, which should guarantee a certain quality of home cinema sound. Needs electronics and speakers made to exacting specs, which tend to be  pricey.

Tonearm
The device on a turntable which holds the cartridge.

Toroidal transformer
Transformers bring mains voltages down to the levels required. Toroidal transformers (doughnut-shaped) get better stability and less  flux leakage (magnetic radiation that can interfere with other circuits).

Transients
Short and sudden events in music (eg a cymbal crash). Difficult  to reproduce.

Treble
High frequencies. When we say treble is splashy, it means cymbals, for example, sound like they're going 'tizzshsh', rather than having a crisp sting.

Triamping/triwiring
Like biamping and biwiring, but for three-way speakers. Needs three runs of cable in the case of triwiring and three stereo amps if you want to triamp the speakers.

Tube
American name for vavle. See valve.

Tunning
Tweaking of sound system using resonance. An untuned system can only give 50% of its performance, or even lower.

Tweeter
The speaker driver handling the treble.

Valve
Amplifying device: electrodes in a glass vacuum enclosure. Produces  a warm, seductive sound.

Wa-lao
Exclamation - can be good or bad.

Watt
Unit of power. More watts mean more power, but how loud a system sounds also depends on speaker sensitivity and room size. See PMPO.

Wavelength
The length of a wave. Sound at 50Hz in air has a wavelength of around 6.9 metres.

WAF
Wife acceptance factor

Woofer
The large drive unit in a speaker to produce bass frequencies.

Wow
Slow variations in speed of a record or tape deck, making sustained  notes sound unsteady.