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 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.
Monoblock:	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.
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.
Tweeter:	The speaker driver handling the treble.
Valve:	Amplifying device: electrodes in a glass vacuum enclosure. Produces a warm, seductive sound.
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.
Woofer:	The large drive unit in a speaker to produce bass frequencies.