16-Bit Audio	A unit of measure that indicates the resolution of a digitised sound sample. The higher the resolution, the better the audio fidelity. 16-bit audio is the standard used for standard audio Compact Discs (CD-DA).
3D Sound	A blanket term for technologies that alter the way sound is distributed in real-world space. Spatialisation broadens the soundstage (the area in space where the sound seems to be coming from), making it more dramatic and spacious, and gives the illusion of pushing it beyond the physical location of the speakers. Positional audio uses encoded audio streams to position sounds realistically in the space around the listener when the sounds are played back on compatible equipment.
8-Bit Audio	A unit of measure that indicates the resolution of a digitised sound sample. The higher the resolution, the better the audio fidelity. Audio that is digitised using 8 bits of resolution is slightly better in fidelity than normal AM radio.
AC 97	Intel's recommended standard for PC audio circuitry. The specification reduces noise by partitioning analogue and digital components into separate modules.
ADPCM	Adaptive Delta Pulse Code Modulation: the audio encoding and compression method used in CD-I and CD-ROM XA recording.
AIIF	Audio Interchange File Format: used for high end audio applications.
AU	Unix sound file format popular on the Internet.
Audio	Sound for multimedia systems. Audible range is typically from 30Hz to 20,000Hz (20KHz).
Chorus	A doubling effect used to enhance sound.
DAT	Digital Audio Tape: initially a CD-quality audio format which recorded at 41.8kHz. In 1988, Sony and HP defined the Digital Data Storage (DDS) standard enabling DAT to become a magnetic tape technology used for backing up data.
Dolby AC-3	A perceptual digital audio coding technique capable of delivering multichannel digital surround sound. It incorporates 6 (5.1) discrete channels; each channel can carry a different signal simultaneously (left front, right front, centre, left rear, right rear, sub-woofer).
Dolby ProLogic	More advanced form of Dolby Surround that not only recovers the surround information from the encoded program material, but also adds a centre channel to keep dialogue and centre effects firmly positioned on the TV screen. Provides a wider listening/viewing area and provides better channel separation.
Dolby Surround	First generation home theatre format that recovers surround information from encoded program material and feeds it to a pair of surround speakers placed up on the side walls adjacent to the listening area. Outputs three channels: left, right, and surround (usually split into 2 rear speakers).
DVD-Audio	The DVD audio-only storage format similar to CD-Audio. DVD-Audio is facing stiff competition from a number of other high fidelity audio standards.
FM Synthesis	Frequency Modulation Synthesis: an outdated technique for synthesising music reproduction but still widely supported to provide compatibility with older games software.
Gain	The increase in signalling power as an audio signal is boosted by an electronic device. It is measured in decibels.
General MIDI	A table of 128 standard sounds or instruments for MIDI cards and synthesisers.
MIDI	Musical Instrument Digital Interface: a specification that standardises the interface between computers and digital devices that simulate musical instruments. Rather than transmit bulky digitised sound samples, a computer generates music on a MIDI synthesiser by sending it commands just a few bytes in length. These contain all the information a sound board needs to reproduce the desired sound - the type of instrument, the pitch, duration, volume, attack, decay, etc. are all specified by the protocol. Each channel of a MIDI synthesiser corresponds to a different instrument, or 'voice'. Programming several channels simultaneously produces symphonic sound.
MIDI Mapper	Windows multimedia translator for MIDI hardware and software.
MP3	Standardised as ISO-MPEG Audio Layer-3 (IS 11172-3 and IS 138-3), MP3 employs a lossy compression technique, with bits of information being discarded to allow data to be compressed into files which are relatively small in comparison with .WAV files but which retain subjective CD quality.
MPEG Audio	MPEG defined three levels or layers of audio compression. Which layer a type of equipment uses depends on the desired level of compression. These three layers compress audio data streams by roughly four, six and eight times respectively, around 64, 128 and 192Kbit/s  per channel. In practical terms, these compression rates make possible radio broadcasting of CD-quality music. All three layers are defined for both monaural and stereo sound. Definitions for surround sound and other high fidelity applications are under consideration.
MPEG-2 Audio	Supplies up to five full bandwidth channels (left, right, centre, and two surround channels), plus an additional low frequency enhancement channel, and/or up to seven commentary/multilingual channels. The MPEG-2 Audio Standard will also extend the stereo and mono coding of the MPEG-1 Audio Standard to half sampling-rates (16 KHz, 22.05 KHz, and 24 KHz), for improved quality for bitrates at or below 64 Kbits/s, per channel.
Multi-Timbral	The number of simultaneous instruments a synthesiser can play.
Physical Modelling Synthesis	A revolutionary method for generating sound. This technique emulates the impulse patterns of real-world instruments using a software model.
Polyphony	The number of voices a synthesiser can play at any one time.
Psychoacoustics	The study of how the human brain perceives sound. Findings relating to which sounds are and are not heard by the human ear have been used in the formulation of various audio compression techniques, including MP3.
RealAudio	Extreme audio compression scheme used on the Internet to provide streamed audio over ordinary modems
Ripper	The name given to the specialised software that extracts raw audio data from a music CD. The ability to extract audio digitally relies on a feature of newer CD-ROM drives that allows the digital data from audio CDs to be passed through the computer's bus (IDE, SCSI) just like CD-ROM data.
Roland GS	Roland General Synthesiser and General MIDI are two overlapping specifications for defining the standard sets of MIDI sounds that are associated with specific commands.
Sampling	The first step in the process of converting an analogue signal into a digital representation. This is accomplished by measuring the value of the analogue signal at regular intervals called samples. These values are then encoded to provide a digital representation of the analogue signal.
Sampling Rate	In digitising operations, the frequency with which samples are taken and converted into digital form. The sampling frequency should be at least twice that of the analogue frequency being digitised. Thus, the sampling rate for hi-fi playback is 44.1kHz, slightly more than double the 20kHz frequency humans can hear.
SDMI	Secure Digital Music Initiative: A secure digital format for distributing music over the Internet. Announced in February 1999, it is backed by the Recording Industry Association of America (RIAA) and Sony, Warner, BMG, EMI and Universal - the top five music production companies. The new format is expected in products by Christmas 1999.
Sequencer	Software for recording and editing MIDI files.
Sound Blaster	A family of sound cards from Creative Labs. The Sound Blaster protocol has become the de facto audio standard for PCs. Monaural versions of Sound Blaster cards were introduced in 1989, and a stereo version three years later. The Sound Blaster AWE32 and AWE64 are 16-bit sound cards that provide WaveTable MIDI with 32 and 64 voices respectively.
Sound Card	Also called sound board and audio adaptor, this is an expansion board that records and plays back sound, providing outputs directly to speakers or an external amplifier. The de facto standard for sound card compatibility in PCs is Creative Labs' Sound Blaster.
S/PDIF	Sony/Philips Digital Interchange Format: an interface standard that lets users connect sound equipment (such as sound boards and speakers) via a pure digital signal.
TAPI	Telephony Application Programming Interface: permits Windows applications to program telephone-line-based devices such as modems and fax machines in a device-independent manner.
Voice recognition	The conversion of spoken words into computer text. Speech is first digitised and then matched against a dictionary of coded waveforms. The matches are then converted into text as if the words were typed on the keyboard.
WAV	Waveform Audio: the native digital audio format used in Windows. WAV files use the .wav file extension and allow different sound qualities to be recorded. Either 8-bit or 16-bit samples can be taken at rates of 11025Hz, 22050Hz and 44100Hz. The highest quality (16-bit samples at 44100Hz) uses 88KB of storage per second.
WaveTable Synthesis	A common method for generating sound electronically on a PC. Output is produced using a table of sound samples--actual recorded sounds-- that are digitised and played back as needed. By continuously rereading samples and looping them together at different pitches, highly complex tones can be generated from a minimum of stored data without overtaxing the processor.
XG	Yamaha's extension of General MIDI that provides many instrument variations and more digital effects. Many instrument parameters can be controlled in real-time.