Audio Glossary and Definitions

A

A-B Test: A test by which an observor subjectively compares the performance of two components of the same type; for example, a test between two different speakiers. For the test to be scientifically valid, the inputs, levels, and listening conditions should be matched.

ABX Comparator: A device that randomly selects between two components being tested. The listener doesn't know which device is selected.

AC: Alternating Current

Acoustic Coupling: The interaction between two or more speakers stacked together in a PA system which may produce a sound different to (and often better than) the sound produced by the individual speakers.

Acoustic Feedback: A phenomenon where the sound from a loudspeaker is picked up by the microphone or other transducer, like a phono cartridge feeding it, and re-amplifys it through the same loudspeaker only to return to the same microphone to be re-amplified again, etc.. Each time the signal becomes larger until the system runs away and rings, or feeds back on itself producing the characteristic scream or squeal found in sound (mostly, PA) systems. These buildups often occur at particular frequencies called feedback frequencies.

Acoustics: The area of study which deals with the behaviour of sound. Also the effect a given environment has on sound.

Acoustic Suspension: A type of speaker enclosure that is completely sealed with no port or other device to let air inside the enclosure flow outside the enclosure.

Active Crossover: Uses electronics supplied with a power source and acting on the sound to shift sound reproduction tasks from one speaker driver to another.

AIFF: Short for Audio Interchange File Format, a common format for storing and transmitting sampled sound, developed by Apple Computer and the standard audio format for Macintosh computers. Files are 8-bit mono or stereo and generally end with a .AIF or .IEF extension. Normal AIFF does not support data compression so files tend to be large, but another format called AIIF-Compressed (AIFF-C or AIFC) does support compression.

Aliasing: - See "Digital Aliasing"

AM: Amplitude Modulation - A method by which information, usually speech, is mixed with a radio frequency carrier signal to modulate that carrier with the audio information. Used in medium wave, short wave broadcasts as well as in amateur radio, citizens band radio and non licensed communications services.

Ambience: The subjective quality of a space; the feel of the space achieved through a mixture of all elements and characteristics affecting the space.

Amp: Abbreviation for ampere, the unit of electrical current. Also an abbreviation for amplifier.

Ampere: Unit of electrical current.

Amplifier: A device which increases or boosts the level of an input signal by increasing its amplitude.
Amplifier, Power: An amplifier without tone controls, usually with a higher power output than a line amplifier or pre-amp. Commonly used to drive loudspeakers.

Amplification Classes: All sound is a sinosoidial waveform. It has alternating peaks and valleys. The center point of each wave is the zero, or switching point that separates the positive (top) from the negative (bottom) portion of each wave.

Amplitude: The 'level' (perceived as 'volume') of an electrical or acoustic signal. Shown as the value of the vertical axis on a typical graph of a sound wave.

Analog: Any quantity which varies continuously without distinct steps. For sound waves in air, this refers to the continuous variation in air pressure; for an audio signal, this refers to the continuous variation in current or voltage.

Analog-to-Digital Converter: Electronic equipment used to change or convert an analog (waveform style) signal into a digital signal (made up of 1s and 0s).

Analyzer (Audio - Hardware): Device that measures amplitude, bandwidth and distortion characteristics of an audio signal.

Analyzer (Audio - Software): Software program designed to run on a computer that measures amplitude, bandwidth and distortion characteristics of an audio signal.

Anechoic Chamber: A specially designed room in which there are no reverberations of sound waves.

Anechoic Frequency Response: The frequency response of a speaker in an anechoic chamber with no room interactions with the sound.

A&R: Abbreviation for 'Artists & Repertoire', and referring to the responsibility of an individual or company for management of both talent (Artists) and the material they write or perform (Repertoire).

Articulation: A term used to describe clear and well understood audio reproduction in speech.

Attenuate: To reduce the amplitude of an electrical signal usually by using a volume control, fader or 'pad'. Also to reduce sound levels acoustically through the use of acoustic absorbers, resonators or structural materials.

AU: Short for audio, a common format for sound files on UNIX machines. It is also the standard audio file format for the Java programming language. AU files generally end with a .au extension .

Audio: The audible frequency range of sound waves.

Audiophile: A person who is particularly interested in and appreciative of audio.

Audio Generator: A piece of test equipment that produces audio tones from DC to well above human hearing.

Audio Input: In an audio/video system, the audio input is a connection on an electronic device allowing electronic signals with audio information sent by another component to enter.

Audio Output: The connection point from which an audio signal is electronically transferred via a wire from one audio component to another; the origination point of an audio signal as it travels over a wire.

Audio Rack: A stack of audio processors electrically wired together mounted inside a specially made cabinet that houses the equipment.

Audio Rectification: Spurious demodulation of interfering radio-frequency voltages in an audio system.

Audio Scrubbing: See 'Scrubbing'.

AVI: Short for Audio Video Interleave, the file format for Microsoft's Video for Windows standard.

B

Backline: Originally, the line or equipment, such as amplifiers, set up along the back of the stage. Stacks of amps/speakers were often used as much for the look they created as the sound they put out, dressing up the stage and giving it a more theatrical appearance. Loosely, backline is now taken to mean all the artist's stage equipment which is not part of the 'sound reinforcement'.

Baffle: Front panel of a speaker enclosure on which the drivers are placed.

Balance: (1) A term describing the level comparison between two audio channels such as right or left. (2) A term describing the mix of different frequencies to attain evenness between low, mid and high frequencies. (3) A term describing a way of feeding a signal with a separate positive, negative and grounded lines. (See below)

Balanced Line: A pair of ungrounded conductors ('hot' and 'cold') whose voltages are opposite in phase but equal in magnitude. At the destination end, the phase of the 'cold' is reversed thereby doubling the signal strength and cacelling any induced noise. Balanced lines therefore reduce interference from external sources like radio frequencies and light dimmers.

Balanced Modulator: A circuit that receives both an oscillated RF carrier frequency and audio signal at the input and produces only the sum and differences of the carrier plus and minus the audio frequencies, canceling out the carrier frequency.

With a balanced modulator, only the sum and the difference components ("lower sidebands and upper sidebands") of a modulated RF carrier signal appear at the output. The carrier signal has been cleverly balanced out ("cancelled") and does not appear at the output, resulting in a Double Sideband, suppressed carrier RF signal.

Banana Connector: A speaker wire termination consisting of a single, fat shaft which bulges on the sides similar to a banana and inserts in 5-way binding posts.

Band: A grouping of frequencies in the audible frequency spectrum.

Bandwidth: The frequency range across which an audio system can reproduce sound.

Band Pass Filter: A circuit that discriminates between frequencies and allows only the predetermined spectrum of frequencies to pass, eliminating those below and above the desired band.

Basket: A component of a speaker driver which holds the various portions of the driver together.

Bass: Lower register of pitch; also a stringed musical instrument designed to play low frequency sounds; also a voice lower in pitch than a baritone.

Bass Reflex: Type of speaker enclosure which uses a port to increase bass output for a given power input resulting in 2 to 3 dB (decibels) more sound pressure than a similar sealed enclosure (also known as an acoustic suspension enclosure).

Biamplification: The use of separate amplifiers to power woofers and tweeters.

Binding Post: A means of connecting speaker wire to an amplifier or speaker.

Bipolar Speaker: Type of loudspeaker that directs sound in two directions using speaker driver on two sides of the enclosure opposite one another operating in phase (meaning that they both push out at the same time and they both come in at the same time).

Bit: The smallest piece of digital data; bits are represented by a one or a zero.

Bit Rate: The number of bits transferred in one second by a digital device such as a CD player.

Bi-wire: Technique used in connecting speakers to amplification sources in which two wires are run from each amplifier terminal to the corresponding speaker terminal instead of one.

BNC: (Bayonet Fitting Connector) A professional quality cable termination which is used primarily in labs and professional studios as an interconnect.

Bookshelf Speaker: A speaker of a small size, usually under 18 to 24 inches in height, which is best suited to sitting on some sort of stand be it a bookshelf, table, speaker stand or other object.

Board: Alternative name for mixing console or mixing desk.

Boundary Effects: Reverberations and sound irregularities caused by sound waves bouncing off hard surfaces, namely walls, floors and ceilings.

Bridge (Bridging): Amplification term used to describe the process whereby two channels of amplification are combined to operate as a single mono channel.

Bright: Sound quality having a harsh or brittle high-end with too much focus on the upper frequencies.

Brown Noise: Broadband test noise where the amplitude has a linear -6dB per octave attenuation as frequency increases.

Buckshot: A non-technical slang term specifically used to describe a radio frequency signal that is distorted causing the RF bandwidth to exceed the original audio bandwidth contained in it, thus causing interference to adjacent radio frequencies. (See also "Splatter")

Bump In / Out: The installation and removal of production equipment and services at a theatre venue.

Buss/Bus: A signal-carrying conductor or electrical pathway designed to carry multiple signals. e.g. a mixing console auxiliary bus may carry signals derived from several channels on that console

Butterworth Crossover: Type of crossover that uses a low-pass filter design, which results in no amplitude anomalies in the frequencies passed on by the filter (the passband).

C

Canon/Cannon: Brand name of multipoint connector used for professional audio equipment - see XLR.

Capacitor Microphone: See Condenser microphone.

Cardioid: "Heart" shaped pattern exhibited by some microphones which reduces pick-up from the sides and back.

Carousel Changer: Type of optical disc player/transport (namely CD) that holds multiple discs on a rotating platter enabling the component to play numerous discs without the user needing to manually switch discs.

Cartridge (Phono Cartridge): Device used with record players that holds the stylus or needle and attaches to the tonearm of the record player converting signals from the record grooves into electrical energy that can be played on an audio system.

Cassette: Plastic container holding a magnetic tape, which contains audio or video signals that can be read and played back when the tape is pulled over a magnetic reader of the appropriate type.

Cassette Deck: Audio component that accepts standard audiotape cassettes from which it reads information or to which it records information.

CD: Compact Disc

CD Changer: Type of compact disc player that holds more than one disc internally and that can swap discs to play various discs without the need for the user to physically swap discs or add discs.

CD-R: (Compact Disc Recordable) Form of compact disc consumers can record on using special CD "burners" or CD recorders. Can be recorded on only once and then becomes "Read Only" and is commonly used for music playback and data where high comparability is required..

CD-RW: (Compact Disc Re-Writable) Form of compact disc consumers can record on using special CD "burners" or CD recorders. Can be written to several times and is commonly used for archiving data.

CD-ROM: Compact disc read only memory; CD that cannot be written to or recorded making it useful only for data retrieval.

Center Channel: Third front audio channel (in addition to main stereo left and right channels) found in surround sound audio systems with the primary task of reproducing movie dialogue (what the actors are saying) thus locking the voices to the screen for all listeners.

Center Channel Speaker: Speaker used to output information from the center channel in a surround sound audio format.

Channel: A single module of a professional audio console, lighting control console, power amplifier, lighting dimmer or multi-core control cable, designed to carry one signal only and keep it separate from signals in other channels.

Chops: Slang for musical technique.

Chord: A combination of two or more notes played together.

Circuit Breaker: An electrical switch that automatically breaks a circuit if the current through it is too high, then can be manually reset. Performs the same function as a fuse, without the need for replacement after activating.

Click Track: A regular sound, such as from a metronome, usually recorded on one track of a multitrack and used to indicate the required tempo for recording musicians.

Clipping: Audible distortion occurring when the peaks of an amplifier's output are flattened ('clipped'). When the input is too high, an amplifier has insufficient power to accurately reproduce the output waveform.

Coaxial Cable: Specific type of cable design with two conductors, one running through the center of the cable surrounded by some form of non-conductive insulator with a second braided conductor wrapped around the insulation material and serving double-duty as a shield against interference.

Co-axial Speaker: Type of speaker driver in which a high frequency driver (a tweeter in most cases) is placed inside a low or mid frequency driver in the place of the dust cap.

Compact Disc (CD): Thin, round, reflective disc that stores digital data in the form of microscopic pits and lands and that can be read by a laser.

Compander:
This is a device that compresses and expands audio signals, sometimes simultaneously, sometimes as individual processes in one box. The term is a composite of COMPressor/expANDER.

Component: An individual piece of equipment in an audio or audio/video system.

Compression (Audio): The process of reducing the dynamic range of a given analogue audio program by making the loud parts quieter and the quiet parts louder.

Compression (Data): The process of packing digital data, such as computer files, more efficiently for the purpose of storage or transmission. Commonly referred to as 'stuffing' or 'zipping' a file.

Compression (Audio/Video Files): A process of temporarily or permanently reducing audio data for more efficient storage or transmission. A temporary reduction in file size is called 'non-lossy' compression, and no information is lost. A permanent reduction in file size (such as with mp3 files) is called 'lossy' compression, and involves discarding (supposedly) unnecessary information which is irretrievably lost.

Compression Ratio: (See "Ratio")

Compressor: A type of dynamic range processor which reduces the gain of audio signals which are over an adjustable 'threshold' level, therefore reducing the dynamic range. Generally allows the operator control over threshold, ratio, attack and release times. Both analogue and digital types are available.

Concert Pitch: A standard for the tuning of musical instruments, internationally agreed in 1960, in which the note A above middle C has a frequency of 440 Hz. The tuning used with middle 'A' corresponding to a frequency of 440Hz.

Condenser Microphone: A mic that depends on an external power supply or battery to electrostatically charge its condenser plates. Also called a 'Capacitor' microphone.
Conductor: Materials along which electrons will flow, making them suitable for use as connecting links in electrical circuits.

Cone: A type of speaker driver resembling an ice cream cone, with its largest diameter at the front of the speaker enclosure becoming smaller deeper within the enclosure.

Conventional Current: The representation of current as flowing from positive to negative potential when describing the behaviour of electricity, despite the reality that the actual electrons constituting that flow move from negative to positive potentials!

Crossfade: A procedure in which one independent channel of information is raised as the other is lowered so that one smoothly replaces the other e.g. one audio track may 'crossfade' to another.

Crossover: An electronic circuit which splits an audio signal into different frequency bands for routing to different speakers optimised for that frequency.

Crosstalk: Audio distortion resulting from information in one audio channel leaking into the signal of another channel.

Cue: 1. Foldback system used for recording studios. 2. The signal given to a performer to indicate the start of their performance.

Current: The flow of electrons along a conductor.

Cycles per second: See Hertz

E

Early Reflections: Sound waves bouncing or reflecting off a wall, ceiling, floor or object in a room and reaching the listener just after the direct sound waves emanating from the speakers themselves.

Earth: An electrical connection to the earth, which represents 0 volts or 'ground potential' by way of a metal or conductive rod.

Easter egg: A surprise usually coded into computer programs or web pages that is accessed by an undocumented keystroke combination or hidden link.

Echo: The combined effect of a sound and a delayed version of that same sound. A 'Slap-Back Echo' is the original sound plus a single repeat; "Multiple Echo" is the original sound plus several repeats with the same delay spacing.

Effect: A device which modifies sound creatively via processing.

Effects Rack: A cabinet containing outboard equipment. Designed to accommodate a number of standard width (19" or 48.3cm) rack-mountable devices. Pro-audio devices are always designed to have one of several standard heights in 'rack units' (RU), each RU being 1.75" or 4.44 cm.

Electrostatic Speaker: Type of speaker that uses positive and negative electric charges over two thin panels, one stationary and one moveable, to generate sound (two positive or two negative charges repel each other while a positive and negative attract each other enabling movement and thus sound production).

Enclosure: The cabinet or structure of a speaker into which the various speaker elements (the drivers, the crossover, the binding posts, etc.) are placed and attached.

EQ / Equalization: The increase or decrease in level of certain portions of the audio frequency spectrum imposed by a device or acoustic environment. Changing the frequency response of a given audio signal by adjusting the amplitude of the signal usually in an effort to achieve a flatter frequency response (although often misused to alter the audio signal to a more "pleasing" form which is a distortion of the intended signal - for instance, artificially adding bass for a more visceral impact).

ESSB (Audio): Extended Single Side Band. Any J3E SSB transmission mode that exceeds or extends the audio bandwidth of standard or traditional 2.9kHz J3E modes in order to support the fidelity required and desired for relative high fidelity, full range clean and articulate vocal audio.

Excursion: The distance a speaker driver travels to reproduce an audio frequency.

Expander: A type of dynamic range processor which reduces the gain of audio signals which are under an adjustable 'threshold' level, therefore increasing the dynamic range. Generally allows the operator control over threshold, ratio, attack, release and 'hold' times. Both analogue and digital types are available.

F

Feedback: Sound produced by an instrument or microphone picking up and amplifying its own signal from a nearby loudspeaker. Also known as 'howlaround'.

Filter: A device that removes unwanted frequencies or noise from a signal.

Ferrofluid Cooling: Type of cooling material (ferromagnetic liquid) used primarily with tweeters to keep the driver from overheating by dissipating heat away from the voice coil.

FFT: Fast Fourier transform (FFT) is a discrete Fourier transform algorithm which reduces the number of computations needed for points from to , where lg is the base-2 logarithm. If the function to be transformed is not harmonically related to the sampling frequency, the response of an FFT looks like a sinc function (although the integrated power is still correct). Aliasing (leakage) can be reduced by apodization using a tapering function. However, aliasing reduction is at the expense of broadening the spectral response.

Fiber-Optic Cable: A cable that uses light beams to transmit information rather than electrical signals traveling over metal wires.

Flat / Flatness: Audio frequency amplitude is considered to be "Flat" if a faithful reproduction of the original input source is achieved at the output. If the audio amplitude in a given frequency range of an audio signal is the same as the source audio, then it is said to be "Flat".

Fletcher Munson Curve: Tones of the same SPL but with different frequencies are in general judged as having different loudness. SPL is thus not a good measure of loudness, if we inter compare tones of different frequency. Experiments have been performed to establish curves of equal loudness, taking the SPL at 1 KHz as a reference quantity. This relative curve of perceived loudness is referred to as the "Fletcher Munson Curve" named after the audio experimenters who developed it.

Floorstanding Speaker: A specific type of speaker enclosure that stands directly on the floor without needing to sit on something in order to raise its speaker drivers to an acceptable height in line with the listener.

Flutter: Pitch variations heard as a fast wavering or wobbling caused by a software medium (such as an audiotape or CD) moving at varied speeds.

Flying-Erase Head: Feature of high-quality VCRs that makes transitions between recorded material smooth and clean by erasing a fraction of a second of tape just prior to the start of recording.

FM (Frequency Modulation): Method of adding an audio signal to a carrier radio frequency (modulating the signal) so that the audio signal can be transmitted from place to place and later decoded from the radio frequency for reproduction.

FM Synthesis: Synthesiser technology which mimics different musical instruments according to built-in formulas. Generally considered to be inferior to Wave Table Synthesis.

FOH: Front-Of-House. Generally refers to the audience area, or that part of a venue not comprising the stage or backstage areas.

FOH Desk: Refers to audio or lighting control consoles at front-of-house, usually located towards rear of audience area.

FOH Engineer/s: Personnel responsible for operating audio and lighting systems, heard and seen by the audience as part of a performance.

Foldback (Live Sound): Also known as the monitor system, foldback comprises onstage speaker systems which enable the artist to hear his/her own performance, as well as other instruments and/or vocalists to varying degrees as controlled by the 'monitor engineer' or 'foldback engineer'.

Foldback (Studio): The system by which a performer in a studio may hear their performance through headphones. Also known as 'Cue'.

Frequency: The number of complete cycles that a sound wave goes through in each second. Unit used is Hertz, abbreviated to Hz, although some countries still use the older term 'cycles per second' (cps). Humans perceive frequency subjectively as pitch (eg: 440Hz = A).

Frequency Response: Range over which an audio component can effectively produce a useable and fairly uniform, undistorted output signal.

Full Power Bandwidth: The range of frequencies across which an amplifier can supply its full power rating to a speaker.

Full-Range Surround Sound Channels: A feature of 5.1 digital surround sound formats allowing discrete surround sound channels which are capable of playing across the frequency band audible to human hearing (20 Hz to 20,000 Hz).

Function Generator: A piece of test equipment that produces audio test tones from DC to well beyond human hearing.

Fuse: A safety device consisting of a low melting-point wire with a low melting pointwhich breaks an electrical circuit by heating up and melting ('fusing') if the current through it is too high.

G

Gaffer tape: Multi-purpose plasticised cloth tape often used to fasten leads on stage.

Gain: The amount by which an amplifier increases the power of a signal, indicated either in dB (e.g. Gain = +12dB), or as a multiplier (e.g. Gain = x4)

Gate: See 'Noise Gate'

Gig: Slang for job, engagement of musicians to play and perform.

GPO: General Purpose Outlet, or power point, capable of supplying normal mains power.

Graphic Equalizer: An audio equalizer that uses pre-defined center frequencies and Q's with variable amplitude.

H

Harmonic: An additional frequency in an audio signal derived from the fundamental or original frequency as a multiple of that fundamental that is smaller in amplitude (power) than the fundamental.

HDCD (High Definition Compatible Digital): Compact disc encoding/decoding scheme developed by Pacific Microsonics with the goal of improving on the sound of traditional CDs.

HDCP (High-Bandwidth Digital Content Protection): Specification used to encrypt and protect digital video and audio signals transmitted between two HDCP-enabled devices using DVI or HDMI connections.

HDMI (High-Definition Multimedia Interface): Digital video and audio connection system used to connect a variety of audio/video components, particularly high-definition video (HDTV). HDMI supports all HDTV formats along with support for up to eight channels of digital audio.

Headphone Jack: A connection on an audio or audio/video component which receives a headphone connection.

Headphones: Personal audio listening device which covers or in some way goes over or attaches to a listener's ears.

Headroom: An amplifier's ability to go beyond its rated average power for a short time in order to recreate loud or explosive audio signals that rise very quickly.

Heat Sink: A metal object, usually a row of thin metal fins, designed to dissipate heat away from electronic equipment.

Hertz: (Abbreviation: Hz) The unit of frequency. Replaces 'cycles per second' and means the same.

High-Pass Crossover: Type of crossover that attenuates or cuts off low frequency signals and sends on only the high frequency signals falling above the crossover point (crossover frequency).

High Pass Filter: A circuit that discriminates between high and low frequencies and allows only the high frequencies to pass.

Hook: A catchy part of a melody, riff or lyric which 'hooks' the listener's attention.

Horizontal Input: Usually referring to the horizontal (X) input of an oscilloscope that measures an audio, I.F. or R.F. signal source.

Howlaround: see Feedback

Hypercardioid: A narrower heart-shaped pick-up pattern than that of cardioid microphones.

HyperGlossary: A name made up by me to describe a glossary containing the usual text descriptions of terms, plus added hyperlinks to expanded definitions, examples, and images.

I

I.M.D.: Intermodulation Distortion - Nonlinear distortion characterized by the appearance, in the output of a device, of frequencies that are linear combinations of the fundamental frequencies and all harmonics present in the input signals. Note: Harmonic components themselves are not usually considered to characterize intermodulation distortion.

Imaging: Term used to describe the quality of a sound field put out by an audio system giving a subjective measure as to how well a system can recreate depth, width and height from the recording.

Impedance: The measure of the total resistance to the current flow expressed in ohms, in an alternating current circuit. It is an important characteristic of electrical devices (particularly speakers and microphones). Most speakers are rated at 4 or 8 ohms. Microphones are usually classified as being either high impedance (10,000 ohms or greater) or low impedance (50 ohms to 600 ohms).

Integrated Amplifier: Audio component combining the elements of an amplifier with those of a preamplifier but not containing a tuner (making an integrated amplifier different from a receiver which does contain a tuner).

Interconnect: Wire used to connect various pieces of equipment (components) in an audio/video system carrying audio or video information via low-level electric signals (not very powerful) or via light pulses (digital information carried over fiber-optic interconnects).

Input Overload Distortion: Distortion caused by too great an input signal being sent to an amplifier or preamplifier. It is not affected by volume control settings and often occurs when mics are positioned too close to the sound source. This distortion is controllable through the use of an attenuator or pad.

Input Impedance: The measure of the total resistance to the current flow expressed in ohms, in an alternating current circuit at the input of a device. Most modern equipment has a low imput impedance from about 150 ohms to 600 ohms.

Input Sensitivity: The range of input voltages required to produce outputs from the minimum to the maximum output of an amplifier; may also refer to the input sensitivity for maximum output, which is the input in volts required for an amplifier to create its maximum power output.

Inverse Square Law: The law that states that in the absence of reflective surfaces, sound pressure (or light) falls off at a rate inverse to the square of the distance from its source. In other words, every time you double your distance from the sound source, the sound pressure level is reduced by a factor of 4, or 12 dB.

Insulator: Material preventing the flow of electrons, making it suitable for prevention of unwanted current flow in electrical circuits.

Integrated Amplifier: An amplifier containing two stages: a 'Pre-Amplifier' and a 'Power Amplifier'. Commonly used for domestic hi-fi applications.

Interface: A device which facilitates the linking of any two pieces of equipment or systems; or when used as a verb ('to interface'), the process of linking.

Isobaric: A type of speaker enclosure used for subwoofers and bass drivers which uses a small, sealed enclosure with two bass drivers facing each other (one inside the box facing out and the other outside the box facing in at its counterpart) and wired out of phase.

J

Jack: Female audio receptacle, or socket designed for male plug.

Jackfield: See Patchbay

JPEG: Short for Joint Photographic Experts Group, and pronounced jay-peg. JPEG is a lossy compression technique for color images. Although it can reduce files sizes to about 5% of their normal size, some detail is lost in the compression.

Jumper: Used to connect multiple speaker binding posts on speakers capable of bi- or tri-amping.

Jumper Cable (Audio): Used to connect one audio device to another using shielded cables. Comes in the form of balanced or unbalanced configurations.

K

L

Late Reflections: Sound waves that bounce or reflect off room boundaries and objects reaching a listener a relatively long time after the direct signal from the sound source reaches the listener.

Leads: Signal-carrying cables used to connect various pieces of equipment.

LFE (Low Frequency Effects): Audio channel found in 5.1 digital surround sound audio schemes (the .1) that carries only low frequency information of 80 Hz and below.

Limiter: A compressor set up with a high ratio (in excess of 10:1) and used primarily to prevent a signal from exceeding a certain pre-set maximum level. (See also "Peak Limiting")

Line Conditioner: Electronic device that "cleans" the electricity coming from a wall outlet to be used by audio/video components and protects them from electric spikes and surges.

Line Level: A signal whose voltage is between approximately 0.310 volts and 10 volts across a load of 600 ohms or greater.

Linearity: Linearity is the behavior of a circuit, particularly an amplifier, in which the output signal strength varies in direct proportion to the input signal strength. In a linear device, the output-to-input signal amplitude ratio is always the same, no matter what the strength of the input signal (as long it is not too strong).

Load In / Out: The installation and removal of production equipment and services at music performance venues.

Loader/Lugger: Person providing labour for the above function whose responsibility is generally limited to lugging equipment between the production trucks and the stage or FOH positions. Their job generally does not include rigging or setting up the equipment, which is the responsibility of roadies.

Lossy Compression: A type of data compression which permanently discards data that humans supposedly "cannot hear" to create much smaller audio, video and image file sizes. When the file is decompressed by the recipient, this compression method replaces the data for the sections it removed with calculated values to restore the file. The decompressed file is similar but not identical to the original file.

Low-Pass Crossover: Type of crossover that only allows low frequencies to pass cutting off or attenuating frequencies above the crossover point (crossover frequency).

Low Pass Filter: A circuit that discriminates between high and low frequencies and allows only the low frequencies to pass.

M

Mac: Apple Macintosh computer.

Master Fader: A fader which controls the overall level of one or more outputs simultaneously.

Matrix Surround: Sound Method of encoding more than two channels of audio into a pair of analog audio channels.

Metronome: Adjustable mechanical or electronic device which audibly indicates tempo. Some electronic versions may indicate beats per minute (bpm).

MIDI: Acronym for Musical Instrument Digital Interface, a standard adopted by the electronic music industry for controlling devices, such as synthesizers and sound cards, that produce music. At minimum, a MIDI representation of a sound includes values for the note's pitch, length, and volume, but can also include additional characteristics, such as attack and decay time.

Mic: Abbreviation of the word microphone.

Microphone: A device that converts sound pressure variations into electrical signals.

MIDI files: A computer file format containing musical information and performance data.

Midrange: The middle part of the audio frequency spectrum above Bass and below Treble.

Minidisk: Recording and playback device using small disks similar to CDs to store audio using lossy data compression to reduce file size.

Mix: Blend of amplified or recorded sounds. In the recording studio, the process of combining and balancing the signals from two or more tracks of a multi-track recorder resulting in a final mix or 'master tape'.

Mixing console/desk: A signal-management device which receives, combines and balances signals, provides control of volume and tone, and allows routing of signals to selected destinations.

Modem: Short for Modulator -Demodulator, this device modulates data by converting it to audible tones that can be transmitted on a telephone wire, and demodulates received signals to get the data.

Modulation: A method by which information (typically audio) is superimposed on a signal that carries that information. Examples of modulation schemes would include "AM" (Amplitude Modulation), "FM" (Frequency Modulation) etc... used in broadcast, amateur radio and non licensed radio services.

Monitor Desk: A mixing console located at the side of the stage which controls the on-stage sound balance through separate foldback speakers for the performers. The monitor mix, or foldback mix differs markedly from the FOH mix.

Monitors (Studio): Speakers used in the control room of a recording studio. Generally of two types: Main Monitors for overall sound, and Reference Monitors used to check sound quality through less capable speakers, such as might be found in domestic environments.

Monitors (Live Sound): Foldback speakers and associated amplifiers used for stage musicians.

Mono: Consisting of only one channel.

Moving-Magnet Cartridge: Method of interaction between the stylus and cartridge of a phonograph that creates electrical signals by attaching a magnet to the stylus that in turn moves up and down in relation to a coil of wire in the cartridge.

MPEG: Short for Moving Picture Experts Group, and pronounced m-peg. The term also refers to the whole collection of digital compression standards and file formats developed by the group.
MP3, mp3: Is the file extension for MPEG, audio layer 3. Layer 3 is one of three coding schemes (layer 1, layer 2 and layer 3) for the compression of audio signals. Layer 3 uses perceptual audio coding and psychoacoustic compression to remove all superfluous information (that, in the opinion of the developers, the human ear doesn't hear anyway). It also adds an algorithm that increases the frequency resolution 18 times higher than that of layer 2. The result is mp3 encoding shrinks the original sound data from a CD by a factor of 12 without sacrificing sound quality.

MPEG-1: Video compression format developed by the Motion Picture Experts Group using perceptual coding and predictive technologies to eliminate data from an audio/video signal and thus encode it into a smaller size.

MPEG-2: High-quality audio/video compression format developed by the Motion Picture Experts Group using perceptual coding and predictive technologies similar to MPEG-1 but including a higher bit-rate and more control over the compression and technology.

Multicore: Audio or lighting cable containing many bundled leads allowing signal transmission along separate channels. Also known as 'Snake'.

Multimedia: The use of computers to present text, graphics, video, animation, and sound in an integrated way.

Multiple Echo: See 'Echo'.

Multi-tracking: The process of recording a multi-part performance on separate tracks at different times
which allows the engineer to subsequently combine, balance and process those tracks during mixdown.

Mute: No sound or a cessation of all sound; a single button or control to cut off an audio signal and stop the production of sound.

N

Near Field: In close proximity to a speaker or speaker driver.

Negative Peak Limiting: A compressor set up with a high ratio (in excess of 10:1) and used primarily to prevent a signal from exceeding a certain pre-set maximum level. (See also "Limiting")

Neophyte: A beginner or novice.

Noise: Typically low-level electrical distortions and interference created in an electronic component from power supply hum, interactions between internal electrical components, etc. (See also White Noise, Pink Noise and Brown Noise)

Noise Floor: Level at which no useful signal is produced because the signal level is below the level of noise in the system; point at which the volume or power of noise is greater than the volume or power of an intended and desired signal effectively covering up and obscuring that signal thus making it useless (see Noise).

Noise Gate: A special type of expander with a very high ratio (usually about1:100), often used to eliminate low-level hiss, noise or leakage. Especially effective wherever there is a high level of ambient noise, such as around a drum kit.

Noise Reduction: Effort to reduce noise in a system, typically in sound reproduction equipment and sound storage media such as audiocassette tapes, through various mechanical and software based methods (see Noise).

Non-Linearity: Non-Linearity is the behavior of a circuit, particularly an amplifier, in which the output signal strength varies in indirect proportion to the input signal strength. In a nonlinear device, the output-to-input signal amplitude ratio is always different, and can vary with the strength of the input signal.. Usually an undesirable condition.

Non-Lossy Compression: A form of data compression which seeks out chunks of data which are identical, replacing them with markers called keys. In this way, the file is reduced in size, and when it is decompressed by the recipient, the keys are replaced with the large chunks of data that were originally there (this is called Run Length Encoding). Using non-lossy compression, the uncompressed file is identical to the original file.

Notch Filter (Audio): Filter used to eliminate a specific interfering or undesirable frequency by attenuating a very narrow audio passband from the desired signal.

Nyquist's Theorem: This states that a sound must be sampled at at least twice its highest analog frequency in order to extract all of the information from the bandwidth and accurately represent the original acoustic energy. In practice, sampling at slightly more than twice the frequency will make up for imprecisions in filters and other components used for the conversion.

O

Octave: The relative mathematical relationship of a frequency that is two times or one half of the original reference frequency. For example; 500 Hz is said to be one octave below 1000 Hz, and 2000 Hz is said to be one octave above 1000 Hz. This term is used in describing the relationship of musical notes. 440 Hz is reffered to as "Middle A". So 880 Hz would be an A note that is one octive higher than middle A. It is also used to describe the bandwidth (Q Factor) of audio amplitude beyond a given center frequency where the amplitude drops below the -3dB point as compared to the center frequency reference amplitude.

Ohm: The basic unit of the measurement of resistance. Symbol used is (Omega)

Ohm's Law: The law that defines the relationship between current (I), resistance (R) and voltage (V) in an electrical circuit as: Voltage equals Amperage times Resistance (V=IR).

Omnidirectional: Capable of picking-up sound equally from all directions (for microphones) or radiating sound equally in all directions (for speakers).

On-Axis: Directly in front of a speaker; position at a right angle (90-degree angle) to the front of a speaker enclosure on which the speaker drivers are located (the baffle).

Optical Cable: An interconnect cable used to transfer digital data between digital components using bursts of light carried over glass or plastic fibers (see Fiber-Optic Cable).

Outboard Equipment: Audio equipment which is not physically incorporated into the mixing console. If 'rack-mountable', it is generally located in an 'effects rack' and can include processors such as reverbs, delays, external equalisers, compressors, gates and enhancers.

Overdub: To record new tracks on a multitrack recording system in synchronisation with previously recorded tracks.

Oversampling: Raises the sampling rate of digital data providing a smoother signal curve, but does not provide enhanced detail or resolution of the output.

P

PA: Public Address system. A sound reinforcement system enabling live performances to be heard by the audience.

Pad: An electrical circuit used to attenuate or reduce the amplitude of an audio signal by a fixed amount, e.g a -15dB pad reduces the signal by a fixed 15 decibels.

Pan Pot: Short for panoramic potentiometer, this is a knob controlling a voltage divider that can send a signal to a combination of two busses, such as left and right. Always found on mixing consoles to set up (pan) a signal within the stereo field, it is also called a 'balance' control on domestic stereo amplifiers.

Passive Crossover: Crossover that does not require electricity and does not use active circuitry to accomplish its task.

Passive Radiator: Speaker driver that is not powered and is used in conjunction with a woofer generating movement by being vibrated by the back-pressure of the powered woofer.

Parametric Equalizer: An audio equlaizer that uses variable frequency, Q and amplitude control.

Patch Bay: A p