Gain - The amount of increase in audio signal strength, often expressed in dB.

Gain Control - A device that changes the gain of an amplifier or circuit, often a knob that can be turned or a slide that can be moved up arid down. 

Gain Reduction - The working of a limiter or compressor reducing gain during high-level passages. 

Gain Structure - The way in which the gain varies in the stages or sections of an audio system. 

Gate - A dynamic processing device that turns a channel off or down when the signal drops below a certain level. 

Golden Section - A ratio of height to width to length of a room to achieve "good acoustics" and first recommended by the ancient Greeks. The ratio is approximately the width 1.6 times the height and the length 2.6 times the height 

Graphic Equalizer - An device with several slides controlling the gain of audio signal present which is within one of several evenly spaced frequency bands (spaced according to octaves). 

Ground Lift - A switch that breaks the connection between the ground point in one circuit and the ground point in another circuit.

Ground Lifter - An adapter that takes a three prong power cord and plugs into a two prong outlet, used to disconnect the third (ground) pin of the power outlet. WARNING: It can be VERY DANGEROUS to have no ground connection to the case by using a ground lifter and not grounding the unit by other means. 

Haas Effect - Simply stated, a factor in human hearing where delay has a much bigger effect on human perception of direction than level does. 

Head Amp - British name for Preamplifier (A low-noise amplifier designed to take a low-level signal, such as the output of a tape head, and bring it up to normal line level). 

Headroom - 1) The level difference (in dB) between normal operating level and clipping level in an amplifier or audio device. 2) A similar level difference between normal tape operating level and the level where the distortion would be 3%. 

Hearing Limitation - An inability of the ear to hear important characteristics of sound under certain conditions. Characteristics that can be affected include pitch, level, clarity, presence and direction.  

Hertz - The unit of frequency. Equivalent to cycles per second. Abbreviation: Hz. 

Hi-Z - An abbreviation of the term High Impedance (Impedance of 5000 or more ohms). 

High Frequencies - The audio frequencies from 6000 Hz and above. 

High Pass Filter  - A circuit that lets higher frequencies pass unchanged, while reducing the amplitude of frequencies lower than a set point, and reducing them at a fixed rate per octave.  High pass filters, for example, act to direct higher frequencies to satellite speakers -- and keep lower frequencies minimal -- when one sets their size to "small" in a surround system. In this particular case the filter will usually pass frequencies above 80 Hz and attenuate those below.  High-pass filters in general, though, can act at any frequency point for which they're designed.

Highs - Short for the term High Frequencies (the audio frequencies from 6000 Hz and above). 

Horn - A speaker or speaker enclosure where sound waves are put into a narrow opening (by a speaker cone or driver) and the narrow opening flairs out to a larger opening.

Hum - The 60 Hz power line current accidentally induced or fed into electronic equipment.

IC - Abbreviation of Integrated Circuit (A miniature circuit of many components that is in small, sealed housing with prongs to connect it into equipment). 

ID - An index signal (digital data that gives the machine information of where selections start, their selection number, etc.) on a DAT or CD.

IM Distortion - An abbreviation of the term Intermodulation Distortion (Distortion caused by one signal beating with another signal and producing frequencies that are both the sum and the difference of the original frequencies present).

Images - The squaring of the waveform that happens in the conversion of digital audio bits into analog signals.

Impedance -  a measure of the total opposition to current flow in an alternating current circuit measured in ohms.  When applied to speakers, impedance is the load that a speaker places on the power amplifier.  A low impedance device draws a high current flow from a source such as a power amplifier; higher impedance sources draw less.  

This means that given the same voltage level, a 4 ohm speaker will draw twice as much current as an 8 ohm speaker.  This is because a speaker with half the impedance level provide only half the resistance to the voltage approaching them, and will let twice as much power through.  Amplifiers deliver more power into lower impedances -- up to twice their rated power -- making speakers with a low impedance (lower than 6-8 ohms) more difficult for amplifiers to drive.

Impedance Matching - Having or converting the output impetlance of a device so thar it matches the impedance of the input it will feed.

In - Short For "in the circuit," in other words "active."

Input - 1) The jack or physical location of where a device receives a signal. 2) The signal being received by a device. 3) The action of receiving a signal by a device.

Input Impedance - The opposition to current flow by the first circuits of a device.

Input Overload - Sending too high of a signal level into a device so that the first amplifler of the device overloads.

Insulator - A substance such as glass, air, plastic, etc., that will (for all practical purposes) not conduct electricity.

Interface - Any device that allows one unit to work, drive or communicate with another unit when they cannot do so by just feeding each other often because the units are manufacturcd by different companies.

Intermodulation Distortion - Distortion caused by one signal beating with another signal and producing frequencies that are both the sum and the difference of the original frequencies.

Inverse Square Law - Simply stated, the fact that in an un-obstructed area (like an open field) the sound pressure level will drop to half-pressure (-6 dB) every time the distance to the sound source is doubled.

I/O - Short for "Input/Output' and referring to: 1) An in-line console module that contains controls for the input section, output section and monitor section. 2) A module in electronic gear containing input and output amplifiers for the device. 3) A digital port (connector) able to both receive digital data and output digital data.  4) A card or separate unit that converts audio to digital audio for input into a digital system and also do the reverse for the output. 

Jack - A connector mounted on the case of a device or on a panel. 

LED - A light that allows current to flow in one direction only and emits light whenever a voltage of a certain level or beyond is applied to it. 

Level - The amount of signal strength; the amplitude, especially the average amplitude. 

LFO - Low-Frequency Oscillator (an oscillator that puts out an AC signal between .1 Hz and 10Hz used for a control signal). 

Limiter - A protection circuit, either built into an amplifier or packaged as a separate unit, that reduces signal amplitude above a fixed point so that output cannot exceed a certain level, thus preventing damage further down the signal path, whether to other audio equipment or to speakers.  www.oregondv.com Limiters work by monitoring outputs for excessive signal levels, and when they sense it, feeding back control signals to an earlier part of the circuit that lower the systems gain. This prevents signals from clipping; ie, it fundamentally prevents square waves from forming in the signal path.  

Line - 1) Short for line level. 2) A cable.  

Line Input - An input designed to take a line level signal. 

Line Level - An amplified signal level put out by an amplifier and used as the normal level that runs through the interconnecting cables in a control room. 

Linear - The condition of obtaining a change at the output of the device which is proportional to the change occurring at the input.

Load - 1) The opposition to the audio output signal of a device by the input of the device being fed. 2) A resistor that would have the lowest impedance the device was designed to feed into used during testing of a device.

Load Impedance - The opposition to output current flow caused by the input that it feeds.

Masking - The characteristic of hearing by which loud sounds prevent the ear from hearing softer sounds of similar frequency.

MDF (Medium Density Fiberboard) - A composite wood product used in many speaker cabinets because of its acoustically inert properties.

Modulation - The control of one signal by another AC signal.

Modulation Noise - Noise that is present only when the audio signal is present.

Module - A group of circuits and controls that are mounted on a removable housing; often on consoles, all of the controls and circuits for one or two channels.

Mono - Shortened from Monophonic and meaning that there is only one sound source or the signal was derived from one sound source.

Multi/Multi Jack - Short for Multiple Jacks or Multiple Jack and meaning: 1) a jack at the output of a device which is not normalled so that plugging into the jack will allow the output to be sent to a different input and the output will also feed the normal place it feeds. 2) A set of jacks (or one of a set of jacks) with each terminal wired to a corresponding terminal of another or other jacks

Mute Switch - A switch which turns off a channel, takes out a track signal from the monitors, or which turns off the entire monitor signal.