Audio Video Glossary

Please note that the sole purpose of this glossary is to clarify some of the terms commonly associated with audio/video subject matter. Many of the definitions listed below have been simplified or altered to more effectively convey their meanings in an audio/video context.

Amplifier (or Slave Amplifier)
An audio component designed to power a pair (or multiple pairs) of speakers. Amplifiers require a line-level audio signal generally output from a preamplifier or source component, and may also be fed from the "tape-out" of a stereo receiver.

Audio / Video Patching System
A unit designed to allow the output of a selected A/V source to be routed to the input of another A/V component (or components) for recording, playback or dubbing purposes.

Autoformer Volume Control
A device used to control the volume output from an amplifier (or speaker selector) to a pair of speakers. Autoformers offer sound quality superior to that of L-pads or purely resistive volume control designs, while minimizing power loss and heat dissipation.

Automated Switching System
A device used to automatically switch line level, speaker level, or composite video signals. Usually triggered by a control voltage or signal sensing circuit.

Clipping
The undesirable effect on a music signal which is caused by exceeding the amplifier's (or preamplifier's) signal handling capabilities.

Continuous IR Command
An IR command which is issued as long as the button is pressed and held. As an example; a "Volume Up" command is a continuous IR command and a "Play" command is a normal IR command (it only needs to be tapped). See "Normal IR Command".

Convenience Outlets
Wall plates used in custom installations to elegantly terminate wires run through walls. Available with RCA, 5-way binding post, banana jack, or F-connector terminals.

Crossover
An electronic circuit consisting of either a low-pass filter, a high-pass filter, or both. Its main purpose is to determine a crossover point at which frequencies will be filtered and passed to other components (subwoofers, woofers, or tweeters for example).

Decibel (dB)
A logarithmic unit of measure commonly used to gauge relative volume in terms of dB SPL (decibels of Sound Pressure Level). The bel is unit of measure representing the logarithmic equivalent of two powers, and a decibel equals one-tenth of a bel.

Diode
An electronic device that permits electrical current to flow in only one direction.
The white stripe marks the cathode, or negative ( - ) terminal on the diode.

Distribution Amplifier
A device used to distribute the output of a single audio or video component. Used to feed the inputs of several other components without effecting the strength or quality of the original source signal.

Frequency Response
A technical specification describing the range and variation in amplitude of frequencies a speaker or other device is capable of accurately reproducing. The "+/- 3dB" notation represents the industry accepted margin of no more than 3dB variance above or below the theoretical ideal zero dB point. A change of 3 dB represents the smallest change in volume an average listener can perceive in a quiet room. Frequency response is measured in Hertz (Hz) - or cycles per second. High-pass Filter - A type of filter designed to pass the frequencies above (and reject those frequencies below) the filter's cutoff frequency (or crossover point).

Impedance (or impedance load)
A term used to describe the total opposition to the flow of electrical current (music signals) in an AC circuit. Expressed in Ohms. For more information concerning the relevance of the amplifier / impedance load relationship.

Infrared Light (or IR)
A portion of the light spectrum invisible to the naked eye and the most popular method of transmitting codes via line-of-sight from a hand-held remote control.

IR Repeater System
An infrared repeater system allows the user to receive, transmit, and output infrared commands to A/V components located in another room or behind closed doors. A basic system consists of four main components: IR Sensors, IR Cable, IR Main System Units, and IR Flashers.

IR Sensors
These devices receive the infrared codes from your hand-held remotes and convert them to data pulses.

Interference
In terms of IR or RF (radio frequency) data transmission, interference represents any occurance or set of circumstances which may cause the system to operate intermittently or not at all. Interference that can effect IR repeater systems is generally either optical or electro-magnetic in nature.

Optical Interference is categorized as interference caused by light, both visible and invisible. Sunlight contains vast amounts of infrared light, far more than the output of a hand-held remote control. Sensors are not able distinguish IR codes from rays of ambient sunlight, and may cause the sensor's flashback LED to flicker or stay constantly lit. Sources of optical interference may include bright reflections from windows, mirrors, swimming pools, shiny floors, or other objects which reflect light.

Electro-Magnetic Interference (EMI) is generally caused by electro-magnetic fields or electrical noise corrupting the reception or transmission of data. EMI is commonly caused by televisions, light dimmers, variable speed control potentiometers, electronic ballasts found in fluorescent lighting, neon or halogen lighting, large appliances driven by motors, or AC line noise brought into the system by the power supply powering the IR MSU.

Line-level Audio Signal
Refers to an unamplified audio signal. Line-level audio signals are generally output from a source component (CD player, tape deck, TV, etc.) and are usually connected to an amplifier using RCA patch cables (interconnects).Low-pass Filter - A type of filter designed to pass the frequencies below (and reject those frequencies above) the filter's cutoff frequency (or crossover point).

Multi-room Sound System
A system able to play a single source in multiple rooms simultaneously.

Multi-zone / Multi-source System
A system able to play different sources in multiple rooms simultaneously.

Normal IR Command
An IR command which is issued as one short burst when a button on the remote control is tapped. For example; a "Play" command is a normal IR command (it only needs to be tapped) while a "Volume Up" command is a continuous IR command (it must be pressed and held). See "Continuous IR Command".

Ohm
A unit of measure used to gauge both impedance (Z), and resistance (R).

Parallel Circuit
A parallel circuit consists of two or more current paths sharing a common output from an amplifier. This is the preferred method to be used when connecting multiple speaker pairs or volume controls. Note: Most amplifiers require impedance protection when making more than one parallel connection. If the impedance load being presented to the amplifier is lower than the manufacturer's recommended specification, the amplifier may not operate correctly and damage may occur. When connecting speakers or volume controls in parallel, the amplifier's outputs will be connected to their respective terminals on each speaker. For example, the amplifier's left channel positive output will be connected to the left channel positive connections on each pair of speakers (or volume control). Follow this same procedure for the remaining channels (left channel negative, right channel positive, and right channel negative).

Pre-out (abbreviation for "preamplifier output")
A set of connections on a preamp or receiver's rear panel which output a variable (relative to the setting of the volume knob) line-level audio signal. This signal is usually connected to an additional "slave amplifier" to power additional speakers or speaker pairs.

Receiver (or Stereo Receiver)
An audio component featuring a built-in preamp, tuner, and amplification circuitry.

RF (or Radio Frequency)
A wireless method of transmitting information on any frequency within the electro-magnetic spectrum.

Sensitivity (or Efficiency)
When referring to loudspeaker specifications, sensitivity generally specifies how loud a speaker will play with a single watt of power when measured from a distance of one meter.

Sensor - See "IR Sensor"

Series Circuit
A series circuit is wired so that there is only one path for current to flow from the positive to the negative terminal. In a series circuit, each component is connected to the output of the first (+ -, + -, + -, etc.). This is the preferred method of connecting multiple IR flashers to a single flasher output terminal on a IR MSU.

Slave Amplifier - See "Amplifier"

Speaker Selector
A device capable of distributing the output of a single amplifier to those speaker pairs selected. Speaker selectors usually feature a "protection circuit" which protects the amplifier from driving the unusually low impedance load which results from the parallel connection of multiple speaker pairs.

Tape-out (or Record-out)
A set of connections on a receiver or preamp's rear panel used to feed the currently selected source to a cassette deck's record input for taping purposes.

Volume Control - See "Autoformer Volume Control"

Watts per Channel
This specification refers to an amplifier's maximum power output capability. For example, if amplifier's power is rated at 100 watts per channel into 8 ohms, it will only output 100 watts when turned all the way up.