Some of the Common Technical Terms Used in Live Sound Reinforcement

A B C D E F G H I J K L M N O P Q R S T U V W X Y Z

AC

Alternating Current. Electricity is characterised by the movement of electrons through a conductor. In a DC circuit (see DC, below) the electrons always move in the same direction (from negative to positive). In AC circuits the electron movement alternates in direction. In some (e.g. mains) circuits, the direction of electron movement alternates regularly at a fixed frequency (50 Hz, in the case of UK mains). In other circuits (e.g. audio) the electron flow follows a complicated pattern, corresponding with the frequency and amplitude of the combined signal.

Active

Generally the word active is used to describe equipment that requires a power source (as opposed to passive equipment, which does not). Not all active equipment is mains powered (active DI boxes and effects or volume pedals are usually battery or phantom powered). In loudspeaker systems, crossovers are commonly described as active or passive, and historically these terms were also used to distinguish between (active) loudspeakers that required an external crossover with a separate amplifier for each driver and (passive) loudspeakers that could be run directly from a single amplifier channel. In recent years, however, loudspeakers that have an inbuilt amplifier have become very common, and these are also - quite reasonably - described as active. This can give rise to confusion, as many loudspeaker manufacturers and audio professionals still use these terms to refer to their earlier (crossover‑based) meanings. Also, some modern ‘passive’ loudspeakers (e.g. the Martin Audio S15 and S18, which we use), have an active/passive switch. Here, the active setting is for use with an external active crossover, while the passive setting routes the input signal through the speaker's internal passive crossover. According to the more recent idiom, however, whichever setting is used the loudspeaker is nevertheless passive in the sense that it does not contain an amplifier.

AFL

After Fade Listen. A switch routing the post‑fade signal (from a channel, group or auxiliary) to the mixer's meters and headphones. See the Mixers page for more details.

Amp

The word Amp is more commonly used than the word Ampere (Symbol A) for the SI unit of electric current. It is defined as a flow of one Coulomb (the SI unit of electric charge) per second. Amp is also used to mean Amplifier (there is a difference!). The question: ‘how many amps do you need?’ could mean ‘how many amplifiers do you need?’ or ‘how much current does your equipment draw?’. In practice, the context of the question will usually make the meaning obvious.

Amplifier

A device that produces gain - which can be positive or negative - in an electrical or electronic circuit. For information on PA amplifiers see the section on Amplifiers.

Auxiliary

The fader output from a mixer channel can be routed to the main left and right outputs (and, if the mixer has them, to groups). Extra channel outputs (individually controlled by knobs in the channel strip) are usually known as Auxiliary Outputs.

Backline

Instruments and instrument amplifiers/combos/speakers.

Balanced

A signal transmission protocol in which two copies of the signal are transmitted on separate conductors. The two signal copies are opposite in polarity but otherwise identical. The receiving device responds to the difference between the signals, so that any cable‑borne interference (which will be in the same polarity on both conductors) is cancelled. In balanced cables, the signal ground is not connected to system grounds: the "screen" connection (Pin 1 of a standard XLR connector) is just that - a screen - and does not form part of the signal path. Also see Unbalanced, below.

Bandwidth

Frequency range (in Octaves). See the Parametric EQ page for a little more detail.

Bass

A general term for the lowest audible frequencies. There is no universal definition, but Bass generally describes frequencies below about 200Hz. On most mixers, fixed‑frequency Bass EQ controls operate at 80 or 100Hz.

Beamwidth Plot

A graph plotting a loudspeaker's beamwidth (i.e. angle of horizontal dispersion) against frequency. Usually this will be the angle at which the loudspeaker's output has fallen by 6dB from its on‑axis output, but sometimes −10dB or −12dB angles may be given instead or as well; the level(s) will always be stated, as the graph would not otherwise impart any useful information. Also see Isobar Plots and Polar Plots.

Board

Another word for Mixer.

Cardioid

Literally, Heart‑Shaped. A cardioid microphone has a heart‑shaped sensitivity pattern, and is more sensitive to sounds arriving from the front than from the sides or rear of its capsule.

Compressor

A device that reduces the Dynamic Range of an audio signal. See the Compressors page for more details.

Condenser

A type of microphone. See the Microphones page for further details.

Console

Another word for Mixer.

Crest Factor

Peak to RMS ratio. In a signal with an RMS voltage of 2V and a peak voltage of 8V, the crest factor is 4.

Critical Distance

The point at which reflected sound is equal in level to direct sound. See the section on Speaker Position for more details.

Damping factor

The ratio between the load (loudspeaker) impedance and an amplifier's output impedance (damping factor = load impedance ÷ output impedance). The damping factor represents the ability of an amplifier to control loudspeaker cone movement (the higher the damping factor, the greater the control). See the Amplifiers page for more details.

dB

Abbreviation for Decibel. See the Decibel page for further information, and explanation of common suffixes (dBA, dBu, dBV, etc.).

DC

Direct Current. Electricity is characterised by the movement of electrons through a conductor. In a DC circuit the electrons always move in the same direction (from negative to positive). In AC circuits (see AC, above) the electron movement alternates in direction.

Decibel

See the Decibel page.

DI

Direct Input, or Direct Injection. See the DI Box page.

Desk

Another word for Mixer.

Distortion

A non‑linear difference between input and output signals in any audio device. Ideally, any audio device (e.g. pickup, DI box, mixer channel, amplifier or speaker) will change a signal in magnitude, but not in any other way. Any non‑linear change in the waveform (even if - as in the case of compression or EQ - the change is intentional) represents distortion. Proportional changes in magnitude between input and output are linear changes. Distortion describes any non‑linear changes. Some types of distortion are more objectionable than others: the ear can and does adjust to moderate shifts in frequency balance (tone), so that mild tonal colouration that is initially noticeable may become unnoticeable after a short time. Also, some tonal changes (particularly modest reduction in the upper midrange at high volume) may sound ‘better’ than the undistorted signal. The sort of distortion that is produced when circuits are saturated (resulting in squaring of the signal peaks, also known as clipping) is generally noticeable when the total distortion exceeds about 1%, and can become objectionable - and remain objectionable over time - at higher levels. Here too, however, mild distortion - e.g. saturation of analogue recording devices or ‘overdriven’ guitars - can sometimes sound ‘better’ than the undistorted signal.

Dry Hire

Hiring equipment without crew.

Dynamic

A type of microphone. See the Microphones page for further details. The word Dynamic (or sometimes Dynamics) is often also used to describe processing sections, particularly in the digital domain. Compressors and Expanders are dynamic processors, in that they affect the dynamic range - see below - of a signal to which they are applied.

Dynamic Range