The provision on a mixing console or ‘channel strip’ processor of a facility to break into the signal path through the unit to insert an external processor. Budget devices generally use a single connection (usually a TRS socket) with unbalanced send and return signals on separate contacts, requiring a splitter or Y-cable to provide separate send (input to the external device) and return (output from external device) connections . High end units tend to provide separate balanced send and return connections. (cf. Effects Loop)

Resetting a device to its 'start-up' state. Sometimes used to mean restoring a piece of equipment to its factory default settings.

A reactive component that presents an increasing impedance with frequency. (Also see Capacitor.)

An impulse respsonse (IR) is the time-domain equivalent of the much more familiar frequency (and phase) responses in the frequency-domain. A very brief click (technically, a Dirac delta function) which theoretically contains all frequencies at equal amplitude, is passed through the device under test. The resulting output is the 'impulse response' of that device and uniquely describes its signal processing behaviour. Impulse responses are very convenient for digital signal processing applications as the source impulse is very similar to a single digital sample value.

The ‘resistance’ or opposition of a medium to a change of state, often encountered in the context of electrical connections (and the way signals of different frequencies are treated), or acoustic treatment (denoting the resistance it presents to air flow). Although measured in Ohms, the impedance of a ‘reactive’ device such as a loudspeaker drive unit will usually vary with signal frequency and will be higher than the resistance when measured with a static DC voltage.

Signal sources have an output impedance and destinations have an input impedance. In analogue audio systems the usually arrangement is to source from a very low impedance and feed a destination of a much higher (typically 10 times) impedance. This is called a ‘voltage matching’ interface. In digital and video systems it is more normal to find ‘matched impedance’ interfacing where the source, destination and cable all have the same impedance (eg. 75 Ohms in the case of S/PDIF).

Microphones have a very low impedance (150 Ohms or so) while microphone preamps provide an input impedance of 1,500 Ohms or more. Line inputs typically have an impedance of 10,000 Ohms and DI boxes may provide an input impedance of as much as 1,000,000 Ohms to suit the relatively high output impedance of typical guitar pickups.

A wirelessly-connected foldback monitoring system, often used by musicians on stage with in-ear earpieces.

An abbreviation of Integrated Circuit, a collection of miniaturised transistors and other components on a single silicon wafer, designed to perform a specific function.

The SI symbol for Hertz, the unit of frequency.

A condition whereby the state of a system is dependent on previous events or, in other words, the system's output can lag behind the input. Most commonly found in audio in the behaviour of ferro-magnetic materials such as in transformers and analogue tape heads, or in electronic circuits such a 'switch de-bouncing'. Another example is the way a drop-down box on a computer menu remains visible for a short while after the mouse is moved.

Audio Signal contamination caused by the addition of low frequencies, usually related to the mains power frequency.