The unit of electrical resistance.

Directional microphones are inherently more sensitive to sound from one direction, and the direction of greatest sensitivity is referred to as the principle axis. Sound sources placed on this axis are said to be ‘on-axis’, while sound sources elsewhere are said to be ‘off-axis’

A process carried out while a recording is not playing. For example, some computer-based processes have to be carried out off-line as the computer isn't fast enough to carry out the process in real time. Also used to refer to a remote-controlled machine which is not currently active.

When a frequency or pitch is transposed up by one octave, its frequency is doubled.

A slotted plastic or bone (or metal) component at the headstock end of a guitar neck used to guide the strings over the fingerboard, and to space the strings above the frets.

The rule which states that a digital sampling system must have a sample rate at least twice as high as that of the highest audio frequency being sampled, in order to avoid aliasing and thus reproduce the wanted audio perfectly. Because anti-aliasing filters aren't perfect, the sampling frequency has usually to be made slightly more than twice that of the maximum input frequency - which is why the standard audio rate of 44.1kHz was chosen for a nominally 20kHz audio bandwidth.

A specific form of near-coincident microphone array devised by the Nederlandse Omroep Stichting (NOS), the Dutch national broadcaster. The technique employs a pair of small-diaphragm cardioid microphones mounted with a mutual angle of 90 degrees and spaced apart by 30cm. The theoretical stereo recording angle is 81°.

A socket is said to be normalised when it is wired such that the original signal path is maintained unless a plug is inserted into the socket. The most common examples of normalised connectors are the insert points on a mixing console.

A term which describes digital recording systems that allow any parts of the recording to be played back in any order with no gaps. Conventional tape is referred to as linear, because the material can only play back in the order in which it was recorded.

An addition to the basic MIDI spec that allows Controllers 98 and 99 to be used to control non-standard parameters relating to particular models of synthesizer. This is an alternative to using System Exclusive data to achieve the same ends, though NRPNs tend to be used mostly by Yamaha and Roland instruments.