Buffer — An electronic circuit designed to isolate the output of a source device from loading effects due to the input impedance of destination devices.

A system used to verify that a MIDI connection is working. It involves the sending device sending frequent short messages to the receiving device to reassure it that all is well. If these active sensing messages stop for any reason, then the receiving device will recognise a fault condition and switch off all notes. Not all MIDI devices support active sensing.

When creating artificial waveforms in a synthesizer, changes in the signal amplitude (or frequency) over time are controlled by an ‘envelope generator’ which typically has controls to adjust the Attack, Decay, Sustain and Release times, triggered by the pressing and subsequent release of a key on the keyboard.

A system for generating audio waveforms or sounds by combining basic waveforms or sampled sounds at different pitches, prior to further processing with filters and envelope shapers. The Hammond tonewheel organ was one of the first additive synthesizers, allowing harmonically complex waveforms to be created by combining tones of different pitches using 'harmonic drawbars'.

A widely used eight-channel optical digital audio interface developed by Alesis as a bespoke interface for the company's digital eight-track tape machines in the early 1990s (Alesis Digital Audio Tape). The interface transfers up to eight channels of 24-bit digital audio at base sample rates (44.1 or 48 kHz) via a single fibre-optic cable. This 'lightpipe' and its conenctors are physically identical to that used for the TOSlink optical S/PDIF stereo interface found on many digital consumer hi-fi devices. However, while the light-fibre itself can be used interchangeably for either format, the S/PDIF and ADAT interfaces are not compatible in any other way.

A device which converts an analogue audio signal into a digital representation. (Cf. D-A Converter.) (An explanatory video is available when subject link is clicked.)

A loudspeaker system in which the input signal is passed to a line-level crossover, the suitably filtered outputs of which feed two (or more) power amplifiers, each connected directly to its own drive unit. The line-level crossover and amplifiers are usually (but not always) built in to the loudspeaker cabinet.

The term typically describes an electronic circuit containing transistors, integrated circuits (ICs), tubes or other devices that require power to operate, and which are capable of amplification. Also used to describe loudspeaker monitoring systems which employ separate amplifiers to power each drive unit individually. 

A general term embracing a range of products or constructions intended to absorb, diffuse or reflect sound waves in a controlled manner, with the intention of bestowing a room with acceptable reverberation times at all frequencies, and a neutral overall sound character.

An open-celled expanded polyurethane or melamine foam that allows sound waves to enter and flow through the foam to dissipate their energy and thus prevent the sound waves from being reflected. The density and depth of the foam affects the frequency range over which it is effective as an acoustic absorber.