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An electronic circuit capable of generating a control signal which represents the envelope of the sound you want to recreate. This may then be used to control the amplitude of an oscillator or other sound source, though envelopes may also be used to control filter or modulation settings. The most common example is the ADSR generator.

Yamaha's alternative to Roland's GS system for enhancing the General MIDI protocol so as to provide additional banks of patches and further editing facilities.

A specific way of mounting two directional microphone capsules such that they both receive sound waves from any direction at exactly the same time. Information about the direction of a sound source is captured in the form of level differences between the two capsule outputs. Commonly, the two microphones in an X-Y array are mounted with a mutual angle of 90 degrees, although other angles are sometimes used. The two capsules will have the same polar pattern, the choice of which determines the stereo recording angle (SRA). The X-Y configuration is entirely mono-compatible because there are no timing differences between the two channels.

Unit of electrical power named after its founder, James Watt.

Electrical isolation between two circuits. A transformer provides galvanic isolation because there is no direct electrical connection between the primary and secondary windings; the audio signal is passed via magnetic coupling. An opto-coupler also provides galvanic isolation, as the signal is passed via light modulation.

An electronic device (analogue or digital) designed to mute low level signals so as to improve noise performance during pauses in the wanted material. (See also 'Expander'.)

Describes an unwanted short term corruption of a signal, or the unexplained, short term malfunction of a piece of equipment.

A flexible tube often used to support microphones or small lights. Sometimes also known as a 'Swan Neck'.

A condition created when two or more devices are interconnected in such a way that a loop is created in the ground circuit. This can result in audible hums or buzzes in analogue equipment, or unreliability and audio glitches in digital equipment. Typically, a ground loop is created when two devices are connected together using one or more screened audio cables, and both units are also plugged into the mains supply with safety ground connections via the mains plug earth pins. The loop exists between one mains plug, to the first device, through the audio cable screen to the second device, back to the mains supply via the second mains plug, and round to the first device via the building’s power wiring. If the two mains socket ground terminals happen to be at slightly different voltages (which is not unusual), an small current will flow around the ground loop. Although not dangerous, this can result in audible hums or buzzes in poorly designed equipment.

Ground loops can often be prevented by ensuring that the connected audio equipment is powered from a single mains socket or distribution board, thus minimising the loop. In extreme cases it may be necessary to disconnect the screen connection at one end of some of the audio cables, or to use audio-isolating transformers in the signal paths. The mains plug earth connection must NEVER be disconnected to try to resolve a ground loop problem as this will render the equipment potentially LETHAL.