Glossary of PA Terms - X
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The glossary pages provide definitions for over 2680 PA-related terms. If you can't find the term you are looking for, or would like any of the existing definitions to be expanded, please email me − likewise of course if you find any errors in the links etc. Use of this information is conditional upon acceptance of the Disclaimer on the PAforMusic home page.
In the list below, the most commonly looked-up terms are in bold, lighting-specific terms are in pink, and video-specific terms are in orange.
The definitions for these terms are given on the assumption of their use in the context of PA systems; many of the terms have more general meanings when used in a wider context. Where more than one definition is given for a term, the definitions are numbered (1), (2) etc.
Some of the definitions themselves use terms (such as "signal") in a specific way − most of these are links (just the first time they are used, in each definition), so just click on them to see the meanings that are intended.
An abbreviation for 'extended curve'. The response required of equipment to correctly process the analogue optical sound track specified for film audio by ISO Bulletin 2969, now largely replaced by improved techniques. Various forms are specified, to allow for the different acoustics of large cinemas and smaller rooms. Also called the 'wide-range curve'. See also Academy curve.
Abbreviations for 'crossover'.
An abbreviation for 'extended graphics adaptor'. A standard interface for the connection of display equipment (such as monitors and projectors) to computers. The standard gives a resolution of 1024 pixels horizontally and 768 pixels vertically. The aspect ratio is 4:3. See also VGA, SVGA, SXGA, WXGA, UXGA and DVI. The most commonly encountered standards, their resolutions and aspect ratios are tabled under the entry for VGA.
A type of connector commonly used for professional and semi-professional audio interconnections − both analogue and digital (see AES3). In PA work the 3-pole ('3-pin') type is used extensively. In these applications the pole marked "1" is generally used for the signal earth connection. The connector's design ensures that, when being mated, pin 1 is the first to make contact. The metallic outer shell of the connector may in theory be used as an additional earth conductor, but in cable-mounted connectors it is usually left unconnected (rather than being linked to pin 1) in order to avoid earth loops occurring by incidental contact with other connector shells or adjacent metalwork. In chassis-mounted connectors the shell is usually connected to signal earth.
The most common uses of the 3-pole XLR for audio are in balanced interconnections from stage sources (mostly microphones and DI boxes) to mixers − see the diagram − and in balanced feeds from mixers to graphic equalisers, active crossovers and power amplifiers. However, an interconnection should not be assumed to be balanced solely because it uses an XLR connector. Pin 2 is generally used for the hot leg of the balanced pair, and pin 3 for the cold leg (though some early American equipment had this reversed). Caution: Note that balanced analogue interconnections may carry phantom power, which may damage equipment not intended to handle it.
In all such audio interconnections, the standard arrangement is that cables are fitted with a male connector at one end and a female connector at the other; this enables cables to be readily extended by coupling two or more of them end-to-end. The signal direction is from the female end of the cable to the male end (so, the pins 'point' in the direction of signal flow).
The 4-pole XLR is mostly used for carrying DC power. A common pin allocation is for pin 1 to be 0 V (because this makes contact first), pin 2 to be +12 V, pin 3 to be +24 V and pin 4 to be +48 V, but this should not be assumed. On many cameras, pin 1 is 0 V and pin 4 +12 V, but again this should not be assumed. It is strongly advised to always use only the manufacturer's recommended power supply unit.
The 5-pole version is occasionally used for stereo interconnections, and is also used for the control cables in DMX stage lighting applications. However, note that in the DMX application the signal direction is from the male end of the cable to the female end − this is the reverse of the gender standard used in audio applications.
In some DMX applications 3-pole XLRs (just the same as audio ones) are used instead of 5-pole types; this is possible because nearly all DMX applications require only 3 wires. In these cases, the same gender standard applies as for 5-pole DMX interconnections (i.e. the reverse of the audio standard).
The name 'XLR' is believed by many to be an abbreviation for 'extra low resistance', though it is more likely to be just an identifying type code made up by the original manufacturers. Nevertheless, it may be used as a mnemonic for the usual pin-allocation when making balanced connections to the terminals of the 3-pole type: pin 1 = X = Earth, pin 2 = L = Live (hot), pin 3 = R = Return (cold). Also known as a 'Cannon' (frequently mis-spelled 'Canon'), as one of the most popular makes is ITT-Cannon. See also Neutrik, TA4 and Pin 1 problem.
An XLR connector that has female contacts. An XLR socket, either cable-mounted such as commonly attaches to a microphone, or else panel-mounted such as is commonly used as a microphone input connector on mixers.
An XLR connector that has male contacts. An XLR plug, either cable-mounted such as commonly attaches to the microphone input connectors of mixers, or else panel-mounted such as is commonly used for the balanced line output connectors of mixers.
An abbreviation for 'crossover'.
A pair of cardioid microphones at the same location, whose axes of optimal pick-up are positioned at an angle (typically between 90º and 135º). This arrangement is used for stereo recording or for live broadcast purposes (one microphone for the left side, and one for the right), not for PA applications. Also called the 'coincident microphone' technique, because sounds arrive at the two microphones at essentially the same time. See also A-B pair, Mid-side pair, ORTF, NOS (1) and Microphone technique.
a pictorial comparison of stereo microphone techniques.
(To view the image full-size in Explorer, hover your mouse over the image and click on the green 'expand' icon that appears in the bottom right-hand corner. Or, click when a magnifying glass containing a '+' appears.)
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This page last updated 21-Jan-2019.