Click for the PAforMusic home page
www.paformusic.info
Glossary of PA Terms - 0-9

Back to PAforMusic Home

0-9 A B C D E F G H  I  J K L M N O P Q R S T U V W X Y Z

  • If you have arrived here by clicking on a linked term on another page of this site, it may take a moment before your browser jumps to the definition of the term that you clicked on; thank you for your patience. (If there's still no movement after a few seconds, you may have encountered a broken link; please report it.)
  • If you have arrived here from a search engine, or by clicking on an alphabet letter on another page of the Glossary, then click on your required term in the list below.

The glossary pages provide alphabetically-listed definitions for over 1900 PA-related terms. If you're not sure what term you are looking for, then the structured list of topics on the Training page may be a useful place to start, as there are links from there to many of the Glossary entries.

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.

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. For some notable differences between USA and UK terminology, see American terminology.

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 (and then use your browser's 'Back' button to return to where you were).

Use of this information is conditional upon acceptance of the Disclaimer on the PAforMusic home page.

0 dB * 19 inch rack system * 100 volt line * 1080i * 1080p * 2-pi space * 2-TK, 2-TRK * 2-track * 2-way * 3 dB point * 3-phase * 3-to-1 rule * 3-way * 4 mm connector * 4-pi space * 5.1 * 57 * 58 * 5th * 5th-order * 7.1 * 70 volt line * 720p * 75 ohm interconnection

0 dB (1)
Applied to the level of a signal, it refers to the agreed reference level of that signal; the signal's 'zero level'. When 'dB' is followed by other characters, those characters usually indicate the applicable reference level. Common examples of such reference levels are:

For more detailed information on the above, see the Decibels page. See also Metering.

0 dB (2)
Applied to the setting of a level control, it refers to the reference setting of that control. On some level controls of some equipment, this is the setting at which the relevant section of the equipment provides unity gain. For further information see the Decibels page.

0 dB (3)
Applied to the setting of an EQ control (including a band of a graphic equaliser), it refers to the setting that has no effect on the signal being equalised (usually the mid-position of the control). See also Flat. For further information on decibels see the Decibels page.

0 dB (4)
Indicated on a level meter, it indicates a signal level that is equal to the relevant reference level. For meters that indicate the level at line-level outputs, a list of the most common reference levels used is given below. Consult the equipment handbook to check which 0 dB output reference level is applicable to your equipment.

  • +4 dBu − Most professional equipment
  • 0 dBu − Some professional equipment (e.g. some Mackie mixers)
  • −10 dBV − Most amateur and some semi-pro equipment
  • 0 dB FSDigital equipment
For more detailed information on the above, see the Decibels page. See also Metering, PPM and VU.

19 inch rack system
A metal (usually steel) mounting system for equipment. Each item of equipment is secured to the rack by bolts through flanges (or 'ears') at the left and right edges of its front panel. The bolts screw into removable caged nuts that are attached to vertical strips, one at each side of the rack. Plastic washers under the bolt-heads are usually used to protect the flanges from damage. The nuts may be installed, as required, at fixed intervals in order to accommodate equipment of differing front panel heights. All front panel heights are a multiple of one vertical unit, or U. The total width of the equipment front panels (including the flanges) is 19 inches (482 mm), hence the name.

100 volt line
An arrangement for the connection of (passive) speakers to an amplifier, which accommodates a much greater distance between the speakers and the amplifier than would normally be possible without a significant reduction in power due to loss in the interconnecting cable. It works by using a much larger voltage than normal, so that the current flow (and therefore the power loss in the cables) is much reduced − i.e. it operates at a much higher impedance than normal. In the UK the nominal voltage used is 100 volts RMS. In the USA the value is 70.7 volts RMS, and the system there is known as a '70 volt line' or as a 'constant voltage' system.

Special speakers must be used with these systems. These speakers (which usually have a low power rating) are equipped with a transformer which steps the voltage down to a value suitable for the driver(s). The transformer often has several taps, which are usually marked with power ratings such as 5 W, 10 W, 15 W and 20 W. The effect of selecting a higher power tap is that a lower impedance is presented to the line by the speaker, and so a larger current is drawn from it. The speakers are always connected in parallel to the line, which is often looped from speaker to speaker. The total connected load (usually specified in watts) must not exceed the drive capability of the amplifier, or damage to the amplifier may result.

This arrangement is generally used only in public address installations (whether fixed within buildings or for outdoor sports events and the like), where a large number of low-power speakers, located over a wide area, are to be connected to a common amplifier. Historically, these speakers were often designed for cost-effective reproduction of voice frequencies only (rather than music), with maximum efficiency being given higher priority than sound quality. Therefore, in the past 100 V line systems have gained a reputation for poor audio quality. However, systems providing much improved audio quality are now available.

The term 'constant voltage' derives not from the output voltage of a particular amplifier of this type being constant in use, but from the fact that, in contrast to 'normal' (i.e. low impedance) amplifiers, two amplifiers of this type that differ in their power output capability do not differ in their maximum voltage output − their difference in power output is accounted for solely by a difference in the amount of current that they are able to supply. This means that, when additional speakers need to be added to a system, the amplifier can be upgraded to a higher-powered model without affecting the power level supplied to the existing speakers. See also Installation speaker.

1080i
See HDTV.

1080p
See HDTV.

2-pi space
See Half space.

2-TK, 2-TRK
An abbreviation for 2-track.

2-track
An alternative term for stereo. A name often given to a stereo input on a mixer, intended for a playback connection from a stereo audio player (e.g. a CD player); often labelled '2-TK' or '2-TRK'. Such inputs are often equipped with a reduced set of facilities (especially as regards equalisation and routing) as compared to a channel strip.

2-way
Describes a speaker equipped with two different types of driver, each handling a different frequency range. Typically, the two types of drivers will be woofers to handle the low (bass) frequencies and horns to handle the high (treble) frequencies. Such speakers usually include a passive crossover to direct the bass and treble frequencies to the appropriate drivers, but may also be equipped with separate inputs to allow bi-amping.

Similarly, a speaker that incorporates three different types of driver, handling three different frequency ranges (low, mid-range and high) is described as a 3-way speaker.

3 dB point
See Cut-off frequency.

3-phase
See Phase (3).

3-to-1 rule
The rule-of-thumb that recommends that when two or more microphones are used to pick up different sound sources, the distance between the microphones should be at least three times the distance between each microphone and its respective sound source. Or, to put it another way, the microphones' distances from their respective sound sources should be no more than one third the distance they are from each other.

This is to ensure that each sound source is picked up predominantly by just one microphone, and so minimise the extent of undesirable comb filtering effects which can occur when a sound source is picked up equally (or approximately so) by two or more microphones whose outputs are subsequently mixed. See also Microphone technique.

3-way
See 2-way.

4 mm connector
A single-pole connector sometimes used (in pairs) for speaker connections, so-named because the nominal diameter of the male prong is 4 mm. Usually the female connector can be unscrewed by hand for alternative use as a binding post. The male connector is commonly referred to as a banana plug. See also Speakon.

4-pi space
See Full space.

5.1
The multichannel digital audio scheme developed by MPEG to provide a surround sound capability for films in many formats, including DVDs, tape and celluloid. Also used in some high definition television (HDTV) broadcasts. It incorporates five full-range (20 Hz to 20 kHz) channels, for the left front, right front, centre front, left rear and right rear speakers, and one sub-bass (20-120 Hz) channel, hence the designation '5.1'. A 4-pole 3.5 mm jack connector is sometimes used for 5.1 digital connections. See also 7.1 and AC-3.

57
A slang term for a Shure SM57 microphone.

58
A slang term for a Shure SM58 microphone.

5th
See Fifth.

5th-order
See Order.

7.1
A multichannel digital audio scheme similar to the 5.1 scheme but with the addition of 'Left Side' and 'Right Side' channels.

70 volt line
See 100 volt line.

720p
See HDTV.

75 ohm interconnection
See Impedance-matched.

Go to top.

0-9 A B C D E F G H  I  J K L M N O P Q R S T U V W X Y Z

There are no more definitions on this page. (The space below is to facilitate linking to the last few terms above.)































Go to top.

0-9 A B C D E F G H  I  J K L M N O P Q R S T U V W X Y Z

Visited count: since 16-Aug-2000

This page last updated 10-Nov-2009.