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Glossary of PA Terms - M

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The glossary pages provide definitions for over 1900 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.

M-S pair * mA * MADI * Main * Main mix * Mains * Maintained * Male * Margin * Masking * Master * Matching * Matching transformer * Mate * Matrix * Mbit/s * MC * MCB * MD * MDLP * MDM * Media * Megger * Megohm * Melissa * Melody * Membrane * Metal compensation * Meter bridge * Metering * mH * MHz * Mic * Micro... * Microphone * Microphone-level * Microphone placement * Microphone splitter * Microphone technique * Microphonic * Microphony * Mid * Mid-range * Mid-side pair * Middle C * MIDI * MIDI machine control * MIDI show control * MIDI time control * Mike * Mike-up * Milli... * Mini disc * Mini-DIN * Mini-jack * Minimum phase * Mismatch * Mix * Mix bus * Mix buss * Mixer, Mixing console, Mixing desk * Mixer-amplifier * Mixer automation * Mixing solo * MLSSA * MMC * MN-taper * Modem * Modulation * Monitor * Monitor beach * Monitor engineer * Monitor mix * Monitor mixer * Monitor split * Mono * Monophonic * MOSFET * Motorised fader * MOV * Moving fader * Moving head * MP3 * MP4 * MPEG * ms * MS pair * MTC * Muddy * Multi-amping * Multicore * Multimeter * Multiplex * MUSA * Musac * Music power * Muso * Mute * Mute group * Mutual inductance * Mux * mV * mW

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.

M-S pair
An abbreviation for 'mid-side pair'.

mA
An abbreviation for 'milliamp', a unit of current. One mA is one thousandth (10⁻³) of an ampere.

MADI
See AES10.

Main
Describes the front-of-house speakers, or the signal which feeds them. When used in the plural ("mains") be very careful not to confuse this term with the mains electrical supply.

Main mix
The mix that is intended for the front-of-house speakers. Often created by a mix of audio group mixes, usually with the addition of some effects. The main mix may be mono, stereo or Left-Right-Centre (see LCR (1)). The term is used to distinguish this mix from other mixes such as audio groups, auxiliary mixes and matrix mixes.

Mains
The supply of AC electrical power that is available from general and specialist power-outlets within a building, having been delivered to the premises from national generation and distribution facilities (usually via underground or overhead cables), or from one or more generator sets.

The mains supply is nominally at 230 volts (RMS) in the UK and Europe, at a nominal frequency of 50 Hz. (Historical note: The nominal voltage was previously 240 volts in the UK and 220 in mainland Europe, but both figures were changed to 230 in 2001. However, the UK value of 230 has a large positive tolerance and so in practice the actual delivered voltage may easily be as high as 250 volts.)

In the USA the mains supply is variously quoted as 110, 115 or 120 volts (RMS), at 60 Hz. In most parts of the USA the 'delivery voltage' to the premises is quoted at 120 volts. However, it is accepted that some loss of voltage will occur in the wiring of the premises, so most US mains equipment is nominally rated at 115 or 110 volts, the so-called 'utilisation voltage'. (Although there will similarly be some loss of voltage in UK and European wiring, this fact is ignored in their specifications of supply voltage and equipment voltage ratings.)

Caution: Do not confuse the term 'mains', as defined above, with the plural of 'main'! See also BS 1363A connector, IEC, Powercon, CEE-form, Socapex, Schuko connector, Camlock, Powerlock, Snaplock, TCMCC, QTBMC, Safety earth, PAT, Phase (3), Phase conductor, Transformer, Hum, Earth loop, Earth rod, Bonding, Generator set, Balanced mains, Inverter, Class I, Class II, Direct contact, Indirect contact, Basic protection, Fault protection, MCB, RCD, RCBO, TN-S, TN-C-S and TT.

Maintained
Describes emergency lights, illuminated fire exit signs, etc., that are permanently illuminated. Whilst the mains supply is operating normally, they are illuminated using power from that supply, and also charge their internal batteries. If the mains supply fails, their illumination continues by using power taken from those batteries (generally for at least 3 hours). The correct operation of these units must be regularly checked, and records kept of the tests. Compare Non-maintained.

Male
Describes a connector that makes all or most of its connections by means of pins. Such a connector is loosely known as a 'plug', especially when it is of the type that is fixed to a cable. See also Gender and Mate. Compare Female.

Margin
A less 'technical' name for headroom.

Masking
The phenomenon whereby certain sounds are not heard because of the simultaneous (or near-simultaneous) presence of other sounds of a similar frequency but at a higher level. This phenomenon is utilised in certain digital audio compression algorithms such as ATRAC and MP3. See also Upward masking and Psychoacoustics.

Master
A fader that adjusts the level of an overall mix (main or auxiliary).

Matching
The process of ensuring, or arranging for, the compatibility of two items of equipment that need to be interconnected, particularly in regard to the level of the signal flowing between them and/or to the impedance of the signal source and load.

Note that, in the case of impedance, compatibility does not imply equality (except in the special case of an impedance-matched interconnection). Indeed most analogue audio interconnections are arranged to have the load impedance significantly higher than the source impedance − this is sometimes referred to as a voltage-matched interconnection (because connection of the load has little effect on the source voltage).

Where a source and load are not compatible they are said to be 'mismatched', and steps must be taken to resolve this if they are to be interconnected. The matching of signal levels generally requires the use of an attenuator or amplifier, while the matching of impedances is usually performed by means of a transformer. See also Microphone-level, Line-level, Low impedance and High impedance.

Matching transformer
A transformer whose purpose is to provide matching between two otherwise incompatible items of equipment or interconnections, usually by providing an impedance conversion. For example, to enable a high impedance microphone to be connected to a low impedance input, or vice-versa. See also Balun.

Mate
To connect together two compatible connectors. The term arises from the description of the connectors as 'male' and 'female'. See also Gender and Gender changer.

Matrix
A facility of a mixer that enables each of several outputs to consist of a different mix of the various channel-mixes created within the mixer, e.g. the audio groups, Left and Right main mixes and auxiliary mixes.

Mbit/s
A unit of bit-rate, equal to 1024 kbit/s (1,048,576 bits per second). Sometimes written as 'Mbps'.

MC
An abbreviation for 'Master of Ceremonies', the person who speaks to introduce the items of a performance.

MCB
An abbreviation for 'miniature circuit breaker', a device which may be used in place of a fuse to interrupt mains power if the current flowing becomes excessive. Its main advantages over a fuse are the ability to reset the device simply by the operation of a switch or button, and very rapid operation under short circuit conditions. Typical ratings used in electrical supplies in the UK are 6, 10, 16, 20, 32, 40, 50 and 63 A. (As with fuses, these ratings are the values of current that can be carried continuously by the device without operating (tripping) it; the current required to operate it will be substantially higher than this figure. Note that is in contrast to the nominal current rating of RCDs.)

Note that MCBs are designed primarily as protection devices, and are not intended to be used for functional switching (that is, for the regular manual switching on and off of equipment); suitable switches should be provided for this purpose.

As with a fuse, it should be remembered that operation of the device may indicate a serious fault, and therefore the reason for operation should always be investigated. Sometimes informally called a 'trip switch'. See also RCBO.

MD
An abbreviation for 'mini disc' or for 'musical director'.

MDLP
An abbreviation for 'mini disc long play'. There are three common variants: LP2 is a stereo format that provides twice the normal (stereo) playing time, LP4 is a stereo format that provides four times the normal (stereo) playing time, and monaural is a single-channel (mono) format that provides twice the normal (stereo) playing time.

MDM
An abbreviation for 'modular digital multi-track'. This describes any digital multi-track tape machine that can be interconnected with similar machines in order to effectively create a larger machine. An example is the Alesis ADAT.

Media
The physical material on which information is stored, as opposed to the information itself. For example, media suitable for the storage of digital audio would include CD, DAT, DVD and mini disc. The term is often used to refer to the material in its 'blank' state, i.e. without any information recorded on it.

Megger
A manufacturer of test equipment (a registered trademark), notably insulation testers and multimeters. Commonly used as a slang term for any such tester or meter, regardless of its manufacturer. See also AVO.

Megohm
A million ohms.

Melissa
See MLSSA.

Melody
The basic tune of a song. Compare Harmony.

Membrane
See Diaphragm.

Metal compensation
A facility of an induction loop amplifier, enabling it to provide an adjustable boost to the treble frequencies. Such a boost is useful in order to counteract the increased attenuation of the loop current caused to those frequencies by the presence of ferrous materials (such as structural steelwork or reinforcing meshes embedded in concrete floors and ceilings) within or close to the area covered by the loop.

Meter bridge
A part of a mixer or a multi-track recording machine that incorporates only metering facilities. It may be an integral part of the equipment, or may be removable to allow the equipment to be configured with different styles or quantities of metering. The name arises from the fact that it is often located at the highest point of the equipment, and spans all or most of its width.

Metering
Facilities (usually of a mixer) which indicate the level of a signal. The ability is needed to indicate the level through individual channels (to facilitate the adjustment of the gain controls) and to indicate the level of the mixes (to indicate the mixer output levels). Metering facilities may be analogue, in which a needle physically moves across a scale, or digital, consisting of a column (or row) of illuminated segments, usually having green, yellow and red regions. In either case, the meters usually have markings in decibels. Meters are sometimes located on a meter bridge. The response-times of a meter to rising and falling levels make a large difference to the readings displayed for real programme material (as compared to a steady tone) − for further information see PPM and VU. See also the previous definition and 0 dB (4).

MHz
A unit of frequency. One MHz is 1000000 Hz, or 1000 kHz.

Mic
An abbreviation for 'microphone'. Pronounced 'mike'. See also Mike-up.

Micro...
A prefix indicating one millionth (10⁻⁶). It is abbreviated using the symbol 'µ'. For example, a microvolt (µV) is one millionth of a volt, and a microbar (µbar) is one millionth of a bar.

Microphone
A device for converting audible sound into an electrical signal. See the Microphones page. Frequently abbreviated to 'mic' (pronounced "mike"). See also Mike-up, Capsule and Transducer.

Microphone-level
Describes a signal whose level is similar to that to be expected from a microphone, typically in the region of 1 or 2 mV (−58 to −52 dBu), but quite possibly anywhere in the range of 0.2 to 10 mV (−72 to −38 dBu). The output level obtained from a particular microphone will depend upon the sensitivity of that type of microphone and upon the sound pressure level to which it is exposed. This wide range in the output level of microphones is one of the main reasons that pre-amplifiers are provided with gain controls. Compare Line-level and Instrument-level.

Microphone input
A rather imprecise term referring, in general, to any input that is suitable for connection of a microphone. However, in the case of modern mixers having inputs suitable for the connection of balanced low impedance signals (produced by sources such as balanced low impedance microphones and by DI boxes), the term 'microphone input' has come to refer to those inputs − regardless of the use to which they are actually put.

Such an input is generally able to accept signals of considerably higher level than those typically produced by microphones, by use of the associated gain control and/or pad switch. The connector is usually a female 3-pole XLR. Caution: These inputs often have the facility to supply phantom power − take care to ensure that phantom power is not activated unless you are sure that the connected source(s) are able to accommodate it without damage. See also Microphone-level. Compare Line input.

Microphone placement
See Microphone technique.

Microphone splitter
A device which provides two (or sometimes more) balanced microphone-level outputs for each input. Usually used on-stage to enable the microphones (or other balanced sources such as DI boxes) to feed more than one mixer. Typically these would be either the front-of-house mixer and the monitor mixer, or the live sound mixer and a recording system. It is most often found as a multi-channel device, catering for 4, 8, 12, or 16 inputs.

Passive types may either be of a hard-wired design or of transformer-based construction − both of these types will introduce some signal loss, which may only be apparent when more than one output is connected to its destination equipment. (Typically, a loss of around 3 dB per doubling in the number of outputs can be expected from transformer-based types.) Active designs, however, introduce no loss and, in the event of a fault in the cabling or equipment connected to one output of a channel, ensure the continued operation of other output(s) of that channel. Most types will be wired to pass phantom power from just one of the outputs through to the input; phantom power from (or to) the other output(s) is blocked. See also Split output and Direct output.

Microphone technique
The manner in which a microphone is placed, relative to the sound source(s) − either by a performer (usually a vocalist) or by a sound engineer. For technical guidance on this, see Use of Microphones on the Microphones page. (As this is a technically-biased site, it does not prescribe specific ways to do 'artistic' things − see the relevant question and answer on the FAQ page − however for some notes on the effects of vocal mic techniques see Microphone Technique on the Getting Started − for Performers page.)

For the popular stereo recording placements see A-B Pair, Mid-side pair, ORTF, NOS and X-Y Pair.

View a pictorial comparison of the above five 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.)

See also Sensitivity, Polar response, Proximity effect, Critical distance (1), Leakage, 3-to-1 rule, Breath blast, Handling noise and One microphone technique.

Microphonic
Describes an undesirable property of cables or equipment, in which movement or vibration that they experience causes the generation of a signal (i.e. they exhibit behaviour similar to that of a microphone). This behaviour is called 'microphony', and is usually caused by variations in the cable capacitance.

Microphony
See Microphonic.

Mid
A slang term for 'mid-range frequencies'.

Mid-range
Describes an audio frequency that lies between the bass and treble ranges, typically between 250 Hz and 6 kHz. This is sometimes considered to be split into two bands:

• 'Lower' mid-range, or 'LMID', typically 250 to 800 Hz
• 'Higher' (or 'upper') mid-range, or 'HMID', typically 800 Hz to 6 kHz

A mixer will usually provide the facility to control the relative level of these frequencies separately for each channel, leaving other frequency ranges essentially unaffected. Such an equaliser generally has a peaking response with a centre frequency somewhere in the region of 250 Hz to 6 kHz. It may consist of a single control, a pair of controls (one for the lower and one for the higher mid-ranges) or may consist of one or more sweep EQ facilities.

Some speakers are equipped with one or more drivers that are specifically designed to handle the mid-range frequencies.

Mid-side pair
A cardioid microphone (named 'Mid') and a bidirectional microphone (named 'Side'), positioned such that the cardioid microphone faces forwards and the pick-up axes of the bi-directional microphone point sideways (with the 'positive' side to the left), the pair of capsules being located as close together as possible (ideally, 'coincident-ly'). The Left channel signal is obtained by adding the outputs of the two microphones (Mid + Side), and the Right by subtracting them (Mid − Side); some microphone pre-amplifiers incorporate a decoder for this purpose.

This arrangement is useful for stereo recording and for broadcast purposes, firstly because control over the width of the stereo image is possible by adjusting the relative gain given to the Mid and Side microphone signals, and secondly because a mono version of the picked-up sound is available direct from the Mid microphone. (If the first of these advantages is to be retained until mix-down of a recording, then the Mid and Side signals must be recorded without prior decoding; the decoding must then be done at mix-down.) Note that summing the decoded Left and Right channels (at equal levels) to produce a mono mix yields just the output of the Mid microphone (i.e. mono pick-up), because (Mid + Side) + (Mid − Side) = 2 x Mid; this applies regardless of the relative gain given to the Mid and Side signals before decoding, and is useful for mono broadcast purposes. Often abbreviated to 'MS pair', or 'M-S pair', which is sometimes incorrectly, but understandably, believed to stand for 'mono-stereo pair'. See also A-B pair, X-Y pair, ORTF, NOS and Microphone technique.

View 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.)

Middle C
The musical note produced by the 'C' key close to the centre of a full-sized piano keyboard − the fourth 'C' on the keyboard (counting from the left), also called 'C4'. The fundamental frequency of this note is approximately 261.62 Hz. See also Pitch, Octave and Concert pitch.

MIDI
An abbreviation for 'musical instrument digital interface'. A standard originally intended for the interconnection of musical devices (not just instruments), allowing them to communicate with each other digitally. It is most commonly used for connections between keyboards, sequencers (whether dedicated or computer-based), sound-generators and effects units. However, the standardisation and reliability of the MIDI interface has led to its adoption for other control purposes, unconnected with the creation of music, such as stage lighting control (compare DMX) and mixer automation. The general term for such arrangements is 'show control'.

MIDI instrument control links do not carry digital audio, but rather instructions that indicate each musical note to be played, how it is to be played, and on which instrument. The quality of the sound is therefore determined by the instrument (or sound-generator) that is used to create the audio signal, not by the instrument (or computer, etc.) that is used to create the instructions. The MIDI standard allows for up to 16 channels of information to be carried on a single physical interconnection. Typically, each type of created sound (or 'voice') is allocated a channel to control it, allowing for the simultaneous control of up to 16 voices. These may be produced by several different MIDI-controllable instruments fed with the same MIDI signal, or by multiple sound-generators within the same instrument.

The interconnecting cables use a 180º 5-pin DIN plug at each end, and employ screened cable with two signal conductors connecting to pins 4 (positive) and 5 (negative) respectively − these are the two pins immediately adjacent to the middle pin (pin 2) to which the cable's screen connects. Correct polarity is essential. The connection operates as an 'isolated loop' − all the current from the 'sending' end returns to it. (The digital information is extracted via an opto-isolator within the equipment at the 'destination' end; this detects the switching on and off of the current, and correspondingly switches on and off a voltage within the equipment.) Further, although the cable screen is connected to pin 2 of the plugs at both ends of the cable, this connects internally to the equipment signal earth at the 'source' end only. These two measures together ensure that no earth loops can be introduced by MIDI connections. Use of purpose-made MIDI cables is recommended.

A physical MIDI interconnection can be made from one source to one destination only; a single cable cannot be 'looped' between several destinations. However, most 'destination' equipment has a 'through' connection which may be used to forward a regenerated version of the input signal on to another destination. Such an output is usually labelled 'THRO' (or 'THRU'). The signal is usually regenerated in amplitude only; it is not re-timed as this process would introduce a significant delay. The number of items in such a daisy-chain should therefore be limited to about 4, to avoid a build-up of timing errors. A better method is to use an active MIDI distribution box, which has several outputs enabling multiple destinations to be fed 'in parallel' from a single source. Other more clever MIDI boxes are available, which are able to combine the signals from several sources, modify channel allocations, etc.

The bit-rate is 31.25 kbit/s asynchronous, which by modern standards may seem rather low. However, since note-on and note-off instructions require just 3 bytes each (a total of 33 bits, including one start and two stop bits per byte), this data rate supports up to 946 of these instructions per second (i.e. 473 notes begun and ended, per second), across all 16 channels combined. See also Sysex.

MIDI machine control
A protocol that enables a MIDI signal is used to convey commands such as 'play', 'stop', 'rewind' and 'record' (typically from a DAW or other computer-based system), to control the transport of a player or recorder (whether a physical machine such as a DAT recorder or a virtual computer-based machine). Frequently abbreviated to 'MMC'.

MIDI show control
See Show control.

MIDI time control
An arrangement in which a MIDI signal is used to convey a time code, typically to provide synchronisation between items of equipment. Frequently abbreviated to 'MTC'. See also SMPTE.

Mike
See Microphone.

Mike-up
To position a microphone in order to pick up a particular sound source.

Milli...
A prefix indicating one thousandth (10⁻³). It is abbreviated using the symbol 'm' (N.B. always lower-case). For example, a milliamp (mA) is one thousandth of an ampere, a millisecond (ms) is one thousandth of a second, and a millivolt (mV) is one thousandth of a volt.

Mini disc
A recordable and editable digital recording medium, similar to a compact disc but smaller in diameter. The playing time is the same as for a CD − this is achieved on a smaller disc area by compression of the digital information.

Mini-DIN
See DIN.

Mini-jack
See Jack.

Minimum phase
This term has a strict mathematical definition which is outside the scope of this site. However, for our purposes a system can be described as minimum phase if it has the minimum possible group delay of all real systems having the same frequency response. In fact the description 'minimum phase' can be understood as 'minimum group delay'.

A minimum phase system has the property that its phase response can be deduced from its frequency response.

It should also be noted that the description 'minimum phase' is sometimes misused to mean a system having a linear phase response, that is, having a constant group delay (rather than the minimum group delay).

Mismatch
See Matching.

Mix
In audio work, a unique blend of individual sounds into a composite sound. It is usually created by using a mixer to perform an addition of the analogue signal voltages or digital values corresponding to each component sound, in their desired proportions (but compare One microphone technique). Or, as a verb, the act of creating such a blend. See also Main mix Group, Auxiliary, Bus, Summing and Matrix.

Mix bus, Mix buss
See Bus.

Mixer, Mixing console, Mixing desk
An item of equipment used to combine signals in the desired proportions, usually also providing facilities for equalisation, panning, the connection of effects − and often other facilities besides, such as auxiliaries and PFL. A full description of facilities is given on the Mixing Facilities page. Mixers usually accommodate 8, 12, 16, 24, 32 or 40 channels. Also called a desk, a sound board (or just a board) or a console. See also House mixer, Monitor mixer, Mixer-amplifier and Powered mixer. For an introduction to mixing see the Mixing Engineers page.

Mixer-amplifier
An item of equipment incorporating both mixing facilities (see mixer) and one or more power amplifiers to drive the speakers, within a single unit. Usually refers to equipment of a 'box-like' (rather than a 'desk-like') construction, having its controls on a vertical front panel. The channel faders are usually rotary types, not sliders. Compare Powered mixer.

Mixer automation
An arrangement in which settings of a mixer are automatically adjusted (usually during an event) according to a schedule that has been previously determined and programmed into the automation system. Automation is particularly suited to digital mixers, but certain types of analogue mixers (usually large ones) may also be automated to varying degrees. Mixer automation systems are also known as 'show control' systems, although in general that term has a wider scope. Automation features may be built into the mixer, or may be provided by a computer connected to the mixer via a suitable control interface such as MIDI. See also Motorised fader.

Mixing solo
An alternative term for destructive solo.

MLSSA
A trademarked name for a software-based audio analysis system, in which a short burst of a pseudo-random noise sequence is applied to the speakers and the resulting sound is picked up by a measurement microphone. The picked-up signal is then analysed by the software. MLSSA is an abbreviation for 'maximum length sequence spectral analysis', and is pronounced 'Melissa'. See also Real time analyser (RTA) and Fourier analysis. Compare STI.

MMC
An abbreviation for 'MIDI machine control'.

MN-taper
See Taper.

Modem
In a general sense, any device that provides the function of modulation and the corresponding reverse process of demodulation. However, the term is nearly always used to refer to a device that uses these processes to allow digital information to be conveyed through an analogue communication channel − especially an analogue telephone connection. The name is an abbreviation of 'modulator-demodulator'. See also Bandwidth and Codec.

Modulation
The variation of a signal, or, the process by which such a variation is achieved. The most common example of modulation is in information transmission, especially by radio.

In radio communications, to avoid interference between simultaneous transmissions in the same area, it is necessary for each communications channel to use a radio-frequency (RF) 'carrier' signal of different frequency. The carrier is modulated, i.e. varied, by the information to be transmitted (termed the baseband signal) using the required type of modulation. The resultant RF signal is no longer single-frequency, but consists of an upper sideband above the carrier frequency and a lower sideband below it; either of these, or the carrier itself, may subsequently be removed (or be partially suppressed) without loss of information.

There are many kinds of modulation, but those most commonly known are amplitude modulation (AM) and frequency modulation (FM). In AM, the baseband signal varies the level of the carrier, whilst in FM it varies its frequency. In general, FM provides an improved quality of transmission − especially as regards susceptibility to interference − but requires a greater bandwidth.

However, the principle of modulation is by no means exclusive to radio. It is also used, for example, in effects units and in sound synthesisers.

The reverse process, by which the original modulating signal is extracted from the modulated carrier, is called demodulation. See also Modem, Multiplex and Intermodulation.

Monitor
A sound source (usually a speaker) provided on-stage for the benefit of performers, a mix of signals destined for such a sound source, or a facility of a mixer which enables the provision of such a mix (sometimes referred to as 'foldback'). A floor-standing speaker provided for this purpose is often called a 'wedge', because of its shape. Smaller, stand-mounted types are also available. An alternative to using speakers as the sound source is to use in-ear monitoring (IEM). Note: When working with video engineers, with video production staff or with computer equipment, take care to avoid confusion over this word, as it may also refer to a video monitor or to a computer monitor. See also Auxiliary.

Monitor beach
See Beach.

Monitor engineer
A sound engineer who is responsible for creating the monitor mixes; the person who operates the monitor mixer. Compare FOH engineer.

Monitor mix
A mix that is created specifically to meet the needs of one or more performers, rather than for the audience. Monitor mixes are usually created using a dedicated monitor mixer, the auxiliaries of the front-of-house mixer or a personal mixing system, and are fed to floor monitors (wedges) or to in-ear monitors or headphones worn by the performers. A monitor mix may alternatively be referred to as foldback.

Monitor mixer
A mixer used in large systems, solely for the purpose of mixing for the performers' monitors. It is usually located at the side of the stage and is operated by a monitor engineer. (The front-of-house sound is then mixed by a separate mixer referred to as the 'FOH mixer' or the 'house mixer', usually located centrally within, or towards the back of, the audience area). The various on-stage signal sources are arranged to feed both the FOH mixer and the monitor mixer by use of a microphone splitter or other monitor split facility.

Usually several monitor mixes are created (ideally one for each performer). This is normally done by using the post-fade auxiliary sends of the mixer, to allow overall control of the level of each source using the channel faders. See also Listen wedge.

Monitor split
A facility which enables one or more stage signals to be fed to a monitor mixer as well as to the front-of-house mixer. This facility may be provided by a multicore stagebox, by a microphone splitter or (more rarely) by the split outputs of one of the two mixers.

Mono
Describes equipment that handles, or provides, one or more signals, each of which is intended to be ultimately supplied both to the Left and Right front-of-house speakers. Or, describes a system configuration in which an identical mix is supplied to the left and right front-of-house speakers. Compare Stereo. Note: Strictly, 'mono' is an abbreviation for 'monophonic'; however, the term 'monophonic' is now rarely used with this meaning − it more usually has the meaning given in the next definition.

Monophonic
Describes a sound source (usually an instrument) that is capable of producing only one musical note at a time (e.g. a flute). Compare Polyphonic. Note: Rarely, abbreviated to 'mono'; however, 'mono' more usually has the meaning given in the previous definition.

MOSFET
An abbreviation for 'metal oxide on silicon field effect transistor'. Strictly a specific type of FET, but in PA work it is usually used to describe a power amplifier that uses a high-power version of this type of transistor in its output stage. For more information on power amplifiers see the Amplifiers and Speakers page.

Motorised fader
A fader that is equipped with an electric motor, enabling its physical setting to be changed under remote or automatic control (as well as in the usual manual fashion). Such faders are primarily used in digital mixers, to enable pre-programmed mixes to be restored at will, whilst still allowing the facility for manual deviations to be made from the pre-programmed fader settings. See also Mixer automation.

MOV
An abbreviation for 'metal oxide varistor', a device used inside some types of mains power distribution equipment to provide protection against power surges. These devices can be damaged or destroyed if subjected to excessive or often-repeated surges.

Moving fader
See Motorised fader.

Moving head
Describes a lantern that is equipped with a mechanical means to move the part containing the light source and related optics (that is, the 'head'), so as to enable the direction of the light beam to be changed while in operation. Such movement is usually arranged in terms of a rotation angle and a tilt angle, allowing any beam direction in 3 dimensions. The movements are usually controlled remotely via a DMX interface, though some units may have the capability for autonomous movement (for example, in response to ambient sound).

MP3
A digital audio file format employing the data compression scheme specified by Layer 3 of the MPEG-2 (or MPEG-1) specification. (The '3' refers to that Layer.) It was heavily used for reducing the time taken to download digital audio files from the Internet, and for reducing the amount of data storage required by portable music players, but is now largely superceded by improved formats such as AAC. See also ATRAC, Masking, Perceptual coding and Variable bit rate.

MP4
A file format for MPEG-4 digital video and audio files. However, the term is also sometimes used to refer to MPEG-2 AAC audio-only files.

MPEG
An abbreviation for Moving Picture Experts Group (often referred to as the Motion Picture Experts Group), the body which defines coding standards for digital audio and video data. There are several 'Phases' of MPEG standards, identified as MPEG-1, MPEG-2, MPEG-4 and MPEG-7, which co-exist to provide different functionality; the higher-numbered phases do not supercede the lower-numbered ones. Each Phase is broken down into a number of layers, providing different facilities. Frequently used to refer to digital video files. See also MP3 and MP4.

ms
An abbreviation for 'millisecond', a unit of time. One ms is one thousandth (10⁻³) of a second.

MS pair
An abbreviation for 'mid-side pair'.

MTC
An abbreviation for 'MIDI time control'.

Muddy
Describes a sound that is lacking in clarity. See also Clarity and Warm.

Multi-amping
See Bi-amping.

Multicore
A cable for the purpose of conveniently carrying several separate signals between two locations, typically the stage and the mixer (or patch bay). Commonly called a snake (a slang term). In a 'conventional' multicore, each signal is carried on an independent circuit (or channel) within the cable, consisting of 'hot' and 'cold' conductors (known as a 'pair') within their own screen. Each circuit is usually identified by a specific pair of insulation colours (see Colour code). The cable as a whole is protected by an outer sheath.

The stage end of the cable is usually provided with a stagebox, and the mixer end with tails (or with a multi-pole connector for connection to a patch bay).

The circuits intended for the transfer of signals from the stage to the mixer are called 'sends' and are nearly always used in balanced mode. The circuits intended for the transfer of signals from the mixer to the stage are called 'returns' and should preferably be used in balanced mode but are sometimes used in unbalanced mode.

A digital multicore serves the same function, but operates on an entirely different principle (click the link for details.) See also Line, Drain wire, Belden and Powered multicore.

Multimeter
A test meter that is able to measure several different quantities − usually at least voltage, current and resistance. A multimeter provide its indications of measured quantities using either an analogue or a digital type of display; models using a digital display are frequently referred to as DMMs. See also AVO, DVM, Megger and Calibration.

Multiplex
A signal that consists of several other signals, combined together (or 'coded') in such a way that the original constituents can later be separated out again (as opposed to simple 'mixing', which is irreversible). Or (as a verb), to generate such a combined signal. The process of combining the signals is called multiplexing, and is performed using a coder. The process of separating them again is called demultiplexing, and is performed using a decoder.

The purpose of multiplexing is to create a composite signal that can be stored, transmitted, or otherwise processed as a single unit. This is largely for convenience, but also ensures that all the information stays together. An example would be an SPDIF signal, which is a multiplex of Left and Right audio signals, along with other information, interleaved into a single bit-stream, enabling it to be carried on a single cable. Often a multiplex is a digital signal, but is not necessarily so. The term 'multiplex' is frequently abbreviated to 'mux'.

MUSA
A type of screened unbalanced connector, typically used for professional video connections (both analogue and digital). It is most commonly found on broadcast video patch bays. The original analogue version has a characteristic impedance of 50 ohms, but 75 ohm versions have now become available to meet the more demanding requirements of digital video interconnections. See also BNC.

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Musac
Background music (BGM), such as is played over public address systems in public buildings. The term was originally formed as a trademark for a system of transmitting music over telephone lines, patented by General George Owen Squier, who combined the word 'music' with the company name 'Kodak'.

Music power
A power rating sometimes applied to speakers, which attempts to take into account the dynamic nature of real programme material. Also known as 'programme power'. For further information see Power Ratings on the Amplifiers and Speakers page. See also RMS.

Muso
A slang term for a musician.

Mute
A facility of a mixer, enabling the interruption of the signal from an individual channel, a selection of channels, or a mute group without disturbing the settings of the faders. Or, a facility of a radio microphone system, which allows the audio signal to be manually interrupted at the transmitter without causing the clicks and pops that would result from switching off the carrier. In certain circumstances muting may also occur automatically to prevent the passage of avoid unwanted audio signals or noise, for example in the operation of radio system squelch.

Mute group
A facility of a mixer, enabling the simultaneous interruption of the signals from a selection of channels that might not be associated in any other way − i.e. which may be assigned to different audio groups and/or VCA groups.

Mutual inductance
The effect whereby a changing magnetic field that is produced around a conductor, because of a changing current flowing in it, cuts across a different nearby conductor and thereby causes a causes a voltage to be produced in it. This effect is put to good use in a transformer, but may also be the cause of unwanted inductive coupling between conductors of different circuits.

Mux
An abbreviation for 'multiplex'.

mV
An abbreviation for 'millivolt', a unit of voltage. One mV is one thousandth (10⁻³) of a volt.

mW
An abbreviation for 'milliwatt', a unit of power. One mW is one thousandth (10⁻³) of a watt.

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This page last updated 10-Nov-2009.