0-10V Analog- A lighting control system using ten-pin connectors (six channels per connector) that is used on portable and some installed lighting consoles. Carries a control signal for each channel proportional to the amount of light wanted. Being replaced by DMX-512.

A-B microphone pair- A pair of spaced microphones used for a stereo pickup. Generally used for recording, not reinforcement.

A/D converter- Short for "Analog - Digital Converter." Converts an audio signal in its electrical form into a digital binary data stream.

Absorption- The ability of a surface to absorb sound. The absorption coefficient of a material is a figure between 0 and 1, representing its degree of absorption.

AC- abbreviation for "Alternating Current."

Acoustics- The study of sound-wave motion and sound behavior both within an enclosure and out of doors. Also- The qualities of a room in respect to transmission to sound.

Aesthetic- Often applied to theatrical designs or directing styles; in sound, the end product of the sound system and how it evokes mood, enhances the play, etc., etc.

Alternating Current- Current that periodically alternates its phase with relationship to time, as opposed to DC, which does not alternate. Household electricity is AC.

Ambience- Reverberation and early reflections. The characteristic sound of a location that tells the ear it is listening in a particular room, concert hall, etc.

Ambient Noise- The prevailing sound field in a room in the absence of an applied signal from a loudspeaker, musical instrument, or other sound source.

American Wire Gauge (AWG)- A system in the United States for measuring thickness of wire. The lower the number, the larger the diameter of the wire.

Amp- See "Amperage".

Amperage- The amount of current that flows through an electric circuit. Measured in Amps, A; symbolized in equations by I.

Amplifier- A device in which a small amount of input power controls a larger amount of output power. Used in sound systems to convert a small electrical signal into a large electrical signal to power speakers.

Amplitude- The strength of a vibration; more amplitude means more sound.

AMX-192- Another lighting control system using four-pin XLR connectors. Can control up to 192 channels. Relatively little use. Compare with "0-10V Analog" and "DMX-512".

Analog- In sound, opposite of "digital." Analog representations of sound reproduce the exact waveform, transferring it through different mediums; in a sound system, the microphone (a transducer) creates an electrical analog of the sound pressure waves it hears; the amplifier creates a larger electrical analog of the electrical signal it receives; the speaker creates an acoustic (sound pressure waves) representation of the electrical signal it receives. Compare with "Digital."

Anechoic- Echo free; an anechoic room is a room whose walls, ceiling, and floor are covered with a sound-absorbing material.

Array- Generic name for a single collection of loudspeakers centrally hung in an auditorium. Also "Cluster."

Attack Time- In a compressor or expander, the interval during which the output level moves from its pre-threshold level to whatever gain is dictated by the compression/expansion ratio. Translation: how fast a compressor moves.

Attenuator- Device which reduces the signal flowing through a circuit, commonly found built-in to connectors in values of 10dB from 10dB to 60dB. Translation: takes a very "hot" (loud) signal and makes it softer, so it doesn't overload the circuitry in question. Also "Pad."

Automation- Usually refers to "console automation," relatively not-new technology that automates certain functions of sound equipment; consoles, for example, can store specific scenes (certain inputs/outputs at specific levels) and recall them at a later time.

Auxiliary Return- A specific line-level input on a console designed to receive a signal from an effects processor. Usually stereo.

Auxiliary Send- A specific output bus connected to each channel (with its own level control) that sends a signal out of the mixer and supposedly into an effects processor; can also be used as an additional output (for monitors, recording, whatever).

Axis- An imaginary line that is perpendicular to the front face of the microphone diaphragm. Those sounds reaching the microphone at an angle to the axis are said to be off-axis. Can also be applied to loudspeakers.

Background Music- Appropriate music, enhancing the mood of a play.

Baffle- A panel or other surface whose purpose is to prevent the transmission of sound. Also: a panel or other surface in a loudspeaker system that reduces interference between sound radiated from the front and rear of the speaker driver by increasing the path length from front to back. Also: "to stupefy."

Balanced/Unbalanced-An unbalanced line is one where there are only two signal carrying conductors, one of which is the shield. In the balanced line the shield, which is grounded, is in addition to two conductors. Balanced lines are less prone than unbalanced to interference. In balanced lines, one of the signal wires carries the audio signal, while the other carries an inverted copy. When the signal reaches the destination, the inverted copy is flipped and added to the original. Any noise added by the wire is also inverted. When combined with the non-inverted noise, the two noise signals cancel each other out.

Bandwidth- The difference between the lower and the upper cutoff frequencies. (An equalizer with cutoff frequencies of 200 and 2000 Hz has a bandwidth of 1,800 Hz.)

Bass- Low frequency end of the audio spectrum. Also: a musical instrument. Also: a fish.

Beat- A periodic variation in amplitude that results from the superposition or addition of two tones with nearly the same frequency.

Bi-amping- Process whereby the amplifiers are placed in the sound system after the crossover, one channel for low frequencies, one for high. Produces a cleaner sound than if a single amp had been placed before the crossover; crossover is not subject to high power levels; amplifier channels are dedicated to a certain frequency range whereby it can operate much more linearly, lessening distortion.

Bi-directional microphone- A microphone that is equally sensitive to sounds arriving from the front and back, and insensitive to sounds arriving from the sides. A figure-8 microphone.

Binaural- Sound reproduction using two microphones usually in a "dummy head" (to emulate the shape and the response of the human hearing system) feeding a pair of headphones, so that the listener hears the sound he or she would have heard at the recording location.

Bi-radial horn- A horn in which both the vertical and horizontal surfaces flare outward, though usually at different rates.

Boundary Layer- The region in the immediate vicinity of a surface in which the phase shift between a direct and a reflected path wave is negligible within the audio frequency spectrum of interest. The Pressure Zone.

Bridging- A technique used with an amplifier where there is a single input to both channels and the output from both channels is summed into one: provides for more amplifier power. WARNING: not all amplifiers will perform well when bridged. See owner's manual of amplifier in question for information.

Cable- Ambiguous term in theatre. Could refer to heavy-duty electrical cable, light-duty electrical cable, speaker cable, microphone cable, instrument cable, security system cable, low-voltage hookup cable, etc. Usually have copper conductors (either stranded or solid) and have some sort of rubber, plastic, etc. insulation. We'll be writing a section on connectors and cable shortly.

Cam-Lok- A connector made by Crouse-Hinds specifically designed to carry large mains currents, as in those from a power junction box to a portable dimmer pack or power distribution set-up. One connector per phase, per neutral, and per ground.

Capacitance-

Capacitor- An electronic circuit element that stores energy by creating an electrical field between two conductors; at a given parameter, the capacitor will discharge; AC can flow through a capacitor but DC cannot.

Cardioid Microphone- A unidirectional microphone with 6dB of attenuation at the sides (±90 degrees) and a null at 180 degrees. So called due to the cardioid-like shape of its polar pattern. In a few words, it picks up more sound from the front than from anywhere else.

Cascading- The act of connecting two or more mixers to each other in order to extend the number of inputs available.

Catwalk- A walkway usually suspended or cantilevered in the air. A term sometimes given to a fly gallery, loading platform, or a lighting position in the auditorium.

Channel Fader- The level control (usually, a slide fader) on a mixer normally found in the channel path.

Channel Path- In an inline console, the signal path from the mic or line input to the point at which the signal is combined with other incoming signals.

Chorus Effect- The combination of a direct sound and several delayed replicas to simulate the effect of a chorus.

Clipping- Distortion in a mixer or amplifier due to severe overloading. Clipping when using digital equipment (an A/D converter, somewhere) results in static-like noises as the A/D converter doesn't really know what to do with levels over its operation parameters.

Close Miking- Placement of a microphone near a sound source (1" - 3') effectively eliminating all but the direct sound of a source.

Cluster- Generic name for a single collection of loudspeakers centrally hung in an auditorium. Also "Array."

Coloration- Term used to indicate audible alterations to the sound arising from the response pattern of a mic or loudspeaker; also used to indicate alterations to the sound arising from the environment in question.

Compressor- A variable-gain amplifier in which the dynamic range of the output signal is less than that of the input signal. The compression range may vary from 1:1 to 10:1. Translation: it takes a signal with a large dynamic range, keeps the soft sounds soft, but compresses the louder sounds above a certain threshold. It trims the dynamic range.

Connector- The terminating point of a cable. It enables cables to be connected together. Why are we bothering with this definition?

Console- The central system to which multiple input signals are routed for level control and signal processing, and for combination with other input signals and subsequent routing to a tape recorder, broadcast transmitter, or sound reinforcement system. A mixer.

Constant Directivity- Typically, a loudspeaker in which the produced sound does not become more directional as the frequency rises.

Constant Voltage System- A speaker distribution system commonly used in large installations such as airports, department stores, and schools where a single amplifier is driven at its maximum output voltage (70.7V in the U.S.), and transformers are used at each speaker to control volume level. Using this high-voltage and high-impedance system allows for cable to be small in diameter. However, the sound quality usually sucks because in order to reproduce the entire frequency spectrum well, the transformers need to be very heavy and very expensive.

Constructive Interference- The interaction of two or more identical sound waves which support each other. Compare with "Destructive Interference".

Coverage Angle- The included angle between the points on either side of a loudspeaker axis at which the response is attenuated by 6dB with respect to the on-axis level.

Critical Distance- The distance from a sound source at which the direct and reverberant energy are equal. No member of the audience should be further away from the loudspeakers than this.

Crossover frequency- In a crossover network, the frequency at which the outputs of two adjacent filter networks are both attenuated by 3dB.

Crossover - Device which separates parts of the audio signal, typically the high frequencies and the low frequencies; crossovers that appear after the amplifier (they are placed inside the speaker (used inside full-range speaker systems)) are called 'passive,' those which are placed before the amplifiers (in bi- or tri-amplification) are called 'active.' Crossovers are, essentially, a high-pass filter and a low-pass filter in parallel; see handy Intro Electrical Engineering book for more info.

Crosstalk- Any leakage of signals between two channels; i.e. two channels of a multipair cable, two channels of a mixer, etc. Usually not desirable.

Cue Monitors- A small speaker or a pair of headphones used by the operator specifically for cueing microphones, instruments, or recorded media before raising the level to the house sound system.

Current- The flow of electrical charge. Measured in Amperes, or "amps."

Damping- Loss of energy in a vibrating system, usually through friction of some sort.

DAW- see "Digital Audio Workstation."

dB (Decibel)- One dB is the smallest change in loudness that the average human ear can detect. 0dB is the threshold of human hearing. The threshold of pain is between 120 and 130dB. The decibel is a ratio, not an absolute number, and is used to identify the relationship between true power, voltage, and sound pressure levels. Decibels alone have no specific meaning. For example, dBV is a voltage ratio; 0dB = 0.775 V root mean square (RMS). dBSPL is the sound-pressure level ratio. It measures acoustic pressure. dBM is a power ratio. dBA takes into account the unequal sensitivity of the ear, and sound-pressure level is measured through a circuit that compensates for this equal loudness. These measurements are termed A weighted.

Destructive Interference- The interaction of two or more identical waves which cancel each other.

Diaphragm- The moving element of a microphone that converts sound-wave energy into mechanical energy.

Diffraction- The manner in which sound can bend around obstacles.

Digital Audio Workstation- A computer-based system for editing, recording, and playback of audio signals. Examples are Digidesign's SoundTools or ProTools systems.

Diode- A device that allows easy current flow in one direction only.

Direct Box- A small interface box used to take an unbalanced, high-impedance output of a guitar, guitar amp, bass, bass guitar amp, etc, and convert it to a balanced, low-impedance mic-level output for input at the mixer.

Direct Current- Electric current that flows in one direction only, as opposed to alternating current.

Direct Injection (DI)- Process whereby a signal is taken from a keyboard or guitar, etc, direct (via a connector box (the Direct Box)) to the mixer. Used instead of a microphone.

Distant Miking- Placement of a microphone at a distance (3'-5' or greater) from the source, to pick up a larger portion of the overall instrument and/or reflected sound.

Distortion- In Electronics: a measure of the difference between the output and input signals in an amplifier. In Sound Systems: A distortion of a signal that results in dirty sound. Common sources of distortion are in guitar amplifiers (on purpose), and doing such things as plugging a line-level into a mic-level input (overloading the microphone preamp). Basically, you overload something. This occurs due to Harmonic Distortion See "Clipping." In Acoustics: An undesired change in a waveform. Also see "Intermodulation Distortion".

Diversity- A wireless microphone system that employs two antenna positions per mic; the system hunts for the strongest signal and 'locks on' to it. 

DMX-512- A digital lighting control system using a five-pin XLR connector. Can control up to 512 channels of dimming, non-dimming, moving lights, scrollers, etc. Carries all control information digitally. Used often on new and portable lighting equipment.

Doppler Effect- The shift in apparent frequency when the source or the observer is in motion.

Dynamic Microphone- Any microphone whose output is a function of magnetic induction in a voice coil, ribbon, or other conductor moving within a permanent magnetic field.

Dynamic Range- The difference, in dB, between the lowest and highest a system is capable of handling.

Echo- One or several distinct repetitions of a sound.

Effects Send- In a console, the controls used to route an incoming signal to any external signal processing system. Also "Auxiliary Send."

Electro-Magnetic Interference (EMI)- A type of interference caused by mains current flowing through wires in close proximity to audio cables. The magnetic field around the power cables makes its way into the audio cables, causing interference and hum, buzz, etc. Also caused by fluorescent lights, neon lights, switching loads (HVAC equipment), computers, RF transmitters, car ignitions, etc.

Envelope- Time variation of the amplitude of a vibration.

Equalizer- The signal processing device used to modify the frequency response of an audio signal. So called because the first such devices were used to correct, or "equalize," the losses in a transmission line.

EQ Cut- a button on a mixer which cuts out the mixer's equalization enabling the actual sound to be compared with the corrected sound.

FFT- See "Fast-Fourier Transform."

Fader- The master loudness control (usually a fader; sometimes a knob) to the main outputs for each channel on a console. Do not confuse with "gain."

Fader, riding the- A technique used in live sound reinforcement where each channel's fader is constantly being adjusted ("being ridden") by the operator in order to control feedback or background noise.

Fast-Fourier Transform- A long time ago (okay, about 150 years ago), Baron Joseph von Fourier discovered that any complex sinusoidal signal (like that of an audio signal) could be mathematically represented by an infinite series of sine functions by treating portions of the signal as periodic. Apparently he wasn't too hot with the women. Thus, a Fourier series is an infinite series of sine functions of the form 1/n sin nx, where n is an integer, and x is an angle. Nowadays, fast computers can perform this calculation rather quickly, usually in real-time. These computer can thus display a better representation of the audio signal than a real-time spectrum analyzer by displaying the audio waveform. Certain manufacturers have developed products using several FFT processes to properly tune a sound system. See "Meyer Sound SIM System."

Feedback- The high-pitched squeal or ringing caused by sound finding its way out of the loudspeaker back to the mic and out of the speakers again at a resonant frequency dictated by the characteristics of the environment, system, and equipment. It can be lessened by lowering the volume and/or evening out the peaks in the frequency response of the system. Directional mics and speakers are fundamental in helping to overcome this. Frequency shifters can also help. In Electronics, a circuit arrangement in which a portion of the output of an amplifier is fed back into the input. Negative feedback reduces amplifier gain but also decreases distortion; positive feedback increases the gain and may lead to self-oscillation.

Filter- An electrical circuit that passes alternating currents of some frequencies and attenuates others.

Flanging- Mixing a signal with a time-delayed copy in order to produce a new signal. Originally produced by using two tape playback machines mixed to one recorder; one playback machine's reels were slightly delayed with respect to the other by applying slight pressure to the flanges of the reels. The signals constructively and destructively interfere with each other, producing a very effect-laden signal.

Flat- Term used to describe an even frequency response, one in which no frequency is accentuated.

FOH- Front of house; the front of an auditorium, the opposite end to the stage. Typical mixing point for live shows.

Foldback monitors- Wedge-shaped speakers placed on stage so that performers can hear themselves (and the band). Also see "Foldback System."

Foldback System- A cue system that is independent of the main house system. Used both for performers (so they can hear the band and themselves) and for the band (so they can hear the performers and themselves).

Frammel- A strip of wood placed between speaker cabinets to separate and angle them vertically to reduce phase interference between cabinets.

Frequency (Hz)- The number of repetitions of a periodic waveform per unit of time. Given in Hertz (Hz). The higher the frequency, the higher the pitch of the sound.

Frequency Response- The range between the upper and lower limits that a microphone or audio system will adequately transmit (within a range, such as + / - 3dB). A mic might give a frequency response of 50Hz to 20,000Hz.

Frequency Shifters- A device which is sometimes used to reduce the system's liability to feedback. Frequency shifters adjust the output by 5Hz.

Function Generator- An audio generator that provides several different waveforms or functions at the desired frequency.

Fundamental, Harmonics- The initial vibration of a sound wave is the fundamental; harmonics are the subsequent vibrations which are at equal multiples. Thus a fundamental of 100Hz will have harmonics at 200Hz, 300Hz, and so on. The mode of lowest frequency. See acoustics text or music theory text.

Gain- The control which regulates the amount of sound an individual channel preamp is receiving. Do not confuse with "Fader," which comes after the channel preamp and controls the amount sound being delivered to the output groups.

Gain riding- A misnomer. You are really riding the fader... Bad term. Bad.

Gain, unity- A condition in which the output level is equal to the input level. A gain of 0dB. "Sound nirvana." Op-amps operated at unity gain do the least amount of work and introduce the least amount of noise into the circuit.

Graphic Equalizer- An equalizer that has slider-level controls; once set, the sliders represent the response curve. Changes the relative levels of frequencies.

Grazing Effect- The way in which sound is absorbed by the audience; stepping or raking the seating reduces the absorption, and improves sight lines.

Ground Lift- A process used to eliminate ground loops in systems whereby one or more of the many grounds in the system is disconnected. A switch on a direct box that lifts the ground by disconnecting pin one of the XLR connector. WARNING: NEVER cut or otherwise disable the grounding pin on the AC cord-- if a ground fault should occur in the equipment, the potential for electric shock is enormous.

Ground Loop- A state where too many grounds of equipment are connected at different points. The ground potential starts running around the equipment in loops, causing a mains-frequency (60Hz in the U.S.; don't forget the harmonics) hum in the equipment.

Group- The section of a mixer where the sound is brought together in combinations, (either groups or subgroups) which can then be further combined into the main outputs (either stereo outs or groups, respectively).

Haas effect- The phenomenon noted when a sound source arrive from two locations, in which one sound is lightly delayed. Localization is toward the direction of the source that arrives first, but is biased by level difference and actual time delay. Named after Helmut Haas. For example, consider a signal routed to two speakers. If both reproduce the signal at the same level, the sound seems to originate at a position midway between them. However, if a delay line is inserted in the second speaker, the apparent source shifts away from the echo speaker and towards the primary speaker. It was reported by Haas that when the delay reaches only 10 milliseconds, the second speaker is no longer heard, despite its output level matching the primary speaker. 0-10ms delay: as the delay is increased from 0 to 10 ms, the sound source appears to move to the location of the primary speaker. To restore the center image, the second speaker level must be raised about 10 dB. 10-30ms delay: as long as the delay stays within this range, the apparent location of the signal remains exclusively at the primary speaker. However, the second speaker contributes a sense of "liveliness" or "body" and, as might be expected, additional volume. In a concert environment, echoes of 10 to 30ms would be heard but not "seen," that is, the listener would sense the presence of the reflected energy, but not the locations from which it arrives. 30-50ms delay: in this range the listener becomes aware that the second speaker is on, although the apparent sound source remains at the primary speaker.

Handling noise- The noise created by mechanical vibrations or shocks picked up by a microphone.

Harmonic Distortion- In a waveform, harmonics are generated by altering the waveform in some way, for instance, clipping the peaks of the wave.

Headroom- The capacity of a device above its normal operating level in which it can permit peaks to pass undistorted.

Hertz- A measure of frequency. Indicated by cycles per second (abbreviated Hz). It can be found by the formula 1/T, where T equals the period. (See "Period.")

Highpass filter- A filter designed to pass high frequencies with little or no attenuation. A low-frequency filter.

Hiss- Noise that sounds like prolonged sibilant sounds. Can occur from bad cassette tape, from vinyl albums, live snakes, etc.

Horn- A loudspeaker in which the coil is attached to a metal diaphragm which excites the air in front of it, this is attached to the metal horn itself. Horns are more efficient than moving-coil units and deal with the middle and upper frequencies.

House curve- The response of the acoustic of an auditorium to pink noise; this will indicate at which frequency the system will feedback (that most prominent) and can also identify other defects in the acoustics or system.

Hum- Electrical interference caused at mains frequency, which, in the U.S., is 60 Hz. Since 120 Hz is a harmonic of a 60 Hz fundamental, 120 Hz is also a hum frequency.

Hypercardioid microphone- A directional microphone with greater attenuation at the sides than a pure cardioid pattern, but with less attenuation at the rear.

IATSE- The International Alliance of Theatrical Stage Employees. The international bargaining unit for stagehands such as property masters, audio techs, carpenters, riggers, electricians, wardrobe mistresses, etc., etc.

Impedance- The degree to which a circuit impedes the flow of current. Abbreviated by the Greek letter Omega, and measured in Ohms; in electrical equations, symbolized by "Z". Sorta like "resistance" but frequency-dependent. Additionally: the ratio of voltage to current.

Inductance- Production of current across a space due to electrical or magnetic fields. See Physics text and "Magnetic Induction."

Inductor- A device that stores energy by creating a magnetic field, usually within a coil of wire.

Input Channel- The section of a mixer which receives the signal from microphone, tape deck, etc.

Intermodulation Distortion- Refers to the generation of sum and difference tones in a waveform.

Inverse-Square Law- Pertaining to any condition in which the magnitude of a physical quantity follows an inverse relationship to the square of the distance. For point sources of sound, the SPL drops 6dB for every doubling of the distance.

Jack- Term for terminating point of a circuit. A common term for a female phone plug connector.

Lavalier Microphone- A miniature microphone that is designed to be attached to the user's clothing via a clip. Often used in newscasts or productions requiring unobtrusive amplification. Can also be hidden in clothing, hair, over the ear, in plants or pocketbooks, etc.

Leakage- Any unwanted sound picked up by (or "leaking" into) a microphone, generally from instruments other than the one(s) in front of the microphone.

Linear-A term describing the output-amplitude versus input-amplitude characteristics of transducers and signal-processing devices. A linear device or medium is one whose input and output amplitudes have the same ratio at all signal levels. For example, if an amplifier is linear, doubling the input signal will double the output signal amplitude, regardless of the original input signal level. If at certain levels, however, doubling the input signal amplitude increases the output signal amplitude by more or less than a factor of two, the amplifier would be called nonlinear at those amplitudes. The use of the term "linear" comes from a graph that is often called the transfer characteristic of the device in question. Linear means that the graph is a straight line, while nonlinear means that it either has curves or one more angles in it. A device can have both linear and nonlinear operating regions. Restricting operation to the linear section avoids distortion, however.

Line input- Any input designed to accept a line-level input signal.

Line level- Preamplified signal, in contrast to microphone level. The actual signal levels vary, with nominal microphone level being -50dBM and nominal line level being +4dBM.

Line Matching Transformer- A transformer that matches the impedance of one device to another (i.e. 250W microphone to 50kW input).

Longitudinal Wave- A wave in which the vibrations are in the directino of propagation of the wave; i.e. sound waves in air.

Low-impedance system vs. 70v line- Differences in the way in which the amplifier produces its signal. Constant Voltage (70.7V in the US) is usually associated with public address because of its inferior quality. The alternative is low impedance, which refers to the resistance offered to the circuit by the loudspeaker and in which the impedance of the speakers must match the amplifier-- the "normal" way of hooking speakers to amps.

Low-pass filter- A filter designed to pass low frequencies with little or no attenuation. A high-frequency filter.

M

Magnetic Induction- The generation of an electrical signal in a conductor caused by relative motion between the conductor and external magnetic lines of force. When a conductor (wire) moves within a magnetic field and cuts across the magnetic lines of force, a voltage will be set up or "induced" across this conductor. Also, when a stationary conductor is placed in an oscillating magnetic field, a voltage is induced across the conductor.

Masking- The obscuring of one sound by another.

Matrix- Usually refers to additional outputs on a mixing console; subgroups on the console can be routed at different levels to any of the matrices, creating different mixes, in essence, which can be routed to different speakers. See the Sound Processing: Mixers section.

Meyer Sound SIM System- A computer-based system utilizing several fast-Fourier transform processors developed by Meyer Sound Labs. The SIM System takes an input (usually a direct output from the console), and utilizing several microphones located in the environment in question, compares the original signal to the sound the microphones pick up. The data can then be utilized to correct for phase differences, setting delays and equalization, etc., etc.

Microphone- A transducer for converting acoustic energy to electrical energy.

Microphone Level- A signal coming out of the microphone's diaphragm. It has not been preamplified yet, in contrast to line level. Actual level can be anywhere from -60dBM to -20dBM.

Microphonic Noise- An undesirable characteristic of all audio cables in which the cable generates electrical noise and distortion while the cable is moved or compressed. The unwanted signals are amplified along with the microphone signal and degrade the sound. Microphonics is the result of the capacitance changes between the conductors and between the conductors and the shield.

MIDI- Acronym for "Musical Instrument Digital Interface." A digital communications standard established in 1984 by musical instrument manufacturers Yamaha, Roland, and a few others. Enables communication (i.e. note on, note off, velocity, etc.) between musical instruments. MIDI has expanded to include communication with lighting boards, computers, sequencers, consoles, effects processors, and the like. 

MIDI Show Control- A standard developed upon the MIDI standard that integrates stage machinery, lighting, and other effects into the MIDI standard. 

Midrange Driver- A specific speaker used to generate middle-range frequencies, as opposed to a woofer or a tweeter.

Mixer- A console. Generally used to denote a small console.

Monitor- "Monitor" is another name for speaker. When used alone in stage situations, "monitor" usually refers only to foldback monitors; e.g. "I need more in my monitors." When used in a theatrical situation, usually refers to dressing-room program monitors.

Moving Coil Loudspeaker- The loudspeaker which produces sound vibrations by the interaction of a coil within a magnet, the coil being connected to the speaker cone.

Multipair Cable- Cable with a single insulation that contains many balanced lines. Basically, many microphone cables rolled into a single jacket that's lighter and easier to handle.

Mute- Usually, a switch on a console that silences the input/output in question. Some consoles with varying degrees of automation can mute many channels / outputs at once, with one single touch of a button.

N

Node- A point or line where minimal motion takes place.

Noise- Any unwanted sound. Also, an annoying stage manager.

Noise gate- An amplifier that has a zero output until the input level exceeds a chosen threshold level. Translation: it takes a signal, and if the signal isn't loud enough, it won't let it out. If the signal is loud enough (over the threshold value), the noise gate will let the signal through.

Non-linear- See "Linear."

Notch- A filter that operates a correction at a very specific frequency leaving those around it largely unaffected.

O

Octave- The interval between any two frequencies f 1 and f 2, when f 2 = 2f 1.

Omnidirectional Microphone- A microphone that is equally sensitive in all directions.

Op-amp- See "Operational Amplifier."

Operational Amplifier- A high-gain amplifier with a large amount of negative feedback and high input impedance.

ORTF System- A pair of cardioid microphones spaced 17 cm apart with their axes of maximum response at an angle of 110 degrees.

Overload- A state of being in sound land where input levels are too large for whatever they are being sent to, which results in amplifier clipping and distortion, preamp distortion, and generally dirty sound. On a mixer, this state is generally marked by a small red LED located on each channel (the "peak" LED).

Overtone- A mode of vibration (or, a component of a sound) with a frequency greater than the fundamental frequency.

P

P-popping- A microphone noise produced when the diaphragm is struck by a puff of air that is forced out of a speaker's or singer's mouth during pronunciation of plosive sounds (p, b, t).

Pad- see "Attenuator."

Paging- process of issuing instructions to dressing rooms etc. via loudspeakers.

Pan-pot- A potentiometer used to vary the balance of a sound source routed to two tracks, either to create the illusion that the source is actually moving between two locations, or to place the source at some fixed location between the two sound sources. On a mixer, the knob that places the sound location between left / right; or group 1 / 2; etc.

Paragraphic Equalizer- An parametric equalizer with slide-fader control of boost/cut at each frequency. A mix of a graphic and parametric equalizer.

Parametric Equalizer- An equalizer with separate controls for center frequency, bandwidth ("Q"), and boost/cut. Offers greater control of frequency boost / cut than a graphic equalizer. Compare with "Graphic Equalizer."

Patch- To interconnect (i.e. "I'm going to patch the system now"); a set of interconnections that programs a synthesizer to produce a certain sound; originally meant for use with analog synthesizers, but the name has stuck, and "patch" is used to denote the voices in a digital synthesizer. Can also be used to identify programs within an effects processor.

Patch Bay- A panel consisting of many jacks (a jackfield) which are wired to different equipments; usually two rows of jacks interact with each other (in different ways). Makes interfacing different equipments very easy as only short cables to jump are necessary. Patch bay jacks come in several flavors: normalled, which is wired such that the top jack's piece of equipment is automatically (normally) connected to the bottom jack's piece of equipment if there is no cable plugged into either jack. If a cable is plugged into the top jack, the signal flows through cable but not to the corresponding bottom jack. Half-normalled refers to a jack where by the signal is not disconnected when a patch cable is plugged in; other patch bays simply take the outputs and inputs from equipment and wait for you to make a mess of patch cables by interfacing them with each other.

Patch Panel- A panel with many connectors on it that usually terminates in some sort of multipin connector; also confused easily with "Patch bay."

PCC- See "Phase Coherent Cardioid."

Period- The length of time (measured in seconds) it takes for a wave to complete a complete cycle.

Phantom Powering- A technique for supplying power to a condenser microphone, in which the DC voltage is applied equally to each signal conductor (within a balanced microphone cable) and is returned to the voltage source via the cable shield. Commonly, the voltage is 12VDC to 48VDC.

Phase Coherent Cardioid- A type of Pressure Zone Microphone, that, instead of being omnidirectional, is cardioid or even hypercardioid. Great for theatre. The term "Phase Coherent Cardioid" is a registered trademark of Crown, Inc., Elkhart, IN. 

Phase Shift- In the phase relation between one wave and another, phase shift occurs when one wave has been advanced or retarded through its cycle relative to a similar waveform.

Phaser- A series of all-pass filters that have flat amplitude response but introduce a phase shift. When combined with the original signal, an effect similar to that obtained by a flanger is obtained.

Phone Plug- 1/4" diameter connector commonly found as headphone jacks on consumer stereo equipment; used for line inputs and outputs. Occasionally used for speaker connections due to inexpensive cost. Also T/S plug or T/R/S.

Phono Plug- "Pin Plug" developed by RCA (also called "RCA Plug") commonly found as line outputs on consumer stereo equipment. Not used much in pro audio except for tape outputs or inputs.

 

Pink Noise- Electronically generated noise that has equal energy per octave. Essentially has the same amount of energy per frequency in relation to what the human ear can hear. The amount of energy drops 3dB per octave. Compare with "White Noise."

Polar Pattern- The graphic representation of the sensitivity of a microphone over all incident angles at a rated frequency.

Pop Filter- A wind screen that fits over the exterior of the diaphragm/microphone casing to reduce the pressure levels of plosive vocal sounds which cause a popping effect.

Power Output- The rated power an amplifier can reproduce, in watts, in relation to load resistance and frequency.

Pre/Post- Method by which auxiliary effects can be independent or dependent on the main channel fader. If the send is "pre-fader," the main channel fader will not affect the aux send. If it is "post-fader," the main channel fader will affect the aux send.

Pressure Zone Microphone- Microphones which carry with them small reflective surfaces which improve response.

PFL (Pre-Fader Listen)- Facility to listen to the channel without the audience doing so, useful to check mics and cue tapes. A cue-ing mechanism on a console. See Sound Processing, with the section on consoles.

Proximity Effect- An inherent characteristic of certain directional microphones, resulting in a boost at the low-frequency response when a microphone is in close proximity to a source.

Psychoacoustics- The study of the complex reactions of the listener to the surrounding sound field.

PZM- See "Pressure Zone Microphone."

Q

Q- A parameter that denotes the sharpness of a resonance. Also: as "Directivity Factor": Comparison of the sound power radiated directly ahead of a sound source to that radiated in all directions.

R

Radial Horn- A horn with straight vertical sides whose top and bottom surfaces flare outward at whatever rate is required to achieve the desired mouth area. Compare with "Bi-Radial Horn."

Rectifier- A diode that is used to change AC into pulsating DC.

Reflection- The return of a waveform from an obstruction in its path.

Refraction- The bending of a waveform as it passes from one medium to another, or as it experiences a change (i.e. temperature) within the medium.

Resonance- Certain systems, whether they are the sounding board of a grand piano or the air cavities within a microphone or in an electrical circuit, have a natural frequency at which they vibrate. When the movement of air or vibrations borne by the structure hit this frequency the system mass operates in "sympathy" and the system is said to be in resonance. Resonances reinforce certain frequencies because they are in sympathetic vibration with them.

Response, flat- The way in which a microphone de-emphasizes or accentuates particular frequencies. A flat response is an even response and usually the most desirable, although some high frequency lift for vocals and strings is also popular.

Reverberation- The way in which a sound bounces around an auditorium after its original source has been cut off. The amount depends on auditorium shape, strength of signal, and how much absorption is present.

Reverberation Time- The time required for the stored or reverberant sound to decrease by 60 dB.

RMS- The output of the amplifier taken as an average-- root mean square.

Rumble- Low-frequency vibration.

S

SCR- See "Silicon Controlled Rectifier."

Scene- In sound, usually refers to some sort of console automation system; a scene would be a certain set of inputs and outputs at specific levels; advanced automated consoles (Neve, Cadac, Soundcraft, TAC, etc.) will recall many scenes which enables the operator to do very little.

Shield- In an audio cable, a conductive cylinder around one or more center conductors that protects against unwanted electrostatic fields that could induce a signal, heard as a hum or buzz, across the conductors of the cable.

Shock Mounting- Any mounting or suspension system that mechanically isolates equipment from unwanted vibration.

Show relay- An in-house sound system whereby the show dialogue, picked up from a microphone located in the wings or the audience is relayed, typically to dressing rooms or tech booths.

Sibilance- Emphasis of s, sh, or ch sounds.

Signal-to-Noise Ratio- The ratio, usually expressed in decibels, of the average signal (recorded or processed) to the background noise (caused by the electronic circuits).

Silicon Controlled Rectifier- A type of dimmer used in lighting systems that cuts or clips that AC waveform. Causes intense interference if sensitive audio cables are run near them; however, newer models have better filters.

Simple Harmonic Oscillator- Smooth, regular vibrational motion at a single frequency; represented easily by a mass-spring system.

SIM System- A registered trademark. See "Meyer Sound SIM System."

Snake- A moveable patch panel with cable. Usually, a box with many XLR connectors on it that terminates in a multipair cable of undetermined length, which then terminates into a fan-out of corresponding connectors. Basically, many microphone cables rolled into one.

Sound Pressure Levels- The measurement of what sound we hear expressed in decibels in comparison to a zero level.

Speakon- A connector designed by the Swiss company Neutrik specifically for use with speaker-levels. Available in two versions: four pole and eight pole. The chassis (amplifier or speaker) is always a male version; the cable ends are always female.

Speed- The speed relates to the air temperature which should always be quoted. The speed of sound is 331.45 m/sec. (1087.42 ft/sec) at 0 degrees Celsius.

Stage Box- On a snake, the box part with all the connectors.

Stereo Pair- A coincident pair of microphones with their axes of maximum response at an angle of 90 degrees.

Subwoofer- A specific type of speaker dedicated to reproducing very very low frequency sounds. Usually a big cabinet located on the floor [placing the cabinet on the floor mechanically couples the low-frequency vibrations to the floor, enhancing the effectiveness.]

T

Talkback- On a mixer, the input (usually located on the fascia) that enables the sound engineer to yell at people through the loudspeaker system. Some mixers have comprehensive talkback systems whereby the engineer can address any of the aux sends or any of the groups individually and yell at individual groups of people through individual loudspeaker systems.

Threshold of feeling- The minimum SPL of a pure tone which creates the physical sensation of feeling in the ear. About 120dB SPL.

Threshold of hearing- The minimum sound pressure level of a pure tone that can be perceived by a person with good hearing. A sound pressure of 20x10-6 pascals is defined as 0dB SPL.

Threshold of pain- The minimum sound pressure level of a pure tone which causes a sensation of pain in the ear. About 140dB SPL.

Timbre- An attribute of auditory sensation by which two sounds with the same loudness and pitch can be judged dissimilar.

Transducer- Any device which converts an input signal into an output signal of a different energy form (i.e. acoustic to electric). A microphone, loudspeaker, etc.

Transistor- A solid-state ampliying device consisting of a crystal of germanium or silicon with carefully selected impurities. See Electronics text.

Tweeter- A high-frequency speaker.

U

Unbalanced- see "Balanced."

Unidirectional Polar Pattern- see "Cardioid."

V

Voltage- A measure of the electrical force or "pressure" that causes a current to flow. Measuring in Volts, V.

VCA- Voltage Controlled Amplifier. Used in a mixer: instead of the signal being directly manipulated by the fader (and being subject to inconsistencies in the fader itself), the fader controls a voltage that corresponds to a certain sound level. Makes for cleaner sound since the fader quality doesn't have to be as clean. It's like a light board-- the fader tells the dimmers what to do. Same principle. VCAs can often be assigned to different faders at different times; see console instruction manual for more information.

W

Wavelength- The distance between corresponding parts of a waveform.

Wedge- A specially-constructed speaker used for foldback; shaped like a wedge and placed on the stage floor.

White Noise- A full audio spectrum signal with the same energy level at all frequencies. Compare with "Pink Noise."

Windscreen- See "Pop Filter."

Woofer- The low frequency speaker.

Working Distance- The distance between the sound source and the microphone.

X

XLR Connector- A connector designed by ITT-Cannon. Specifications include 3-7 pins, usually hard metal shell, male pins are protected, connectors are lockable, ground (pin 1) makes first contact. "XLR" is an ITT-Cannon part number; look for "XLR-type," "QG," or simply "three-pin" connectors.

X-Y Pair- A coincident pair of cardioid microphones with their axes of maximum response at an angle of 135 degrees.

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