LOUDNESS CONTROL
   A volume control with special circuitry added to compensate for the normal decreased hearing ability of the human ear at the extreme ends of the audio range when listening to lower sound levels. A typical loudness control boosts the bass frequencies and to a lesser extent the high frequencies. Sometimes this control is called contour.

LOUDSPEAKER EFFICIENCY
   The ratio, expressed in percentage, of signal output to signal input used to state the power needed to drive a loudspeaker. An example: Power output 2 watts; Power input 10 watts; Ratio 2/10=20% efficiency. Efficiency can vary from 2% to as high as 25%.

LOW PASS
   All of the frequencies below a given crossover frequency.

LOW Z OR LOW IMPEDANCE
   Any resistance to AC voltage or current flow generally less than 2000 Ohms.

MASTER
   Main level or gain control for a bus or mix.

MICROPHONE
   A microphone is a transducer that changes acoustical energy (sound) into electrical energy.

MIXER
   A device in sound reinforcement that has two or more signal inputs and a common signal output, which is used to combine separate audio signals linearly in desired proportions to produce an output audio signal.

MODE
   Another word for room resonance. When sound energy is restricted by boundaries, such as walls, floor, and ceiling, waves are developed at certain frequencies, or wavelengths that are integers of the distance between the room boundaries. Room modes, or resonances, cause standing waves because once the wave is generated it stands there, i.e., the positive pressure peaks (anti-nodes) and negative pressure troughs (nodes) stay stationary within the boundaries.

MONITOR
   A loudspeaker or system of loudspeakers that permits the performer to evaluate or monitor his sound alone, or in conjunction with other sounds that may be desired, and is mixed to the listeners preference by means of a separate monitor or reference mix.

MONO
   Monophonic Sound - Sound produced by a system in which one or more microphones feed a single signal processing amplifier whose output is coupled to one or more loudspeakers.

MULTIMETER
   Also called a Volt-Ohm-Meter (VOM). A measuring instrument that can measure different ranges of voltage, current, and resistance. A multimeter can have an analog needle indicator or a digital read out. Every sound person should own one of these and be familiar with the different measurements that can be made with it.

MUSIC POWER
   This is a power rating generally applied to high fidelity amplifiers for tones of short duration. It takes into account the fact that most amplifiers can produce a greater amount of power in short bursts than they can continuously. The rationale is that music is made up of such bursts rather than sustained single frequencies. It is higher than continuous power ratings for the same amplifiers. It is measured at a signal frequency of 1000 Hz for a specified distortion.

NOISE
   Any extraneous sound or signal that intrudes into the original as a result of environmental noise, distortion, hum, or defective parts in the equipment.

NOTCH FILTER
   A band rejection filter that produces a sharp notch in the frequency response of a system, thus reducing the gain or amplitude of a narrow band of frequencies centered on a given frequency.

OCTAVE
   The interval between any two frequencies having a ratio of 2 to 1. Example: "A 440" is an octave above "A 220".

OHM
   The unit of electrical resistance, equal to the resistance through which a current of one ampere will flow when there is a potential difference of one volt across it. Ohm is the unit of measure used to express opposition to current flow. Every wire or part through which electricity passes has some resistance to that passage.

OMNIDIRECTIONAL
   Applied to microphones to refer to uniform pickup of sound from all directions.

OSCILLOSCOPE
   A test instrument that shows a picture of electrical waveforms by means of a cathode ray tube. An oscilloscope is calibrated so one can measure the instantaneous values and waveforms of electrical signals that are changing rapidly or varying as a function of voltage or time. Also known as a Scope.

OUTPUT IMPEDANCE
   The internal output impedance of an amplifier presented by the amplifier to the load. (Output impedance is many times used incorrectly instead of load impedance.)

OVERTONE HARMONIC 
     Multiples of frequency of a fundamental waveform.

PAD
   A fixed passive network which reduces the electrical level of a signal. An attenuator.

PARALLEL
   An electric circuit in which the elements or components are connected between two points with one of the two ends of each component connected to each point.

PARAMETRIC
    A type of equalization circuit that has three variable parameters: frequency, cut or boost bandwidth, and Q.

PASSIVE
   An electronic circuit composed of passive elements, such as resistors, inductors, or capacitors, without any active elements, such as vacuum tubes or transistors generally resulting in a signal loss.

PEAK
   The maximum instantaneous value of a signal amplitude.

PEAKING
   A term used to indicate an increase in gain of a frequency or band of frequencies when equalizing an audio signal.

PEAK POWER
   Peak power is used by manufacturers in an attempt to "look better" in print and has no bearing on the actual performance of a product. Usually peak power works out to be twice continuous power. Some of these same manufacturers have come up with yet another power term referred to as "Instantaneous Peak Power," which is a further inflated and equally meaningless specification. Amplifier power should be judged on an equal basis when comparing one amplifier with another. Disregard "ad copy" such as that just described.

PEAK-TO-PEAK
   Amplitude of an alternating voltage measured from negative peak to positive peak.

PFL
   Pre Fade Listen. A button that permits a channel or sub to be monitored before that channel or sub's level control or fader.

PHASE
   Phase is the time interval between two related events. Two signals are in phase when they reproduce the same sound or signal simultaneously; they are out of phase to the extent that one leads or lags behind the other in time. A signal is said to be in phase with another when the voltage and current amplitudes begin at the same time and move in the same direction.

PHASE CANCELLATION
   Signals that are out of phase will cancel one another according to the difference in phase in degree. A transducer (speaker or microphone) wired out of phase with another will result in reduced output from both; instead of their combined outputs adding, they will subtract due to phase cancellation.

PIEZO-ELECTRIC
   Having the ability to generate a voltage when mechanical force is applied; or to produce a mechanical force when a voltage is applied, as in a Piezo-electric crystal.

POINT SOURCE
   A source of acoustic sound waves having definite position but no extension into space. A point source is an ideal, an imaginary single point in space. This imaginary point source provides a good approximation for distances from the point source that are much larger compared to the actual dimensions of the source. A cluster or array of horns and loudspeakers is positioned using this imaginary point in space as a reference for the actual source of the sound. Properly configured the array will perform as a single or point source of sound.

POLARITY
   The quality of having opposite poles.In electro-magnetic-mechanical systems, some form of potential is

referenced to one of two poles with different (usually opposite) characteristics, such as one which has opposite charges or electrical potentials, or opposite magnetic poles.

POST
   (after) on a mixer; post indicates that the function is derived after the channel slider or gain control.

POWER
   Electrical energy, measured in watts, such as the current from an amplifier used to drive a loudspeaker. Power in Watts W = V2/R

POWER AMPLIFIER
   The final active stage of the audio chain, designed to deliver maximum power to the load or speaker impedance for a given percent of distortion.

PRE
   (before) On a mixer, pre fade listen (PFL) indicates that the function is derived before the channel slider or gain control pre monitor send, the monitor send is before and independent of the channel slider or gain control. A pre monitor send is usually pre channel EQ also.

PREAMP (preamplifier)
   An amplifier whose primary function is boosting or amplifying the output of a low level audio-frequency source, (such as a microphone), so that the signal may be further processed without appreciable degradation of the signal-to-noise ratio of the system. An amplifier which increases electrical signals from a microphone or other instrument to a level usable by a power amplifier. Preamp levels are approximately 1 volt.

PREAMP OUT
   A means of obtaining an output signal from the preamplifier of a channel of a mixer or musical instrument amplifier. The preamp out is actually a line level signal or 1 volt.

PROXIMITY EFFECT
   Increase in low-frequency response when a unidirectional or proximity effect microphone is used close to a sound source.

REACTANCE
   A resistive like property that offers opposition to electron flow in an alternating current (AC) circuit. There are two types of reactance; capacitive reactance (XC) and inductive reactance (XL). Reactance varies with frequency.

REAL TIME ANALYZER (RTA)
   An electronic instrument used to measure the combined response of an audio system and the room in which the system is operating.

REFLECTION
   The bouncing back or return of sound waves from walls or other obstacles which they strike.

REFRACTION
   A change in direction or bending of the propagation of a sound wave when it passes from one medium to another in which the velocity of sound is different.

REGENERATION
   In audio, regeneration is another word for feedback; when something regenerates it continues or sustains itself as an oscillation. When an electronics engineer designs an oscillator, he takes the output of a gain stage and feeds it back into the input through a tank circuit (an RC, resistor and capacitor or an LC, inductor and capacitor combination); when the circuit is turned on, it begins to regenerate or oscillate at a specific frequency determined by the value of the RC or LC combination. When the output of a loudspeaker in a sound reinforcement system is able to get back into a microphone or sound system input, at some level and resonant frequency, the system is going to go into regeneration or feedback oscillation (squeal).

RESISTANCE
   Opposition to the flow of electrical current. Measured in ohms.

RESISTOR
   An electronic component designed to have a definite amount of resistance; used in circuits to limit current flow or to provide a voltage drop.

RESONANCE
   A tendency of mechanical parts, loudspeaker cone, enclosure panels or electrical circuits to vibrate at or emphasize one particular frequency, every time that frequency, or one near it, occurs.

RESPONSE
   The range of frequencies to which an amplifier or speaker will respond, and the relative amplitude or intensity with which these frequencies are reproduced.

RETURN
   An input used to patch a signal returning to a particular BUS after having been further processed, such as an echo or effects return.

REVERB (Reverberation, acoustical)
   The prolongation of sound at a given point after direct sound from the source has ceased, due to such causes as reflection from physical boundaries. (Electro-mechanical) An electro-mechanical device usually employing springs which randomly reflect as great an amount of sound as possible, therefore simulating natural reverberation. (Digital Reverb) An electronic reverberation effects processor that uses digital electronics to introduce the multiple delay paths.

REVERBERATION
   The sustaining of acoustical energy in a room after the reception of the direct field (the sound coming directly from the source) ceases in producing sound. Reverberation is caused by the reflections and scattering of sound energy from the boundary surfaces of the room.

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