RIAA
   Stands for Recording Institute Association of America. A type of preamplifier used for turntables. It is necessary to use an RIAA preamp when using a magnetic cartridge.

RING MODE
   A tone or frequency sounded in a room with a live sound reinforcement system prior to the system breaking into feedback. A ring mode lies just below the threshold of feedback.
RMS (root means square value)
The square root of the time average of the square of a quantity; for a periodic quantity the average is taken over one complete cycle. RMS voltage is .707 times the peak voltage of a sine wave.

ROLL OFF
   A signal is rolled off when it is attenuated or reduced in level above (high pass roll off) or below (low pass roll off) a certain frequency. The amount of roll off is rated at so many decibels per octave. A signal that is rolled off below 100 Hz at a rate of 18 dB/octave would be reduced in level or attenuated -18 dB at 50 Hz, -36 dB at 25 Hz, etc.

RT60 (Reverberation Time)
   The time required for sound to drop to - 60 dB in level once the source of sound has been stopped; the -60 dB is below that of the measured level in the steady state or while the sound system was on and after any initial transients or fluctuations settled.

SEND
   An output used to patch a signal from a channel or Bus of a mixer to an external signal processor such as an echo or digital delay.

SENSITIVITY
   The minimum input signal required to produce a specified level of output. In an amplifier, the input sensitivity is the amount of voltage at the input necessary to drive the amplifier to its rated power output. Loudspeaker sensitivity is the power level necessary to produce a stated SPL at a given distance from the loudspeaker, usually rated at 1 watt 1 meter.

SERIES
   An arrangement of circuit components, end-to-end, to form a single path for current.

SERIES-PARALLEL
   A circuit in which some of the components or elements are connected in parallel, and one or more of these parallel combinations are in series with other components of the circuit.

SHELVING
   A type of equalization circuit that has a shelf-like characteristic at the upper or lower ends of the spectrum. A shelving EQ at 15 kHz would in the boost position increase the high frequencies up to 15 kHz where it would shelf.

SHIFT
   A control found on some Peavey model guitars or bass amplifiers that shifts the center frequency of the mid-range control.

SIGNAL-TO-NOISE RATIO (S/N )
   The ratio of the amplitude or level of a desired signal at any point to the amplitude or level of noise at the same point.

SINE WAVE
   A wave whose amplitude varies as the mathematical sine of a linear function of time, also known as the sinusoidal wave.

SINGLE SOURCE
   A single speaker or cluster of speakers arranged into an array that produces sound as if it originated from a single or point source. See Point Source.

SLAPBACK ECHO
   A echo caused from reflections off the rear wall in many auditoriums. Severe slapback echo is very distracting for a musician onstage, as it can cause confusion that makes following that beat in time extremely difficult. A professional high quality stage monitor system can mask some of the slapback echo to a certain extent by providing more direct sound from the monitor speaker in the first 25 milliseconds, which the performer perceives through auditory fusion as more direct field, thus increasing the ratio of the level of the direct field to that of the slapback echo.

SLEW LIMITING
    The failure of the amplifier's output to move as fast, voltage-wise, as the input would have it move.

SLEW RATE
   Refers to the ability of an amplifier's output to accurately reflect the input waveforms' rise time transients. An amplifier is said to have a slew rate of so many volts per microsecond. A slew rate of 20 volts per microsecond (20 V/U sec.) means that the amplifier is capable of swinging 20 volts positive or negative in the period of one microsecond.

SNAKE
   A multiconductor shielded input cable employed when necessary to locate a mixer a long distance from the stage and the microphones.

SOUND
   A pressure wave motion propagated in an elastic medium (air) producing an auditory sensation in the ear by the change of pressure at the ear. Sound waves are produced by a vibrating body in contact with air.

SOUND LEVEL METER
   The instrument is used to measure noise and sound pressure levels, SPL, calibrated in decibels.

SOUND FIELDS: DIRECT FIELD
   The sound that emanates directly from a sound source or loudspeaker.

INDIRECT FIELD
   That sound perceived from behind a speaker system, i.e., when no direct field is present.

NEAR DIRECT FIELD
   The sound field that is generated close to the source or loudspeaker. Generally considered, the sound field that is within a distance from the source of less than two wavelengths.

FAR DIRECT FIELD
   The sound field that is perceived at a distance from the source loudspeaker that is greater than 2 wave lengths; as when you hear the out front loudspeaker system from behind the speakers themselves, you are listening to the indirect sound field of the mains.

FREE FIELD
   That portion of the direct field of a sound source or loudspeaker that is reflection free or not yet affected by boundaries, such as walls or ceiling.

REVERBERANT FIELD
   That sound field beyond critical distance where most of the energy arriving at the listener is in the form of reflected energy off the room's boundaries.

SPECTRUM
   Refers to a particular band of frequencies. The normal acoustic sound spectrum is the range of human auditory perception (20 Hz to 20,000 Hz). There is also a Subsonic spectrum (considered to be below about 40 Hz) and an Ultrasonic audio spectrum (above 20,000 Hz).

SPECTRUM ANALYZER
   See Real Time Analyzer (RTA).
SPL (sound pressure level)
The level or intensity at a point in a sound field (loudness). The deviation above and below normal atmospheric pressure. The unit of measurement of Sound Pressure... the microbar. One microbar is equal to the sound pressure of 1 dyne per square centimeter, which is a sound level of 74 dB above the threshold of hearing (0.0002 microbar.) It is also equal to approximately one-millionth of normal atmospheric pressure. Sound pressure levels are stated in decibels as follows: Where P is the RMS sound pressure in microbars, and the reference is the threshold of hearing of 0.0002 microbars (50% of young men, 1 to 4 kHz).

SPLITTER
   A box into which one microphone or signal is connected and has two or more individual outputs available for that signal. Used when a separate monitor mix is required.

STANDING WAVE
   Standing waves occur in rooms because of the boundaries. A standing wave is a soundwave that once excited it stands there, i.e., the positive air pressure peaks (antinodes) and negative air pressure troughs (nodes) remain in the same position within the room's boundaries. Also known as a stationary wave. See Modes.

STEREO
   In a sound reproducing system, stereo refers to the use of two separate signal processing channels driving two separate power amplifiers, which in turn power two separate speaker systems. However, most times in sound reinforcement, a stereo mixer is employed to drive a mono (single channel) system in order to have (sub-mixes) separate instrument vs. vocal mixes of the program.

SUB-MASTER
   A separate mixing bus assigned to a group of instruments (drums, brass, strings) or vocals that enable the sound mixer to regulate the level of that group of instruments or vocals with one control called the Sub-Master.

SUB-MIX
   A level control preceding the main (master) level control that regulates the level of an individual sub-mix.

SWITCHING JACK
   An input or output 1/4" phone jack that performs some switching function in addition to providing an input or output for a signal. On Peavey sound equipment and musical instrument amplifiers, the graphic input and the power amp input are both switching jacks. These jacks disconnect the normal flow of signal and allow for additional patching capabilities.

THD (Total Harmonic Distortion)
   When a single frequency of specified level is applied to the input of a system, the ratio (of the voltage of the fundamental frequency to the voltage of all harmonics) observed at the output of the system because of the nonlinearities of the system; THD is expressed in percent.

TIMBRE
    Timbre is a word that relates to the of the fundamental frequency to the level and number of the associated harmonics. The human ear can perceive differences in timbre. For example, two different instruments, such as a saxophone and a flute playing the same note or fundamental at the same loudness is sound different to the listener, due to the two instruments different number and level of related harmonics, which is also produced at the same time as the fundamental. The two instruments are said to have a difference in timbre.

TRANSDUCER (X-DCR)
   Any device or element which converts an input signal into an output signal of a different form. A transducer changes energy from one form to another. A microphone is a transducer that changes acoustical energy (sound) into electrical energy (voltage). A loudspeaker is a transducer that changes electrical energy into mechanical energy, producing sound or acoustical energy.

TRANSFORMER (X-FMR)
   An electrical component consisting of multiturn coils of wire placed in a common magnetic field (medium) which will transfer electrical energy from one electrical circuit to the next. A transformer will only pass alternating currents (AC) and will not pass direct current (DC). By adjusting turn ratios, a step up or down condition of voltage can be achieved.

TRANSFORMER BALANCED (X-FMR BAL)
   An input or output that is coupled by means of a transformer in a configuration that makes it balanced or capable of being operated, so that the voltages of the two conductors at any transverse plane are equal in voltage and opposite in polarity with respect to ground. A transformer balanced input or output will offer common-mode rejection, which means any common-mode interference signal will not pass through the transformer because it will be cancelled out.

TRANSIENT
   Rapidly changing peaks of short duration in the level of musical instruments such as a cymbal crash or a rim shot on a snare drum. A wave having a very short or no sustain time.

TRANSIENT DISTORTION
   Transient distortion interferes with the ability of an amplifier to follow accurately abrupt changes in volume, such as the sudden burst of sound when an instrument is first played. Minimum transient distortion is vital to clean and crisp overall sound.

TRANSIENT RESPONSE
   Ability of an amplifier or loudspeaker to follow accurately abrupt changes, such as the sudden burst of sound generated by an instrument. Good transient response is vital to "clear" or "crisp" overall sound.

TRIAMP
   Separating the audio spectrum into three band, i.e., high frequencies, mid-band frequencies and low frequencies by means of an electronic crossover and using three separate power amplifiers to amplify the three outputs of the crossover (high pass, mid pass, low pass outputs) driving three separate components of a speaker system; This results in increased headroom and dynamic range.

UNBALANCED CABLE OR LINE
   A single conductor cable with a surrounding shield that connects to ground. Such a system is called unbalanced because it cannot be balanced or offer common mode rejection.

UNBALANCED INPUT
   An input in which one of the two terminals is at ground potential or connected to the chassis ground.

VELOCITY
    In audio the velocity or speed of sound is approximately 1130 feet per second. The speed of sound changes slightly with changes in temperature, humidity, and altitude.

VOLTAGE
   Voltage is a measurement of electrical pressure or the potential to do work. Voltage is sometimes called EMF or Electro Motive Force. The familiar 120 lts at the wall socket is an example of available electrical pressure. If the prefix "m" is used (as in mv), it stands for millivolts... thousandths of volts.
Microvolts, abbreviated "µV", are millionths of volts.
VOLTS (voltage)
Potential difference or electromotive force (EMF).

VOLUME
   The intensity or loudness of sound.
SPL VU (volume unit)
A unit for expressing the audio frequency power level of a complex electronic waveform such as that corresponding to speech or music. Zero (0) VU is referenced to 1 milliwatt of power.

VU METER
   A meter than indicates the audio frequency power level or volume units of a complex electronic waveform.

WATT
   A unit of measure of power. The electrical wattage of an amplifier describes the power it can develop to drive a speaker. The greater the voltage capability, the higher the wattage. Amplifier wattage requirements are greatly dependent upon the speakers that will be used, the size of the listening room, and average loudness that will be played through the speakers. W =V2/R

WAVELENGTH
   In audio the wavelength of sound is the actual physical size that one complete cycle of sound energy requires in air for a given frequency. The wavelength is found by dividing the velocity of sound, 1130 ft/sec, by the frequency of interest. A sound wave with a frequency of one thousand Hertz would have a wavelength of 1.13 ft. (1130 divided by 1000).

WOOFER
   A low frequency speaker specialized in bass or low frequency reproduction.

XLR
   A connector (sometimes called a cannon connector) used in interfacing audio components. The connector on a low impedance microphone is an XLR connector.

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