4:2:4 matrix – A Dolby® technology that enables a four-channel L, C, R, S mix to be matrix-encoded to two channels for transmission by film, broadcast, video, or other media. The original four channels are re- created after matrix decoding.

5.1 mix –A six-channel Dolby Digital discrete mix. The “.1” is used for the sixth channel, as the LFE channel has a bandwidth with an upper limit of 125 Hz.

A-B test: A test between two components or rooms. For example, a test between two different pre-amplifiers. For the test to be scientifically valid the levels should be matched.

A-weighting: A frequency-response adjustment of a sound-level meter that makes its reading conform, very roughly, to human response.

Absorb: Sound waves are converted into energy such as heat that is then captured by insulation.

Absorption – The tendency of sound waves to be soaked up by soft surfaces. Opposite: reflection.

Absorption coefficient: The fraction of sound energy that is absorbed at any surface. It has a value between 0 and 1 and varies with the frequency and angle of incidence of the sound.

Absorption: In acoustics, the changing of sound energy to heat.

AC (Alternating Current) – Electrical current that alternates direction (positive to negative). AC is often contrasted with direct current (DC), commonly produced by batteries.

AC3: See Dolby Digital.

Acoustic Feedback – Feedback, the dreaded “sound man’s (and sound woman’s)curse,” is caused by a regeneration of sound leaving a speaker and entering a microphone. This tone – a sustained shriek – is a self-perpetuating cycle which can be stopped by decreasing the volume. Sometimes referred to as a standing wave.

Acoustic impedance: Z=R+jX ; [ML-4T-1] ; mks acoustic ohm *(Pa•s/m3) —of a surface, for a given frequency, the complex quotient obtained when the sound pressure averaged over the surface is divided by the volume velocity through the surface. The real and imaginary components are called, respectively, acoustic resistance and acoustic reactance.

Acoustic material: Any material considered in terms of its acoustical properties. Commonly and especially, a material designed to absorb sound.

Acoustic Power Output – The output, as measured in watts, of anything that generates sound.

Acoustic Suspension – A type of speaker cabinet which is sealed to control the action of its woofer and prevent the leakage of air.

Acoustics – The science or scientific study of sound. 2. The properties of a room or environment that affect the qualities of sound.

Acoustics: The science of sound. It can also refer to the effect a given environment has on sound.

AES: Audio Engineering Society.

Airborne sound: Sound that arrives at the point of interest, such as one side of a partition, by propagation through air.

Airflow resistance, R: [ML-4T-1]; mks acoustic ohm *(Pa•s/m3) —the quotient of the air pressure difference across a specimen divided by the volume velocity of airflow through the specimen. The pressure difference and the volume velocity may be either steady or alternating.

Airflow resistivity: *[ML-3T-1]; mks rayl/m *(Pa•s/m3) —of a homogeneous material, the quotient of its specific airflow resistance divided by its thickness.

Alcons: The measured percentage of Articulation Loss of Consonants by a listener. % Alcons of 0 indicates perfect clarity and intelligibility with no loss of consonant understanding, while 10% and beyond is growing toward bad intelligibility, and 15% typically is the maximum loss acceptable.

Ambience: The acoustic characteristics of a space with regard to reverberation. A room with a lot of reverb is said to be “live”; one without much reverb is said to be “dead”.

Ambient Noise Level – “Background” noise – from any source – that affects the listener’s ability to hear what is produced by a sound system. Machinery, hum from florescent lights, traffic, et.

Ambient noise: The composite of airborne sound from many sources near and far associated with a given environment. No particular sound is singled out for interest.

Amperes, Amperage (Amps) – Units of electrical current.

Amplifier (Amp) – An electronic device that increases the amplitude of a signal. 2. A combination speaker/ampflier designed for use with an instrument, as with a guitar amp or keyboard amp.

Amplitude – The strength of sound waves or an electrical signal, as measured against a mean. 2. That which determines loudness.

Amplitude: The instantaneous magnitude of an oscillating quantity such as sound pressure. The peak amplitude is the maximum value.

Analog: An electrical signal whose frequency and level vary continuously in direct relationship to the original electrical or acoustical signal.

Anechoic – The complete absence of reflected sound (echo). 2. An environment that prevents (through dissipation and absorption of sound waves) all reflected sound, as in an anechoic chamber.

Anechoic chamber: A room designed to suppress internal sound reflections. Used for acoustical measurements.

Anechoic: Without echo.

Arithmetic mean sound pressure level: Of several related sound pressure levels measured at different positions or sound pressure levels measured at different positions or different times, or both, in a specified frequency band, the sum of the sound pressure levels divided by the number of levels.

Articulation: A quantitative measure of the intelligibility of speech; the percentage of speech items correctly perceived and recorded.

Artificial reverberation: Reverberation generated by electrical or acoustical means to simulate that of concert halls, etc., added to a signal to make it sound more lifelike.

ASA: Acoustical Society of America.

Attack: The beginning of a sound; the initial transient of a musical note.

Attenuate – To make weaker. An attenuator uses resistance to reduce output voltage, as with a volume control.

Attenuate: To reduce the level of an electrical or acoustical signal. Reduction in sound level.

Audible frequency range: The range of sound frequencies normally heard by the human ear. The audible range spans from 20Hz to 20,000Hz

Audiophile: A person who is interested in sound reproduction.

Auditory area: The sensory area lying between the threshold of hearing and the threshold of feeling or pain.

Aural: Having to do with the auditory mechanism.

Average room absorption coefficient: Total room absorption in sabins or metric sabins, divided by total room surface area in consistent units of square feet or square meters.

Average sound pressure level: Of several related sound pressure levels measured at different positions or different times, or both, in a specified frequency band, ten times the common logarithm of the arithmetic mean of the squared pressure ratios from which the individual level were derived.

Axial mode: The room resonances associated with each pair of parallel walls.

Background noise: Noise from all sources unrelated to a particular sound that is the object of interest. Background noise may include airborne, structureborne, and instrument noise.

Baffle: A moveable barrier used to achieve separation of signals from different sources. The surface or board upon which a loudspeaker is mounted.

Balanced Line – A pair of ungrounded conductors whose voltages are opposite in polarity but equal in magnitude. Balanced lines reduce interference from external sources like radio frequencies and light dimmers since they are typically shielded by a third conductor surrounding them.

Bandpass filter: A filter that attenuates signals both below and above the desired passband.

Bandwidth: The total frequency range of any system. Usually specified as something like: 20-20,000Hz plus or minus 3 dB.

Basket – The frame to which a driver’s cone is mounted.

Bass - The lower end of the frequency range, from about 20 Hz to about 300 Hz.

Bass Reflex – A speaker that, as a means of enhancing the efficiency of the reproduction of bass frequencies, channels some of the sound pressure generated by its woofer(s) through an opening (port) in its cabinet.

Bass: The lower range of audible frequencies.

Beaming: The phenomenon of sound being emitted within a comparatively small solid angle. This characteristic becomes more acute as the frequency increases.

Beats: Periodic fluctuations that are heard when sounds of slightly different frequencies are superimposed.

Biamplification – The use of separate amplifiers to power woofers and tweeters.

Binaural: A situation involving listening with two ears.

Block: Building a continuous barrier that traps or stops air movement from one side of a partition to the other, greatly reducing airborne sound transmission.

Boomy: Listening term, refers to an excessive bass response that has a peak(s) in it.

Break: A physical break in the assembly or construction which acts to decouple sound vibrations from traveling through the structure.

Bright: Listening term. Usually refers to too much upper frequency energy.

Broad band noise: Spectrum consisting of a large number of frequency components, none of which is individually dominant.

Byte: A term used in digital systems. One byte is equal to 8 bits of data. A bit is the elemental “high” or “low” state of a binary system.

Cardioid – “Heart” shaped pattern exhibited by some microphones which reduces pick-up from the sides and back.

Cavity: A space between wall studs or attic joists where insulation is typically installed.

Channel balance: In a stereo system, the level balances between left and right channels. Properly balanced, the image should be centered between the left-right speakers. In a home-theater system, refers to achieving correct balance between all the channels of the system.

Characteristic impedance of the medium: [ML-2T-1]; mks rayl *(Pa•s/m) – the specific normal acoustic impedance at a point in a plane wave in a free field. It is a pure specific resistance since the sound pressure and the particle velocity are in phase and it is equal in magnitude to the product of the density of the medium, p, and the speed of sound in the medium, c. Its value when the medium is air at 20 degrees Celsius and 101.25 kPa is 413 mks rayl (Pa-s/m),

Clipping – Audible distortion that occurs when a signal’s level exceeds the limits of a particular circuit. When an amp is “turned up too loud,” and begins to distort, it is said to be clipping. On an oscilloscope clipping appears to flatten the tops and/or bottoms of the wave forms as if someone took a scissors and “clipped or cut” the top and bottom of the wave.

Clipping: Refers to a type of distortion that occurs when an amplifier is driven into an overload condition. Usually the “clipped” waveform contains an excess of high-frequency energy. The sound becomes hard and edgy. Hard clipping is the most frequent cause of “burned out” tweeters. Even a low-powered amplifier or receiver driven into clipping can damage tweeters which would otherwise last virtually forever.

Coherence: Listening term. Refers to how well integrated the sound of the system is.

Coloration: Listening term. A visual analog. A “colored” sound characteristic adds something not in the original sound. The coloration may be euphonically pleasant, but it is not as accurate as the original signal.

Comb filter: A distortion produced by combining an electrical or acoustical signal with a delayed replica of itself. The result is constructive and destructive interference that results in peaks and nulls being introduced into the frequency response. When plotted to a linear frequency scale, the response resembles a comb, hence the name.

Compression Driver – A transducer, designed for use with a horn, which utilizes a diaphragm (rather than a cone) to reproduce mid and high frequencies.

Compression: In audio, compression means to reduce the dynamic range of a signal. Compression may be intentional or one of the effects of a system that is driven to overload. It is also the portion of a sound wave in which molecules are pushed together, forming a region with higher-than-normal atmospheric pressure.

Compressor - A device that reduces – compresses – a signal’s dynamic range.

Condenser Microphone - A mic that depends on an external power supply or battery to electrostatically charge its condenser plates.

Conductor - A substance – in electronics, usually a metal – that allows the free flow of electrons.

Cone - The vibrating diaphragm, employed in some speakers designs, that generates sound waves.

Console - A large or elaborate mixer required to massage the ego of the band’s sound man.

CPS (Cycles Per Second) – The number of plus/minus voltage swings or compressions/rarefactions of air molecules occurring each second in an electrical or audio signal; usually expressed as hertz (Hz).

Critical band: In human hearing, only those frequency components within a narrow band, called the critical band, will mask a given tone. Critical bandwidth varies with frequency but is usually between 1/6 and 1/3 octaves.

Critical Distance - The distance from a sound source at which sound pressure levels emitted by the source equal those being reflected off of other surfaces.

Critical distance: The distance from a sound source at which direct sound and reverberant sound are at the same level.

Critical frequency: The frequency below which standing waves cause significant room modes.

Cross-modulation test -  A test signal recorded on optical film to ensure the correct density match between a sound negative and a print, thus producing a correct reproduction of a studio print master.

Cross-talk: Unwanted breakthrough of one channel into another. Also refers to the distortion that occurs when some signal from a music source that you are not listening to leaks into the circuit of the source that you are listening to.

Crossover (Crossover Network) – Passive - An electronic device that, when inserted after the amplifier, divides the audio spectrum into individual frequency ranges (low, high, and/or medium) before sending them to specialized speakers (see: tweeter, woofer, and mid-range).

Crossover (Crossover Network)- Electronic - An electronic device or circuit that, when inserted between a mixer and amplifier, divides the audio spectrum into individual frequency ranges (low, high, and/or mid) before sending them to specialized amplifier/speaker combinations. An advantage of this type of crossover is that it increases efficiency.

Crossover frequency: In a loudspeaker with multiple radiators, the crossover frequency is the 3dB point of the network dividing the signal energy.

Current - The movement – or flow- of electrons.

Cutoff frequency: Of an anechoic wedge or set of wedges, the lowest frequency above which the normal incidence sound absorption coefficient is at least .990.

Cyan dye track – A new development in optical sound printing that eliminates the need for the problematic silver redeveloping process. To be played correctly, the soundtrack requires a red LED soundhead on the projector.

Cycles per second: The frequency of an electrical signal or sound wave. Measured in Hertz (Hz).

Damp: To cause a loss or dissipation of the oscillatory or vibrational energy of an electrical or mechanical system.

DB (A): A sound-level meter reading with an A-weighting network simulating the human-ear response at a loudness level of 40 phons.

DB (B): A sound-level meter reading with a B-weighting network simulating the human-ear response at a loudness level of 70 phons.

DB (C): A sound-level meter reading with no weighting network in the circuit, i.e., flat. The reference level is 20 uPa.

dB (Decibel) - A relative unit of measure between two sound or audio signal levels. A difference 1 dB is considered to be the smallest that can be detected by the human ear. An increase of 6 dB equals twice the sound pressure. 2. As a measure of sound pressure levels, used to indicate loudness.

DB: See decibel.

DC (Direct Current) - Electrical current that flows in only one direction.

Decade: Ten times any quantity or frequency range. The range of the human ear is about 3 decades.

Decay rate: d, [T-1]; dB/s—for airborne sound, the rate of decrease of vibratory acceleration, velocity, or displacement level after the excitation has stopped.

Decibel: dB—the term used to identify ten times the common logarithm of the ratio of two like quantities proportional to power or energy. (See level, sound transmission loss.) Thus, one decibel corresponds to a power ratio of 100.1.

Delay – The postponement of an audio signal for a specific amount of time, usually measured in milliseconds. 2. A device designed to delay an audio signal.

Diaphragm - The radiating surface of a compression driver; its vibrations emit sound waves. 2. The moving element of a microphone.

Diaphragm (also diaphragmatic): Any surface that vibrates in response to sound or is vibrated to emit sound, such as in microphones and loudspeakers. Also applied to wall and floor surfaces vibrating in response to sound or in transmitting sound.

Diffraction: A change in the direction of propagation of sound energy in the neighborhood of a boundary discontinuity, such as the edge of a reflective or absorptive surface.

Diffuse field: An environment in which the sound pressure level is the same at all locations and the flow of sound energy is equally probable in all directions.

Digital: A numerical representation of an analog signal. Pertaining to the application of digital techniques to common tasks.

Dimmer Noise (hash) - The noise that originates in the switches used to dim lights and can be heard in a sound system.

Dipole: An open-back speaker that radiates sound equally front and rear. The front and rear waves are out of phase and cancellation will occur when the wavelengths are long enough to “wrap around”. The answer is a large, wide baffle or to enclose the driver creating a monopole.

Directivity - The ability of a speaker or horn to direct sound to a given area which can be described by its directivity factor (Q).

Directivity index (DI): The difference between sound pressure level in any given direction in the acoustic far field and the average sound pressure level in that field.

Discrete mix - A term used for the Dolby Digital mix that uses six (often called 5.1) discrete audio channels.

Dispersion - The area throughout which the sound produced by a speaker is distributed.

Distortion - Any discrepancy between the source material and the sonic output of a sound system.

Distortion: Anything that alters the musical signal. There are many forms of distortion, some of which are more audible than others.

Divergence: The spreading of sound waves which, in a free field, causes sound pressure levels in the far field of a source to decrease with increasing distance from the source.

Dolby AC-3 - The multichannel coding technology used on Dolby Digital film soundtracks, DVD, and broadcast applications.

Dolby Digital – A high-quality, six- channel (often called 5.1) audio system using Dolby AC-3 coding technology. With a high degree of transparency and data rates as low as 320 kbps, Dolby Digital is used for applications including 35 mm film soundtracks, DVD, and broadcast.

Dolby Digital Surround EXTM – The technology that adds a third surround channel in the cinema while retaining compatibility with regular Dolby Digital channel systems.

Dolby Digital: Is a five-channel system consisting of left, center, right and left rear, right rear channels. All processing is done in the digital domain . Unlike Dolby Prologic in which the rear effects channels are frequency limited to approx. 100-700Hz, Dolby Digital rear channels are specified to contain the full 20-20Khz frequency content. The AC3 standard also has a separate subwoofer channel for the lowest frequencies.

Dolby noise reduction – The signal processing system that reduces the inherent noise in recording media without affecting the sound. Dolby A-type and, subsequently, Dolby SR were originally used on commercial music recordings and later on film soundtracks. Dolby B-type, C-type, and S-type were designed for the consumer audio cassette.

Dolby Pro Logic® – 4:2:4 matrix technology, when applied to domestic formats such as video, broadcast, and DVD.

Dolby Prologic: Is a four-channel system consisting of left, center, right and rear channel, (the single rear channel is usually played through two speakers).

Dolby SR (Spectral Recording) – The most powerful analog Dolby recording system, currently still used on film soundtracks, offers greater noise reduction and a wider frequency range than Dolby A-type.

Domestic version – The original language soundtrack of a film, often used in comparison tests with a foreign-language version of the same film.

Double head/Sep mag – The practice of running a separate reel of magnetic film containing the soundtrack in sync with the optical film containing the picture. Often used for special screenings before a married (combined) print is produced.

DSP: Digital Signal Processing. DSP can be used to create equalization, compression, etc. of a digital signal.

DTS: Digital Theater System. A multi-channel encoding/decoding system. Used in some movie theaters. Also now included in some home-theater processors. A competitor to Dolby Digital.

Dubbing studio See Mixing studio

Ducking - The use of an electronic device to automatically reduce the volume of music or other background fill when an announcer begins speaking.

DVD (digital versatile disc) - A domestic release medium widely used for feature films. Dolby Digital is the standard audio format used with options for each disc to contain multiple language versions.

DVD: Digital Video Disc or Digital Versatile Disc. A relatively new standard that seeks to combine better-than-laser-disc quality video with better-than-CD quality audio in a disc the size of a CD. Requires special players. Seems to be a viable candidate to replace both Laser Discs and CDs, but the jury is still out.

Dynamic headroom: The ability of an audio device to respond to musical peaks. For example, an amplifier may only be capable of a sustained 100 watts, but may be able to achieve peaks of 200 watts for the fraction of a second required for an intense, quick sound. In this example the dynamic headroom would equal 3 dB.

Dynamic Microphone – A microphone that converts sound into electrical pulses by means of a moving electromagnetic coil.

Dynamic Range - The difference between the softest and loudest extremes within an audio signal.

Dynamic range: The range between the loudest and the softest sounds that are in a piece of music, or that can be reproduced by a piece of audio equipment without distortion (a ratio expressed in decibels). In speech, the range rarely exceeds 40 dB; in music, is greatest in orchestral works, where the range may be as much as 75 dB.

Dynamics Processing - The use of electronic devices to control the levels of audio signals and compress or expand their dynamic range.

Dyne: The force that will accelerate a 1-gram mass at the rate of 1 cm/sec. The old standard reference level for sound pressure was .0002 dyne/sq. cm. The same level today is expressed as 20 micro pascals, or 20 uPa.

Echo: A delayed return of sound that is perceived by the ear as a discrete sound image.

Echograms: A record of the very early reverberatory decay of sound in a room.

EES: Early, early sound. Structure-borne sound may reach the microphone in a room before the air-borne sound because sound travels faster through denser materials.

EFC: Energy-frequency curve.

Effects – Sound effects; that is, the nonmusical elements on a soundtrack other than dialogue.

Effects Loop - Inputs and outputs that allow the sending of an audio signal to and from a signal processor such as a reverb unit, delay, gate or limiter.

Efficiency - The ratio of a device’s energy output to its energy intake.

EFTC: Energy-frequency-time curve.

Electret Microphone - A condenser microphone which, instead of employing an external high voltage power source, relies on permanently polarized plates, a low voltage power supply, and internal preamp.

Ensemble: Musicians must hear each other to function properly; in other words ensemble must prevail. Diffusing elements surrounding the stage area contribute greatly to ensemble.

Equal loudness contour: A contour representing a constant loudness for all audible frequencies. The contour having a sound pressure level of 40 dB at 1,000Hz is arbitrarily defined as the 40-phon contour.

Equalization (EQ) - The electronic manipulation of specific frequencies.

Equalization: The process of adjusting the frequency response of a device or system to achieve a flat or other desired response.

Equalizer (EQ) - A device that permits the precise control of specific frequency ranges. Examples are: Graphic, Parametric, Notch Filter, Cut only.

Equalizer: A device for adjusting the frequency response of a device or system.

ETC: Energy-time curve.

Euphonic: Pleasing. As a descriptive audio term, usually refers to a coloration or inaccuracy that none-the-less may be sonically pleasing.

Expander - An electronic device that increases dynamic range by reducing a signal’s level any time it falls below a specific threshold.

Extension: How extended a range of frequencies the device can reproduce accurately. Bass extension refers to how low a frequency tone will the system reproduce, high-frequency extension refers to how high in frequency will the system play.

Fader The signal output control found on the channel, submaster, and master sections of a mixer.

Far field: That part of the sound field in which sound pressure decreases inversely with distance from the source. This corresponds to a reduction of approximately 6 dB in level for each doubling distance.

Feedback, acoustic: Unwanted interaction between the output and input of an acoustical system, e.g., between the loudspeaker and the microphone of a system.

FerroFluid – An emulsion containing metal particles, used to conduct heat away from a speaker’s voice coil.

FFT: Fast Fourier Transform. An iterative program that computes the Fourier Transform in a shorter time.

Fiber glass insulation: An energy-efficient glass fiber insulation used to ensure the best thermal and noise control performance available.

Fidelity: As applied to sound quality, the faithfulness to the original.

Field sound transmission class, FSTC: Sound transmission class calculated in accordance with Classification E 413 using values of field transmission loss.

Field transmission loss, FTL: Sound transmission loss measured in accordance with Annex A1 of Test Method E 336.

Film platter/Tower – Equipment used in the cinema to join separate reels of film together for continuous play through a projector.

Film Sound Glossary, Courtesy of Dolby Labortories

Filter – A device that removes unwanted frequencies or noise from a signal.

Filter, band pass: A filter that passes all frequencies between a low-frequency cutoff point or a high-frequency cutoff point.

Filter, high pass: A filter that passes all frequencies above a cutoff frequency.

Filter, low pass: A filter that passes all frequencies below a certain cutoff frequency.

Final mastering – The mixing stage at which all the separate elements and premixes are mixed together to produce the printing master recording that is sent to the optical transfer stage.

Flame spread: A measure of the time it takes for flame to spread. Compared to red oak, whose Flame Spread Index (FSI) is 100 in accordance with ASTM E 84. The infill of IAC sound absorptive metal panels has an FSI of 20.

Flanking transmission: Transmission of sound from the source to a receiving location by a path other than that under consideration.

Flat - The state of an audio signal or tone whose frequency is unaltered by equalization. On most mixers and equalizers flat is indicated by the tone controls being at dead center.

Fletcher Munson Curve - A graphic representation of average hearing responses of carbon based units at particular sound pressure levels.

Fletcher-Munson Curve: Our sensitivity to sound depends on its frequency and volume. Human ears are most sensitive to sounds in the midrange. At lower volume levels humans are less sensitive to sounds away from the midrange, bass and treble sounds “seem” reduced in intensity at lower listening levels.

Flutter: A repetitive echo set up by parallel reflecting surfaces.

Foldback – An output, that by splitting an input signal (independently of the mixer controls), allows that signal to be sent a separate device. Foldback makes it possible for a performer to create his/her own monitor mix without affecting the front of house mix.

Foley – Sound effects, such as foot- steps, rustling clothes, and traffic noise, recorded by specialists during the post production sound- dubbing process. (Named after one of the first such specialists.)

Fourier analysis: Application of the Fourier transform to a signal to determine its spectrum.

Free field: An environment in which a sound wave may propagate in all directions without obstructions or reflections. Anechoic rooms can produce such an environment under controlled conditions.

Frequency – The number of sound waves that pass a given point in one second. The determiner of pitch. (Ask Kenneth).

Frequency Response The range of frequencies that are reproducible by a speaker or electronic component.

Frequency response: The changes in the sensitivity of a circuit ,device, or room with frequency.

Frequency: The measure of the rapidity of alterations of a periodic signal, expressed in cycles per second or Hz.

Front of House (FOH) - The components of a PA that are directed toward the audience, as opposed to the back of the house or monitor system.

FTC: Frequency-time curve.

Fuel contributed: A measure of temperature rise in flame as a function of the time compared to red oak whose fuel contribution index (FCI) is 100 in accordance with ASTM E 84. The infill of IAC sound absorptive metal panels has an FSI of 15.

Fundamental: The lowest frequency of a note in a complex wave form or chord.

Fusion zone: All reflections arriving at the observer’s ear within 20 to 40 msec of the direct sound are integrated, or fused together, with a resulting apparent increase in level and a pleasant change of character. This is the Haas effect.

Gain – 1. The amplification characteristic of an electrical or mechanical device. 2. The amount of volume that may be achieved before acoustical feedback occurs.

Gain: To increase in level. The function of a volume control.

Gate - An electronic device that increases dynamic range by cutting off a signal when its level falls below a specific threshold. Used to control leakage of sound source into adjacent mics (ie drums).

Grain: Listening term. A sonic analog of the grain seen in photos. A sort of “grittiness” added to the sound.

Grating, diffraction: An optical grating consists of minute, parallel lines used to break light down into its component colors. The principle is now used to achieve diffraction of acoustical waves.

Grating, reflection phase: An acoustical diffraction grating to produce diffusion of sound.

Haas effect: See fusion zone. Also called the precedence effect. Delayed sounds are integrated by the auditory apparatus if the fall on the ear within 20 to 40 msec of the direct sound. The level of the delayed components contributes to the apparent level of the sound, and it is accompanied by a pleasant change in character.

Hard room: A room in which the surfaces have very low values of sound absorption and are therefore highly reflective.

Harmonics: Also called overtones, these are vibrations at frequencies that are multiples of the fundamentals. Harmonics extend without limit beyond the audible range. They are characterized as even-order and odd-order harmonics. A second-order harmonic is two times the frequency of the fundamental; a third order is three times the fundamental; a fourth order is four times the fundamental; and so forth. Each even-order harmonic second, fourth, sixth, etc.-is one octave or multiples of one octave higher than the fundamental; these even-order overtones are therefore musically related to the fundamental. Odd-order harmonics, on the other hand third, fifth, seventh, and up-create a series of notes that are not related to any octave overtones and therefore may have an unpleasant sound. Audio systems that emphasize odd-order harmonics tend to have a harsh, hard quality.

Headroom: The ability of an amp to go beyond its rated power for short durations in order to reproduce musical peaks without distortion. This capability is often dependent on the power supply used in the design.

Hearing sensitivity: The human ear is less sensitive at low frequencies than in the midrange. Turn your volume knob down and notice how the bass seems to “disappear”. To hear low bass requires an adequate SPL level. To hear 25Hz requires a much higher SPL level than to hear 250Hz.

Helmholtz resonator: A reactive, tuned, sound absorber. A bottle is such a resonator. They can employ a perforated cover or slats over a cavity.

Hertz: the unit of frequency, abbreviated Hz. The same as cycles per second.

Hi 8 - An eight-track DAT master, as used by the Tascam DA-88 and Sony PCM-800 machines. For film mastering, the track layout is often L,C,R,Ls,Rs,SW,Lt,Rt.

High magenta track - A method of printing optical sound that enables correct playback on both white- light readers and red LED readers on projectors. The track is still redeveloped, but uses a different color balance to accommodate both light source wavelengths.

High Pass Filter - A circuit that discriminates between high and low frequencies and allows only the high frequencies to pass.

High-pass filter: See filter, high pass.

Horn - An acoustical transformer which, when coupled to a driver, provides directivity and increases the driver’s loudness.

Hpercardioid - A narrower heart-shaped pick-up pattern than that of cardioid microphones.

Hz (Hertz) - A unit of measure that equals one cycle per second.

Imaging: Listening term. A good stereo system can provide a stereo image that has width, depth and height. The best imaging systems will define a nearly holographic re-creation of the original sound.

Impact insulation class, IIC: A single-number rating derived from measured values of normalized impact sound pressure levels I accordance with Annex A1 of Test Method E 492. It provides an estimate of the impact sound insulating performance of a floor-ceiling assembly.

Impedance - The measure of total resistance to the current flow in an alternating current circuit; expressed in ohms, as a characteristic of electrical devices (particularly speakers and microphones). Most speakers are rated at 8 ohms. Microphones are usually classified as being either high impedance (10,000 ohms or greater) or low impedance (50 to 250 ohms).

Impedance: The opposition to the flow of electric or acoustic energy measured in ohms.

Impulse response: Sound pressure versus time measurement showing how a device or room responds to an impulse.

Impulse: A very short, transient, electric or acoustic signal.

In phase: Two periodic waves reaching peaks and going through zero at the same instant are said to be “in phase.”

Inductance - A circuit’s opposition to a change in current flow.

Initial time-delay gap: The time gap between the arrival of the direct sound and the first sound reflected from the surfaces of the room.

Input Overload Distortion - Distortion caused by too great an input signal being directed to an amplifier or preamplifier. Input overload distortion is not affected by volume control settings and most frequently occurs when mics are positioned too close to the sound source. Input overload distortion is controllable through the use of an attenuator.

Insertion loss, IL: Of a silencer or other sound-reducing element, in a specified frequency band, the decrease in sound power level, measured at the location of the receiver, when a sound insulator or a sound attenuator is inserted in the transmission path between the source and the receiver.

Intensity: Acoustic intensity is sound energy flux per unit area. The average rate of sound energy transmitted through a unit area normal to the direction of sound transmission.

Interference: The combining of two or more signals results in an interaction called interference. This may be constructive or destructive. Another use of the term is to refer to undesired signals.

Inverse Square Law - The law that states that in the absence of reflective surfaces, sound pressure 9or light) falls off at a rate inverse to the square of the distance from its source. In other words, every time you double your distance from the sound source, the sound pressure level is reduced by 6 dB.

Inverse-square law: Under far field/free field conditions, sound intensity varies inversely with the square of the distance from the source. In pure spherical divergence of sound from a point source in free space, the sound pressure level decreases 6 dB for each doubling of the distance.

Isolate: A dampening mechanism made a part of the assembly or system, which reduces structureborne vibrations from passing through the structure.

ITD: Initial time-delay gap.

Jack – A female input or output connector, usually for a mic or an instrument

JAES: Journal of the Audio Engineering Society.

JASA: Journal of the Acoustical Society of America.

Joist: Horizontal wood framing member set from wall to wall to support the boards of a floor or ceiling.

KHz: 1,000Hz.

Law of the first wave front: The first wave front falling on the ear determines the perceived direction of the sound.

LEDE: Live end dead end.

Leq (loudness equivalent) measurement - A method of measuring the perceived loudness of a section of audio material. The Dolby Model 737 Leq meter uses time averaging and frequency weighting to produce an Leq(m) measurement of film sound.

Level reduction, LR: In a specified frequency band, the decrease in sound pressure level, measured at the location of the receiver, when a barrier or other sound-reducing element is placed between the source and the receiver.

Level, L: Ten times the common logarithm of the ratio of a quantity proportional to power or energy to a reference quantity of the same kind. (See sound power level, sound pressure level.) the quantity so obtained is expressed in decibels.

LFE (low-frequency effects) - The channel used for sounds (such as explosions) that are fed into the subwoofer loudspeaker. Often referred to as a “.1” channel, hence Dolby Digital 5.1.

Limiter - A device that electronically controls or “limits” the peak levels of program material.

Line Level - A signal whose voltage is between approximately 0.310 volts and 10 volts across a load of 600 ohms or greater.

Linear: A device or circuit with a linear characteristic means that a signal passing through it is not distorted.

Live end dead end: An acoustical treatment plan for rooms in which one end is highly absorbent and the other end reflective and diffusive.

Load – Any device to which power is delivered

Logarithm: An exponent of 10 in the common logarithms to the base 10. For example, 10 to the exponent 2=100; the log of 100=2.

Loudness: A subjective term for the sensation of the magnitude of sound. The subjective response to a sound level.

Loudspeaker: An electroacoustical transducer that changes electrical energy to acoustical energy.

Low Pass Filter - A circuit that discriminates between high and low frequencies and allows only the low frequencies to pass.

Lt, Rt (Left total, Right total) – A four-channel L, C, R, S mix, matrix-encoded to two channels to be transmitted either by film, broadcast, video, or other media. The original four channels are re- created after matrix decoding.

M&E (music and effects) – An original film soundtrack that has had all dialogue removed before being distributed to foreign language studios for a new language dub to be added.

Married print – A film print that contains both the picture and the sound; that is, the sound negative is “married” with the picture negative onto the same piece of print film.

Masking: The amount (or the process) by which the threshold of audibility for one sound is raised by the presence of another (masking) sound.

Mass law: An approximation that describes the Sound Transmission Loss (TL) of a limp, flexible barrier in terms of mass density and frequency. For each doubling of the weight or frequency of a partition, mass law predicts a 6 dB increase in TL.

Mean free path: For sound waves in an enclosure, it is the average distance traveled between successive reflections.

Metric sabin: [L2]—the unit of measure of sound absorption in the metre-kilogram-second system of units.

Microphone Processor - A device that, when installed between a mic and an amp or preamp, allows the manipulation of the signal originating at the mic.

Microphone: An acoustical-electrical transducer by which sound waves in air may be converted to electrical signals.

Midrange: A speaker, (driver), used to reproduce the middle range of frequencies. A midrange is combined with a woofer for low frequencies and a tweeter for high frequencies to form a complete, full-range system.

Millisecond: One thousandth of a second, abbreviated ms or msec.

Mixer - An electronic device that permits the combining of a number of inputs into one or more outputs. Mixers commonly provide a variety of controls – tone, volume, balance and effects – for each “channel.” See: Board,Console.

Mixing studio – A special theatre equipped for mixing film sound- tracks. These rooms contain the necessary Dolby encoding and decoding equipment and are calibrated and aligned to meet Dolby specifications and standards.

MO (magneto optical) disk - A computer disk used in Dolby Digital mastering equipment to record both the six-track mix and the Lt/Rt mix. The whole soundtrack is mastered onto this one disk, which is then sent to the optical transfer stage for the sound negative to be produced.

Modal resonance: See mode.

Mode: A room resonance. Axial modes are associated with pairs of parallel walls. Tangential modes involve four room surfaces and oblique modes all six surfaces. Their effect is greatest at low frequencies and for small rooms.

Monaural: See monophonic.

Monitor - A speaker or earphone dedicated to making it possible for a performer to hear – or monitor – his/her own performance. Examples are: floor wedges, sidefills, or mini-monitor.

Monitor: Loudspeaker used in the control of a recording studio.

Monophonic: Single-channel sound.

Monopole: Any speaker that encloses the back-wave of the speaker device even though part of this back-wave may be released via a port or duct. The primary radiation at most frequencies will be from the driver front. If the driver is not enclosed it becomes a dipole.

Motor - The magnet structure of a speaker

Muddy: Listening term. A sound that is poorly defined, sloppy or vague. For example, a “muddy” bass is often boomy with all the notes tending to run together.

Muting: To greatly decrease the volume level. Many receivers and pre-amplifiers have a muting control which allows the volume level to be cut way down without changing the master volume control. Great for when the phone rings.

NAB: National Association of Broadcasters.

Near field: Locations close to the sound source between the source and the far field. The near field is typically characterized by large sound pressure level variations with small changes in measurement position from the source.

Noise criteria: Standard spectrum curves by which a given measured noise may be described by a single NC number.

Noise Gate - A device that attenuates a signal when the program level falls below a preset threshold.

Noise isolation class, NIC: A single-number rating calculated in accordance with Classification E 413 using measured values of noise reduction. It provides an estimate of the sound isolation between two enclosed spaces that are acoustically connected by one or more paths.

Noise reduction (NR): The difference in sound pressure level between any two points along the path of sound propagation. As an example, noise reduction is the term used to describe the difference in sound pressure levels between the inside and outside of an enclosure.

Noise reduction coefficient (NRC): The arithmetic average, to the nearest multiple of .05, of the sound absorption coefficients in the 1/3 octave bands centered at 250Hz, 500Hz, 1000Hz, and 2000Hz..

Noise: Interference of an electrical or acoustical nature. Random noise is a desirable signal used in acoustical measurements. Pink noise is random noise whose spectrum falls at 3 dB per octave: it is useful for use with sound analyzers with constant percentage bandwidths. Unwanted, bothersome, or distracting sound.

Normal incidence sound absorption: *; [dimensionless]—of a surface, at a specified frequency, the fraction of the perpendicularly incident sound power absorbed or otherwise not reflected.

Normal mode: A room resonance. See mode.

Normalized noise isolation class, NNIC: A single-number rating calculated in accordance with Classification E 413 using measured values of normalized noise reduction. (See normalized noise reduction.)

Normalized noise reduction, NNR: Between two rooms, in a specified frequency band, the value that the noise reduction in a given field test would have if the reverberation time in the receiving room were .5 s.

Null: A low or minimum point on a graph. A minimum pressure region in a room.

Oblique mode: See mode.

Octave bands: Frequency ranges in which the upper limit of each band is twice the lower limit. Octave bands are identified by their geometric mean frequency, or center frequency.

Octave: An octave is a doubling or halving of frequency. 20Hz-40Hz is often considered the bottom octave. Each octave you add on the bottom requires that your speakers move four times as much air!

Ohm – The basic unit of measurement of resistance.

OHM’S Law - The law that states the relationship between current, resistance and voltage in an electrical circuit: Amperage times resistance equals applied voltage.

Omnidirectional - Capable of picking-up sound or radiating sound equally from all directions; as with an unidirectional microphone or subwoofer.

One-third octave bands: Frequency ranges where each octave is divided into one-third octaves with the upper frequency limit being 2* (1.26) times the lower frequency. Identified by the geometric mean frequency of each band.

Optical sound camera – Equipment used to transfer the printing master from the mixing studio (normally a Dolby MO disk) to an optical sound negative. The sound camera exposes the raw sound negative stock using a combination of light from LEDs, valves, and/or lasers.

Oscilloscope - An electronic device that displays, on a video screen, a representation of an electrical signal.

Overlaps – A short section of sound from the beginning of a reel added to the end of the previous reel. Due to the offset between picture and sound on the print, overlaps ensure there are no gaps in the sound when the reels are joined together.

Overtone: A component of a complex tone having a frequency higher than the fundamental.

PA - Abbreviation of public address system: one or more speakers connected to an amplifier; may include a mixer and any combination of sound reinforcement devices.

Pad - An attenuator.

Particle velocity – A fluctuating velocity superimposed by the presence of sound on the other velocities that the particles of the medium may have. In analogy with alternating voltage its magnitude can be expressed in several ways, such as instantaneous particle velocity or peak particle velocity. In air, the other velocities are those due to thermal agitation and wind currents.

Passive absorber: A sound absorber that dissipates sound energy as heat.

Patch Cord - A short electrical cable used to connect individual components of a sound system

Peak sound pressure level: LPK[nd] —-ten times the common logarithm of the square of the ratio of the largest absolute value of the instantaneous sound pressure in a stated frequency band during a specified time interval to the reference sound pressure of 20 micro pascals.

Personal Monitor - A monitor that is small enough to be directed at a specific performer. Before these devices, monitors were usually arrayed along the front of the stage and shared by the entire ensemble.

PFC: Phase-frequency curve.

Phantom Power - Operating voltage supplied to a condenser mic by a mixer or external power source.

Phase – The relationship of an audio signal or sound wave to a specific time reference.

Phase shift - The phase relationship of two signals at a given time, or the phase change of a signal over an interval of time.

Phase shift: The time or angular difference between two signals.

Phase: Phase is the measure of progression of a periodic wave. Phase identifies the position at any instant which a periodic wave occupies in its cycle. It can also be discribed as the time relationship between two signals.

Phon: The unit of loudness level of a tone.

Piezo Tweeter - A driver which is dedicated to the reproduction of high frequencies and operated by means of a crystal rather than an electromagnet.

Pin 2 Hot - Considered the standard polarity for pro audio.

Pink noise: Noise with a continuous frequency spectrum and with equal power per constant percentage bandwidth. For example, equal power is any one-third octave band.

Pitch Tone - A function of frequency.

Pitch: A subjective term for the perceived frequency of a tone.

Plenum: An absorbent-lined cavity through which conditioned air is routed to reduce noise.

Polarity - A condition which has two states (in or out) and is usually described in one of three ways: 1. Acoustical to electrical (microphone): Positive pressure at diaphragm produces positive voltage at pin 2 of XLR or at the tip of a ¼-inch phone plug. 2. Electrical to acoustic: Positive voltage into the “plus” terminal of a speaker causes the speaker’s diaphragm to move forward (produces positive pressure). 3. Electrical to electrical: Positive voltage into pin 2 of an XLR plug or at the tip of a ¼-inch phone plug produces positive voltage at the output (pin 2 of XLR jack, the tip of a ¼-inch phone plug, or the red (plus) connector of a binding post (banana terminal)).

Polarity: The positive or negative direction of an electrical, acoustical, or magnetic force. Two identical signals in opposite polarity are 180 degrees apart at all frequencies. Polarity is not frequency dependent.

Potentiometer (Pot) - A variable resistor (rotary or linear) used to control volume, tone, or other functions of an electronic device.

Power Amplifier - An electronic device that increases the volume of a signal. A basic unit of all sound systems. Power amps are typically connected to a preamp which provides controls for individual functions: level, tone, etc.

Premix – A mix (usually six or eight tracks) containing only one of the three elements of a soundtrack (dialogue, music, or effects). May be used to produce stems (see Stems) or the final printing master.

Pressure zone: As sound waves strike a solid surface, the particle velocity is zero at the surface and the pressure is high, thus creating a high-pressure layer near the surface.

Printing master – The master tape of the final mix produced in the mix- ing studio and sent to the optical sound camera. For Dolby Digital, this takes the form of an MO disk.

Proximity Effect - An increase in the bass response of some mics as the distance between the mic and its sound source is decreased

Psychoacoustics: The study of the interaction of the auditory system and acoustics.

Pullups – See Overlaps QC (quality control) system A software-based system used in film laboratories to analyze the print quality of Dolby Digital data blocks and provide a summary of all parameters.

Pure tone: A tone with no harmonics. All energy is concentrated at a single frequency.

Q - A ratio obtained by complex mathematical calculations involving the relationship of a speaker’s direct radiated energy to its total radiated energy (directivity index). When measured on-axis, Q (which is dependent on frequency) is used to determine a speaker’s suitability for a particular application.

Radio Frequency Interference (RFI) - Radio signals from external sources that invade and can be heard through, sound systems.

Random noise: A noise signal, commonly used in measurements, which has constantly shifting amplitude, phase, and a uniform spectral distribution of energy.

Rarefaction: The portion of a sound wave in which molecules are spread apart, forming a region with lower-than-normal atmospheric pressure. The opposite of compression.

RASTI: Rapid Speech Transmission Index expressed in a decimal range of 0.2 for “bad” to 1.00 for “Excellent”

Ray: At higher audio frequencies, sound may be considered to travel in straight lines, in a direction normal to the wave front.

RC (Room Criteria) curves: Undesirable rumble can result if NC curves are determined mainly by low frequency noise. Similarly, a hissing effect can result from NC level being controlled by higher frequency sounds. To achieve a better balance between low frequency and high frequency components, RC curves have been established for which the objective is to design spectra that meet an RC curve within + 2 dB at all frequencies. A spectrum that exceeds an RC curve by more than 5 dB at frequencies below 250Hz is likely to result in unacceptable rumble. Above 2000Hz, on the other hand, a spectrum more than 5 dB higher than the RC curve might have too much of a hissing quality.

Reactance: The opposition to the flow of electricity posed by capacitors and inductors.

Reactive absorber: A sound absorber, such as the Helmholtz resonator which involves the effects of mass and compliance as well as resistance.

Receiving room: In architectural acoustical measurements, the room in which the sound transmitted from the source room is measured.

Reflection - A term that describes the amount of sound “bouncing” off of hard surfaces.

Reflection-phase grating: A diffuser of sound energy using the principle of the diffraction grating.

Reflection: For large surfaces compared to the wavelength of impinging sound, sound is reflected much as light is reflected, with the angle of incidence equaling the angle of reflection.

Refraction: The bending of sound waves traveling through layered media with different sound velocities.

Rejection - A microphone’s ability to selectively exclude sounds coming from outside it’s pickup pattern.

Release print – The actual film played in the cinema. A release print consists of reels approximately 20 minutes long which are played consecutively without interruption, either by alternating between two projectors, or by splicing the individual reels together into one large reel mounted on a film platter.

Resistance - Opposition measured in ohms to the flow of electrical current.

Resistance: The quality of electrical or acoustical circuits that results in dissipation of energy through heat.

Resonance: A natural periodicity, or the reinforcement associated with this periodicity.

Resonant frequency: Any system has a resonance at some particular frequency. At that frequency, even a slight amount of energy can cause the system to vibrate. A stretched piano string, when plucked, will vibrate for a while at a certain fundamental frequency. Plucked again, it will again vibrate at that same frequency. This is its natural or resonant frequency. While this is the basis of musical instruments, it is undesirable in music-reproducing instruments like audio equipment.

Response: See frequency response.

Reverberant sound field: The sound in an enclosed or partially enclosed space that has been reflected repeatedly or continuously from the boundaries.

Reverberation - Sound waves that continue to bounce around a space after the sound source has ended.

Reverberation room: A room so designed that the reverberant sound field closely approximates a diffuse sound field, both in the steady state when the sound source is on, and during the decay after the source of sound has stopped.

Reverberation time: The tailing off of a sound in an enclosure because of multiple reflections from the boundaries.

Reverberation: The persistence of sound in an enclosed or partially enclosed space after the source of sound has stopped; by extension, in some contexts, the sound that so persists.

RFZ: Reflection-free zone.

Room - Any enclosed space in which a performance is staged. It can be as small as a closet or as large as the Superdome.

Room mode: The normal modes of vibration of an enclosed space. See mode.

RT60: Reverberation time.

Sabin: The unit of measure of sound absorption in the inch-pound system.

Sabine: The originator of the Sabine reverberation equation.

Screen illumination – For35mm presentations, screen luminance at the center of the screen should be 16 fL +2 fL. Screen luminance at the edges of the screen (5 percent in from each edge) should not be less than 75 percent of the center. The distribution of the screen illumination should be evenly dispersed and symmetrical about the geometric center of the screen, and no portion of the illuminated area should be less than 10 fL. The white point image on the screen should be 5,400 degrees Kelvin, +600 degrees, –200 degrees. (Reference: SMPTE RP 98-1995, ANSI/SMPTE 196M-1995)

Self-extinguishing: A material which will not support combustion when external source of flame is removed.

Self-noise, n: Extraneous non-acoustical signals, generated or induced in a measurement system.

Sensitivity - The sound pressure level directly in front of the speaker (on axis) at a given distance and produced by a given amount of power.

Shelving - The setting of the on-axis output of complementary drivers (woofers, mid-range, tweeters) to provide the desired frequency response.

Shield - A metal enclosure that prevents electronic components from being affected by unwanted interference. Shielded speakers may be placed near a TV, for instance, because their magnets cannot affect the picture tube.

Sibilance - A hissing sound produced when pronouncing S and Z. Sibilance is undesirable in professional sound reinforcement and can be controlled through the use of a “de-esser” like Valley Audio’s 401 Microphone Processor, 815 Dynamic Sibilance Processor, or 730 DynaMap Digital Dynamics Processor.

Signal – An electrical impulse. First popularized by Paul Revere.

Signal-to-noise (SN) ratio: The range or distance between the noise floor (the noise level of the equipment itself) and the music signal.

Signal-To-Noise-Ratio - The ratio, expressed in dB, of an electronic device’s nominal output to its noise floor.

Sine wave: A periodic wave related to simple harmonic motion.

Slap back: A discrete reflection from a nearby surface.

Smoke developed: Measure of smoke density developed by a material when compared with red oak, which has a smoke density index (SDI) of 100 in accordance with ASTM E 84. The infill of IAC sound absorptive metal panels has an SDI of 20.

Snake – A cable – often runing between the stage and control board – that combines multiple lines; used to connect mics, instruments and monitors to a mixer.

Soft room: Room with highly sound absorptive surfaces.

Sone: The unit of measurement for subjective loudness.

Sound absorption coefficient, *: [dimensionless]; metric sabin/m* —of a surface, in a specified frequency band, the measure of the absorptive property of a material as approximated by the method of Test Method C423. Ideally, the fraction of the randomly incident sound power absorbed or otherwise not reflected.

Sound absorption: (1) The process of dissipating sound energy. (2) The property possessed by materials, objects and structures such as rooms of absorbing sound energy. (3) A: [L2]; metric sabin—in a specified frequency band, the measure of the magnitude of the absorptive property of a material, an object, or a structure such as a room.

Sound attenuation: The reduction of the intensity of sound as it travels from the source to a receiving location. Sound absorption is often involved as, for instance, in a lined duct. Spherical spreading and scattering are other attenuation mechanisms.

Sound energy density, D: [ML-1T-2]; J/m—the quotient obtained when the sound energy in a region is divided by the volume of the region. The sound energy density at a point is the limit of that quotient as the volume that contains the point approaches zero.

Sound energy, E: [ML2T-2]; J-energy added to an elastic medium by the presence of sound, consisting of potential energy in the form of deviations from static pressure and of kinetic energy in the form of particle velocity.

Sound insulation: The capacity of a structure to prevent sound from reaching a receiving location. Sound energy is not necessarily absorbed; impedance mismatch, or reflection back toward the source, is often the principal mechanism.

Sound intensity, I: [MT-3]; W/m2 the quotient obtained when the average rate of energy flow in a specified direction and sense is divided by the area, perpendicular to that direction, through or toward which it flows. The intensity at a point is the limit of that quotient as the area that includes the point approaches zero.

Sound isolation: The degree of acoustical separation between two locations, especially adjacent rooms.

Sound Level Meter - A device that measures, in dB, the amplitude of sound waves.

Sound level: Of airborne sound, a sound pressure level obtained using a signal to which a standard frequency-weighting has been applied.

Sound power level, Lp: Of airborne sound, ten times the common logarithm of the ratio of the sound power under consideration of the standard reference power of 1 pW. The quantity so obtained is expressed in decibels.

Sound power, W: [ML2T-3]; W—in a specified frequency band, the rate at which acoustic energy is radiated from a source. In general, the rate of flow of sound energy, whether from a source, through an area, or into an absorber.

Sound Pressure Level (SPL) - The measurement of loudness, or amplitude, of sound, expressed in dB.

Sound pressure level (SPL): Given in decibels (dB) is an expression of loudness or volume. A 10 dB increase in SPL represents a doubling in volume. Live orchestral music reaches brief peaks in the 105 dB range and live rock easily goes over 120 dB.

Sound pressure, p: [ML-1T-2]; Pa-a fluctuating pressure superimposed on the static pressure by the presence of sound. In analogy with alternating voltage its magnitude can be expressed in several ways, such as instantaneous sound pressure or peak sound pressure, but the unqualified term means root-mean-square sound pressure. In air, the static pressure is barometric pressure.

Sound receiver: One or more observation points at which sound is evaluated or measured. The effect of sound on an individual receiver is usually evaluated by measurements near the ear or close to the body.

Sound Reinforcement - The use of electronic devices to reinforce, alter or increase the level of sound.

Sound spectrograph: An instrument that displays the time, level, and frequency of a signal.

Sound transmission class, STC: A single-number rating, calculated in accordance with Classification E 413 using values of sound transmission loss. It provides an estimate of the performance of a partition in certain common sound insulation problems. A single number rating that indicates the sound transmission loss of a partition or ceiling system between adjacent closed rooms, abbreviated STC.

Sound transmission coefficient, r: [dimensionless]—of a partition, in a specified frequency band, the fraction of the airborne sound power incident on the partition that is transmitted by the partition and radiated on the other side.

Sound transmission loss, TL: Of a partition, in a specified frequency band, ten times the common logarithm of the ratio of the airborne sound power incident on the partition to the sound power transmitted by the partition and radiated on the other side. The quantity so obtained is expressed in decibels. The reduction in sound level when sound passes through a partition or ceiling system.

Sound waves: Sound waves can be thought of like the waves in water. Frequency determines the length of the waves; amplitude or volume determines the height of the waves. At 20Hz, the wavelength is 56 feet long! These long waves give bass its penetrating ability, (why you can hear car boomers blocks away).

Sound: Sound is vibrational disturbance, exciting hearing mechanisms, transmitted in a predictable manner determined by the medium through which it propagates. To be audible the disturbance must fall within the frequency range 20Hz to 20,000Hz.

Soundstage: A listening term that refers to the placement of a stereo image in a fashion that replicates the original performance. A realistic soundstage has proportional width, depth and height.

Source room: In architectural acoustical measurements, the room that contains the noise source or sources.

Speaker level: Taken from the speaker terminals. This signal has already been amplified.

Specific airflow resistance, r: [ML-2T-1]. Mks rayl (Pa-s/m)—the product of the airflow resistance of a specimen and its area. This is equivalent to the quotient of the air pressure difference across the specimen divided by the linear velocity, measured outside the specimen, of airflow through the specimen.

Spectral balance: Balance across the entire frequency spectrum of the audio range.

Spectrum analyzer: An instrument for measuring, and usually recording, the spectrum of a signal.

Spectrum: the distribution of the energy of a signal with frequency.

Specular reflections: Mirrorlike reflections of sound (angle of incidence equals angle of reflection) from a flat surface. Reflections that do not spread out.

Speech intelligibility: A measure of sound clarity that indicates the ease of understanding speech. It is a complex function of psychoacoustics, signal-to-noise ratio of the sound source, and direct-to-reverberant energy within the listening environment.

Speech transmission index, STI: A single number that indicates the effect of a transmission system on speech intelligibility.

Spherical divergence: Sound diverges spherically from a point source in free space.

Spider - An internal speaker component whose function is to precisely position the voice coil in relation to a gap in the motor.

SPL (sound pressure level) – A measure of the loudness of sound at a particular point in an auditorium. All cinemas and mixing studios are aligned to the same SPL to ensure the audience hears the film soundtrack at the level the director intended.

SPL (Sound Pressure Level) - A measurement of the volume of sound, expressed in decibels (dB): a function of amplitude.

Splaying: Walls are splayed when they are constructed somewhat “off square,” i.e., a few degrees from the normal rectilinear form.

Standing wave: A resonance condition in an enclosed space in which sound waves traveling in one direction interact with those traveling in the opposite direction, resulting in a stable condition.

Steady-state: A condition devoid of transient effects.

Stems – Final-stage premixes, fully balanced and positioned, which still contain the individual elements (music, dialogue, and effects) separately. Stems are combined to produce the final printing master and other delivery requirements.

Stereo variable area (SVA) – A matrixed stereo optical soundtrack used in the Dolby analog formats. The variable area for each matrixed track is used to change the amount of light passing through the film to the soundhead on the projector. Two independent variable tracks are used for the Lt and Rt signals, which are then decoded to become Left, Center, Right, and Surround channels.

Stereo: From the Greek meaning solid. The purpose of stereo is not to give you separate right and left channels, but to provide the illusion of a three-dimensional, holographic image between the speakers.

Structureborne noise: Generation and propagation of time-dependent motions and forces in solid materials which result in unwanted radiated sound.

Stud: An upright 2 x 4 or 2 x 6 wall framing member.

Subwoofer (SW) – The loudspeaker used to reproduce the signal from the low-frequency effects (LFE) channel.

Subwoofer: A speaker designed exclusively for low-frequency reproduction. A true subwoofer should be able to at least reach into the bottom octave (20-40Hz). There are many “subwoofers” on the market that would be more accurately termed “woofers”.

Superposition: Many sound waves may transverse the same point in space, the air molecules responding to the vector sum of the demands of the different waves.

T60: See RT60.

Tangential mode: A room mode produced by reflections off four of the six surfaces of the room.

TDS: Time-delay spectrometry.

TEF: Time, energy, frequency.

Threshold of feeling (pain): The sound pressure level that makes the ears tickle, located about 120 dB above the threshold of hearing.

Threshold of hearing: The lowest level sound that can be perceived by the human auditory system. This is close to the standard reference level of sound pressure, 20uPA.

THX – A technical specification for the entire playback environment (picture and sound) regardless of film format.

THX: Refers to a series of specifications for surround sound systems. Professional THX is used in commercial movie theaters. Home THX specifications are not published and manufacturers must sign non-disclosure waivers before submitting their products for THX certification. Manufacturers that receive certification for their products must pay a royalty on units sold.

Timbral: Refers to the overall frequency balance of a system. In a perfect world, all systems would have complete tonal neutrality. With current technology, this ideal is approached but not met. Listening to many equally “good” speakers will reveal that some sound warmer than others, some sound brighter etc. In a surround sound system it is important that all speakers have a close timbral match for the highest degree of sonic realism.

Timbre: The quality of a sound that distinguishes it from other sounds of the same pitch and volume. The distinctive tone of an instrument or a singing voice.

Time-delay spectrometry: A sophisticated method for obtaining anechoic results in echoic spaces.

Toe-in - The degree to which the inside front edges of a pair of speakers are angled toward each other.

Tonal:, adj.: In reference to audible sound, capable of exciting an auditory sensation having pitch.

Tone burst: A short signal used in acoustical measurements to make possible differentiating desired signals from spurious reflections.

Tone: A tone results in an auditory sensation of pitch.

Total harmonic distortion (THD): Refers to a device adding harmonics that were not in the original signal. For example: a device that is fed a 20Hz sine wave that is also putting out 40Hz, 80Hz, etc. Not usually a factor in most modern electronics, but still a significant design problem in loudspeakers.

Transducer - A device which converts sound into electrical energy (a microphone), or electrical energy into sound (a speaker).

Transformer – A device that alters electrical current.

Transient response: The ability of a component to respond quickly and accurately to transients. Transient response affects reproduction of the attack and decay characteristics of a sound.

Transients: Instantaneous changes in dynamics, producing steep wave fronts.

Transparency: Listening term. An analog that can be best “pictured” in photography. The more “transparent” the sound, the clearer the auditory picture.

Treble: The higher frequencies of the audible spectrum.

Tuning frequency: The helmholtz resonant frequency of a box. Also refers to the resonant frequency of other types of systems.

Tweeter - A speaker (driver) that reproduces only frequencies above a certain range, usually about 3 kHz.

Unbalanced Line - Cable that consists of one conductor and a shield. Here the shield is also carrying the other half of the signal.

Unidirectional - A mic that picks up sound primarily from one direction.

VCA - (Voltage Controlled Amplifier) An amplifier whose output is controlled by varying its voltage rather than by direct resistance (as with a potentiometer).

Vibration isolation: A reduction, attained by the use of a resilient coupling, in the capacity of a system to vibrate in response to mechanical excitation.

Voice Coil - Wire, usually copper, wrapped around a former (tubular core). When attached to a cone or diaphragm, surrounded by a magnetic field, and set into vibration by an alternating current, a voice coil causes a speaker to emit sound waves.

Voltage - The electrical pressure (electromotive force) of a current within a circuit.

Volume: Colloquial equivalent of sound level.

Warmth: A listening term. The opposite of cool or cold. In terms of frequency, generally considered the range from approx. 150Hz-400Hz. A system with the “proper” warmth will sound natural within this range.

Watt - 1. A unit of measurement that equals about 1/746 horsepower or enough electrical energy to perform 1 joule per second. A joule describes the energy of 1 newton displace 1 meter in the direction of the applied force. A newton is the amount needed to accelerate 1 kilogram 1 meter per second. 2. One volt multiplied by one amp.

Watt: The unit of electrical or acoustical power.

Wattage: Is the unit of power used to rate the output of audio amplifiers. For a wattage number to have meaning the distortion level and impedance must also be specified.

Wave: A regular variation of an electrical signal or acoustical pressure.

Wavelength: The distance the sound wave travels to complete one cycle. The distance between one peak or crest of a sine wave and the next corresponding peak or crest. The wavelenth of any frequency may be found by dividing the speed of sound by the frequency. (speed of sound at sea level is 331.4 meters/second or 1087.42 feet/second).

Wedge - A monitor speaker, in the shape of a wedge, designed to sit on the floor and be directed toward the performer(s).

Weighting: Adjustment of sound-level meter response to achieve a desired measurement.

White noise (ANS): Noise with a continuous frequency spectrum and with equal power per unit bandwidth. For example, equal power in any band of 100-Hz width.

Woofer - A speaker (driver) that reproduces only frequencies below a certain range, usually about 800 Hz.

X-curve – A standard replay characteristic that makes it possible for cinemas of different sizes to sound similar by compensating for the different reverberation characteristics.

XLR - Connector A three pin connector widely used in the audio industry.