E

E Archaic symbol for voltage (stands for electromotive force, since it is measured in volts) but the official SI symbol is V, although E is still seen in many equations.

e Mathematics. The base of the natural system of logarithms, having a numerical value of approximately 2.71828. [AHD] See Maor.

EAD (equivalent acoustic distance) Sound Reinforcement. In a live situation without sound reinforcement there is a speaker, or other source, and a listener separated by a straight line distance. Introducing sound reinforcement acts to make the speaker louder thus effectively shorting the distance to the listener. This is called the equivalent acoustic distance.

EAE (electronic acoustic enhancement) (seen shortened to acoustic enhancement and called electronic architecture) Any of several systems that make use of adding sound energy to a listening space rather than using sound absorbers to improve the quality. For examples see: LARES, VRAS, SIAP, and Carmen®.

ear Anatomy. The vertebrate organ of hearing, responsible for maintaining equilibrium as well as sensing sound and divided in mammals into the external ear, the middle ear, and the inner ear. [AHD]

ear buds See: personal monitors.

Eargle, John Morgan (1931-2007) American audio engineer, musician, author, educator, recording engineer and Grammy winner.

early decay time (EDT) Time (in seconds) that it takes for a signal to decay from 0 to -10 dB relative to its steady state value.

Early, James (1922-2004) American scientist and engineer who pioneered bipolar transistors.

early reflections Acoustics. The first sound that arrives at a listener is called the direct sound; the next to arrive is the first reflected sound waves, which take a little longer to reach the listener due to traveling a slightly longer path length. The first several reflected sound waves to reach the listener after the direct sound are called early reflections.

ears See: personal monitors.

earth Electronics. Alternate term meaning ground; chiefly British.

Earth's Cries A dreadful sound created high above the planet related to the Northern Lights. Hit the link to learn more and hear for yourself.

Earth's hum A mysterious infrasonic sound that reverberates through the Earth, believed caused by stormy seas.

earthshine The sunlight reflected from the Earth to the moon and back again. Leonardo da Vinci was the first person to figure out that when the Earth reflects enough light, we can see the entire moon, not just the crescent.

Earth surface loudspeaker Hit the link to read this fascinating article found at redOrbit.com.

EASE (Enhanced Acoustic Simulator for Engineers) A computer modeling tool distributed by Renkus-Heinz for ADA (Acoustic Design Ahnert), who developed the software and introduced it in 1990 at the 88th AES Convention in Montreux.

EBow (energy bow or electronic bow) Musical Instruments. An electric guitar accessory that allows the player to create very eerie sounds. It works by creating a magnetic field near the guitar's pick-ups that causes feedback rich in harmonics and sounds somewhat like a bow on the strings.

EBU (European Broadcasting Union) An international professional society that, among other things, helps establish audio standards.

echo 1. Acoustics A discrete sound reflection arriving at least 50 milliseconds after the direct sound, and significantly louder than the background reverberant sound field. Contrast with reverberation. 2. Psychoacoustics A perceptually distinct copy of the original sound; a delayed duplicate. A single echo may be the result of multiple surface reflections. [Blesser]

echo canceller See: AEC

echoic Of or resembling an echo [AHD].

echolocation (also called echo ranging) 1. A sensory system in certain animals, such as bats and dolphins, in which usually high-pitched sounds are emitted and their echoes interpreted to determine the direction and distance of objects. 2. Electronics A process for determining the location of objects by emitting sound waves and analyzing the waves reflected back to the sender by the object. [AHD]

echo ranging See: echolocation above.

ECM (electret condenser microphone) See: electret microphone.

ECS (Engineered Conference Systems) Rane Corporation trademark for their original teleconferencing equipment, now discontinued.

EDC See: Electric Daisy Carnival

eddy current An electrical current induced in electrical conductors by fluctuating magnetic fields in the conductors. The current moves contrary to the direction of the main current, just below the surface of the material, flowing in circular motion like river eddies. First noted by Michael Faraday after his discovery of electromagnetic induction in 1831. Non-destructive testing based on eddy currents is a fast growing industry. Electrical currents are generated in a conductive material by an induced alternating magnetic field. Interruptions in the flow of eddy currents, caused by imperfections, dimensional changes or changes in the material's conductive and permeability properties, can be detected with the proper equipment.

Edison effect In 1883, Thomas Edison noticed that certain materials, when heated by a filament in a vacuum, emitted electrons that could be attracted to an electrode held at a positive potential with respect to the emitter. This became known as the Edison effect and according to Edison, was discovered by accident when experimenting with his new invention, the incandescent lamp. Twenty years later, this effect became the basis for inventing the vacuum tube.

Edison plug An ordinary household plug with two flat blades and a ground pin.

Edison, Thomas (1847-1931) American inventor extraordinaire

EDLC (electric double-layer capacitor) Electronics. A primary energy storage technology used to replace batteries. Also called ultracapacitors or supercapacitors.

EDM (electronic dance music) Generic term for all types of club dance music. See: History of the Rave Scene: How DJs Built Modern Dance Music by Sara Simms. Also see: electronic music genres.

EDT See early decay time.

EEBAD (Earthed equipotential bonding and automatic disconnection) British abbreviation for a system with all grounds ("Earths") bonded together.

EEPROM or E2PROM (electrically erasable programmable read-only memory) A version of read-only memory that can be electrically erased and reprogrammed by the designer. Differentiated from standard EPROM (one "E") which requires ultraviolet radiation for erasure.

effects boxes or effects units Abbr. EFX or just FX Any outboard unit designed to produce an alteration of a musical instrument's sound, used chiefly by guitarists. Go to GM Arts for an excellent discussion complete with real-world schematics of the most popular effects boxes. These are also called stompboxes due to most of them being designed to be footswitch operated and are placed in front of or to the side of the musician. Hit the link to read about all the variations created over the years.

effects loop A mixer term used to describe the signal path location where an external (outboard) signal processor is connected. The loop consists of an output Send jack connecting to the effects box input, and an input Return or Receive jack that comes from the effects box output. This is the preferred term when two separate 1/4", or other connectors are provided to patch in an outboard processor using separate cables for send and receive. These jacks are usually unbalanced, but could be balanced. A stereo effects loop requires four jacks. Compare with insert loop.

efficiency Electronics. The useful power output of an electrical device or circuit divided by the total power input, expressed in percent.

E-field Physics. Electric field.

E-flat Music. The strike note of The Liberty Bell is E flat. (Snapple Real Fact #660)

EFM (eight-to-fourteen modulation) Compact Disc. A data encoding technique that creates a disc that is highly resilient to handling and storage problems such as dust, scratches, etc. The name comes from the fact that each 8-bit block is translated into a corresponding 14-bit codeword.

EFP (electronic field production) mixer Pretentious equivalent for ENG mixer.

EFX See: effects boxes.

 

EHF See frequency bands.

EIA (Electronic Industries Alliance) Founded in 1924 as the Radio Manufacturers Association (RMA), The EIA is a private trade organization made up of manufacturers which sets standards for voluntary use of its member companies (and all other electronic manufacturers), conducts educational programs, and lobbies in Washington for its members' interests.

EIA-422 See RS-422.

EIA-485 See RS-485.

EIAJ (Electronic Industry Association of Japan) A standards body in Japan begun in 1948, now merged into JEITA.

eigentone (from German eigen meaning "self" or "own") See room mode.

Eight Track Museum No, really.

EIN (equivalent input noise) Output noise of a system or device referred to the input. Done by modeling the object as a noise-free device with an input noise generator equal to the output noise divided by the system or device gain. See the RaneNote Audio Specifications.

Elco plug See connectors.

electone (electronic tone) A trade-marked symbol of the Yamaha Corporation; the brand name of Yamaha's organ instrument line.

electret microphone A microphone design similar to that of condenser mics except utilizing a permanent electrical charge, thus eliminating the need for an external polarizing voltage. This is done by using a material call an electret [acronym for electricity + magnet] that holds a permanent charge (similar to a permanent magnet, i.e., a solid dielectric that exhibits persistent dielectric polarization). Because electret elements exhibit extremely high output impedance, they often employ an integral built-in impedance converter (usually a single JFET) that requires external power to operate. This low voltage power is often supplied single-ended over an unbalanced connection, or it may operate from standard phantom power. Electret technology was co-pioneered by Jim West and Gerhard Sessler in the 1960s at Bell Labs. Their original research into polymers (an electrical analogy of a permanent magnet) led to electret transducers.

electric Anything operated by electricity.

Electric Daisy Carnival Billed as North America's largest music festival, it is held in various US and international cities since 1993 and put on by Insomniac. "Founded by Pasquale Rotella and built upon his creative vision, the company's core philosophy is to encourage audience participation through interactive art, roaming theatrical performers, and fully immersive state-of-the-art production design. Behind every corner and inside every area of Insomniac's festivals is a new adventure waiting to be explored." [From website]

Electric Festival Held on the island of Aruba, just off the northern coast of Venezuela, it is billed as the biggest electronic festival in the Caribbean.

Electric Forest Festival Four-day music festival, begun in 2008, held yearly in Rothbury, MI, with overnight provisions.

electric guitar Musical instrument derived from the standard guitar but having a solid-body and electric pickups using electromagnetic induction to convert metal string vibrations into audio signals that require further amplification before driving a loudspeaker. First invented by George Beauchamp in 1931.

Electric Zoo (aka E-Zoo) Music festival held Labor Day weekend in NY City since 2009, featuring all genres of electronic music.

electroacoustics The science that deals with the interaction or interconversion of electric and acoustic phenomena. [AHD]

electroacoustic transducer A transducer designed to receive electric input signals and to supply acoustic output signals, or vice versa. [Harris]

electromagnetic induction The generation of an electromotive force (voltage) and current in a circuit or material by a changing magnetic field linking with that circuit or material. Electricity and magnetism are kinfolk and form the foundation of audio transducers found at both ends of any audio chain: dynamic microphones and loudspeakers with voice coils. The principle is beautifully simple: if you pass a coil of wire through a magnetic field, electricity is generated within the coil (dynamic microphone), and if you pass electricity through a coil of wire (voice coil), a magnetic field is generated. Move a magnet, create a voltage; apply a voltage, create a magnet. This is the essence of all electromechanical objects.

electromotive force Abbr. EMF Physics. The energy per unit charge that is converted reversibly from chemical, mechanical, or other forms of energy into electrical energy in a battery or dynamo. [AHD]

electronic acoustic enhancement See: EAE.

electronic architecture See: EAE.

electronic music genres Hit the link for an astonishing look at electronic music genres.

Electronic Sackbut Musical Instrument. Very early electronic instrument created in the '40s by Hugh Le Caine, which made use of the first known modulation wheel, and is now recognized as the first voltage-controlled synthesizer. [The name "sackbut" is an ancient trombone-like musical instrument.]

electrostatic loudspeaker See loudspeaker.

electrostatic microphone See condenser microphone.

elephant hearing Hit the link to read all about elephants hearing through seismic vibrations.

elephant teeth Piano keys. [Decharne]

Elliot Sound Products An outstanding collection of audio technical articles by Rod Elliot (and DIY audio projects).

elliptic filters or elliptic-function filters also called Cauer filters after network theorist Wilhelm Cauer. A filter having an equiripple passband and an equiminima stopband. [IEEE] Butterworth filters are all-pole types, while elliptic filters have zeros as well as poles at finite frequencies. The location of the poles and zeros creates equiripple behavior in the passband similar to Chebyshev filters. Finite transmission zeros in the stopband reduce the transition region so that extremely sharp roll-off rates result; however the improved performance is obtained at the expense of return lobes ("bounce") in the stopband.

elocution 1. The art of public speaking in which gesture, vocal production, and delivery are emphasized. 2. A style or manner of speaking, especially in public. [AHD]

EMC Directive (ElectroMagnetic Compatibility) 1. A directive issued by the European Commission aimed at establishing product compatibility within the EU (European Union). Article 1.4 defines electromagnetic compatibility as the ability of an electrical and electronic appliance, equipment or installation containing electrical and/or electronic components to function satisfactorily in its electromagnetic environment (immunity requirement) without introducing intolerable electromagnetic disturbances to anything in that environment (emission requirement). 2. Due to the significant increases in development time and product costs imposed by the EMC Directive, many believe the initials really stand for "eliminate minor companies." [Thanks DC.]

EMD (electronic music distribution) Distributing digital music files (compressed using MP3, AAC, AC-3, etc.) from a server to a client.

EME (electromagnetic environment) "The spatial distribution of electromagnetic fields surrounding a given site."

EMF (electromotive force) Physics. Voltage. See electromotive force & volt; also back-emf.

EMI (electromagnetic interference) A measure of electromagnetic radiation from equipment.

emitter follower See buffer amplifier.

emo A genre of dance music.

emoacoustics (emotional acoustics) " ... deals with the relationship between sounds characteristics, the individual, and the situation with a focus on the induced emotional reactions." [From website; hit the link]


EMP (Experience Music Project) Paul Allen's (cofounder of Microsoft) interactive music museum, located in Seattle, that celebrates and explores creativity and innovation in American popular music as exemplified by rock 'n' roll. [Very cool place ... come visit sometime.]

empath 1. One who practices empathy, i.e., a person who strongly identifies with and understands another's situation, feelings, and motives. 2. A DJ performance mixer combining the vision of Grandmaster Flash and Rane technology.

EMT plate reverb Invented in 1957 by the German company, EMT (Elektromesstecknik), and used in all the famous recording studios in the '60s and '70s, it is still considered by many to be the best sounding reverb.

EMT 250 Digital Reverb Invented in 1976, this was the first commercial digital reverb.

emulate Computer Science. To imitate the function of (another system), as by modifications to hardware or software that allow the imitating system to accept the same data, execute the same programs, and achieve the same results as the imitated system. [AHD] For example digital vinyl systems such as Serato Scratch LIve and Native Instruments Traktor use vinyl emulation control records to manipulate digital audio files.

end-user The ultimate consumer of a product, especially the one for whom the product has been designed. [AHD]

energy time curve See: ETC.

ENF (electric network frequency) Criterion Forensics. A method for the authentication of digital audio and video recordings.

ENG (electronic news gathering) mixer Portable battery-powered mixer accommodating at least two or three mic inputs, used in the field to record speech and outdoor sound effects. Some specialized models have built-in telephone line interfacing.

Englebart, Douglas C. (1925-2013) American engineer famous for inventing the computer mouse while at Stanford Research Institute.

English guitar Musical Instrument. A 10-string cittern-type instrument.

enhancers See exciters.

enharmonic Music. Of, relating to, or involving tones that are identical in pitch but are written differently according to the key in which they occur, as C sharp and D flat, for example. [AHD] Contrast with inharmonic.

ENOB (effective number of bits) A figure of merit for A/D data converters useful in specifying a converter's real AC accuracy and performance. We all know that the data sheet says it's 24 bits, but what is it really? For a perfect sine wave, it can be approximated from the SINAD measurement by subtracting 1.76 from the SINAD (dB) and then dividing by 6.02. (For down-and-dirty quick calculations just divide the SINAD by 6 and you'll be in the ballpark.) For example, if a 24-bit A/D converter has a real world measured SINAD = 100 dB, then it has an ENOB equal to 16, nowhere near the claimed 24 bits.

ENR (excess noise ratio) The ratio of a source's noise power when it is on to when it is off. A normalized measure of how much noise the device creates above the rule of thumb thermal limit of -174 dB/Hz.

ensemble Music. 1. A group of musicians, singers, dancers, or actors who perform together. 2. A work for two or more vocalists or instrumentalists. 3. The performance of such a work. [AHD]

entropy coding Audio Compression. A lossless audio coding technique.

envelope Waves. The boundary of the family of curves obtained by varying a parameter of the wave. [IEEE]

envelope control Synthesizers. A voltage controlling pitch and volume to create a distinctive contour (envelope).

envelope delay See group delay.

Epidaurus Acoustics. The Greek theater of Epidaurus is considered one of the most extraordinary acoustic spaces of antiquity. A study by Nico F. Declercq and Cindy Dekeyser of the Georgia Institute of Technology concluded that it was the use of limestone in the seats that created its wonderful acoustic qualities. More details here.

épinette des Vosges Musical Instrument. A French dulcimer-type instrument; a type of zither.

E Pluribus Unum Latin. Out of many, one.

eponym A person whose name is or is thought to be the source of the name of something, such as a city, country, or era. For example, Romulus is the eponym of Rome. [AHD]

EQ (equalizer) A class of electronic filters designed to augment or adjust electronic or acoustic systems. Equalizers can be fixed or adjustable, active or passive. Indeed, in the early years of telephony and cinema, the first equalizers were fixed units designed to correct for losses in the transmission and recording of audio signals. Hence, the term equalizer described electronic circuits that corrected for these losses and made the output equal to the input. Equalizers commonly modify the frequency response of the signal passing through them; that is, they modify the amplitude versus frequency characteristics. There are also fixed equalizers that modify the phase response of the transmitted signals without disturbing the frequency content. These are referred to as all-pass, phase-delay, or signal-delay equalizers. See the RaneNote Exposing Equalizer Mythology, the RaneNote Operator Adjustable Equalizers, and RaneNote Signal Processing Fundamentals.

equal level curves (aka isobaric contours) Loudspeakers. A way of mapping loudspeaker coverage pattern. Here is Bob McCarthy's explanation: "The equal level contours are found by mapping the points of equal pressure between the on-axis and off-axis points at half the distance of the on-axis reference point. In such a case, the 6dB loss from moving off-axis is compensated by the 6dB gain from approaching the source. This creates a balloon-like shape that represents equal pressure. If you were to walk along this line, you would experience level uniformity. In a typical room, the response in the far-field on-axis area would have low-frequency buildup due to room reflections. In the off-axis near-field position, there would be HF attenuation because of the axial loss. These two opposing factors come together to create a high potential for frequency response uniformity, depending upon the particular room and array design factors. Therefore, the contour lines represent both level and (potentially) frequency response uniformity, two of our primary goals in array design."

equal loudness curves Hearing. See: Fletcher-Munson Curves.

equal-tempered scale or equal temperament, also even temperament Music. Today's normal musical scale, it divides a musical octave into twelve equal parts (semitones), i.e., each is 2 1/12 above the other. Compare with just temperament.

equivalent acoustic distance See: EAD

equivalent continuous A-weighted sound pressure level Acoustics. For airborne sounds that are non-stationary with respect to time, an equivalent continuous sound pressure level (see below) formed by applying A-weighting to the original signal before squaring and averaging. [Morfey] Abbreviated LAeq (15) for a time duration of 15 minutes.

equivalent continuous sound pressure level Acoustics. Of a non-stationary sound pressure signal between specified time limits, the sound pressure level of a notional unvarying sound that, for the same specified duration has the same signal energy as the original signal. [Morfey] Abbreviated Leq.

equivalent input noise See EIN.

erhu Musical Instrument. Chinese 2-stringed fiddle.

Eric "Hoss" Cartwright's given name -- "Hoss" was a nickname. This, for all you Jeopardy! fans.

ERL (echo return loss) The difference between a frequency signal and the echo on that signal as it reaches its destination. [Newton]

ERLE (echo return loss enhancement ) A measure (in dB) of how much echo signal reduction is taking place.

error correction A method using a coding system to correct data errors by use of redundant data within a data block. Often data is interleaved for immunity to burst errors. Corrected data is identical to the original.

ESD (electrostatic discharge) Electrical discharges of static electricity that build up on personnel or equipment, generated by interaction of dissimilar materials. [IEEE]

Eskimo pi Ratio of an igloo's circumference to its diameter.

ESL (electrostatic loudspeaker) See: loudspeaker.

ESO (equipment superior to operator) Satirical term popular among service technicians used to code invoices for units returned with nothing wrong -- similar to NPF (no problem found). [Thanks, CD!]

ESP See: Elliot Sound Products

ESPA (Electronic Systems Professional Alliance) A non-profit organization specializing in entry-level electronic systems technicians (EST).

ESR (effective series resistance) Capacitors. The sum of many resistive losses in a capacitor. It includes resistance of the dielectric, plate material, electrolytic solution, and terminal leads at one specified frequency and acts like a resistor in series with a perfect capacitor. It is measured in ohms and is the real part of impedance.

ESSENCE Festival Music festival put on by ESSENCE magazine, held annually in New Orleans.

EST (electronic systems technician) See: ESPA.

ESTA (Entertainment Services & Technology Association) A non-profit trade association representing the North American entertainment technology industry. Now merged with PLASA.

E-taper See: potentiometer.

ETC (energy time curve) Originally a three-dimensional graphical plot of acoustic response where frequency, energy and time represent the three axes. Today it is more commonly seen as a two-dimensional graph with energy (in dB-SPL) and time being the axes. In simplest terms it is a plot of the envelope, or instantaneous amplitude decay of the test signal.

ETCP (Entertainment Technician Certification Program) Industry certification program "focusing on the disciplines that directly
affect the health and safety of crews, performers, and audiences." ETCP was created under the auspices of ESTA.

ether From a Greek word meaning "upper air," a term used in early physics (based on ancient beliefs), a magical medium thought to explain the propagation of electromagnetic waves.

Ethernet A local area network (LAN), originally developed by Xerox in 1973 (the name was coined by its inventor Bob Metcalfe, et al. [who went on to found 3Com in 1979] after the old science term ether), receiving US Patent 4,063,220 in 1975, used for connecting computers, printers, workstations, terminals, etc., now extended to include audio and video using CobraNet and other new technologies (see: AoE, also see: AVB: Audio/Video Bridging). Ethernet operates over twisted-pair, coaxial cable, or fiber optic cable at various speeds designated "10Base-T" up to 10 megabits/sec (Mbps), "100Base-T", a.k.a. Fast Ethernet, up to 100 Mbps, and "1000Base-T" up to 1 gigabit/sec, or 1000 Mbps, aka Gigabit Ethernet (GE) [uses all 8 conductors and can be up to 100 meters long], and "10Gbase-T" aka. 10-Gbit Ethernet. (The number in the front designates the speed in megabits/second. "Base" indicates the network is baseband. The letter following determines the type of cable and its requirements. 10Base-T, for example is unshielded twisted-pair, using a star topology, and 1000Base-F uses fiber cable.) Other Ethernet designators include:

1000Base-CX A standard for GE connectivity where the "C" means copper and "X" is a placeholder.

1000Base-SX ("S" for short wavelength laser) for laser fiber cabling based on the Fiber Channel signaling specification for multimode fiber only.

1000Base-LX ("L" for long wavelength laser) for laser fiber cabling also based on the Fiber Channel signaling specification for multimode or single-mode fiber.

1000Base-LH ("LH" for long haul) for a multivendor specification (each vendor has a set of transceivers covering different distances). While not an IEEE standard, the vendors are working to interoperate with IEEE 1000Base-LX equipment using the gigabit interface connector (GBIC) multivendor specification in order to provide a common form factor and greater flexibility.

Ethernet crossover cable A connection cable consisting of two pairs crossed plus two pairs uncrossed. Hit the link for a diagram and chart.

EtherSound Networks. Digigram's patented real-time digital audio network based on standard Ethernet cabling and components (see above).

EULA (end user license agreement) Software. The terms and conditions of a user rights with respect to purchased software.

euphonic Agreeable sound, especially in the phonetic quality of words. [AHD]

euphonium Musical Instrument. A brass wind instrument similar to the tuba but having a somewhat higher pitch and a mellower sound. [AHD]

Euroblocks Shortened form for European style terminal blocks. See connectors.

Eurorack Nickname for 3U high 19" wide powered rack designed to accommodate modular synthesizer modules available from many manufacturers. Similar to FracRack but with minor (but important) differences; also similar but different from 500 Series card frames.

Eventide H910 Harmonizer Offered for sale in 1975, it was the first and still the most famous.

EVD (enhanced versatile disc) The Chinese national DVD standard developed to get around paying royalties to the DVD alliances.

even temperament See equal-tempered scale.

EVP (electronic voice phenomenon) Noises resembling speech or music, created electronically, usually not wanted. Most common example is static interference in communication systems, often misinterpreted as conveying intelligence, and being from the dead or aliens. Hit the link for its fascinating history.

exciters (or enhancers) A term referring to any of the popular special-effect signal processing products used primarily in recording and performing. All exciters work by adding harmonic distortion of some sort - but harmonic distortion found pleasing by most listeners. Various means of generating and summing frequency-dependent and amplitude-dependent harmonics exist. Both even- and odd-ordered harmonics find favorite applications. Psychoacoustics teaches that even-harmonics tend to make sounds soft, warm and full, while odd-harmonics tend to make things metallic, hollow and bright. Lower-order harmonics control basic timbre, while higher-order harmonics control the "edge" or "bite" of the sound. Used with discrimination, harmonic distortion changes the original sound dramatically, more so than measured performance might predict.

expander A signal processing device used to increase the dynamic range of the signal passing through it. Expanders complement compressors. For example, a compressed input dynamic range of 70 dB might pass through a expander and exit with a new expanded dynamic range of 110 dB.
Long answer: Just like compression, what "expansion" is and does has evolved significantly over the years. Originally expanders were used to give the reciprocal function of a compressor, i.e., it undid compression. Anytime audio was recorded or broadcast it had to be compressed for optimum transfer. Then it required an expander at the other end to restore the audio to its original dynamic range. Operating about the same "hinge" point and using the same ratio setting as the compressor, an expander makes audio increases and decreases bigger. From this sense came the phrase that "expanders make the quiet sounds quieter and the loud sounds louder." Modern expanders usually operate only below a set threshold point (as opposed to the center hinge point), i.e., they operate only on low-level audio. The term downward expander or downward expansion evolved to describe this type of application. (The term upward expander is sometimes used to refer to expanders operating only on high-level signals, i.e., increasing dynamic range above threshold.) The most common use is noise reduction. For example, say, an expander's threshold level is set to be just below the smallest vocal level being recorded, and the ratio control is set for 3:1. What happens is this: when the vocals stop, the "decrease below the set-point" is the change from signal (vocals) to the noise floor (no vocals), i.e., there has been a step decrease from the smallest signal level down to the noise floor. If that step change is, say, -10 dB, then the expander's output will be -30 dB (because of the 3:1 ratio, a 10 dB decrease becomes a 30 dB decrease), thus resulting in a noise reduction improvement of 20 dB. See the RaneNote "Dynamics Processors -- Technology & Applications."

exponent The component of a floating-point number that normally signifies the integer power to which the radix is raised in determining the value of the represented number (IEEE-100). For example if radix =10 (a decimal number), then the number 183.885 is represented as mantissa = 1.83885 and exponent = 2 (since 183.885 = 1.83885 x 102).

exponential horn Loudspeakers. A horn design characterized by having an exponentially increasing cross-sectional area.

"Expressman Blues" The first rock and roll song, recorded May 17, 1930 by "Sleepy" John Estes, Yank Rachel and Hammy Nix. [McCleary]

extensible Of or relating to a programming language or a system that can be modified by changing or adding features. Capable of being extended: AES24 is an extensible protocol.

Extreme Programming See: XP.

Eye of Dionysius Acoustics. The legend says that "Dionysius used the cave as a prison for political dissidents, and by means of the perfect acoustics eavesdropped on the plans and secrets of his captives."

eye pattern An oscilloscope display of the received voltage waveform in a transmission system. So named because portions of the display take on a human eye-like shape. The eye pattern gives important information. An eye pattern is obtained when a high speed transmission system outputs a long pseudorandom bit sequence. A sampling oscilloscope is used to observe the output such that the scope is triggered to sample on every fourth or eighth pseudorandom clock cycle, and every sample point is plotted on the screen. (The pseudorandom digital data signal from a receiver is repetitively sampled and applied to the vertical input, while the data rate is used to trigger the horizontal sweep.) The picture obtained is a superposition of ones and zeros output. The horizontal "fatness" of the lines indicates the amount of jitter and the rise and fall times is measured from the crossing points. See Siemon publication Data Throughput Validation: Making Every Bit Count for an example and more details.

E-Zoo See: Electric Zoo.