Glossary of Audio Terminology

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Index | References




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

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.

EIA (Electronic Industries Association) Founded in 1924, 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), set standards, conducts educational programs, and lobbies in Washington for its members' interests.

electret microphone A microphone design similar to that of condenser mics except ultiziing 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 (buffer amplifier usually a single JFET) that requires external power to operate. This low voltage power is often supplied single-ended over an unbalanced connection.

Electromagnetic Radiation Spectrum  The electromagnetic radiation spectrum ( or Radio Spectrum ) is the complete range of the wavelengths of electromagnetic radiation, beginning with the longest radio waves ( including those in the audio range used for very low frequency transmission ) and extending through visible light (a very small part of the spectrum) all the way to the extremely short gamma rays that are a product of radioactive atoms.

Electromagnetic Radiation ( EM ) Do you listen to the radio, watch TV, or use a microwave oven? All these devices make use of electromagnetic waves. Radio waves, microwaves, visible light, and x rays are all examples of electromagnetic waves that differ from each other in frequency.  Electromagnetic waves are produced by the motion of electrically charged particles. These waves are called "electromagnetic radiation" because they radiate from the electrically charged particles. They travel through empty space as well as through air and other substances.  Just like sunlight, under normal conditions there are perfectly safe and harmless. ( of course normal safety precautions must be taken when working with sources of very strong fields just as you must take safety precautions when working with ordinary electrical power sources. )  See our TechNote  About Electromagnetic Radiation for more information

Electromagnetic Interference (EMI)  Any electromagnetic disturbance, or emission that causes undesired responses or degradation of performance in electrical or electronic equipment.

Encryption Alteration of transmitted information to protect it from unauthorized use.

enhancers See: exciters

EQ (equalizer) A class of electronic filters designed to augment or adjust electronic or acoustic systems. Equalizers can be fixed or adjustable. 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.

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.

Ethernet A local area network (LAN) originally used for connection and interaction between computers, printers, workstations, terminals, etc., now extended to include audio and video using CobraNet technology. Ethernet operates over twisted-pair, coaxial cable, or fiber optic cable at various speeds designated "10Base-T" up to 10 megabytes/sec (Mbps), "100Base-T" up to 100 Mbps, and on the horizon, based on fiber interconnect: "1000Base-F" up to 1 gigabytes/sec, or 1000 Mbps. (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.)

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 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.

extensible Of or relating to a programming language or a system that can be modified by changing or adding features. Capable of being extended: AES-24 is an extensible protocol.



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