ear buds. Compact transducers some what like headphones, but designed to fit inside the ears of the listener. Some ear buds, especially those used for live in-ear monitoring purposes, completely seal out external sound. Others, such as the low-end models included with many portable MP3 players, do not seal out external sound as well.
ear fatigue (a.k.a. tired ears). A condition that occurs after listening at high volume levels or for long periods of time. Ear fatigue may be as simple as lack of focus, or as significant as TTS (Temporary Threshold Shift), a change in the ears’ response. Ear fatigue can lead to poor tracking and mix decisions. The best way to prevent it is to control listening levels (85 dB is the recommended listening level for accurate ear response and long sessions) and to take frequent “silence” breaks.
early reflections. 1. In acoustics, the first reflections to be heard after the direct sound from a source. Early reflections tell the listener a great deal about the size of a room. 2. In reverb effects, there are often two parts to the effect: the tail, or wash of ambience, and the early reflections, a group of echo-like short delays used to give the impression of being in a real room. See Figure E.1.
Figure E.1. In a reverb processor, early reflections are very short delay-like repeats that simulate the acoustic reflections heard in a room.
earth. 
See ground.
EASI. Enhanced Audio Streaming Interface. An older driver protocol developed by Emagic (now owned by Apple) that provides audio software applications with low-latency multichannel access to audio interface I/O. EASI bypasses the operating system audio functions to provide direct, high-speed communication.
EBU. European Broadcasting Union. An organization of broadcasters that develops cooperation and standards for the audio-visual community. www.ebu.ch.
echo (a.k.a. delay). 1. In acoustics, a discrete reflection of a sound wave arriving after the listener hears the direct sound. 2. In effects processors, a delayed duplicate of the original signal heard at some time after the direct sound.
Edac. The Canadian-manufactured version of Elco connectors.
Edison effect. A tendency of some materials to emit electrons when heated. This phenomenon was discovered by Thomas Edison when he was experimenting with light bulbs. The discovery of the Edison effect led to the later development of the vacuum tube.
edit. To modify audio or MIDI data in some way. DAWs, MIDI sequencers, and audio editing software offer a wide variety of editing possibilities, including cut, copy, paste, transpose, quantize, trim, crossfade, and many more.
edit buffer. A temporary memory area in a synthesizer, sampler, or effects processor where presets are loaded to be edited. Changes to the preset are saved into the edit buffer. When the editing is finished, the contents of the edit buffer can be saved back to a user preset location.
Edit Decision List. See EDL.
editor. 1. A window in a DAW, sequencer, or audio software optimized for editing a particular kind of data or for viewing and editing data in different ways. 2. Software for editing audio recordings or samples, MIDI data, or synthesizer or processor presets. 3. A person who edits audio or other data.
editor/librarian. Many synthesizers, effects processors, controllers, and other devices offer very limited built-in programming interfaces—small screens, limited numbers of knobs and switches, and many layers and pages that the user must wade through to edit or create a preset. An editor/librarian is a piece of software that provides access to the parameters in a hardware device using MIDI System Exclusive messages. The software can display the parameters on the computer’s screen in a visually friendly manner, make edits to presets, and store a library of presets for the device on the computer’s hard drive.
EDL. Edit Decision List. A listing of the takes, cuts, edits, and changes that will comprise the master recording. EDLs are most common in video and film work but are also used by DAWs and CD mastering programs.
effect. A hardware device or software processor that modifies a signal. Examples include delay, echo, phase shifting, flanging, chorus, tremolo, and many others.
effects loop. An output and an input on a device, which are intended for routing signal out to an external effects processor then back into the device. Examples include the effects loops commonly found on guitar amplifiers, aux send and return buses on mixers, and insert points on outboard gear. Effects loops may be either serial, where the effects process the entire signal, or parallel, where the signal is split and one half is routed out to the effects and back in. See Figure E.2.
Figure E.2. An effects loop provides a way to insert an effects device or processor into a piece of gear’s signal path.
effects return (a.k.a. FX return). An input used to bring the output from an effects device into a mixer. See also return.
effects routing. The signal path in a multi-effects device that configures how a signal will be sent through one or more effects processing modules and what order those processors will be put in.
effects send (a.k.a. FX send). An output used to route signal from a mixer or other device to an effects processor, such as a reverb or delay. In a mixer, sends used for effects are typically positioned post-fader. See also aux send.
efficiency. A speaker specification that indicates how well a driver will convert electrical signals into sound energy—the remainder of the signal is converted to heat and lost. Typical direct radiator efficiency ratings are 1 or 2%. Horns typically fall around 20%, though some can reach 30% efficiency. While more efficient speakers can generate higher volume levels with lower-power amplifiers, lower-efficiency speakers typically have better damping and resistance to resonances.
EFX. Short for effects, a.k.a. FX.
EG. See envelope generator.
egg carton. A type of “home brew” acoustical device, originally designed to transport and store chicken eggs, which provides little acoustical benefit.
EIA. Electronic Industries Alliance. A manufacturers’ trade association that sets voluntary standards for its member companies. www.eia.org.
EIDE. Enhanced Integrated Drive Electronics. A version of IDE developed by Western Digital that used DMA, which reduced the load on the CPU during disk operations. DMA was later added to the “official” ATA standard.
eigentone. See room mode.
eighth space. A sound source, such as a speaker, located at the junction of three surfaces, such as the corner of two walls and the ceiling, is said to be in eighth space. Eighth-space placement of a speaker or other sound source results in a 9-dB level increase (mainly in the low frequencies) over free space placement. See also free space, half space, quarter space.
EIN. Equivalent Input Noise. A specification for the self-noise of a microphone preamp, assuming a 200-ohm impedance microphone is connected to the input. The lowest theoretical EIN rating is –129.6 dBu, though EIN is one of those specs that a manufacturer can manipulate or spin in a variety of ways, including using different mic impedances and dBV instead of dBu ratings. EIN is not a significant spec for most applications, except recording very low-level sounds, as self-noise for most preamps is extremely low.
EL34. A common pentode vacuum tube used in guitar and power amplifiers.
Elco. A brand of multi-pin audio connectors. There are several different configurations, including 20-, 38-, 56-, 90-, and 120-pin versions. Elco connectors are designed to only fit together in one direction and have a screw/nut arrangement that locks the male and female connectors together.
electret (a.k.a. back-electret). A type of condenser microphone that has a permanently charged back-plate. An electret element has the advantage of not requiring an external voltage to power the plate, though power may still be required for internal preamp circuitry. Electret elements may lose some charge over time, resulting in reduced sensitivity and increased self-noise. Electret elements are generally found in lower-priced microphone models, while true condensers are used in higher-priced models.
electric piano. A keyboard instrument that produces sound when metal strings, tines, reeds, or other vibrating items are struck by hammers in a fashion similar to an acoustic piano. The vibrations are picked up by pickups and sent to an amplifier. Electric pianos are not synthesizers, but rather electromechanical instruments. Some of the most popular electric pianos include the Rhodes, which used vibrating metal tines of stiff wire; the Wurlitzer, which used metal reeds; and the Helpinstill and Yamaha CP-70, which used metal strings.
electro-optical (a.k.a. ELOP). A type of circuit employed in some compressors and limiters that uses photo-resisters or light-dependent resistors with an LED or other light source to reduce gain instead of a VCA. Some engineers believe that electro-optical compressors have smoother response characteristics than other types.
electrode. A positively or negatively charged conductive terminal in a component. A diode has two electrodes, a triode has three electrodes, a pentode has five electrodes, and so on. (Trivia note: Though most people assume an anode is a positive electrode, and a cathode is a negative electrode, this is not necessarily true. The terms anode and cathode refer to the direction of flow of anions and cations, which can vary depending on the circuit.)
electromagnetism. The physics of particles, magnetic fields, and electrical charges. Dynamic speakers, dynamic microphones, motors, analog and digital tape, hard drives, and other common items depend on electromagnetism for their operation.
electrophone. An instrument that produces sound using electricity. Electrophones include instruments that create sound using electricity, but not those that use amplifiers to make their sound louder. Other categories of instruments include chordo-phones (strings), aerophones (winds), membrano-phones (instruments with drum heads), and idiophones (various percussion and other instruments that do not use strings, heads, or wind to produce sound).
ELOP. See electro-optical.
EMI. Electromagnetic Interference. Errant electromagnetic fields that are picked up through the air by circuitry or cabling and that result in hum or buzz in the audio signal. EMI can be prevented or reduced using shielding, proper grounding, balanced lines, isolation transformers, and other methods.
emphasis. Modifying a signal as it is recorded (called pre-emphasis), by, for example, boosting the high frequencies. As the signal is played back, the modification is removed (called de-emphasis), in this example, by reducing the high frequencies. As the emphasis is removed, any noise added during the recording process is removed. In this example, hiss generated during recording will be removed when the high frequencies are reduced on playback.
emulation. Using modeling or other digital processing to re-create the sound or functions of a device or instrument.
encoder. 1. A device or algorithm that creates a representation of information that must be translated or decoded to be understood. Encoders are used to create versions of data that can be easily and safely stored and transmitted. 2. A knob found on some control surfaces, digital mixers, and other devices used to send digital control messages that are used to control parameter settings in a DAW or other destination.
encrypt. To encode information so that it cannot be understood without a key or other means of translation. Encryption is used to protect the privacy of data for storage and transmission. See also data encryption.
end address. A microphone that is physically designed so that its diaphragm is perpendicular to the body of the mic, with the capsule oriented to pick up sound best from the end of the mic, rather than from a side or sides (see Figure E.3). See also side address.
endian. A system for ordering the bits in a binary word. Some computers use “little endian” systems, in which the bits go up in binary value toward the left of the binary word. Others use “big endian” systems, in which bits go up in binary value toward the right of the binary word.
engine. The algorithms that provide the audio or MIDI processes in a DAW, sequencer, audio editing software, or plug-in.
ensemble. 1. A group of vocalists and/or instrumentalists. 2. An effect similar to chorusing, designed to create the sound of many instruments playing a part at once.
envelope. 1. The volume “shape” of a sound. For example, most drums have a fast attack and a quick decay, with little sustain. A violin has a slower attack (unless it is played pizzicato) and sustains for as long as the player draws the bow across the string. 2. A multistage response curve that takes place over time and can be applied to control a synthesis parameter, such as volume or pitch (see Figure E.4). For example, the stages of a volume envelope might include an attack time, or how fast a sound begins; a decay time, or how fast the sound’s initial transient settles to the sustain level; a sustain level, which determines how loud the sound will be while it is being held; and a release time, which determines how long the sound rings on after the sound ends. Other stages are also possible, depending on the capabilities of the envelope generator. See also ADSR, AHDSR, AHDSFR.
Figure E.4. An envelope is a multistage control signal that can be routed to control the volume, pitch, or other parameter of a synthesizer or sampler sound.
envelope filter. See auto-wah.
envelope follower. A device or algorithm that converts the envelope characteristics of a sound into a control signal, either digital or a control voltage. The envelope follower’s control signal output can be routed to control another parameter in the device or system.
envelope generator (a.k.a. EG). A module or algorithm in a synthesizer or sampler that outputs a multistage control signal, or “envelope,” that is used to control a parameter, such as volume, pitch, or others. See also envelope.
envelope tracking. See rate scaling.
envelopment. The sense of audio completely surrounding or enveloping the listener.
EOX. End of Exclusive. A MIDI System Common message that indicates the end of a System Exclusive message.
EPP. Enhanced Parallel Port. A computer port that supports two-way communication and high-speed transfers from multiple daisy-chained devices.
EPROM. Erasable Programmable Read-Only Memory. A type of ROM chip that can be reprogrammed as required. The chip retains the contents of its memory until it is exposed to ultraviolet light.
EQ. See equalizer.
equal temperament. A tuning system that divides each octave into 12 equal parts (called semitones). Most modern Western musical instruments use equal temperament.
equalizer (a.k.a. EQ). An audio processor that boosts or cuts the level of a particular frequency or range of frequencies. Equalizers are used to modify the frequency response of a system or the tonal shape of a signal. Equalizers were originally developed by the telephone company to enhance the audio quality of phone lines.
equilateral triangle. A triangle in which all three sides have the same length. An equilateral triangle is the ideal positioning for studio monitor speakers, where the monitors are set up at two corners of the triangle, with the listener’s head as the final corner.
equivalent input noise. See EIN.
erase head. A head on a tape recorder used to randomize the tape’s magnetism before it passes the record head. This gives the record head “fresh” tape on which to record and eliminates the need for the record head to record over existing magnetic signals.
error correction. A variety of schemes used to ensure that the data written and read by a digital storage system is accurate. See also CRC, CIRC, parity.
eSATA. External Serial Advanced Technology Attachment. A version of SATA designed for use with external hard disks or optical drives. eSATA is hot-swappable and can be faster than USB or FireWire protocols.
Ethernet. A family of networking technologies developed by Xerox for LAN (Local Area Network) applications. Ethernet cables have been adopted by some manufacturers for additional proprietary applications.
Euroblock. A type of terminal strip used for audio products intended for permanent installation. With a Euroblock connector, the insulation at the end of the wire is stripped off, and then the wire is inserted into a slot in the block. A screw is tightened down to hold the wire securely.
even-order harmonic distortion. A type of distortion that results primarily in extra even harmonics being added to a signal. Even-order harmonic distortion is often produced when tube devices clip; it tends to be more pleasant sounding to most listeners than other types of distortion (and even desirable in guitar amplifiers).
event. A MIDI Channel Message command. Examples include note on, note off, and program change messages. Continuous controllers, aftertouch, pitch bend, and similar types of messages produce a stream of events.
event list. A text list of the events that are recorded into a MIDI track in a sequencer or DAW. Event lists make certain types of event processing easier and allow precise editing of values and placement of events. See Figure E.5.
Figure E.5. An event list editor provides a text list of MIDI events (in this case, a stream of notes) that can be precisely edited and processed.
excite. In acoustics, to add energy to a room.
exciter. A type of audio processor that increases the brightness in a signal without increasing the signal’s level, as would happen when using EQ. Some exciters work by adding a small amount of controlled harmonic distortion to the signal. Others use compression and filtering to create high-frequency content that can be added back into the dry signal to increase brightness.
excursion. The maximum distance a speaker driver can move in and out from its resting position. A larger excursion can move more air, creating high SPLs, but there are tradeoffs, such as poor damping.
expand. To enlarge a DAW or sequencer track so that its data can be viewed more easily.
expander. The opposite of a compressor. An expander is used to increase the dynamic range of a signal. In an expander, when the input signal crosses a threshold setting, the output level of the signal is processed to decrease based on a ratio. For example, with a 1:2 ratio, a drop of 1 dB in signal level at the expander input results in a reduction of 2 dB in signal level at its output. Expanders are often used to reduce the amount of background noise in a signal.
expansion slot (a.k.a. slot). An internal expansion interface in a hardware device, such as a computer, sampler, or other device, used for adding expansion cards or optional hardware. Slots can be used to add RAM to a sampler or computer, an audio interface to a computer, an A/D converter to a preamp, or a variety of other options. Expansion slot formats range from “standards,” such as PCI, to proprietary formats.
export. Saving data out of a program in a format that allows it to be opened by another program. For example, an audio program that uses AIFF as its “native” audio file format might export an audio file in WAV file format so that it can be opened by other programs that don’t support AIFF.
ExpressCard. A card format from the PCMCIA that is about half the size of a PC card and that supports wireless communication, more memory, and security.
expression. MIDI Continuous Controller #11, with a range from 0 through 127. Expression is often routed to control musically expressive volume changes that do not affect the overall volume of the track. For example, MIDI Controller #7 is used to set the overall level, and Controller #11 might be used for slight crescendos and decrescendos.
expression controller. A foot pedal or other device that is connected to a keyboard or MIDI controller’s expression input and used to manipulate parameters. Expression controllers usually have 1/4-inch connectors.
extension. An older Macintosh term for a piece of software similar to a device driver.
external sync. A setting in keyboard workstations, drum machines, hardware DAWs, and other devices that determines whether the unit is using its internal clock or slaving to an external clock.